Orbiting Debris: A Space Environmental

Problem

October 1990

OTA-BP-ISC-72

NTIS order #PB91-114272
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Orbiting Debris: A Space Environmental

Problem-Background Paper, OTA-BP-ISC-72 (Washington, DC: U.S. Government Printing

Office, September 1990).

For sale by the Superintendent of Documents

U.S. Government Printing Office, Washington, DC 20402-9325

(order form can be found in the back of this report)
Foreword

Man-made debris, now circulating in a multitude of orbits about Earth as the result of the

exploration and use of the space environment, poses a growing hazard to future space

operations. The 6,000 or so debris objects large enough to be cataloged by the U.S. Space

Surveillance Network are only a small percentage of the total debris capable of damaging

spacecraft. Unless nations reduce the amount of orbital debris they produce, future space

activities could suffer loss of capability, destruction of spacecraft, and perhaps even loss of

life as a result of collisions between spacecraft and debris.

Better understanding of the extent and character of “space junk” will be crucial for

planning future near-Earth missions, especially those projects involving humans in space. This

OTA background paper summarizes the current state of knowlege about the causes and

distribution of orbiting debris, and examines R&D needs for reducing the problem. As this

background paper notes, addressing the problem will require the involvement of all nations

active in space. The United States has taken the lead to increase international understanding

of the issue but much work lies ahead.

In undertaking this background paper, OTA sought the contributions of abroad spectrum

of knowledgeable individuals and organizations. Some provided information, others reviewed

drafts. OTA gratefully acknowledges their contributions of time and intellectual effort. As

with all OTA studies, the content of this background paper is the sole responsibility of the

Office of Technology Assessment and does not necessarily represent the views of our advisors

or reviewers.
Workshop on Orbiting Debris:

A Space Environmental Problem

LTC Jim Ahern

Representative for Assistant Secretary

for the Defense Policy

Office of International Security Policy,

U.S. Army

Howard A. Baker

Consultant

Ottawa, Canada

Peter Banks

Professor

Department of Electrical Engineering

Star Lab, Stanford University

Richard DalBello

Director, Office of Space Commerce

U.S. Department of Commerce

Elaine David

Office of General Counsel

U.S. Department of Transportation

Stephen Doyle

Senior Analyst, Strategic Planning

Aerojet Solid Propulsion

Daniel Jacobs

International Relations Specialist

NASA Headquarters

Nicholas Johnson

Advisory Scientist

Teledyne Brown Engineering

William Kendall

Foreign Affairs Office

OES/SAT

U.S. Department of State

Donald Kessler

Space Scientist

NASA Johnson Space Flight Center

Lt. Brian H. Lillie

Technology Planning and Assessment Officer

Air Force Space Technology Center

Joseph Loftus

Assistant Director, Planning Department

NASA Johnson Space Flight Center

Bobby Quisenberry

Chief of Systems Safety and Security

General Dynamics, Space Systems Division

Jerry L. Weinberg

Director

Institute for Space Science and Technology

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the workshop participants.

The Participants do not, however, necessarily approve, disapprove, or endorse this report. OTA assumes full responsibility

for the report and the accuracy of its contents.

iv
OTA Project Staff on Orbiting Debris:

A Space Environmental Problem

Lionel S. Johns, Assistant Director, OTA

Energy, Materials, and International Security Division

Alan Shaw, International Security and Commerce Program Manager

Ray A. Williamson Project Director

Contributors

Michael Callaham, OTA

Carol Carnett

Darren McKnight, U.S. Air Force Academy

Contractor

Howard Baker

Administrative Staff

Donna Reynolds

Jackie Robinson

Louise Staley
Acknowledgments

The following organizations generously provided OTA with information and suggestions:

Aerospace Corporation NASA Headquarters

Aerojet Corporation NASA Johnson Space Center

Department of Defense National Academy of Sciences

Department of State Teledyne Brown Engineering

General Dynamics Space Systems Division U.S. Air Force Academy

Office of Commercial Space Transportation, U.S. Air Force Directorate of Space Systems

Department of Transportation U.S. Space Command

Office of Space Commerce, Department

of Commerce

This report has also benefited from the advice of experts from the government and the private

sector. OTA especially would like to thank the following individuals for their assistance and

support. The views expressed in this report, however, are the sole responsibility of the Office of

Technology Assessment.

M. J. Baxter

Aerospace Corporation

W. S. Campbell

Aerospace Corporation

Val A. Chobotov

Aerospace Corporation

Leonard David

Consultant

William Djinis

NASA Headquarters

William D. English

Attorney

Richard Hujsak

Applied Technology Associates

General Martin Menter (ret.)

Attorney

Scott Pace

Department of Commerce

D. B. Spencer

Aerospace Corporation

Col. Parker Temple, III

U.S. Air Force

Paul Uhlir

National Academy of Sciences
Contents

Hazards to space Operations From Orbital Debris . . . . . . . . . . . . . .......13

The Nature of Space Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 15

Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . ● . . . . . . ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 21

Debris Reduction Strategies . . . . . . . .... . .........- 2 l

Preventive Measures . . . . . . ........ . . . . . . 22

Shielding and Other Protective Measures . . . . . . . . . . . . . . . . . . . . .......25

Geostationary Orbit . . . . . . . . . . . . . . . . . . . . . . . ● . . . ● . . ● . . . ● . . . . . . ● ● 26

Legal

The Definition of Orbital Debris . .............. . . . . . . . ........ ...27

Jurisdiction and Control . . . . . . . . . . . . . . . . . ........ .. ..-..29

Detection and Identification . . . . . . . . . . . . . . . . . . . . . . ..30

Liability for Damage Caused in Outer Space . ........... ... .. ..31

Future Directions for Reducing Orbital Debris . . . . . . . . . . . . . . . . ..... ...33

Characterization of the Debris Environment . . . . . . . . . . . . . . . . . .......34

Mitigation and Protection Techniques . . . . . . ...... . . . . . . ....... 36

U.S. Research Plans . . . . . . . . . . . . . . . . . . . . . . . . . . ● ● . . . . . . . . . ● ● . . . ● . 37

International Cooperation . . . . . . . . . . . . . . . . . . . . . . . ........ ... ..38

Special Concerns About Geostationary Orbit. . . . . . . . . . . . . . . . . . . . . .. ..41

National Security Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ...42

The Private Sector . . . . . . . . . . . . . . . . . . . . . . . ........ .. .. ... ... .42

Appendix A Collision Probabilities for Satellites. . . . . .............. .. .....47

Appendix B U.S. Statutes Governing Outer Space . . . . . . . . . . . . . . . . . . .......49

Appendix C U.S. Commercial Regulatory Programs . ........... . . .......51

vii
Contents

Figures

Figure Page

1

2

3

4

5

6

7

8

9

10

11

Table

1

2

3

4

5

6

7

8

9

10

A-1

1

2

3

4

5

6

7

. . . Vlll

Cataloged On-Orbit Population . . . . . . . . ● . . . . . . . . . . . . . ● . . ● ● . . . . ● ● ● . ● 2

Orbital Debris Relationships . ............ ● 4

Yearly Changes to the Cataloged Debris Population . .............13

Annual Launch Rate By All Nations . . . . . . . . . . . . . . ...14

U.S. and U.S.S.R. Contributions to the Orbital Population

of Cataloged Objects . . . . . . . . . . . . . . .....’1 4

Detection Capabilities of the Space Surveillance Network . . . . . . . .......16

The Evolution of a Debris Cloud . . . . . . . . . . . . . . . . . . . . . . ● . . . . . . . . ● ● ..19

Relative Kinetic Energy Content of Space Debris Objects . . . . . . . .......20

Debris Cataloged from the Breakup of the Transit 4A Rocket Body .. ....22

Spatial Densities in LEO for Various Sizes of Debris . . . . . . . . . . . .......24

Total Number of Orbital Objects in the Space Surveillance

Network Catalog by Nationality . . . . . . . . . . . . ● . . . ● . . . . . . . . . . . ● . . ● . ● .39

Tables

Page

Elements of Orbital Debris . . . . . . . . . . . . . . . . . . ● . . . ● ● . . . ● . . . . . . . . . . ● 2

Types of Hazardous Interference by Orbital Debris . . . . . . . . . . . . . . . . . . . 3

Space Weapons Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ● . . . ● . ● . . . ● 19

Classes of Space Debris . . . . . . . . . . . . . . . . . . . . . . . . . ● . . . . . . ● . . .......29

Key Program Needs for Characterizing the Debris Environment . .......34

Spacecraft Surfaces Returned From Space Analyzed

for Debris Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ● . . . . . . ● . ● ● ● 35

Radar Performance Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Key Program Needs for Debris Mitigation . . . . . . . . . . . . . . . . . . . . .. .....37

Key Program Needs for Protection From Debris . . . . . . . . . . . . . . . . . . . . ..37

Phase I Summary of Projected Expenditures for the

NASA/DOD/DOT Research Plan . . . . . . . . . . . . . . . . . . . . . . . . . ● . . .......38

Probability of Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Boxes

Page

Some Categories of Earth Orbits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Nine Common Misconceptions About Orbital Debris . . . . . . . . . . . .......11

Selected U.S. Efforts To Increase Awareness of Orbital Debris . . . .......14

The Evolution of a Debris Cloud . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......18

International Space Treaties and Agreements . . . . . . . . . . . . . . . . . . . . .. ..28

The Long Duration Exposure Facility (LDEF) . . . . . . . . . . . . . . . . . . ● .. ..35

Orbital Debris Radar Observations . . . . . . . . . . . . . . . . . . . . . . . . . . .......36
Oribiting Debris: A Space Environmental Problem

INTRODUCTION

Debris, left in a multitude of orbits about

Earth as the result of the exploration and use

of the space environment, poses a growing

hazard to future space operations. Unless nations reduce the amount of orbital debris they

produce each year, future space activities

could suffer loss of capability, loss of income,

and even loss of life as a result of collisions between spacecraft and debris.

Because of their concerns about the safety

of spaceflight, the Senate Committee on Commerce, Science, and Transportation, and the

House Committee on Science, Space, and

Technology requested an assessment of the

future hazard from orbital debris,l and an examination of strategies for reducing that

threat. This background paper derives primarily from a workshop on orbital debris held

at OTA on September 25, 1989. In preparing

this paper, OTA also received assistance from

other contributors. OTA gathered information from many other sources, including the

1989 U.S. Report on Orbital Debris2 prepared

by the Interagency Group (Space), the 1988

European Space Agency (ESA) Report, Space

Debris,3 and a workshop convened jointly by

OTA and the U.S. Space Foundation in April

1989.4

Since the launch of Sputnik 1 by the Soviet

Union in 1957, nations and organizations involved in the exploration and exploitation of

space have completed over 3,200 launches,

which have placed more than 3)800 payloads

into orbit around the Earth. About 6,500 artificial objects orbiting Earth, weighing about 2

million kilograms in sum, are now cataloged

by the Space Surveillance Network (SSN),

operated by the U.S. Space Command

(USSPACECOM).5 However, only 6 percent of

the cataloged objects in Earth orbit are functional satellites;6 the rest fall into the category

of “orbital” or “space” debris7 (figure 1).

Moreover, analysts believe that the total orbital debris population is much greater, because orbital debris includes a wide variety of

artificial objects (table 1), which range in size

from a millimeter or smaller to the full bulk of

a deactivated satellite or spent rocket stage.

Orbital debris travels in the full range of orbits used by Earth-orbiting satellites (box l).

Unlike natural meteoroids, which pass

through near-Earth space in a matter of a few

minutes as the Earth sweeps through space,

orbital debris, depending on its altitude, may

continue to orbit Earth for periods as long as

centuries.8 It moves in many different orbits

IThe Hou=Committ= on ~ienm, s~ce, and Techno]o~he]d a hearingon July 13, 19880n the subject oforbi~ debfis. witnesses

included representatives from NASA DOD, the Department of State, and the Department of Transportation, as well as legal and

technical experts from the private sector. Witnesses expressed concern about the potential hazards from orbital debris and the need

for technical and policy mechanisms to address those hazards.

aNation~ &rity council, RPrt on ().rbitd Debris, Interagency Group (spice), Februq 19$9.

3Europm Spce &nq, fj?pucw Debris (Paris: European SPce AgencY, November 1~)”

4U.S. Congress Ofllce of Technology Assessment and U.S. Space Foundation, Joint Workshop on Space Debris and Its Policy Implications, Proceed”zngs of the Fi/lh Natiorud SpCUX Symposium (Colorado Springs, CO: U.S. Space Foundation, 1989), pp. 1-24.

%eSSN was earlier operated by the North American Aerospace Defense Command (NORAD). However, in 1988, responsibility

for surveillance passed from NORAD to USSPACECOM.

6Nicho]as L Johnmn ~d Da~d J. Nauer) H~~v of ~-~it Sa&Jz& Fm~en~~m, 4th ed. (Colorado Springs, CO: Teledyne

Brown Engineering, January 1990), NASA Contract NAS 918209.

~th terms are in common use. The term orbital debris will be used throughout this background paper to assist in distinguishing

between artifical objects in space, which orbit Earth, and cosmic dust, meteoroids, and other natural objects, which pass by or strike

Earth as it travels through the interplanetary medium.

aMuch debri9, however, falls back into the atmosphere within months or Ye~s.

1
2 . Orbiting Debris: A Space Environment Pronblem

Figure 1 -Cataloged On-Orbit Population

On-orbit population

8 Dec 1989

Operational

payloads

(6.0%)

Rocket

bodies ...

(16.0%) bris

.0%)

Inactive

payloads /

(21.096) Debris from

space

operations

(12.0%)

SOURCE: Nicholas L Johnson and Davld J. Nauer, History of On-Orbit Satellite

Fragmentatons, 4th ed. (Colorado Springs: Teledyne Brown Engineering, January 1990), NASA Contract, NAS 18209,

Table 1 -Elements of Orbital Debris

● deactivated Spacecraft

● spent rocket stages

● fragments of rockets and spacecraft and their instruments

● paint flakes

● engine exhaust particles

● spacecraft rocket separation devices

● spacecraft coverings

● spent Soviet reactors

SOURCE: Office of Technology Assessment, 1990

and directions, at velocities ranging from 4

kilometers per second to over 7 kilometers per

second, and constitutes a potential hazard to

working spacecraft (table 2). In the nearvacuum of outer space, no forces act to slow

debris down. Even very small objects, if they

have high velocities relative to the objects

they hit, may do considerable damage. For example, in 1983, a tiny titanium oxide paint

chip, estimated to have been about 0.2 millimeter in diameter, collided with the Shuttle

Box 1 -Some Categories of Earth Orbits

● Low-Earth-Orbit(LEO)-any orbit below about

2,000 kilometers (1,250 miles) above Earth’s surface,* which correspmds to an orbital period of

127 minutes, or less. Space Station Freedom will

reside in LEO at altitudes between 300 and 500

kilometers.

. Medium-Earth-Orbit (MEO)-orbits between

LEO and GSO.

. Geosynchrynous Orbit (GSO)-orbits at an average altitude of 35,787 kilometers (22,365 miles)

in which a satellite has a 24-hr period.

● Geostationary Earth Orbit (GEO)-a special case

of GSO in which a satellite orbits above Earth’s

Equator at an angular rotation speed equal to the

rotation of Earth. It thus appears to remain stationary with respect to a point on the Equator.

Positions along the GEO are highly sought for

communications satellites because the geostationary vantage point allows one satellite continuous coverage of a large portion of Earth. In

addition, GEO satellites can be repositioned

along the orbit to change their coverage at reasonable cost.

• Supersynchronous Orbit-an orbit with a longer

period, and greater average altitude than GSO.

. Sun Synchronous Orbit-an orbit synchronized

with the sun in such a way that it passes over the

Equator the same time each day. Such orbits are

therefore highly important for remote sensing

satellites that must view Earth’s surface at the

same time of day on each pass in order to maintain consistent data sets.

* the boundary between LEO and higher orbits is not

well defined.

orbiter Challenger9 at very high velocity and

damaged a window. Although the damage

posed no immediate danger, the window was

weakened beyond the allowable safety limits

for reflight and was replaced before the orbiter’s next launch.

Cataloged objects, some weighing up to several tons, reenter the atmosphere at a rate of

two to three per day. Over the past 30 years,

some 14,000 trackable objects have fallen to

gNicholag L. Johnson and Darren S. McKnight, Artificicd Space Debris (hklabar, n: Orbit ~k1%7), P. 4.
Orbiting Debris: A Since Environmential Problem ● 3

Table 2--of Hazardous Interference by

Orbital Debris

1. Loss or damage to space assets through collision;

2. Accidental re-entry of space hardware;

3. Contamination by nuclear material of manned or unmanned

spacecraft, both in space and on Earth;

4. Interference with astronomical observations, both from the

ground and in space;

5. Interference with scientific and military experiments in space;

6. Potential military use.

SOURCE: Space Debris, European Space Agency, and Office of Technology Assessment.

Earth. The largest have attracted worldwide

attention. 10 Although the risk to individuals is

extremely small, the probability of striking

populated areas still finite.11 For example: 1)

the U.S.S.R. Kosmos 954, which contained a

nuclear power source,12 reentered the atmosphere over northwest Canada in 1978, scattering debris over an area the size of Austria; 2) a

Japanese ship was hit in 1969 by pieces of

space debris that were assumed to be of Soviet

origin, injuring five sailors; 3) in October of

1987, a 7-foot strip of metal from a Soviet

rocket landed in Lakeport, California, causing

no damage; 4) portions of Skylab came down

over Australia in 1979. The biggest piece of

Skylab that reached the ground weighed over

1,000 pounds.13

This background paper treats the issue of

artificial debris in space, its causes, and the

potential for reducing the hazards that it

poses to space activities and the outer space

environment. Yet, orbital debris is part of a

larger problem of pollution in space that includes radio-frequency interference and interference to scientific observations in all parts of

the spectrum. For example, emissions at radio frequencies often interfere with radio astronomy observations. For several years,

gamma-ray astronomy data have been corrupted by Soviet intelligence satellites that

are powered by unshielded nuclear reactors. 14

The indirect emissions from these satellites

spread along the Earth’s magnetic field and

are virtually impossible for other satellites to

escape. The Japanese Ginga satellite,

launched in 1987 to study gamma-ray

bursters, has been triggered so often by the

Soviet reactors that over 40 percent of its

available observing time has been spent transmitting unintelligible “data.”15 All of these

problem areas will require attention and positive steps to guarantee access to space by all

countries in the future.

FINDINGS

Finding 1: If space users fail to act soon to reduce their contribution to debris in

space, orbital debris could severely restrict the use of some orbits within a decade or two.

Orbital debris is a growing problem. Continuing steady growth of orbital debris could,

by 2000 or 2010, render some well-used

low-Earth orbits (LEOs) too risky to use.

l~Wt7,themoth~]~~~et Swm ~tion, which had beenorbitingin a storage orbit of somes~ kilometers, h- slowIY sliPPed

to lower altitudes as a result of increased solar activity and is expect to fall to Earth in April 1991. It will be the largest object to reenter

Earth’s atmosphere since Skylab. Lon Rains, S’News, vol. 1, No. 8, p. 1.

I IE~lyintheU.s. SP@ Prowm, rwket launches dmppeddebris over portions ofAfrica, which CSUA mnsiderableconcern tou.s.

officials. See K H. Meyer and H. H. Hunt, “Investigation of Atlas Booster Fragments Recovered in South Africa,” December 1963

(NASA contract NASW-637), General Dynamics Astronautics, San Diego, CA.

1-Eilene~]oway, “NUCIW powered Satellites: The U.S.S.R. Cosmos 954 and the Canadian Claim,” Akron k~e~kq VO1. 12,

No. 3, pp. 401-415, for a comprehensive summary of the legal and political ramifications of this incident.

ISR. ~inhold, “SpMW Junk Emits Clatter From Coast to Coast,” New York Times, Oct. 14, 1987.

14M. w~d~p, “Spce ~a~or5 Hinder Gamma-Ray Astronomy,” Science, vol. 242, November 1988, p. 119. The U.S. %lm MSIC

spacecraft picked up bursts of gamma rays Iastinganywhere from a few seconds to almost 2 minutes. The reactors provide power for

the Soviet military’s Radar Ocean Reconaisssance Satellites (RORSATS)) which are used to track Weetern fleet movements, and

which have been launched at the rate of two or three per year since the 1980s.

‘

s

Ibid.
4 ● Orbiting Debris: A Space Environmental Problem

Other orbits, including the economically and

strategically important geostationary orbital

band (GEO), are vulnerable to the growth of

debris. Debris can collide with both active and

inactive satellites, damaging the active satellites and producing more debris from both.

Pollution in the form of gases and small particles of rocket exhaust may erode and contaminate spacecraft surfaces. Debris may also

interfere with inspace and ground-based observations and experiments. International action will be needed to minimize the generation

of new orbital debris and to cope with debris

already in orbit. The United States and other

countries have already taken initial steps to

reduce their contributions to orbital debris.

Future planning needs to consider the potential long-term effects (50 years and longer) of

space debris.

Three critical areas require particular attention:

. developing cost-effective strategies to reduce the contributions to orbital debris;

● encouraging immediate action to minimize debris production by all space-faring nations and organizations; and

. increasing the awareness and involvement of the international community.

Finding 2: Lack of adequate data on the orbital distribution and size of debris will

continue to hamper efforts to reduce the

threat that debris poses to spacecraft.

The distribution of orbital debris is determined by a variety of means (figure 2), including the use of radar, optical telescopes, and direct observations of damage to items returned

from space. Although the Space Surveillance

Network (SSN), operated by the U.S. Space

Command, currently tracks about 6,500 orbital objects 10 centimeters across and larger

(6 percent of which are active spacecraft),

smaller debris cannot be followed with current systems. The nature and extent of the

hazard from smaller particles is therefore

highly uncertain. Some analysts estimate

Figure 2-Orbital Debris Relationships

Size (cm) 0.0001 0.001 0.01 0.1 1 10

I

USSPACECOM radars

LEO detection ‘ New radar, telescopes

Returned materials

I I I

Telescopes

I

GEO detection I

t

USSPACECOM

radars

Damage

, Insulation blanket penetration

1 Space suits, windows, mirrors

I

Spacecraft and tanks

Pressurized modules

I Little to no data I

SOURCE: National Aeronautics and Space Administration
Orbiting Debris: A Space Environmental Problem ● 5

that some 30,000 to 70,000 bits of debris, one

centimeter or greater in diameter, now orbit

the Earth. Many more smaller objects are estimated to be in orbit.16 Other analysts are

skeptical of such projections. However, all

agree that neither the number nor the distribution of these objects is sufficiently well

known to predict which methods of protection

would be most cost-effective.

Reducing these uncertainties to acceptable

levels will require the development of devices

capable of sensing and cataloging smaller objects, and sampling debris in orbit. The Haystack Auxillary Radar, under development by

NASA and the Department of Defense (DOD)

(operated by USSPACECOM), together with

data from the existing Haystack Radar, will

assist in characterizing the number and distribution of objects as small as 1 centimeter in

diameter. The information supplied by examining the Long Duration Exposure Facility

(LDEF),17 which remained in LEO nearly 6

years, will help in estimating the debris density in LDEF’s orbits and in evaluating the

long-term effects of the space environment on

a wide variety of materials used in spacecraft.

Similar future experiments in orbit would

continue to assist the accumulation of information on microscopic orbital debris.

To define the space environment adequately, more and better data must also be acquired in the laboratory on the types of explosions that can occur in space and on the effects

of impacts, especially hypervelocity impacts

(relative velocities of 3 kilometers per second

and greater). Impacts occuring at velocities of

5 to 7 kilometers per second and greater lead

to great damage because they can cause the

impacting materials to liquify and produce

many thousands of small particles. The remainder of a satellite may also fragment into

hundreds of large pieces capable of causing

catastrophic damage to other satellites. However, the details of these mechanisms are not

completely understood.

Better orbital debris information will contribute to the development of more accurate

predictive models for the evolution of space

debris. These data will also support efforts to

develop debris reduction and spacecraft protection techniques.

Finding 3: The development of additional

debris mitigation techniques could

sharply reduce the growth of orbital

debris.

A number of relatively simple preventive

measures taken by national governments and

space organizations would greatly reduce the

production of orbital debris. Governmentfunded research has shown that it is possible

to design and operate launch vehicles and

spacecraft so they have minimum potential

for exploding or breaking up. For example,

since 1981 NASA has depleted propellants

and pressurants from Delta launch vehicle upper stages after they have completed their

mission. NASA has also added electrical protection circuits to spacecraft batteries in order

to preclude battery explosions resulting from

electrical shorts. Spent upper stages can be removed passively by reducing their altitude to

the point where atmospheric drag effects will

bring them down. The U.S. Government may

implement this technique in the future. Although these and other techniques add a few

kilograms to the weight of the spacecraft and

the launch vehicle, and therefore increase the

cost of a mission, such extra costs maybe necessary to avoid potentially greater costs from

failed missions later. In other words, they may

well be cost-effective in the long-run.

Further, the use of new materials on spacecraft could reduce the natural degradation

le~formation regard ingobj~s sm~]er than 0.10 centimeters can only be obtained from materials returned from sPam. Although

these objects might number as much as 3,500,000, objects of this size are not considered a great threat.

17w bx 5 for findings from LDEF.
6 ● Orbiting Debris: A Space Environmental Problem

and fragmentation that occurs in the harsh

environment of outer space. Moreover, nations could avoid deliberately fragmenting

satellites. Finally, some experiments can be

planned for execution in very low orbit, where

the atmospheric drag will bring objects down

relatively quickly.18

Finding 4: Although it is technically feasible

to remove existing debris from low altitudes, the cost of removal is not warranted at this time.

Proposals for debris removal have ranged

from developing large balloon-like objects

that would “sweep up” debris in certain orbits, to using the Space Shuttle and/or the

planned Orbital Maneuvering Vehicle (OMV)

to capture inactive satellites and remove them

from orbit.

All methods for removing debris exact some

economic cost. However, for LEO, the least expensive technique is to remove inactive payloads and spent propulsion stages before they

can break up into smaller objects. Removal involves reserving some fuel to send spent propulsion stages or inactive satellites into the atmosphere, where they will break up and bum

or fall to Earth.19 Adding a small device directly to a propulsion stage that would later

expand and increase atmospheric drag would

also substantially shorten the stage’s lifetime

on orbit.

The capture and return of space objects is

expensive. 20 The present degree of risk does

not make debris worthwhile to remove from

space. In addition, the potential salvage value

of a used satellite, unlike that of an abandoned

ship, is extremely small compared to the cost

of retrieval at present. Further, unless the

launching state were to agree, it is contrary to

current international law21 to interfere with

space objects belonging to another state or

states. Even inactive satellites, which could

threaten the operation of other satellites, remain the property of the states of registry and

continue under their jurisdiction. No concomitant duty to dispose safely of inactive satellites exists, and no liability accrues if they

substantially interfere with active satellites,

though activities generating inactive satellites

may be made the subject of consultation pursuant to Article IX of the 1967 Outer Space

Treaty.22

Finding 5: Protection technologies could reduce the harm that debris can do.

Orbital debris ranges from submillimetersized particles to objects several meters long.

Although the chances that one of the few large

pieces of debris would strike a functioning

spacecraft is extremely small, the probability

that collisions with objects in the millimeter

to centimeter size range would reduce spacecraft performance is growing.

‘eFor example, the Delta 180experiment fortheStrategic Defense Initiative Organization was carried out in low orbit, in compliance

with DOD policy on space debris (Department of Defense Space Policy, Mar. 10, 1987).

l~eu.s.~Wmment is actively considering followingthis practice. Full implementation will require ftiher effort to desisn the

procedures for each spcific application.

me recent return of LDEF and its many experiments to Earth demonstrates that such retrieval is pasible. However, LDEF was

retrieved to recover its valuable experimental results, not for its salvage value, or because it might harm active spacecraft. NASA will

charge Intelsat more than $90 million to capture and repair an Intelsat VI communications satellite now stuck in a useless low orbit.

James R. Asher, “Astronauts to Catch Stranded Intelsat for $90 Million for Reboost in 1992,” Aviation Wed and Space Techndqy,

June 18, 1990, pp. 26-26.

~~~ic]e TTIII of the IM7~ on Hwipks &werningthe Activities ofStates in the Expbmtion and Use of tib SpaCS, Iddng

theMoon and Other CekstialBodies: “A State Party to the Treaty . . . shall retain jurisdiction and control over such object . . . while in

outer space . . . .“

~~icle IX titis: “Asti& ptiy t,o the Treaty which has reason to believe that an activity or experiment planned by mother state

Partyin outer space, includingtheMoon and other celestial bodies, would cause potentially harmful interference with activities in the

peacefid exploration and use of outer space, including the Moon and other celestial bodies, may request consultation concerning the

activity or experiment. ”
Orbiting Debris: A Space Environmentald Problem ● 7

Efforts to develop protection technologies

and methods include materials research, active and passive avoidance techniques, and

new shielding designs. Current shield designs

make use of an outer wall that causes the

striking object to fragment and disperse before hitting the inner wall. A specific dual-wall

design is effective for all debris velocities in excess of about 5 kilometers per second and particle size of about 0.5 centimeter. Additional

research and development will be needed to

design more effective, lightweight shields.

New materials and techniques will assist that

effort. However, some shielding materials

could add to the debris hazard. Hence, research on shielding will have to include study

of the breakup or degradation of shielding

over time.

Finding 6: The presence of debris in lowEarth orbits, where fast moving objects

could pierce inhabited spacecraft such

as the planned international space station, Freedom, and the Soviet space station, Mir, is especially troublesome because of the risk to human life.

The tiny paint chip that damaged the Shuttle Challenger’s windshield in 1983 is evidence

of a large population of very small particles.

The paint chip would likely have punctured

the spacesuit of an astronaut involved in extravehicular activity, had it struck him,

though the probability of such an impact is

extremely small.23 Operation of the Space

Shuttle could be endangered by orbital debris,

especially as Shuttle flights increase in

length.24

Objects quite a bit larger than the paint

chip could pierce the Shuttle and/or space Station Freedom. Soviet cosmonauts aboard Mir

have noted some impacts from small pieces of

artificial debris.25 Although these encounters

have not resulted in life-threatening damage,

they illustrate the potential threat. Additional

data from Mir regarding Soviet experience

with orbital debris could be very useful in designing appropriate shielding for Freedom.

Space station designers will need additional

data in order to design effective shielding for

Freedom, particularly for debris less than 2

centimeters in diameter.26 The final design requirements for the space station are needed

by 1992 in order for them to be incorporated

in the hardware. NASA has recently revised

its estimates of the debris hazard,27 which new

data shows may have been understated,28 and

continues to refine its understanding of the

space environment. Study of the actual experience of debris encounters with LDEF and

observations by the Haystack Auxillary Radar, under development by NASA and the Air

Force, will play important roles in providing

the necessary data.

Freedom will also require tight environmental control to limit generation of orbital

debris. Space stations, especially because they

are large and have a large surface area also

have the potential to produce debris. Over

several years, as debris generated by the space

station changes orbit slightly and expands

into a doughnut-shaped belt, space stations

themselves, as well as launch vehicles supplying them, would become targets of space station debris.

~sL. p~ker Ternp]e~, ‘ime~~ct ofSpace Debris on Manned Space Operations” (W%88-4Z()), presented at the 37th ConfTessof

the International Astronautical Federation, Innsbruck, Austria, Oct. 4-11, 1988.

24u.s. Conwess, ~ner~ Accounting Offke, “Space Debris a Potential Threat to Space Station ~d Shuttle,” GAO-CC-90-18

(W-hin@n, DC: GeneraI Accounting Offke, April 1990), ch. 5.

a~illim Djinis, Nation~ Aeronautics and Space Administration, personal mmmunimtion, 1~.

2SShielding for obj~s ~~r th~ 2 ~ntime~rs in dimeter Wou]d ~ impracti~ly massive. Fortunately, the risk to the SpMX

Station of encountering objects larger than 2 centimeters is much lower than for the smaller ones.

27R. Ni~er, ‘t~p]i~tion of Orbital Debris for Space Station Design” (WW1331). AIM/NASA/DOD Orbital Debris Conference:

Technical Issues and Future Directions, Apr. 1619, 1990, Baltimore, MD.

ZqJ.S. Conwess, General Accounting Offke, op. cit., fmtnote 24, P. 28.
8 . Orbiting Debris: A Space Environmental Problem

Finding 7: Addressing the orbital debris

problem will require the active involvement of all space-capable nations.

Outer space is by nature and treaty a global

commons. Solving orbital debris problems

will require the cooperation of countries capable of reaching orbit. The United States and

the Soviet Union are the two largest contributors to the orbital debris population. As other

nations increase their space activities, their

contribution to the debris population will increase dramatically, unless they also take preventive measures.

The United States has assumed the lead in

analyzing the orbital debris distribution and

in developing mitigating technologies and

methods. The 1989 report of the Interagency

Group (Space)29 has assisted in making the

hazards posed by orbital debris more widely

appreciated and understood.

Informal discussions among technical representatives of most of the launching nations,

convened by the United States, have already

proven highly beneficial in developing orbital

debris control policies and practices. For example, the Japanese National Aeronautics

and Space Development Agency (NASDA) and

the European Space Agency (ESA) have both

incorporated procedures in their launch sequences to dispense unused propellant after

upper stages are used. Discussions between

these agencies and NASA have also resulted in

the prospect of sharing information on debris

tracking, modeling, and hypervelocity testing.

In November 1988, ESA released its report on

space debris,30 which reached conclusions

similar to those of the later U.S. orbital debris

report.

Initial discussions with Soviet officials in

December 1989 have proven fruitful to representatives from NASA, who have hitherto had

little insight into Soviet efforts to study the

problem or to curb its contributions to the orbital debris population.31 The United States

has not yet formally discussed the problems

of orbital debris with the People’s Republic of

China, which has a growing space program.

Finding 8: Existing international treaties

and agreements are inadequate for minimizing the generation of orbital debris

or controlling its effects. An international treaty or agreement specifically

devoted to orbital debris maybe necessary.

One major objective of the international

treaties and agreements on space activities is

to ensure that space activities can be conducted safely, economically, and efficiently.

Yet, existing international treaties and agreements do not explicitly refer to orbital debris.

As a result, they leave uncertain the legal responsibilities of nations for minimizing the

growth of orbital debris.

The economic value of maintaining a safe

operational environment for all nations provides strong motivation for nations to take independent action. Yet nations that conduct

relatively few launches might consider their

contribution to orbital debris to be small.

However, as the November 1986 breakup of

an Ariane third stage demonstrated,32 even

one breakup can cause a large amount of debris. An international agreement on orbital

debris could set the framework for tackling

the hazards of orbital debris. To be effective,

an international legal regime for debris

~Nation~ %curity council, Op. Cit., fOOtnOte 2.

30Euro- S@@ A@ncy, op. cit., f~tnote 3-

3

1 Djinis, op cit., footnote 25.

32Nicho]m L. Johnmn, ~~~]iminw &~ysi9 of the Fra~en~tion of the Spot 1 Arime ~i~s~,” in Jo~ph P. LOhS (d),

Odital Debris Fmm Upper-Stuge Breakup, Progress in Astronautics and Aeronautics, vol. 121, 19S9, pp. 41-106.
Orbiting Debris: A Space Environmental Problem . 9

should address the generation of debris, its removal from orbit, and the possible remedies

for damage sustained from debris. However,

experience with the development of other

treaties suggests that negotiating such an

agreement could be arduous and timeconsuming.

The United States, and some other governments, are currently reluctant to enter into

negotiations over an international agreement

on orbital debris, because the uncertainties

about debris distribution and potential mitigation methods are still high. In addition,

when addressed in a broad multilateral context in which states having no current capability to launch objects into space would participate, the subject has a high potential for

becoming the subject of acrimonious debate

in which the technical issues and solutions

could be lost. However, eventually a formal

agreement will probably be necessary in order

to encourage all space-faring nations to minimize the production of orbital debris.

It maybe appropriate for the United States

to convene a working group limited to spacefaring nations that would discuss mitigation

strategies and seek to reach agreement on

them. The United States is now urging these

nations, both informally and formally, to

adopt as policy a statement similar to the U.S.

policy on orbital debris: “all space sectors33

will seek to minimize the creation of orbital

debris. Design and operations of space tests,

experiments, and systems will strive to minimize or reduce accumulation of space debris

consistent with mission requirements and

cost effectiveness.” This follows U.S. policy,

adopted in 1989, that “the United States Government will encourage other space-faring nations to adopt policies and practices aimed at

debris minimization.”34

In the long run, enlightened self-interest is

likely to draw most nations with an interest in

outer space into such negotiations. Many of

the partners in such international organizations as Intelsat, Inmarsat, and Intersputnik,

or regional entities such as ESA, Arabsat, and

Eutelsat, have an economic interest in maintaining the ability to exploit space, even if they

lack the ability to launch spacecraft themselves.

Finding 9: For an international legal regime

on orbital debris to be established, several legal issues, including the definition of orbital debris, jurisdiction and

control over orbital debris, and the

treatment of liability for damage from

orbital debris, need to be resolved.

Legal experts do not now agree on a definition of space debris. For example, one major

point of debate is whether inactive satellites

should be categorized as “debris.” Without a

common definition, agreements over jurisdiction and control and liability will be extremely

difficult to achieve. Hence, if the United

States and other nations enter into negotiations over an international agreement on orbital debris, one of the first items of business

will be to reach agreement on a definition of

orbital debris, and what items are included in

or excluded from the category.

It will also be necessary to provide more explicit guidelines concerning the ownership of,

and jurisdictional control over orbital debris.

Existing legal opinion favors the view that

jurisdiction and control of a State over its

space objects is permanent, even if the object

no longer serves a useful purpose. However,

most space debris consists of objects too small

to be identified. It maybe necessary for the international community to develop a set of

principles regarding the treatment of spent

satellites.

Under existing law, launching States cannot

beheld liable for the mere presence of orbital

debris in outer space. Lack of international

agreements on debris is of particular con-

~~ other Wofis, civ-i]i~ and mi]it.ary government programs, and the private -r.

~Whi& HoU~, president Bush’s Space Policy, November 1%9, Fad Sheet.
10 . Orbiting Debris: A Space Environmental Problem

cern because launching States have no legal

incentive to avoid generating orbital debris,

although they have the practical, self-serving

incentive of protecting their own spacecraft.

An international agreement on space debris

should include provisions dealing with these

and other issues.

Reaching agreement will eventually require

abroad international approach, supported by

individual national efforts. Considerable additional research on the distribution and hazard posed by space debris will be needed to

support international legal efforts. Meanwhile, nations and organizations that launch

or operate spacecraft can voluntarily take immediate steps to minimize debris.

Finding 10: Private-sector space activities

have already benefited from orbital debris research carried out by governments. As private space activities increase, firms will have to bear their

share of the burden of mitigating future

contributions to the orbital debris population.

The private sector has a major stake in reducing space debris, because an increased debris population could harm private activities.

As noted in Findings 3, 4, and 5, Federal investment in debris research has resulted in

greater knowledge of the potential harm of

space debris and in a variety of measures to

mitigate its threat to space operations.

U.S. private-sector space activities are regulated by the U.S. Government in accordance

with several U.S. laws. In particular, The

Commercial Space Launch Act of 198435 mandates that all commercial payloads must be

reviewed prior to being licensed for launch.

The Act gives the Office of Commercial Space

Transportation (OCST) in the Department of

Transportation the responsibility for licensing commercial launches. This licensing process includes a review of intended safeguards

against proliferation of space debris.

Although some safeguards will require additional costs for payload owners and providers of launch services, the Federal Government does not wish to prejudice unnecessarily

the international competitiveness of the U.S.

launch industry.36 Hence, to avoid overburdening the private sector, regulation will have

to be measured and in concert with reducing

the threat of space debris while maintaining

U.S. competitiveness with other nations.

Private-sector input to the process of minimizing space debris generation will be extremely important in ensuring that regulations take into account the concerns and needs

of private fins, consistent with providing appropriate protection to spacecraft and people

in space. Private firms could be especially

helpful in comparing the costs of instituting

certain debris reduction procedures with the

costs of losing spacecraft capability as a result

of debris impacts.

Finding 11. Many misconceptions about orbital debris exist. An international educational program about orbital debris

would assist in making the hazards of

space debris better understood.

Even individuals knowledgeable in other

areas of space activities have developed misconceptions about the distribution of space

debris and potential hazards (box 2). Continued research and promulgation of results will

be needed to improve knowledge of this critical area. The many research reports written

by officials at NASA, the Air Force, and industry have alerted the space community to the

hazards of space debris. These have been presented over the years at national and international technical symposia sponsored by organizations such as the American Institute for

Aeronautics, the American Astronautical Society, the International Astronautical Federation, and the Committee on Space Research.

The recent reports by the U.S. Interagency

Group (Space) and ESA have reached an even

3549 U.S.C. 2601-2623 (19S4 & ~pp. 1%7).

*Nation~ ~rity Council, op. cit., fOOtnOte 2, pp. 49~0.
Orbiting Debris: A Spa ce Environment Problem ● 11

Box 2-Nine Common Misconceptions About Orbital Debris

One of the major impediments to reducing orbital debris is the lack of knowledge and understanding of the

problem. The following paragraphs explore some of the most common misunderstandings about orbital debris.

Misconception 1. Space debris is a larger problem today because the international space launch rate has increased.

On the contrary, the cataloged debris population has steadily grown while the international launch rate

has remained stable.

Since 1965 the international space launch rate has averaged 117 a year, never dipping below 100,yet the cataloged

population has increased sixfold (figure 3 and figure 4) in the same period. There is no clear dependency between

the launch rate and catalog growth. Catalogd space objects have increased at an average linear rate of 240 objects

per year (including active payloads and debris).

Misconception 2. The hazard from orbital debris is well defined.

On the contrary, there is significant uncertainty (orders of magnitude) in the probability of collisions

and the effect of the impact of debris.

The hazard to a functioning satellite is determinedby the probability of collision and the lethality of impact. Because the number of debris objects in various orbits is uncertain, the probability of collision calculated from the

density and velocities of cataloged objects (app. A) is also uncertain. Hence, estimates of future hazard reflect, or

should reflect, that uncertainty. Because the number of small objects in each orbital regime is thought to be much

greater than those that can be tracked by the SSN, the hazard is likely to be much greater than that estimated from

cataloged data.

The actual effects of collision on an active spacecraft are also uncertain. A collision might destroy an active

spacecraft or it might only damage part of it. For example, although a 100 gram debris fragment traveling at 10

kilometers per second (the average relative velocity in LEO) possesses the destructive energy of one kilogram of

TNT, it may strike the satellite in an area that would damage, but not destroy, the satellite.

In addition, the nature of the debris environment is very dynamic; both the sources and sinks of debris will

change over time, adding to the difficulties of defining the debris environment.

Misconception 3. The cessation of satellite breakups will solve the orbital debris problem.

On the contrary, the hazard from debris already residing in space, coupled with other sources of new

debris, such as debris resulting from space operations, will still create a concern for many years to

come even if no more satellites were to fragment in the future.

About 45 percent of the cataloged population is the result of nearly 100 satellite fragmentations (figure 1).1 Elimination of spacecraft explosions is more effective than any other method of controlling space debris growth. Yet,

there are still other significant sources that must be controlled. The remnants of successful space missions, spent

rocket bodies, and inactive payloads account for one third of the catalog. These objects are large and maybe the

source of future debris. Satellite deterioration as the result of reaction with atomic oxygen and thermal cycling

could produce fragments that range in size from micron-size paint chips to large solar panels. These payloads and

rocket bodies may also remain in orbit a longer time than fragmentation debris.

The last category, operational debris, makes up 12 percent of the trackable objects in orbit.2 This debris is released during normal operations of satellites: lens covers, explosive bolts, springs, shrouds, spin-up mechanisms,

empty propellant tanks, etc. Crews have even accidently released items during extravehicular activities and been

unable to retrieve them. However, at altitudes in which the Shuttle operates, objects reenter relatively frequently.

Misconception 4. International laws and treaties help to control the growth of the orbital debris population.

On the contrary, no formal laws or treaties have any impact on the control of orbital debris.

There is at present no international law or treaty that specifically calls for the control, reduction, or elimination of

“space debris.” Some feel that an international legal agreement formulated now may unnecessarily restrict future

space operations. Yet, if the spacefaring nations do not act soon on an international level, the effects of continued

debris growth may make future space activities more dangerous. The next 10 years are pivotal for the future of

debris growth and control treaties and regulations.

Informal discussions among technical representatives of the European Space Agency, France, Germany, Japan, and the United States, have already proven to be useful in developing technical policies and practices for controlling orbital debris. Discussions with the Soviet Union have begun and may prove fruitful in the future.

Misconception 6. The danger of satellite collision is greater in GEO than in LEO.

On the contrary, the current collision hazard in GEO is estimated to be hundreds of times less than in

LEO.

INiChol~ L. Johnson and D. Nauer, History of On-OAit Satellite Fnzgrnentations, 4th ed. (Colorado Springs, CO: ‘1’eledyne

Brown Engineering, January 1990), NASA Contract NAS 9-18209.

21bid. Continued on next page
12 . Orbiting Debris: A Space Environmental Problem

The probability of collision between a satellite and the debris population is a function of:

. the spatial density of objects in space;

. the relative velocity between debris and a satellite;

. the effective cross-section of the satellite; and

. the duration of the satellite on orbit.

The estimated probability of collision is a factor of 100 to 10,000 less in the GEO band than in LEO because

there are fewer objects in the former and they would cross paths at lower relative velocities. Further, because relative velocities are lower, the consequences of a collision are significantly less. However, even though the hazard to

satellites in GEO is much less than it is today in LEO, there are concerns for the future. For one thing, we have less

data about potential GEO hazards. GEO likely contains other orbiting objects too small to be tracked by current

methods (less than about 1 meter at GEO altitude), which could increase the hazard. In addition, more satellites are

being launched into GEO and there is no natural cleansing effect such as atmospheric drag to control debris growth

in these orbits. A series of satellite breakup events (i.e., a chain reaction) could have catastrophic effects on the

GEO satellite population.

Misconception 6. The Soviet Union, which has been responsible for more than 70 percent of all space launches

and satellite breakups during the past 25 years, has historically been the source for the majority of Earth’s

debris population.

On the contrary, the United States and the Soviet Union are about equally responsible for the present

cataloged population.

Up until the mid-1980s, the United States was responsible for a larger percentage of debris in orbit. The debris

produced by Soviet breakups is usually shortlived since it has historically been produced at lower altitudes. Thus

even though the Soviets have produced more debris over time, at present they have less in orbit than the United

States (figure 5), but more cataloged objects as a result of a larger number of inactive payloads and rocket bodies.

The rate at which Soviet satellites fragment has actually been increasing while the cataloged population has

been decreasing. Since 1961 the number of non-Soviet satellite breakups has consistently averaged less than one

per year. The Soviet breakup rate has increased steadily from one per year in the 1960s to four per year in the 1980s.

However, recently, the Soviet Union has fragmented its satellites in very low orbits, where the resulting debris falls

back into the atmosphere relatively quickly.

Misconception 7. Debris from weapons tests in space is a major component of Earth’s satellite population.

On the contrary, the 12 breakup events associated with space weapons tests are responsible for less than

7 percent of the cataloged population.

Despite the attention given to weapons tests in space, they have contributed very little to cataloged debris, in large

part because they have decayed from orbit relatively quickly. However, such tests may have added smaller debris

that cannot be detected with existing methods. Weapons tests could contribute substantially to the debris environment if they were carried out in higher orbits where the effects of atmospheric drag are extremely small.

Misconception 8. Bumper shielding can easily protect a space system from the debris environment.

On the contrary, a bumper system can protect a satellite from only a portion of the debris environment.

Although bumper shielding can protect a spacecraft from impact by some classes of objects, this shielding must be

“tuned” to specific types and velocities of debris threats. Hence it will only partially protect satellites. One that

would be effective for all sizes and velocities would be prohibitively costly in weight, complexity, and cost. Additional

research will be required to protect spacecraft from the most likely collision events. However, shielding will not

provide absolute protection. Debris minimization by all parties will also be required to reduce the hazard to acceptable levels. For some large systems, collision avoidance may be necessary.

Misconception 9. People are likely to be killed by fragments of reentering debris.

On the contrary, the chances of being struck by debris fragments are extremely small.

Thousands of debris fragments of all sizes reenter the atmosphere each year. Most disintegrate in the atmosphere

and are converted to gases and ash, or breakup into extremely small pieces. Very few actually reach Earth’s surface

intact. The chances of harm from reentering space debris is much smaller than the chances of being hit by one of

the 500 or so meteorites that strike Earth each year. Nevertheless, the uncertainty associated with our inability to

predict precisely, in advance,3 when large objects such as the U.S. Skylab or Soviet Cosmos spacecraft will enter the

atmosphere and where they may fall to Earth, coupled with considerable press attention, has led to unwarranted

public alarm.

SOURCE: Darren S. McKnight, 1990.

%e closer in time an object is to enteringthe atmosphere the more precisely can its entry be predicted by the Space Surveillance Network.
Orbiting Debris: A Space Environmental Problem • 13

Figure 3-Yearly Changes to the Cataloged Debris Population

1000

Number

o

-200

-400

— 5758596061 6263646566 676869 7071 727374757677787980 8182838465 868788 8 9

Year

The chart illustrates the yearly additions or deletions from the cataloged debris population, which average about 240 per year. The increases are mainly a function of sateilite breakups

rather than changes in the International launch rate. The reductions of the debris population which occurred in the periods 1979-81 and 1988-present resulted primarily from increased solar activity, which expands Earth’s atmosphere and increases drag on space objects in LEO

SOURCE: Darren S McKnight, 1990

broader audience. Additional educational ef- tion describes the hazards posed by orbital deforts, many already underway (box 3), are bris and summarizes how they are generated.

needed on all levels to assist in dispelling some

of the misconceptions about orbital debris.

Hazards to Space Operations From

THE ORBITAL DEBRIS

ENVIRONMENT

Orbital Debris

Functioning spacecraft face a variety of potential hazards from orbital debris:

Space debris can interfere with scientific,

commercial, and military space activities. In . Collisions of space debris with functional

some orbits, debris deposited today may af- satellites could result in damage that

feet these activities far in the future. This sec- could significantly impair the perform-
14 . Orbiting Debris: A Space Environmental Problem

Figure 4-Annual Launch Rate By All Nations

120

100

Number 80

of

launches 60

I ,,, ,

v

40

20

n

“55 60 65 70 75 80 85 90

Year

SOURCE: Darren S. McKnight, 1990.

Figure 5-U.S. and U.S.S.R. Contributions to the

Orbital Population of Cataloged Objects

Number

1500

USSR us

I

 Active payload Dead payload Rocket body Debris I

This chart shows that the Soviet Union has nearly an identical number of active payloads as the United states but the Soviets have many more inactive payloads and

spent rocket bodies in orbit than the United States.

SOURCE: Darien S. McKnight, 1990.

ance of a spacecraft or its subsystems.

For example, according to one calculation, the Hubble Space Telescope, which

was launched in April 1990, faces a

Box 3-Selected U.S. Efforts To Increase

Awareness of Orbital Debris

. Orbital Debris Monitor-A commercial newsletter devoted to promoting an awareness of spac e

environment problems. ’

. American Institute of Aeronautics and Astronautics (AIAA)/NASA/DOD Conference in Baltimore, April 1990.

. International Institute of Space Law (IISL)

meeting: “Environmental Implications and Responsibilities in the Use of Outer Space,” during

the 40th meeting of the International Astronautical Federation, Malaga, Spain, October

1989.2

. On March 30,1989, the IISL sponsored a meeting

for delegates to the Legal Subcommittee of the

U.N. Committee on the Peaceful Uses of Outer

space.”

● Short Course on orbital debris at the 1990 AIAA

Astrodynamics Conference, Portland, Oregon,

August 1990.

. The American Institute of Aeronautics and Astronautics has established a Committee on Space

Debris.

. The International Astronomical Union has established a Working Group on Interplanetary

Pollution (Commission 22).

SOURCE: Office of Technology Assessment, 1990.

IAvai]ab]e from: Orbital Debris Monitor, P.O. BOX 136,

USAF Academy, CO 80840-0136.

Zpawrs Pub]ished in the Proceedings ofthe32ndInte~

national Colloquium on the Law of Outer Space.

3Published in Proceedings of the 32nd International

Colloquium on the Law of Outer Sjmee.

chance of one in one hundred of being severely damaged by orbital debris during

its planned 17-year lifetime.37 Orbital debris has already hit active payloads.38 Af3~chae] Shera ~d ~k Johnston, “~ifici~ Earth Wte]lites Crossing the Fields of View of, ~d Colliding With, Orbitingsw=

Telescopes,” Publications of the Astronomical Society of the Pacific, vol. 98, pp. 814-820, 1986.

-B. cour-p~~s, “shie]ding~nst Debris,)’ Aemqxuxknwica, June 1988, p. 24. Examination of insulation blankets ~d aluminum louvers taken from thesolarhfaximum Mission satellite (Solar Max) revealed 1,9(M) holes and pits rangingin diameter from 0.004

to 0.03 centimeters. Over half of these can be attributed to particles ofartificial debris, many of which were aluminum oxide particles.
Orbiting Debris: A Space Environmental Problem . 15

ter the reentry of Kosmos 954 in 1978 a

Soviet spokesman attributed the fall to

an earlier (January 1978) collision with

another object.39 Kosmos 1275 may have

been completely destroyed by collision

with space debris.40 Further, evidence

derived mainly from statistical analyses

of the increases in orbital debris and

from other circumstantial evidence suggests that the fragmentation of some

spacecraft may have resulted from high

velocity impacts.41 Given that the capability of tracking technology decreases as

the altitude of the tracked objects increases, there is no way to establish if collisions have occurred in GEO,42 where

the current ability to catalog fragments

is limited to objects larger than about

one meter (see below).

Pollution in the form of gases and particles is created in the exhaust clouds

formed when second stage rockets are

used to boost a payload from LEO into

GEO. A single solid rocket motor can

place billions of particles of aluminum

oxide into space, creating clouds that

may linger up to 2 weeks after the rocket

is fired, before dispersing and reentering

the atmosphere. The particles therefore

represent a significant threat of surface

erosion and contamination to spacecraft

during that period.43

Interference with scientific and other observations can occur as a result of orbital

debris. For example, the combination of

byproducts from second stage firings –

gases, small solid particles and “spaceglow” (light emitted from the gases) –

will often affect the accuracy of scientific

data.44 Debris may also contaminate

stratospheric cosmic dust collection

experiments or even interfere with the

debris tracking process itself.45 The presence of man-made objects in space complicates the observations of natural phenomena.

46 Astronomers are beginning to

have difficulty determining whether an

object under observation is scientifically

significant or if what they observe is just

apiece of debris. As the number of debris

particles increases, the amount of light

they reflect also increases, causing “light

pollution,” a further interference with

astronomers’ efforts. Space debris has

also disrupted reception of radio telescopes and has distorted photographs

from ground-based telescopes, affecting

the accuracy of scientific results that

might be obtained.47

The Nature of Space Debris

Since the first satellite break up in 1961,

nearly 100 satellites have violently fragmented in orbit. Over 20,000 objects have now

been cataloged by the SSN, with nearly 35 percent of this compilation a result of these

breakup events (as of January 1990).48 Cur-

~Johnmn and McKnight, op. cit., footnote 9, p. 93.

40DWren se Mcfii@t, ~~~temining the Cau= of A &te]]ite Fra=en~tion – A Case Study of the ~smos 1275 Breakup,” presented at the 38th Congress of the International Astronautical Federation, Brighton, U.K, 1987.

dlJohnmn and Mcfiight, op. cit., footnote 9, pp. 19-20.

daNation~ Security Council, op. cit., footnote 2, P. 8.

43~c. Mueller ~d D*J. ~ssler, ~~The Eff~s ofp~im]ates From $o]id ~ket Motors Fir.ed in Space,’’#Uances in S@ce Reseumh,

vol. 5, 1985, pp. 77-86,

44~n~d E. Hun~n, “Shutt]e G]ow,” Scientific Americun, vol. 264 No. 5, PP. 92-%.

● Nation~ -ity Council, op. cit., fOOtnOte 2, P. 14.

apaul ~ey, ~~sw]m ~~]]i~ fifl~ion and the K)fE March 19 Optical Outburst in Perseus, ” T~~~P~YS~~ JOWTUZL ‘o]”

317, pp. L39-L44, June 1, 1987.

4~u~s Perek, “Impact of the Development of Space Technology on the ~wof fiter SPa% “Proceedings of the32nd Colloquium on

thel+uwof Outer S’ (Washington, DC: American Institute ofAeronautics and Astronautics, 1990); International &ronomical Union Colloquium No. 112 on Light Pollution, Radio Interference, and Space Debris, Aug. 13-16, 1988.

48Johnmn ~d Nauer, Op. Cit., footnote 6“
16 . orbiting Debris: A Space Environmental Problem

rently the SSN follows about 6,500 cataloged

objects. However, in LEO the SSN is limited

to tracking objects 10 centimeters in diameter

or larger (figure 6). Some analysts estimate

that some 30,000 to 70,000 additional debris

fragments ranging in size from 1 to 10 centimeters are also in orbit around Earth.49 The

probabilities of collision with these objects depends on the density of debris objects in different orbits, their relative velocities, and the

cross section of the spacecraft.50

Low Earth Orbits (LEO)

Objects in LEO pose the greatest concern

because these orbits are used the most.

The very low orbits (up to about 500 kilometers) are self-cleaning within a few

years; debris there encounters the upper

reaches of Earth’s atmosphere and

bums up or falls to Earth in a short time.

Although only about 39 percent of the

cataloged debris resulting from spacecraft breakups is still in orbit (as of January 1990), continued contributions to orbital debris would replenish debris

washed out by atmospheric drag. In fact,

most debris in very low orbits derives

from objects that decay slowly from

higher orbits (termed “rain down”).

Medium Earth Orbit (MEO)

The lifetimes of objects in MEO are extremely long. Because the spatial density

of objects is low, and these orbits are

used less frequently than LEO and

geosynchronous orbit (GSO), debris

poses less of a concern today than in

other orbits. However, nations are placFigure 6- Detection* Capabilities of the Space

Surveillance Network

100,OOO

50,000 – Undetected objects

–

20,000 –

10,OOO – optical**

- - -

5,000 –

Attitude,

km

2,000 –

1,000 –

-

I I I I I I I I I I

.5 1 2 5 10 20 50100200500

Limiting diameter, cm

● Once detected, an object may be tracked at greater range (altitude) than indicated

here. This figure indicates the approximate maximum range at which an object may

be detected by an optical or radar system operating in search mode.

● *The abiIity to detect space debris optically is highly dependent on the optical

characteristics of the debris.

SOURCE: National Aeronautics and Space Administration.

●

ing an increasing number of spacecraft in

these orbits, leading to future concerns.

Because spacecraft last so long in these

orbits, the increasing population in them

could pose a possible threat to future

space operations, especially in the Sunsynchronous orbits used for navigational

satellites.

Geostationary Orbit (GEO)

GEO, a special case of GSO, is especially

important because it is a limited natural resource51 of considerable economic

value52 for satellite communications.

~p. Eich]er ~d D. Rex, “chfin Reaction of Debris Generation by Co]]isions in Spm - A Final Threat to Spaceflight?” presented at

the 40th Congress of the International Astronautical Federation, Oct. 7-12, 1989.

SOV. A Chobotov, “Clmsifimtion of Orbits With Regard to Collision Hazard in Space,” JournulofSpocecm/l and R~he@ VO1. 20, No.

5, September-October 1983, p. 484-490.

~lThe ~~tiong orbit has ~n declared a “limited natural resource that must be used efficiently and economically” – 1982 ~-

temational Telecommunication Union Convention, art. 33.

gZFor a &~ssion of the economic impo~m of GEO, see U.S. Congress, OfXce of Technolo~Assessment, l~M~fio~ @YMWtion and Competition in Civilian Space Activities, OTA-ISC-239 (Washington, DC: U.S. Government Printing Offke, July 1986), ch. 6.
Orbiting Debris: A Space Environmental Problem ● 17

This orbital band53 contains a fastgrowing spacecraft population, the result, primarily, of its economic and political importance for communications

satellites and other commercial applications.

GEO has a current population of almost 400 trackable objects, including

about 100 active communications and

other satellites. The exact quantity of objects in GEO is not known, because objects smaller than about 1 meter are currently untraceable at that distance from

Earth (figure 6). One analyst estimates

that it may contain another possible

2,000 non-trackable objects.54 Objects

placed in GEO will effectively remain

there forever if not intentionally removed. Yet, because objects in this orbit

all move in the same general direction

(toward the east) at low velocities relative to each other, collisions between active, controlled satellites, and derelict

spacecraft that wander about in the orbit55 would occur at moderately low relative velocities. As a result, experts estimate that the current hazard from

orbital debris is less than the hazard

from meteoroids passing through the orbit. Because of the lower velocities, chain

reactions are less likely to occur than in

LEO. However, as more active satellites

are placed in this important orbit, and as

greater numbers of uncontrolled, inactive satellites drift around in it, destructive collisions could become inevitable.56

Destructive collisions will also be more

probable as inactive satellites that drift

throughout the GEO band gain increasingly higher velocities as a result of small

gravitational and other forces. At current densities for GEO debris and satellites, some analysts estimate that a large

functioning satellite (30 - 50 meters

square) will experience a 0.1 percent

chance of being hit during its total operational lifetime.

However, by the end of the century, if

current trends for the number of satellites placed in GEO continue, that

chance may increase dramatically to

about 5 percent per year if no mitigating

actions are initiated.57 T If this estimate

becomes reality, the typical satellite in

GEO, which is expected to operate 10

years, would then experience a 40 percent chance of being struck by debris

during its operational life.

Sources of Orbital Debris

Operational activities provide the source of

much space debris, including the largest objects. Nearly 50 percent of the total mass of

space debris derives from spent upper stages

that are left in orbit after depositing their

spacecraft in orbit. Individually, they are less

massive than spacecraft, but present a relatively large cross-section to other space objects. Because upper stages are often placed in

high, long-lived orbits,58 they can become a

major source of debris. The exhaust from

solid rocket upper stages, which places small

%trictly speaking, satellites in GEO deviate slightly from an ideal geostationary orbit, and travel in geosynchronous orbits somewhat inclined to the Equator. Their orbits thus define an orbital band about the Equator.

MD. H. Suddeth, “Debris in the ~s~tionq Ring, ‘The Endless Shooting Gallery,’” Orbitul k%s, NASA Conference fiblication

2360, NASA 19S5, pp. 349-364.

~fin~ion~spc=r~ me hi@ly controlled by their operators. ARer control ceases, over time, &u? a result of sol- pressure md

perturbations from the gravity fields of the Earth, Moon, and Sun, non-functional spacecraft develop small additional velocities that

send them both along and perpendicular to GEO. The result is that non-functional satellites will drift out of control along and across

GEO.

*Don~d J. ~ssler, “Techni~ Issues Associated with Orbital Debris in GEO,” CMitul Debris Monitor, VO1. 2, No. 4, Oct. 1, 19$9.

sTJohnson and McKnight, op. cit., fOOtnOte 9, p. ~.

5EFor e=p]e, the upPr ~ws that tie sw=r~ t. ~~chronous tr~sfer orbit (GTO) on their way to ~synchronous orbit,

continue to travel in highly eliptical orbits and spend most of their time far away from the Earth.
18 . Orbiting Debris: A Space Environmental Problem

particles of aluminum oxide in orbit, can also

be considered operational debris. Paint flakes

and particles from thermal insulation are also

released into space during space operations.

Conducting operations in space has also resulted in the ejection of miscellaneous hardware into orbit. For example, spacecraft are

generally separated from their upper stages

by explosive devices that may eject dozens of

small fragments. In addition, the process of

deploying a spacecraft on orbit often involves

the release of protective shields, covers, and

other incidental hardware items. Even ice

from the Shuttle waste management system

has been suspected of contributing to orbital

debris.59 Finally, inactive spacecraft that have

remained in space beyond their useful lives

also contribute to the debris population.

Fragmentation is the most significant

source of orbital debris by number. Since

1961, 25 breakups have contributed more

than 100 cataloged fragments apiece; eight

events exceeded 240 pieces each.60 What

makes fragmentation such a hazard is the

continual spread of fragmentation remnants

about the center of mass of the original spacecraft (box 4). Fragmentation derives from a

variety of causes that fall into three general

classes: accidental failures related to the propulsion systems, deliberate actions, and unknown causes.

. Propulsion-related failures often produce a striking amount of debris because

they result from explosions of the propellant, either while carrying spacecraft

into high orbits, or, in the case of liquidfueled rockets, afterward, because some

propellant is left in the stage. Some of

the latter explosions have occurred from

Box 4– The Evolution of a Debris Cloud

Prior to breakup, a satellite follows a fairly welldefined elliptical path about Earth. After a fragmentation, whether caused by structural failure,

explosion, or external impact, a debris cloud will expand over time, eventually creating a wide toroidal

band about the earth.

The explosion or collision that causes the fragmentation of a satellite propels pieces of debris in

all directions. Some debris will receive an impulse

along the initial satellite orbit, some in opposition,

and some at right angles. As a result of the velocities impartd to each fragment, the cloud will

evolve into a toroidal cloud; it takes hours to days

for an ensemble of debris fragments to reach this

phase. Over time the torus will spread into a band

about Earth, bounded only by the inclination and

altitude extremes of the debris. This last phase will

be reached months to years after the initial

breakup. Figure 7 illustrates the evolution of a debris cloud. All satellites with an altitude within the

cross-section of this wide toroidal band may encounter this debris cloud.

The rate at which the debris cloud moves into

these phases is a function of the velocity imparted

to the fragments: the greater the velocity, the more

quickly the cloud evolves. The rate at which the

cloud spreads is also a function of the parent satellite’s altitude and inclination.

SOURCE: Darren S. McKnight, 1990.

several months to 3 years after the stages

delivered their spacecraft to orbit.61 The

chances of such explosions have been

greatly reduced; ESA Japan, and the

United States now often vent their upper

stages following payload delivery.

● Deliberate destruction of satellites in

space, as opposed to accidental explosion, is another source of orbital debris;

most of these have been carried out by

~~~is ofa ho]ethat extended through three layers ofa 17-layer thermal blanket on the Solsr Msx satellite suggested that it may

have been caused by ice from the Shuttle. L.S. Schramm, et. al., “Particles Associated with Impact Features in the Main Electronics

Box (MEB) Thermal Blanket from the Solar Max Satellite,” Lunar and Planetary Scisnces, vol. 17, 1986. Ice particles are, however,

extremely short lived.

~Johnson and Nauer, op. cit., fbotnote 6.

elExp]osions of the Delta ELV second stage have contributed a lar~ number of debris fr~ents. see National *rity Council, oP.

cit., footnote 2, pp. 17-18. A third stage of the Ariane launcher has also exploded in orbit. See Johnson, op. cit., fmtnote 32.
Orbiting Debris: A Space Environmental Problem . 19

Figure 7-The Evolution of a Debris Cloud

Phase 1

Phase 2

Phase 3

SOURCE: Teledyne Brown Engineering, 1988.

the Soviet Union when its military satellites reach the end of their useful lives.62

Some have come about as a result of

space weapons testing. A total of 12

breakups are attributed to space weapons tests, which amount to about 7 percent of the current cataloged debris

population. Table 3 lists each weapons

test breakup and its impact on the nearEarth satellite population. However, table 3 does not reflect the total amount of

debris produced by these events because

small objects cannot be cataloged. Many

fragments do not stay in orbit long

enough to be cataloged. For example,

381 objects were detected as the result of

the Delta 180 Strategic Defense Initiative Organization (SDIO) experiment of

1986, but only 18 were ever cataloged.

Hypervelocity impacts. The high velocity of

some space debris relative to spacecraft gives

the debris extremely high energy on impact

with the spacecraft (figure 8). Such “hypervelocity” impacts63 are much more probable

in LEO, where collision velocities are higher

(averaging about 10 kilometers per second)

than in other orbits. Impacts involving relative velocities above about 5 kilometers per

second generate such temperatures and pressures that the impacting materials may vaTable 3-Space Weapons Tests

No. of No. debris No. debris

Class of breakups events cataloged in orbit

Phase 1:

Soviet ASAT . . . . . . 7

Phase 2:

Soviet ASAT . . . . . . 3 189 154

P-78 Breakup . . . . . . 1

D-180 Test . . . . . . . . . 1 18 0

12 1,037

SOURCE: Nicholas L Johnson and D. Nauer, “History of On-Orbit Satellite Fragmentations,” Teledyne Brown Engineering, CS88-LKD-001, 3d cd., Oct.

4, 1987; Nicholas L Johnson, personal communication, October 1989.

%Johnson and McKnight, op. cit., footnote 9, pp. 13-16.

SSA hmm]mityimP~ is one that ~ars at re]ative Ve]mities seater th~ the speed of Sound within the ti@ (3-6 kilometers

per second).
20 ● Orbiting Debris: A Space Environment Problem

Figure 8-Relative Kinetic Energy Content of Space Debris Objects

Log Hit

energy

with a

(joules) baseball

Speck of sand in

a sandstorm

8

6

t

I / A

●

✎

-2

/

+

.

●

●

.

.

+

.

v /

u V = 10 MIS

V = 100 MIS

-6 -4 -2 0 2 4 6

Log mass (grams)

SOURCE: Darren S. McKnight, 1990.

porize, producing hundreds of thousands of

smaller debris objects, and gaseous products.

The smaller objects themselves then become a

hazard to other functioning satellites.

Lower velocity impacts create a special problem from a shielding perspective. If the object

does not vaporize when it hits the outer

shield, and remains relatively solid, successive

layers are less effective in stopping it. In lower

velocity collisions, all of the ensuing debris is

likely to be large. There is no vaporization,

and hence no molecular condensation.

Chain reactions. The most serious consequence of collisions with space debris is the

possibility of a cascade effect,64 or chain reaction, in which debris proliferates as collisions

generate more and more debris, independent

of any further introduction of man-made objects. 65

Many current mathematical models indicate that if existing trends continue, a chain

reaction of collisions, some involving hypervelocity impacts, could create a debris envi-

~fiomas the ~ss]er eff~.~Don~d J. Kessler and B.G. CoursPalais, “Collision Frequency ofArtifici&d *@]lites:the C-tion

of a Debris Belt,” Journul of (?eophysicd Resetamh, vol. 83, 1978, pp. 2637-2646; D. J. Kessler, and S.Y. Su, “Contribution of Explosion

and Future Collision Fragments to the Orbital Debris Environment,” D. J. Kessler, E. Gruen, and L. Sehnal (eds.) “Space Debris,

Asteroids and Satellite Orbits,” Advances in S’ Reseumh, vol. 5, No. 2, 1986, pp. 2535.

Wal A. Chobotov, manager of the Space Hazards Section at the Aerospace Corporation in Los Angeles, estimates an 800 percent

increase in collision hazards within the next 20years. ( Mqjor John Graham, USAF, “Space Debris-A Definite Hazard to Hypersonic

Flight” unpublished paper, 1988.
Orbiting Debris: A Space Environmental Problem . 21

ronment that would make certain orbits in

LEO unusable for most long-term operations.

One model suggests that the critical population to support a chain reaction “is only about

2 to 3 times the current population and could

be reached within 20 to 50 years.”66 However,

the models used today, and the data that support these models, contain many uncertainties. Some debis experts question the modeling approaches taken to date.67 Modeling

technology needs improvement. In addition,

observational and experimental data are

needed to reduce uncertainties in data upon

which the models are based.

Trends

Historically, the number of objects in the

SSN catalog at the end of each year has been

used to map trends in the population.

Straightforward examination of limited portions of this catalog would lead to the conclusion that Earth’s satellite population has

grown at a rate of 5 percent per year. However,

this rate does not entirely represent an increase in hazard; it also reflects an increase in

our understanding of the hazard. A recent

analysis has shown that delayed cataloging of

debris significantly affects the determination

of the cataloged growth rate.68

For example, because tracking techniques

have improved, many of the objects added to

the catalog in the 1980s were actually generated in the 1960s and 1970s but are just now

being included. Figure 9 plots the history of

the debris cataloged from the fragmentation

of the Transit 4A (1961-Omicron) rocket

body. This event was the first satellite

breakup, occuring in 1961. For the last 20

years an average of 4 pieces have been added

per year with over 40 fragments being added

in the last 8 years.69 The delay in cataloging

these objects resulted from changes in operations, improvements in technology and, possibly, the orbital decay of the objects. Nevertheless, much of the increase in cataloged debris

is the result of new contributions to the debris

population.

From 1975 to 1985 the percentage of cataloged objects that are deep space objects (orbital period greater than 225 rein) has doubled from 7 percent to 14 percent.70 Most of

this growth is the result of increased activity

in the geosynchronous region. Other growth

results from additional surveillance and

tracking sensors dedicated to these altitudes.

The move toward placing spacecraft in higher

altitudes is a positive trend for the cluttered

LEO region. Yet, debris at higher altitudes

will be more difficult to detect and will have

longer orbital lifetimes. This trend may lead

to an environment that will be more difficult

to characterize and control.

DEBRIS REDUCTION

STRATEGIES

More than 30 years of experience in designing and operating spacecraft has led to the development of a variety of strategies to limit

the generation of new debris and to mitigate

the effects of existing debris. These strategies

vary in cost and effectiveness; overall, it is generally cheaper to limit the production of future debris than to cope with the economic

losses that debris can inflict on functioning

spacecraft.

~Eich]er and Rex, op. cit., footnote @ p. 1.

e~ch~s. H~@ Applied Technology Associates, Inc., personal communication, JUIY 1~.

68D-n S. Mc~i~t,~d Nichol=L. Johnmn, “Under~dingthe T~e Earth ~tel]ite Population,” 40th ~Congress, Mdam

Spain, October 1989.

-Ibid.

70W. ~1, ~~~ E~ima~ of the Trac~b]e~.orbit Population Gro~h to 2010,’” SMC Techni~ Report CS 386-S/S9-lCM)2/lC, Aug.

15, 19s9.
22 . Orbiting Debris: A Space Environmental Problem

Figure 9-Debris Cataloged from the Breakup of the Transit 4A Rocket Body

250 —

Cumulative

number 150

100

50

o

I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I

61 62 63 64 65 66 67 66 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 65 86 87 88

SOURCE:

Year

Nicholas L.Johnson and David J Nauer, History of Om-Orbit Satellite Fragmentations,4th ed. (Colorado Springs, CO: Teledyne Brown Engineering, January 1990), NASA

Contract, NAS 9-18209.

There are two basic classes of action that

can minimize the orbital debris burden – preventive measures to preclude explosive failures of spacecraft and upper stages and eliminate placement in outer space of space debris

objects, and removal procedures, which by reducing the number and mass of objects on orbit, reduce the probability and severity of onorbit hypervelocity collisions.

Preventive Measures

The most effective near term measures are

to design and operate launch vehicles and

spacecraft so they have minimum potential

for exploding or breaking up.71 For example,

launch vehicle upper stages should be depleted of propellants and pressurants after

they have completed their mission. Batteries

should include electrical protection circuits to

preclude battery explosions resulting from

electrical shorts. Such measures reduce or

eliminate the potential for chemical explosions and reduce the severity of collisions

when they occur because they also remove additional energy stored in the object. Since

1981, NASA has operated its upper stages in a

manner that sharply reduces the likelihood

that they would explode in space. Japan and

ESA have recently adopted similar operational procedures. Costs of these procedures

vary, depending directly on the design of upper stages and spacecraft, but can be measured in terms of the equivalent weight of

TINation~ ~rity Council, op. cit., footnote 2, ch. 6.
Orbiting Debris: A Space Environmental Problem. 23

spacecraft that would have to be given up to

include such measures,72 or the costs required

to reduce the dry weight of a spacecraft.73

Other preventive measures include designing and building spacecraft so they resist environmental degradation from atomic oxygen

and solar radiation, and devising spacecraft

and upper stage separation procedures that

limit the spread of operational debris. Abandoning the practice of deliberately fragmenting inactive satellites in orbits where atmospheric drag is extremely weak and debris life

correspondingly long would contribute markedly to reducing generation of future orbital

debris. 74

In very low orbits (less than about 250 kilometers), atmospheric drag causes objects to

fall into the atmosphere and burn up or plummet to the surface75 over time scales of a few

months to a year. Though extremely small,

drag forces as far out as 500 to 600 kilometers

will force space objects down over periods of a

few years. High levels of solar activity76 

cause

an expansion of Earth’s upper atmosphere,

leading to increased atmospheric drag and

significant reductions in the debris population in LEO (figure 10). The reentry of the Solar Maximum scientific satellite on December

2, 1989, demonstrated this phenomenon.77

The current cycle of increased solar activity,

which has been especially strong, brought it

down much sooner than expected.

The atmospheric drag experienced at these

altitudes has been used on many occasions to

remove upper stages and other objects that

have completed their missions. For example,

the Delta 180 experiment conducted for the

Strategic Defense Initiative Organization78

was carried out in low orbit so that the many

small objects deployed as part of the experiment would be removed from orbit within a

few days. With redesign of the upper stages, it

would be possible to place upper stages in elliptical orbits that bring them into the upper

reaches of the atmosphere at perigee, causing

them to fall back to Earth (deorbit) relatively

quickly.

Active Removal Procedures

A few observers have proposed active removal of existing debris. Some proposed

methods would be prohibitively expensive

and might even be counter-productive.79 One

proposed method would use an orbiting object with a very large cross section, perhaps a

spherical balloon filled with some type of

foam, to “sweep up” small debris over time.80

TzFor e=p]e, sendingthe up~r Sta@ ~fingamtellite inta Sun-synchronous orbit toward the atmosphere rather than leavingit

in orbit exacts a one p-cent penalty on the weight of spacecraft delivered to such an orbit. See Joseph P. Lcilus, Jr., E. Lee Tilton, and

L. Parker Temple, III, “Decision Time On Orbital Debris,” Aemspuce America, vol. 16, June 1988, pp. 16-18.

73~ucingthe dry we@t of a sP=rfi while maintaining its capability can cost more than $100,000 a pound. see U.S. Consress?

Offkeof Technology Assessment, ~odubkSpacecm/l: Design andLuunchAlternatives, OTA-BP-ISC!-60 Washington, DC: U.S. Government Printing Office, January 1990), p. 7.

TdThe ~~et Union h= made it a practice to fragment certain reconnaissance satellites after their usefu] ]ife, presumably to prevent

them from being recovered by the United States. Recently, they have fragmented these satellites in very low orbits, where the debris

quickly enters Earth’s atmosphere.

73sWm obj~s that f~] ~ E~h may cause d~a~ on Earth. See Section V., Lt@ ksues for a discussion of lef@ regimes and

remedies.

T8For e=p]e, the SOkW mtimum of 1980 and the one we are now experiencing that is expected to IE* in IW1.

~sol~ ~ had ~n orbiting at abut 570 kilometers above Earth’s surface tier being redeployed fol]owing repirs in 19~,~

orbital altitude that would normally leave it in orbit for much longer than 5 years.

TB~@ment of~fen= Stratetic ~fen= Initiative OtYice/Kinetic Energy Oilim, “DeltA 180 Final RePorL” vol. 5, ~ch1~’”

T~me prop~ methods for remo~ng efisting s~ce debris could inadvertently add more debris m the s~ce environment th~

they remove.

~A.J. Petro and D. L. Talent, “Removal of Orbital Debris. ” See Joseph P. Lofius, Jr. (cd.), in OAitaZ Debris Fmm Uppr-Stage

Breakup, Prqpss in Astronautics and Aeronautics, vol. 121, 1989, pp. 169-182.
24 . Orbiting Debris: A Space Environmental Problem

7000 “

Cumulative

number

Solar activity affects debris the most

240 annually

,

Figure 10- Spatial Densities In LEO for Various Sizes of Debris

catalog

Rocket bodies

Payloads

Frag debris

Oper debris

Year

SOURCE: Darren S. McKnight, 1990.

For deorbiting large objects, an Orbital

Manuevering Vehicle (OMV) similar to that

which NASA had under developmental might

be effective in LEO. The OMV would attach itself to the space object and propel it to a lower

altitude. 82 The use of space tethers has also

been suggested. This technique would require

attaching a tether between the debris object

and a “remover” spacecraft and letting the

tether out, causing the remover spacecraft to

move higher in orbit, and the debris to move

lower. Eventually the debris object moves

close enough to the upper atmosphere that after release from the tether it spirals in and

burns UP.83

Spacecraft launched in the future to orbits

between about 250 and 750 kilometers could

be brought down within a few years by deploying a balloon-like device-at the end of their

useful lives-to increase atmospheric drag.

Spacecraft in low and medium orbits could be

sent back into the atmosphere at the end of

their useful life by reserving some fuel for the

purpose, or by adding a propulsive device Specifically designed to deorbit the spacecraft.

Launch vehicle upper stages can also be designed to be brought back to Earth after delivering their spacecraft to orbit. High costs will

limit the use of many such procedures. If possible, reserving some fuel is the most eco81AS a ~mlt of ~vem m% overruns, NASA recently canceled the OMV development Pmlpm – “OrbitalManeuveringVehicle Program is Terminated,” NfiA News, Release 90-78, June 7, 1990.

~Ibid.

Npo Eichler ~d A Bade, “Removal of Debris From Orbit,” AIAA/NASA/DOD Orbital Debris Conference: Technical Issues and

Future Directions, Apr. 18-19, 1990, Baltimore, MD.
Orbiting Debris: A Space Environmental Problem ● 25

nomical means of deorbiting spacecraft and

upper stages.84 Adding a deorbiting device to

satellites and rocket stages appears to be the

next most economical method.* Some cases

might call for using a combination of these

two methods.

On several occasions, NASA demonstrated

that the Space Shuttle could be used to capture and repair,86 or return to Earth,87 

nonfictional satellites. However, at the present

time the cost of retrieving them far outweighs

any benefit that could be derived strictly from

salvage. In addition, because they may involve

extravehicular activity (EVA), such operations may be dangerous to the crew.

Shielding and Other Protective

Measures

Designers have included various shielding

devices on spacecraft. In the 1960s Astronomer Fred Whipple suggested using a dual-wall

system to protect space systems from

micrometeoroid impacts. Such a design was

employed on the U.S. Skylab space station

and on the European Giotto spacecraft, which

flew through the tail of Comet Halley. In this

design the outer wall (bumper) sacrifices itself

to breakup the impacting projectile. As a result, the inner wall is subjected only to the impact of many smaller fragments, traveling at

lower velocities. This inner wall is often a pressure vessel for the primary satellite structure.

The key to the effectiveness of most protective bumper systems is that they are “tuned”

to a specific hazard: mass, velocity, size, and

density of impacting object. For example, a

shield designed to protect against an 8 millimeter diameter aluminum fragment traveling at 6 to 10 kilometers per second, is not necessarily effective against slower moving

fragments. That is to say, the bumper will not

cause a comparable-sized projectile moving at

a lower 3 kilometers per second to fragment

because the latter does not carry enough kinetic energy. Thus, the slower projectile

pierces the outer wall and moves onto strike

the inner wall with greater impulse per unit

area than a comparable object initially moving much faster.

In summary, a bumper shield is effective

for a specific hazard within some margin of

tolerance. However, the bumper system will

not adequately protect the satellite from all

impacts of lesser or greater energy. The debris

environment in LEO contains hazards from

objects ranging from milligrams to kilograms,

with relative velocities ranging from O to 14

kilometers per second. Thus, bumper shielding can only shield spacecraft from a portion

of the debris hazard.

Areas in which shielding research is being

pursued include methods to shield astronauts

engaged in extravehicular activity (EVA),

coatings on optics and windows, the use of several intermediate shielding layers, the use of

nonmetallic and composite materials for

shields, and stronger insulation between

bumpers and spacecraft.

Providing redundancy for critical spacecraft systems would allow the backup system

to function even if the primary system fails as

a result of collision with space debris. Some

critical spacecraft elements, like solar panels

or antennas, cannot be shielded without destroying their effectiveness and are too heavy

~~ ~dition, the oPration~ ]ife of some stages may have to be extended to position it for ocean disposal. Both measures will generally exact some penalty in spacecraft performance, as the stage must carry extra propellant, and therefore additional weight.

*A.J. Petro and H. Ashley, “cost Estimates for Removal of Orbital Debris. ” LOfiUS, Op. cit., footnote ~, PP. Iw-lw.

~In April 19$4, NASA retrieved the Solar Maximum Satellite from an orbit about 500 kilometers above Earth ~d repaired it *r

the satellite’s attitude control system had failed. The repaired Solar Max continued to function until Dec. 2, 19S9.

8WASA retfiev~ two ~mmunications mt,e]]ites whose upper stages had failed after being launched from the Shuttle. Although

this was an important demonstration of the Shuttle’s ability to retrieve space objects, from an economic point of view, it was not cost

effbctive, as the cost of retrieval and refurbishment of the payloads outweighed the cost of building a replacement satellite.
26 ● Orbiting Debris: A Space Environmental Problem

to make redundant systems. Making solar

panels and antennas some 10 to 20 percent

larger would compensate for losses from collisions with small debris.88

Providing shielding, redundant systems,

and extra large systems adds considerable extra weight to payloads and therefore increases

overall operating costs. Hence, more accurate

characterization of the space environment

that would allow spacecraft designers to determine more precisely the protection needs

of particular spacecraft could reduce costs accordingly.

Geostationary Orbit

GEO represents a special case because objects placed there remain for millions of years,

and because certain segments of the orbit are

used more intensively than others.89 To reduce the chances of accidental collisions between inactive and active satellites, some organizations, including agencies of the U.S.

Government, just prior to retiring a satellite

from service have used a satellite’s last remaining fuel to place it in a higher orbit beyond GEO. Just how effective this practice

will prove to be is currently under study. Analysts do not yet know the minimum safe distance necessary to prevent objects drifting

back through GEO years afterward, but believe that inactive satellites should be boosted

into a circular orbit at least 300 kilometers

farther outgo If a satellite in an orbit less than

160 kilometers beyond GEO were to breakup,

roughly half of its fragments would eventually

drift back through GEO, posing a greater hazard to active satellites along the orbital band

than if the satellite had remained in GEO.91

However, because boosting satellites out of

GEO reduces their potential lifetime on orbit,

and therefore their economic value, operators

are reluctant to spend more fuel than necessary on this procedure. Additional theoretical

modeling analysis would assist in determining

the most economical removal orbit.

Other hazards may pose greater threats.

For example, the explosion of a single upper

stage (orbital transfer stage), used to carry a

communication satellite to GEO, could create

more pieces of fragmentation debris passing

through GEO than would be removed by hundreds of end-of-life maneuvers.92 Yet, because

orbital transfer stages follow a highly elliptical orbit that takes them between LEO and

GEO altitudes after they have deposited their

satellites in GEO, it may be possible to control

the stage’s perigee and place it low enough

that the upper reaches of the atmosphere will

slow it down every time it cycles through perigee. Eventually, the upper stage would tumble back into the atmosphere and bum up.

LEGAL IMPLICATIONS

Domestic and international law regulating

space activities began to develop in the late

1950s and early 1960s. Yet only recently have

managers of space systems recognized that

the hazards of space debris might require

some sort of regulatory regime. Earlier law,

including the international treaties and agreements on space, failed to address orbital debris explicitly. Any domestic and international legal regimes for debris should address

the generation of debris, its removal from or-

~~appropna~]y design ed,the ~]m~els Could suffer losses of individual cells without causing total IOSS of the Panel’scalability.

8Q~ orbi~ ~cs ~fingthe UnitiS~@s, tr~~At]mtic tr~c, and Europe, where the volume of digital, video, and voice trfic is

particularly high and of high economic value, the density of communications satellites is particularly high.

eov.~ cho~~v, ~~~sw~ of@=r~at Endaf.fife in ~Wchmnous orbit,’” ~/~Astrod~amic Specialist Conference,

StOwe, Vermont, Aug. 7-10, 1989 (paper No. AAS 89-378).

el~ss]er, op. cit., fmtnote 56.

921bid.
Orbiting Debris: A Space Environmental Problem . 27

bit, the question of jurisdiction and control

over space debris, detection and identification

of space debris, international responsibility

for space debris, and possible remedies for

damage caused by debris. This section explores the legal implications of orbital debris

and suggests areas where new international

agreements may eventually be needed.

The Definition of Orbital Debris

One of the impediments to developing new

laws to address the problems posed by space

debris is the lack of an adequate definition of

space debris. Existing national laws and international space treaties and agreements (box 5)

contain neither a definition nor a description

of orbital debris. While orbital debris maybe

divided into four classes for descriptive purposes (table 4), legal experts disagree whether

the legal scope of orbital debris includes all

technical classes.

The seriousness of the debris problem for

space operations, the possible confusion over

the literal meaning of “debris,” and the need

to define the scope of debris all suggest the

need for a legal term of art. Such a term would

provide a starting point for discussing the legal issues arising from the orbital debris problem.

An explicit definition of orbital debris

might not be necessary, however, if that term

were subsumed under an existing space law

treaty definition. Although the term “contamination,” found in Article IX of the Outer

Space Treaty, might be thought to serve this

purpose, it refers only to harmful microbiological organisms of terrestrial origin, which

might be accidentally released in the aftermath of a collision or explosion in outer

space.

93 The term “space object” is more

promising. The Liability Convention provides

that “space object” includes a spacecraft, the

launch vehicle, and the component parts of

both. The Registration Convention also contains this description. However, existing international law does not define space object.

During the debates over the terms of the Liability Convention, negotiators could not

agree on a description for “space object,” nor

was the question of whether orbital debris is

included in “space object” specifically addressed. Negotiators were primarily concerned with which artificial objects should be

considered “space objects,” not with the effects of those objects following their active

lives. During these debates, legal experts put

forward two definitions of “space object.”94

The narrow definition included the object itself and its component parts, as well as the

means of delivery and its component parts.

Although some delegates offered a much

broader definition, which would have included articles on board the space object and

articles detached, thrown or launched from

the space object, the narrower interpretation

was adopted. Consequently, it is unclear

which classes of space debris, if any, are included implicitly in “space object.” Consider,

for example, inactive payloads. The Liability

Convention is silent on whether a payload

must be active to qualify as a “space object”

capable of causing damage. If inactive payloads are included, then they are space debris,

with liability for compensation attaching to

the launching state.

Orbital debris may also be considered a

“space object” if it falls under the term “component parts.” Yet what exactly constitutes

“component parts” is not settled. According

to the description of space object in the Liability Convention, all operational debris except

*Howard ~er,S-W*: h@/ ati Policy Implications (Dordrecht: Martinus Nijhoff Publishers, 1989), P. 103.

-The hi~~of re]evantu.s. nation~ positions, and the negotiation of relevant UN treaties involvingissues related to debris, @lution, and contamination can be found in Carl Christol, The Modem International Law of Outer Space (New York, NY: Pergamon Press,

1982), chap. IV, pp. 129-151; For a detailed discussion of this issue, see Baker, op. cit., footnote 92, pp. 83-85.
28 . Orbiting Debris: A Space Environmental Problem

Box 6 – Internatwnal Space Treaties and Agreements

1. The Outer Space Treaty of 1967,1 to which the United States and more than 100 countries are signatories, provides that a State party assumes international responsibility for space activities conducted by its government agencies and non-government entities.2 The Treaty establishes that State parties are internationally liable for damages

to the persons or property of other State parties, if the damage is caused either by an object launched into outer

space or its component parts, whether the damage occurs on the ground, in air space or in outer space. This liability

applies to States launching and procuring launches, and to States whose territory or facilities are used for

launches. 3 Of great importance to environmental considerations is the treaty’s statement obligating States to engage in appropriate international consultation in circumstances where it can be established that there is a reasonable belief that a space activity of one State party would cause potentially harmful interference with space activities

of other State parties.4

2. The Liability Convention of 19725 provides that both intergovernmental organizations and State parties are

liable on the basis of fault for damage of their space objects, launch vehicles, or component parts thereof may cause

in outer space.6 States collaborating in launch activities are also jointly and severally liable for damages.7 The standard of compensation is to be in accordance with international law and principles of justice and equity.8 Because the

Liability Convention defines a “space object” as “including component parts of a space object as well as its launch

vehicle and parts thereof, ’’9

the launching State’s liability would continue whether its “space object” was functional

or had reached the non-functional status of “space debris. ”10

3. The Registration Convention of 197611 provides a system whereby any space object launched into Earth orbit or

beyond is to be registered with the United Nations.12 In the case of two or more launching States, an agreement

among or between those States will determine who registers the object.13 Where identification of debris causing

damage cannot be obtained from the registration information, the Convention requires other parties with space

monitoring and tracking facilities to assist to the greatest extent feasible in identifying the space object.14

4. The Rescue and Return Agreement of 196815 establishes State party obligations regarding the return to Earth

and recovery of space objects or their component parts.16 A State party discovering such material must notify the

launching authority and the United Nations.17 The discovering State shall take practical steps to recover returned

material in its territory if the launching authority so requests. If a discovering State reasonably believes that the

returned material is dangerous or hazardous, the launching authority, under the direction and control of the discovering State, is to take immediate effective action to eliminate possible danger or harm.18

I Treaty on Princip]e9 ~verning the Activities of States in the Exploration and Use of Outer Spce~ kcludingthe M~n ~d

Other Celestial Rodies, 18 U.S.T. 2410, T. I.A.S. No. 6347,610 U. N.T.S. (Apr. 22, 1968).

2Article VI.

3Article VII.

4Article IX.

%onvention on International Liability for Damages Caused by Space Objects, 24 U.S.T. 2389, T. I.AS. No. 7762 (Mar. 29,1972,

effective Oct. 9, 1973).

eArt.ic]es I, III, IV, nd ~1.

7Article V.

8Article XII.

‘Article I.

l~here i9 n. retirement in either the Liability Convention or the Outer Space l’reatythat SPWX objects, launch vehicles, or

any components must be functional when damages occur in order for liability of the launching State@tate of Registry to attain.

l~convention on ~~stration of obj~s Launched into Outer Space, 28 U.S.T. 695, T. I.A.S. No. 8480, U. N.T.S. 15 (Oti. 9,

1973.)

‘2Articles I-IV.

lsfiic]e II, paragraph 2.

“Article VI.

Continued on next page
Orbiting Debris:A Space Environmental Problem .29

5. The Moon Agreement of 197919 entered into force on July 11, 1984. However , none of the major spacefaring

nations, including the United States, is party to the Agreement. The Agreement establishes obligations of States

parties and international organizations regarding environmental protection.20 Measures must be taken to prevent

the disruption of the existing balance of the environment of the Moon, other celestial bodies in our solar system, and

orbits around or other trajectories to or around them, and to avoid harmfully affecting the environment of Earth.21

Notice is to be given to the Secretary-General of the United Nations of the placement and purpose of radioactive

materials. 22 Mandatory consultation procedures and subsequent means for settling disputes are provided.23

15Agreementon the Rescue and Return ofAstmnauts, the Return ofAstmnauts and the Return of Objects Launched into Outer

S@ce, 19 U.S.T. 7570, T.I.AS. No. 6599,672 U. N.T.S. (Apr. 22, 1968).

‘

eArticle V.

17~ic]e V, paragraph 1“

18Artic]e V, paragraph 4.

IST~ ~mmt ~vming ~tivi~ of S&&5 on t~ Mwn ad Ot&r ceks~~ -s,United Nations General Assembly,

Resolution 34/6S (Dec. 5, 1979).

mfiicle~~d Micle~.

zl~icle9 I, paragraphs 1 and 2; and Article VII, par~aph 1.

22fiicle VII, para~aph 2“

as~icle XV, paragraphs 2 ~d 3.

Table 4- Classes of Space Debris

● Payloads that can no longer be controlled by their operators;

● Operational debris (objects produced as a result of normal

space activities, remaining in outer space);

● Fragmentation debris (products o fexplosions and collisions);

and

● MicroParticulate matter (micron-size objects such as solidpropellant rocket motor effluent, paint flakes, and thermal

coatings).

SOURCE: Office of Technology Assessment, 1990 .

litter appears to be “component parts,” although jurists do not agree on this point.

Whether all fragmentation debris and

microparticulate matter are included is even

more problematic, even if the broader interpretation of “space object” is invoked. This

fuzziness is unfortunate because fragmentation debris represents about half of the orbital

debris population.

Summarizing, the only classes of orbital debris included in current treaty law, with any

degree of certainty, are operational debris, to

the exclusion of inactive payloads, fragmentation debris, microparticulate matter, and litter. The degree of difficulty already manifest

in attempting to obtain international agreement on the definition of debris clearly suggests that early voluntary national action to

limit and reduce debris may be far more effective than attempting to obtain any international agreement on debris reduction procedures in the near term.

Jurisdiction and Control

Who has jurisdiction and control over space

debris? If remedial action is to be included in

any regulatory scheme for orbital debris, consideration should be given to the issue of who

is authorized to remove orbital debris. Article

VIII of the Outer Space Treaty provides that

the State of registry of “an object launched

into outer space” has the right to make and

enforce domestic law in relation to that object

and “any personnel thereof,” and that ownership of a space object is not affected by its

presence in outer space. Two legal issues

raised by this provision are whether orbital

debris falls within the scope of Article VIII

and the extent to which jurisdiction and control over space objects is permanent.
30 . Orbiting Debris: A Space Environmental Problem

Legal analysts agree that both active and inactive payloads fall under Article VIII. They

do not agree, however, on an appropriate

method for distinguishing active payloads

from inactive ones. Although a test of “effective physical control” has been proposed, successfully applying this test is hampered by

several obstacles. First, legal opinion favors

the view that jurisdiction and control of a

State over its space objects is permanent.95

Moreover, because ownership of a space object also is permanent, regardless of its use

and condition, and because the owner retains

the rights of possession, use, and disposal,

states or other legal entities would require the

consent of the State of registration in order to

interfere in any way with that space object.

Applying a doctrine of permanency to debris objects appears to impede attempts to

minimize the quantity of orbital debris as it

only accounts for inactive payloads, and it applies only to identifiable space objects. There

may be two possible exceptions to this doctrine, however: the analogy to abandonment,

and sentence 1 of Article IX of the Outer Space

Treaty. 96

In maritime law, abandonment arises

where no personnel remain on board a vessel

and there is no intent to return and reactivate

it. Then the vessel becomes a derelict subject

to salvage. It is not yet clear, however,

whether the hazard posed by orbital debris is

sufficient justification for its removal without

the consent of the State of registration. Sentence 1 of Article IX of the Outer Space Treaty

provides in part that State parties to the

Treaty have obligations to cooperate, to provide mutual assistance, and to have due regard for the corresponding interests of other

State parties. Although some have suggested

that these legal obligations fetter the absolute

nature of jurisdiction and control and ownership, application of sentence 1 may be limited.

First, some have argued that corresponding

interests exclude threats posed by orbital debris.97 Second, the Outer Space Treaty provides for competing interests among states,

but does not lay down any rules for designating priority among these interests, which include a right to hazard-free space navigation

as well as a right to leave an inactive payload

in orbit.

Suggestions providing for timely removal

of hazardous space objects, without consent of

the State of registration, are limited in their

effectiveness. They refer at best to inactive

payloads and other identifiable space objects,

and offer no preventive measures, but only

compensation after the fact. Given the inchoate nature of the law regarding orbital debris,

a rigorous analysis of analogous provisions in

other legal regimes would probably be quite

useful.

Detection and Identification

To remove orbital debris from outer space

and to hold States accountable for damage

caused by their orbital debris entails a

method of identifying the State responsible

for the debris. Identification of space objects

is addressed in the Registration Convention.

Identification of space objects involves two

phases: detection of the object and identification of its State of registry. The Registration

Convention contains no provisions for detection and does little to establish a system that

%ee, for example, I. Diederiks-Verschoor, “Legal Aspects of Environmental Protection in Outer Space Regarding Debris,” 30th

Colloquium on thebw of Outer Sjuu.w, 1907, p. 131.

SE~ theexploration mduse ofouter space, includingtheMoon and other celestial bodies, States Parties tothetreaty shall be Wided

bytheprincipleofcooperation and mutual assistance and shall conduct all their activities in outer space, includingtheMoon and other

celestial bodies, with due regard to the corresponding interests of all other States Parties to the Treaty.

97CmI Q. Crist,.ol, The Mo&rn In~‘ ncd Luw of Outer Space (New York, NY: Pergamon Press, 1982), p. 139.
Orbiting Debris: A Space Environmental Problem ● 31

would identify the States of registry of space

objects that do not appear in the registration

lists.98 Consequently, this treaty is of little use

in identifying orbital debris, especially in its

untraceable manifestations. Without proper

identification, the Liability Convention cannot be invoked because the State of registry

cannot be ascertained. Another possible weakness of this treaty is the absence of a provision

for compulsory markings, although markings

must be registered if they are used. Therefore,

what would be the most obvious and convenient method for identifying space objects is

voluntary. Large components could be identified relatively easily. Very small components

and microparticulate debris cannot readily be

marked.

Liability for Damage Caused in

Outer Space

The Liability Convention sets out a legal regime to provide compensation for damage

caused in outer space by space objects. In

outer space, liability is based on fault. It is significant to note that negotiations for the Liability Convention did not consider the question of the risks posed by orbital debris. As a

result, the negotiators did not address several

liability issues of extreme importance related

to damage caused by orbital debris. These issues include the meaning of “damage” and the

reasonableness of a fault-based liability99 regime for damage caused in outer space by orbital debris.

Experts generally agree that damage to the

outer space environment per se is not within

the scope of the Liability Convention. Consequently, launching States cannot be held liable for the mere presence of orbital debris in

outer space. In this regard, microparticulate

matter and very small pieces of fragmentation

debris are of particular concern because

launching States have no legal incentive to

avoid generating these types of orbital debris,

although they have enormous operational incentives to do so. It would be possible to

amend the Liability Convention so as to include damage to the outer space environment

per se, based on the fact that outer space is a

global commons. Yet, even if accepted, resolution of three significant legal issues beyond

the scope of space law would still remain: legal

standing for claimant States (who is going to

speak for mankind?), assessment of damages,

and the nature of the liability.

The principle of fault-based liability is a further impediment to compensation for damage

caused in outer space by orbital debris. Application of the fault-based outer space liability

regime of the Liability Convention to orbital

debris is doubtful because the Convention

“appears to be primarily concerned with a

possible collision between [active] space objects. "

100 Even if damage caused by orbital debris were within the scope of this regime, several other important legal issues, such as

proof of negligence, and contributory negligence, among others, would remain unresolved.

Article III of the Liability Convention does

not specify whether the damage caused must

be reasonably foreseeable, that is, whether the

damage caused by orbital debris is of a kind

that specialists in the field would expect to

occur. It has been argued that, as a result of

the impossibility of foreseeing all the different

situations that could lead to damage in outer

space, only two factors need to be established

–the damage, and a cause-and-effect rela-

*& ]onga~m ~bj~ is in~~, ~d ha~~n registered bythe ]aunchings~te, as re@red bythe convention, the stikOf IW@StryCLUl

be established by observing its orbital parameters. However, the State of registry of most space debris, especially debris that cannot

be tracked by existing technology, is uncertain.

wFault.& liability is liability based on the ability to establish direct or indirect fault for d~~.

l~unit~ S~~sConWess, s~of~natecommit~ on Aeronautic~ ~d s~m$ciences, 92d C!Ong., Zd %ss., Report on tk.e Conuention on Interndional Liability for Damage Caused by Space Objects: Analysis and Background Data (Comm. Print 1972), p. 27.
32 ● Orbiting Debris: A Space Environmental Problem

tionship between the damage and the incident

giving rise to the damage.

The terms of the Liability Convention place

restrictions on who may seek compensation

for damage caused in outer space by orbital

debris. For example, compensation is unavailable for any damage resulting from a collision

between two space objects, each owned by a

different private entity, if both entities are under the jurisdiction of the same launching

state.101 The same result would follow if one

of the space objects were a piece of identifiable

orbital debris. Nor is compensation available

under the convention to injured parties who

are either nationals of a launching State or

foreign nationals participating in any phase of

a space activity. This restriction extends to nationals of all States participating in any one

launch activity, and to nationals of all States

entering into joint ventures with any State

participating in any launch activity. Additionally, certain provisions of NASA launch agreements that allocate risk among the participating parties further limit eligible claimants by

arranging reciprocal cross-waivers of claims

among participants.

One serious shortcoming of the decision to

base damage in outer space on fault has been

that the rationale for fault-based liability

must be applied to damage caused in outer

space by orbital debris. This rationale, ostensibly based on the equality of States in undertaking space activities, makes three fundamental assumptions: States participating in

space activities accept the risks involved;

States are free to conduct any space activity as

long as fault-based damage does not result;

and absolute liability102 for damage to space

objects in outer space would lead to absurdities and inequities.

Although the fault rationale may well be

justified in the event of collisions between two

active, and therefore controlled, satellites, its

application seems unreasonable where damage in outer space is caused by orbital debris.

In this situation, application of the rationale

for absolute liability may be more appropriate. First, space flight and space activities may

be considered ultrahazardous or abnormally

dangerous activities for which “responsibility

[should be] imputed to the person or entity

making the initial decision to engage in the activity which exposes others to risks where possibly no amount of foresight or feasible protective measures may avert injuries.”103

Therefore, in cases where orbital debris

causes damage, those who create the risk

should bear the cost of not only compensating

for damage done to persons and property in

outer space, but also protecting the space environment itself. Second, absolute liability is

considered necessary when it is unlikely that

fault can be established. In the outer space

context, and particularly when orbital debris

is being considered, problems of establishing

the proof of fault necessary for satisfying the

courts are magnified. The problems encountered with making the case under existing or

even strengthened liability provisions make it

essential to concentrate on establishing a preventive set of measures and enforcement

mechanisms.

The Kosmos 954 incident illustrates how a

claim may be based upon the Liability Convention and principles of international law.

Canada’s claim consisted of compensation for

search, recovery, testing, and clean-up. Under

principles of international law, Canada had a

duty to take the necessary measures to prevent and reduce the harmful consequences of

the damage (mitigation).104 The settlement

procedures of the Liability Convention were

Iol~ that -,~ i~ur~ -y would have to seek redress under national ]aVVS of the *K mn~rned.

IOaIn other WOr&, where liability is incurred by a party reglll’dless of fault.

IMLJ.S. ~na~ mprt on Liability Convention, op. cit., fbotnote W, P. 26.

1~~ Cmada: Clfim A@nst the Union of ~~et ~i~ist ~publics for Damage caused by soviet hsnms !)64, reprinted inhb

national Legal Materials, vol. 18, 899, par. 15 & 17, 1979.
Orbiting Debris: A Space Environmental Problem .33

never actually applied to the matter, however,

as the dispute was resolved without invoking

them. Officially the Soviet Union did not admit liability for the damage,105 but agreed to

pay Canada $3 million (Canadian) “in full and

final settlement of all matters connected with

the disintegration” of Kosmos 954.106

FUTURE DIRECTIONS FOR

REDUCING ORBITAL DEBRIS

The effect of orbital debris on future space

activities depends in part on the success nations have in instituting procedures to reduce

their future contributions to orbital debris.

The first spacecraft was launched into space

in October 1957; the first serious fragmentation of a satellite occurred in June 1961.107 Yet

nearly two decades passed before the potential hazard from orbital debris began to be

widely appreciated. Although the technical

community had developed concern about the

debris hazard,108 several additional years of

observation and experimentation passed before the United States adopted a formal policy

on space debris. The first formal policy step

was the adoption by the DOD in February

1987 of a space debris policy as part of its overall space policy.109 Prior to 1987, NASA and

the Air Force had already begun to adopt informal operational strategies to minimize

space debris. For example, as noted earlier,

shortly after the last explosion of a Delta upper stage in 1981, NASA instituted the practice of eliminating excess fuel from these upper stages after placing payloads in orbit.

Administration policy on orbital debris was

first publicly articulated in February 1988 as

part of a comprehensive statement of space

policy: “all space sectors will seek to minimize

the creation of orbital debris. Design and operations of space tests, experiments, and systems will strive to minimize or reduce accumulation of space debris consistent with

mission requirements and cost effectiveness.”110 The Bush Administration has continued that same policy, but has extended it to

include outreach to other nations: “The

United States government will encourage

other space-faring nations to adopt policies

and practices aimed at debris minimization."111

One of the important frost results of the

1988 policy was the Report on Orbital Debris,

which was developed and published by the Interagency Group (Space) for the National Security Council in February 1989. That report,

and the earlier ESA report on orbital debris,112 along with a number of technical

workshops and briefings, have made substantial contributions to a wider understanding of

the debris problem. These efforts have assisted in garnering support for further study

of the increasing threat, and the development

of possible mitigation strategies.

IuL.~ ~~u]t ~d A. Fm~d, “C~ada’s C]aim for D~~ Caused by the Soviet Cosmos ~l%ite]]ite,” ~tawa, 1984, pp. 1%23.

1064@mada.Union of~~~i~ist ~pub]ics: fitoco] on Settlement of Canada’s Claim for D~~Caused by ‘Cosmos ~4’,”

Intmnatiorud L@ M@erids, vol. 20, p. 689.

lo~is w~ a fimsit 4A rocket My) which “unexxly blew itself apart only a few hours atler launch”: Johnson ~d McK.night,

op. cit., fbotnote 9.

l~FOre~p]q the~erim Institute ofAeronautics and Astronautics issued a position Paper on s~=debris in 1%1 thatw~ned

of the hazard and urged action to reduce it: AIAA Technical Committee on Space Systems, Space Debris, An AMA Position Paper,

American Institute of Aeronautics and Astronautics, New York, 19S1.

l-eDOD ~]iq~~,~~DOD fill seek ~ finimize the impct of space debris on its military operations. Design ~d operations

of DOD space tests, experiments and systems will strive to minimize or reduce accumulation of space debris consistent with mission

requirements.” Off’ce of the Secretary of Defense, Department of Defense Space Policy Statement, Mar. 10, 19S7 (unclassified).

I lo~i~ Houge Fact sheet, “Prt@jent.ia.l Directive on National Space Policy,” Feb. 11, 1%, P. 4.

1 I lspmpolicy, op. cit., fmtnote 34.

112Europm Syce Agency, Op. cit., footnote 3“
34 ● Orbiting Debris: A Space Environmental Problem

Chamcterizatwn of the Debris

Environment

The limited data available on the extent and

character of the orbital debris environment

inhibits the development of mitigation strategies. In the United States, both NASA and the

Air Force have modest programs to expand

our understanding of the space environment.

As noted in box 2, the orbital debris catalog

baseline for extrapolation into the future is a

growth rate of 240 objects per year. Yet, some

experts expect the growth rate to increase as

the number of space activities increases. The

increasing numbers of spacecraft placed in

high, long-lived orbits are particularly worrisome. If launch and breakup rates113 increase

during the coming period of low solar activity,

when the “wash out” effect will below, the debris growth rate may approach 5 or 10 percent

per year. For example, preliminary analysis

has shown that deterioration of certain types

of satellites may produce numerous trackable

objects over time. This type of breakup may

prove to be a significant source of debris as

more satellites linger in orbit after their operational lifetime.114

Determining which rate to use for future

projections is very important for future planning. For example, at a 10 percent debris

growth rate, the cataloged debris population

would double in only 7 years. At a 5 percent

growth rate, the period needed to double the

debris population is 14 years, and for a linear

growth of only 240 cataloged objects per year,

the doubling rate would be 29 years. Knowing

the number and mass of objects capable of being included in the SSN catalog helps to quantify the hazard from debris, but derelict pieces

of hardware too small to be cataloged still

Table 5-Key Program Needs for Characterizing the

Debris Environment

Concern/Uncertainty Program Needs

Nontrackable debris Improved sensing capabilities,

in situ experiments and database

Debris creation Analytic models based on

empirical data

Trigger for breakups Experiments (explosion/collision)

Population trends Analytical studies

Improve database and Expand number of radar sites

ability to moniter debris and add more optical and

infrared observations

Enhance data Improve communications

management capacity between data sources and

database

Long term evolution Traffic models and propagation

techniques

Define mass of debris Correlate radar, optical, and

infrared observations

SOURCE: Darren S. McKnight end the Office of Technology Assessment, 1990.

pose a more significant hazard to space systems than do cataloged items.

Table 5 lists some of the key needs for improving the characterization of the space debris environment. In order to establish the

necessary information base on which to build

strategies for effective future management of

orbital debris, the United States and other

countries will have to develop sustained programs to characterize the existing space environment and to model potential future

growth of space debris.

Data from spacecraft surfaces exposed to

the outer space environment and returned to

Earth for analysis (table 6) have provided the

United States with information on direct impact damage from natural and artificial space

debris. 115 These surfaces show that, compared

to natural objects, artificial debris causes a

larger number of impact craters less than 20

1 IsNote that ]aunch rates mu]d increase and the debris population stay constant or even decrease if the bre~up rate d=reased

accordingly.

1 ldNicho]as L. Johnson, Pre]iminq in-house analysis for Teledyne Brown Engineering, 19$9.

115H.A. hk, 1).S. Mcny, and R. P. Bernhard, “Results from Returned Spacecraft Surface%” AIAA/’NASA/DOD Orbital Debris

Conference: Technical Issues and Future Directions, April 16-19, 1990, Baltimore, MD, p. 1.
Orbiting Debris: A Space Environmental Problem ● 35

Table 6-Spacecraft Surfaces Returned From Space

Analyzed for Debris Impacts

● windows from Mercury, Gemini, Apollo, Skylab, and Shuttle;

● meteroid experiments exposed on Gemini, Skylab, and Shuttle flights;

● parts of Surveyor III spacecraft returned from the Moon;

● Palapa and Westar satellites; and

● Solar Max surfaces.

SOURCE: H.A. Zook, DS. McKay, and R. P. Bernhard, “Results From Returned

Spacecraft Surfaces,” AIAA/NASA/DOD Orbital Debris Conference:

Technical Issues and Future Directions, Apr. l&19, 1990, Baltimore, MD.

microns in diameter, and may cause a greater

number of impacts larger than a few millimeters; but the data on this finding are inconclusive. Natural micrometers cause the greatest

number of impact craters in size ranges between 100 microns and a few millimeters.

These data support the conclusion that debris

densities in LEO have increased since the

1970s when Skylab was orbited and that particles from solid rocket motors and surface

paints clearly contribute to the debris population.

The LDEF– (box 6), which NASA retrieved

from orbit in January 1990, provided an unparalleled opportunity to gather data on the

debris environment of LDEF’s orbits. Because

the planned Space Station will be located in

similar orbits, this information will be invaluable in designing the means to help protect

the Space Station from orbital debris impact.

The existing Haystack Radar and the future

Haystack Auxiliary Radar, which USSPACECOM will operate for NASA (box 7), will provide the most cost-effective means to study

the general distribution of space debris at

LEO altitudes (below 500 kilometers). Eventually, a space-based system maybe required

(table 7). It maybe important to place optical

and infrared systems on space station Freedom to characterize and monitor its particulate environment. Otherwise, Freedom’s use

as a scientific observing platform may be deBox 6-The Long Duration Exposure

Facility (LDEF)

LDEF, a spacecraft the size of a small school bus,

was designed to measure the effects of atomic oxygen, space radiation, micrometeroids, orbital debris, vacuum, and other space-related phenomena

on a variety of materials. It carried more than

10,000 test specimens in 57 experiments. More

than 200 investigators from 9 countries were involved in these experiments.

On April 7,1984, NASA deployed LDEF from the

Shuttle orbiter Challenger. It had been scheduled

for retrieval in the fall of 1966. However, the failur e

of Challenger in January 1966 and the necessity to

launch more critical payloads in 1966 and 1969 after the Shuttle returned to service, kept LDEF in

orbit for nearly 6 years. As a result, LDEF represents an unexpected opportunity to observe theresults of long-term exposure to the space environment, including the effects of orbital debris.

The orbiter Columbia retrieved LDEF in January 1990. Although some experiments aboard

LDEF had been degraded by the unexpected

length of time the satellite was in orbit, the extra

exposure to the space environment has produced

results that are of great interest to spacecraft designers. Detailed examination of LDEF and interpretation of the results will take months. Initial observations revealed the following

Thin films-Some thin-film test specimens appear to have degraded or completely eroded.

Kapton-Thermal covers on two trays for experiments on heavy ions in space were partially peeled

back. In addition, the thermal cover strips around

the detectors of a space plasma high voltage drainage experiment eroded away.

Debris damage-The thermal cover of a cosmic

ray nuclei experiment, located at the leading edge

of the spacecraft, sustained damage from either artificial or natural debris.

Cosmic dust impacts-the first year of LDEF’s

operation revealed 15,000 impacts from interplanetary dust, from six directions.1 The experimental surface facing the direction of flight experienced 4,500 dust impacts.

SOURCE: National Aeronautics and Space Administration

IS. F. Singer et al., paper presented at the 21st Meeting

of the Division on Dynamical Astronomy, American Astronomical Society, Austin, ~ April 1990.

graded.
36 . Orbiting Debris: A Space Environmental Problem

Bo x 7– Orbital Debris Radar Observations

In 1989 NASA and USSPACECOM completed

an agreement to develop aground-based radar program that will be capable of examining the debris

population density of objects of 1 centimeter or

greater diameter at altitudes up to 500 kilometers.

It will provide much needed data for:

. extended duration Shuttle orbiter;

• long-duration extravehicular activity by astronauts;

● future modifications to Space Station Freedom

shielding,

● determination of sources of debris;

. effectiveness of operations designed to minimize debris.

USSPACECOM will make near-term observations (through 1991) of space debris from the existing Haystack antenna in Massachusetts. Haystack

is a high-power, X-band radar. Haystack provided

frst test results in May 1990, and demonstrated

that it could observe orbital debris with diameters

smaller than 10 centimeters. Full calibration of the

antenna to determine the sizes of objects it is observing will require more tests. By September 21,

1990 NASA expects to have data from about 400

hours of observations.

NASA will be responsible for the costs of developing a Haystack Auxiliary (HAX) Radar at Millstone

Hill, Massachusetts, and a copy on Ascension Island. The USSPACECOM will operate HAX, which

will gather data in the Ku-band, after the new facility becomes operational in late 1991, and continue

to provide debris information for NASA and Air

Force needs. The HAX Radar will have a broader

beam. Its data will supplement data from Haystack

and, when correlated with Haystack observations,

w-ill provide additional information on the size of

observed particles.

SOURCES: National Aeronautics and Space Administration; U.S. Air Force; and J. Beusch and I

Kupiec, “NASA Debris Environment Characterization with the Haystack Radar”

(AIAA 90-1346). Presented at the AMA/

NASA/DOD Orbital Debris Conference:

Technical Issues and Future Directions, Baltimore, MD, Apr. 16-19, 1990.

Table 7-Radar Performance Requirements

Near-Term for Space Station Freedom

● 50 percent probability of detection of 1 centimeter diameter

debris at 500 kilometer altitude;

● irregular debris objects;

● attitude determined to +/- 25 kilometers over altitude range of

300-600 kilometers;

. 100 detections in 3 months to reach accuracy of +/- 30 percent;

● radar operational by 1 October 1991 to support Freedom critical design review.

Long-Term Monitoring

● detect debris at inclinations of 7° or greater with an accuracy

of +/- 5°;

● determine altitide to +/- 1 kilometer over range of 300-2,000

kilometers;

● 90 percent detection probability of 1 centimeter diameter particles at 500 kilometers altitude.

SOURCE: National Aeronautics and Space Administration and U.S. Air Force.

Mitigation and Protection

Techniques

Mitigation

If the space-faring nations are to reduce the

hazards posed by orbital debris, research on

debris mitigation techniques must continue,

and nations must continue to assess their ability to reduce the growth of orbital debris (table 8). In particular, work is still needed on reducing the amount of debris from space

operations, in reducing the risk of breakup as

a result of collisions, and in limiting the erosion of spacecraft parts and other space objects because of materials degradation. The

research conducted on LDEF will provide

critical information on the performance of

various materials used on spacecraft. As yet,

no government or industry studies on alternative spacecraft design have been carried out.
Orbiting Debris: A Space Environmental Problem. 37

Table 8-Key Program Needs for Debris Mitigation

Concern/Uncertainty Program Needs

Debris mitigation policies Develop laws/regulations

Assign national points of contact

Derelict rocket bodies Vent excess propellants and

pressurants

Derelict payloads Design for removal by propulsion

and/or drag enhancement

Reduce number of

GEO derelicts Propulsion and hazard analysis

Operational debris Redesign and use degradable

material

Reduce secondary

debris Advanced materials

Minimize debris

production All of the above

SOURCE: Damn S. McKnight and the Office of Technology Asseesment, 1990

Protection

Additional means to protect against debris

impacts will be important. The conventional

dual wall system, designed to protect spacecraft from meteoroids, has also been used to

defend against small pieces of artificial debris.

Yet, there is still no cost-effective way to shield

against debris impacts from fragments larger

than 0.5 centimeters in diameter. Equally as

uncertain are the effects of collisions with

these larger objects.

Work is underway within NASA and the Air

Force on means to provide spacecraft with

greater protection from small space debris

(table 9). However, work on protecting from

impacts of larger objects, and on debris avoidance, is needed.

U.S. Research Plans

The U.S. Interagency Group report on orbital debris recommended that NASA, DOD,

and DOT develop a research plan to improve

orbital debris monitoring and modeling, and

management of accumulated data; and deTable 9-Key Program Needs for Protection From

Debris

Concern/Uncertainty Program Needs

Response to large System level interactions,

debris impact materials

Passive avoidance Redesign mission profile

Active avoidance Prediction, propulsion, structures,

sensors

Response to small

debris impact Shielding, materials

SOURCE: Darren S. McKnight end the Office of Technology Assessment, 1990.

velop “generic technologies and procedures

for debris minimization and spacecraft survivability. ’’116 This plan was completed and

disseminated in early June, 1990.117 The three

agencies envision preceding in two phases.

Phase I (near-term, fiscal year 1990-92)

would:

assess the orbital debris environment;

develop space station Freedom protection design criteria;

develop new (and document existing) debris minimization practices and procedures;

develop new breakup models for spacecraft and techniques for assessing survivability against debris; and

collect data to support future development of regulations, standards, nation-d

policy, and international understanding.

Table 10 summarizes projected expenditures for Phase I studies.

Phase II would build on the information developed in Phase I; hence, specific activities

cannot be planned today. However, the agencies are likely to pursue the following types of

activities:

. monitor the debris environment;

1 leNation~ Security Counci], op. cit., fbOtnOte 2, p. 52.

1 l~OD/N ~~OT) “orbiti Debris %=arch PhuM,” my 1~.
38 ● Orbiting Debris: A Space Environmental Problem

Table 10-Phase I Summary of Projected Expenditures for the NASA/DOD/DOT Research Plan

Fiscal year ’90 Fiscal year ’91 Fiscal year ’92

Program includes: DOD NASA DOT DOD NASA DOT DOD NASA DOT

Debris environment

assessment

● Measurements/data analysis

. Modeling

● Data management

Space Station Freedom

Criteria

Debris Minimization

● Commercial regulatory

options and economic

impacts

Spacecraft Survivability

● Commercial regulatory

options and economic

impacts

Total budgeted ($K) (1,000) 14,986 80 (1,500) 12,121 110 (1,500) 7,578 180

NOTE: DoD ( ) = unfunded requirements.

SOURCE: National Aeronautics and Space Administration.

. update debris characterization models;

. improve hazard assessment capabilities;

. improve protection techniques;

. minimize debris generation; and

● review commercial regulatory options.

International Cooperation

The United States has taken the lead in

studying the orbital debris environment, providing a debris database for the rest of the

world, and in developing strategies to reduce

the potential for generating new orbital debris. However, even if the United States were

able to eliminate completely its future contribution to the orbital debris environment, little effect on the overall debris environment

would result unless similar practices were

adopted in other countries. At present, the

United States, the Soviet Union, Europe,

China, and Japan are capable of launching

payloads into the full range of Earth orbits.

India is developing its own independent

launch capability and should be able to place

objects routinely in low-Earth orbits in a few

years. In addition, Brazil, Iraq, and Israel are

also working toward independent launch capabilities.116

The existing debris population poses a

small, but finite, hazard today. Despite

cleansing effects during periods of high solar

activity, most experts agree that fragmentations and collisions of existing debris will continue to add objects to this population. Hence,

it is in the best interest of the United States

and other space faring nations to tackle these

problems in concert. Working with the Department of State and other agencies, NASA

has briefed space officials in Australia, Canada, the European Space Agency (ESA),

France, India, Japan, the Soviet Union, and

West Germany. Officials from NASA and ESA

have met several times to discuss concerns of

mutual interest on orbital debris and to identify specific areas for future cooperation. In

1987 NASA convened a conference on orbital

I laISrae] ]aunch~ its second satellite in April 1990.
Orbiting Debris: A Space Environmental Problem .39

debris from upper stage breakups,119 which

included participants from ESA, France, and

Japan, and has sponsored other meetings on

orbital debris issues. European and Japanese

participants contributed papers to the orbital

debris conference held by the American Institute of Aeronautics and Astronautics, NASA,

and DOD in Baltimore in April 1990.120

The United States and the Soviet Union are

the two major contributors to orbital debris

(figure 11). However, to date, any efforts the

Soviet Union might have taken to characterize and reduce the hazard posed by orbital debris are poorly understood in the United

States. Although “Glasnost” has made working with Soviet officials much easier than in

the past, access to Soviet policy thoughts or to

reliable Soviet data on debris has been difficult to obtain. In December, 1989, NASA officials traveled to Moscow to brief Soviet space

officials on U.S. progress and to learn about

the efforts the U.S.S.R. has made toward understanding the orbital debris environment.

Although U.S. officials failed to reach a thorFigure 11 -Total Number of Orbital Objects in the

Space Surveillance Network Catalog by Nationality

(48.0%) —

The United States and U.S.S.R are about equally responsible for the total cataloged

population.

SOURCE: Darren S. McKnight, 1990.

ough understanding of any Soviet efforts to

study the orbital debris problem, the meeting

furthered prospects for cooperating with the

Soviet Union on limiting the production of orbital debris. Soviet officials showed concern

about the problem and expressed interest in

cooperating to limit the future growth of debris.121 Independent indications, derived from

Space Surveillance Network data, suggest

that the Soviet Union has stopped its practice

of fragmenting its own satellites in the higher

altitudes of LEO. Recent fragmentations were

carried out at altitudes where the debris

would enter Earth’s atmosphere within 90

days.

These efforts, though extremely important

first steps, do not go far enough. Some sort of

concerted international action to reduce the

threat of orbital debris is needed. It may

therefore be appropriate for the United States

to convene a working group of spacefaring nations that would discuss mitigation strategies

and seek to reach agreement on them. As soon

as feasible, other nations that have an interest

in space activities, even though they cannot

yet launch spacecraft into orbit, should also

be brought into such discussions on the

ground that their investment in space systems

is at risk. For example, the International Telecommunications Satellite Organization (Intelsat) and the International Maritime Satellite Organization (Inmarsat) purchase launch

services on the international market to place

their communications satellites in GEO. Both

organizations are owned by nations only a few

of which have the capability to place satellites

in orbit. Yet the communications satellites

they own are threatened by space debris. Likewise, regional organizations such as Arabsat

(Middle East) and Eutelsat (Europe), as well

as individual countries, own assets in GEO. In

the future, when more nations make use of

I 19~~u5 (cd.), op. cit., footnote 80, PP. 41-1~.

I“AIAA/NASA/DOD Orbital Debris Conference: Technical Issues and Future Directions, Baltimore, MD, Apr. 1619, 1990.

lzlJo=ph Lofius, NASA personal communication, 1990.
4(I . Oditing Debris: A Space Environmental Problem

LEO for remote sensing satellites and other

uses, their satellites will be placed at risk in

these orbits.

Crews in Space

The destructive consequences of orbital debris are of special concern when considering

human spaceflight, especially long-term

stays. Crews in space require habitats of much

larger cross section than are required for automated spacecraft. For a given orbital debris

flux, the larger cross section substantially

raises the probability that such spacecraft

would experience a destructive impact during

a given period of time. Human crews currently operate in LEO, where the debris flux is

already relatively high and where the relative

velocities between debris and spacecraft are

also high. Cosmonauts aboard the Soviet station, Mir, experience small hits from artificial

and natural debris, which they hear as “pings”

against the exterior shell.122 Although none of

these encounters have caused serious damage,

some have broken the exterior light bulbs on

Mir, which as a result are now protected.

As the aftermath of the 1986 Challenger

failure demonstrated, our society places great

importance on the personal safety of humans

in space. Hence, in planning space station

Freedom and in operating the long-duration

Shuttle orbiter,123 it will be extremely important to understand fully the risks that debris

poses to their operation. The overall costs to

the space program of losing human lives from

debris encounters could far outweigh the simple cost of repair of Freedom or replacement

of a long-duration orbiter.124 In building the

Shuttle, designers took into account the risk

of collision from natural debris, but did not

consider the risks of orbital debris. Even

though the yearly probability of encounters

with orbital debris may be extremely low, impact with a large debris object could cause significant damage. Freedom is being designed to

last 30 years on orbit, and should be capable of

shielding against small objects (less than

about 2 centimeters) and, infeasible, avoiding

larger ones.

NASA plans to provide shielding for critical

elements of the space station, such as the

habitation modules.125 It is studying possible

collision avoidance maneuvers for Shuttle

and Freedom. 126 However, before completing

the station’s shield design, NASA will have to

provide an up-to-date model for characterizing the orbital debris environment.127

A probabilistic risk analysis of space station

Freedom should take into account both the

probability of a significant impact event (the

estimation of the hazard) and its consequences (the total cost to NASA to the nation,

and to the other participating countries of

such an event). A risk analysis also should examine the proposed use of Freedom as a transportation node and service depot for launching cargo and crews to the Moon and Mars.

How would fuel and other volatile substances

be handled, for example? Although NASA

may be able to reduce the probability of a fuel

tank explosion to extremely small levels,

some small chance of explosion, as a result

l=Djinis, op. cit., footnote 25.

123NASA is now deve]opingthe mens to allow the Shuttle orbiters to remain in space for up to 28 days, which is more thn twice as

long as the longest Shuttle mission to date.

lz4pub]ic rea~ion to 10SWX Of life k difficult to predict but could result in a much more conservative approach th~ now efists to

placing humans in space.

IZSNeider) op. cit., fOOtnOte 27.

l~Ffith Vilas,~chael F. Collins,Paul C. Kramer, G. Dickey Arndt, and Jerry H. Suddath, “Collision Warning ~d Avoid~ce Considerations for the Space Shuttle and Space Station Free&m,” AW+90-1337, AIAA/NASA/DOD Orbital Debris Conference: Technical Issues and Future Directions, Baltimore, MD, Apr. 18-19, 1990.

Izm.s. Congess, (kmer~ Accounting Offke, op. cit., fmtnote 24, P. 28.
Orbiting Debris: A Space Environmental Problem .41

either of structural failure or human error,

would remain. Even if a fuel depot were located several hundred kilometers from the

Space Station, such an explosion would cause

debris to spread rapidly to Freedom, placing

at risk the entire facility and the crews in it

(figure 7). The debris cloud formed may decay

only slowly with time, forcing NASA to make

difficult decisions about the safety of crew and

equipment. In addition, the debris cloud

could threaten other spacecraft in nearby orbits, including the Shuttle orbiters, future escape vehicles, and perhaps, the successor to

the Soviet Mir and crew-carrying launch vehicles and habitats of other nations.

Space stations, especially because they are

large, complicated structures and have a large

surface area, may also produce debris. Over

several years, as debris objects generated

by space station operations change orbits

slightly and expand into a toroidal belt (figure

7), space stations, as well as launch vehicles

supplying them, become targets of their own

debris. Freedom will therefore require tight

environmental control to limit generation of

space debris.

NASA is developing shielding for Freedom

and is weighing the risks of carrying out other

space activities in Freedom’s orbits. Most objects resulting from activities in or near its orbital range will generally have small relative

velocities with respect to the space station,128

hence the protection necessary from such debris will be relatively lightweight. However,

other debris, in orbits that would intersect the

plane of Freedom’s orbits, could have much

higher relative velocities and cause considerable damage. Fortunately, the probability of

damaging encounters with this debris is extremely small.

Special Concerns About

Geostationary Orbit

As noted in Section IV, experts do not yet

agree about the minimum safe distance to remove spacecraft from GEO in end-of-life maneuvers. Considerable additional study will be

necessary to characterize the existing debris

environment in GEO and to predict the longterm results of potential mitigation strategies.129 As satellite owners need to plan for disposal of their satellites when they are being

designed, the relevant technical committees

of the International Telecommunication Union, as well as international organizations

such as Intelsat and Inmarsat, should be involved in such studies.

Raising satellites to a level beyond the GEO

altitude currently recognized as the minimum required for efficient protection (200 -

300 kilometers) can require the same amount

of fuel required as keeping a satellite on orbit

for an additional year. Hence, boosting satellites beyond GEO may exact a significant cost

from the operator.130 For example, the loss of

a year’s revenue for an Intelsat VI satellite is

estimated to be more than $20 million.131

However, for many satellites, lost revenue will

be considerably less; satellite designers are investigating ways to measure residual fuel

more accurately. Removing spacecraft to supersynchronous orbits 300 to 600 kilometers

above GEO could reduce the collision hazard

by factors of as much as 1,000.132 However, the

128A ]Ong as they do not resu]t from explosions or hypervelocity collisions with IWS debris objms.

l~For e~p]e, the mount of fue] necessq to remove satellites above the GEO band varies with respect to the m=-~mms ratio

oftheabandoned satellite. See A. G. Bird, “Special Considerations for GEOES&” AI.A4/NASAJDOD Orbital Debris Conference: Technical Issues and Future Directions, Baltimore, MD, Apr. 18-19, 1990,

I*One of the problems oPrators face is ~ugingmrr%ly the amount of fuel they have lefi in an operational satellite. AA.G. Bird,

ibid.

lslNation~ ~rity Council, op. cit., footnote 2, p. 33.

“~ical propellant requirements for this maneuver are estimated to be less than 10 kilograms of fuel. See Chobotov, op. cit.,

footnote 89.
42 . Orbiting Debris: A Space Environmental Problem

value of such procedures must be balanced

against the probability of experiencing other

harm from them. For example, firing a satellite thruster may result in an explosive failure

of the thruster. Although the probability of

such an event maybe very small, it should be

weighed against the probability of collision if

the satellite is not removed.133

National Security Concerns

Military activities involving sensitive instruments used to gather information from

space could be adversely affected by orbital

debris that damages sensors or disrupts communications.134 Impact of space debris with a

crucial national security satellite, such as one

used to verify international treaty compliance, could heighten tension at times when international tension was already high, as such

damage may be extremely difficult to separate from intentional attack.

Some commentators have noted that orbital debris could actually be used to military

advantage.135 If a non-functioning satellite is

considered to be debris, there maybe a military advantage to leaving it in orbit. An adversary might not be able to distinguish it from a

spare. On the other hand, the deliberate introduction of debris into outer space either to

deny access to a particular orbital region or to

interfere with surveillance activities is certainly antithetical to existing international

treaties and agreements. Deliberately introducing debris into an orbit would also harm

the perpetrator, as it would deny all users the

use of it and nearby orbits. Nevertheless,

either clouds of debris or individual, larger

objects could be used to inflict damage on the

spacecraft of other nations. The United States

may well wish to place these and other related

considerations on the table in discussions of

international approaches

bital debris.

The Private

to minimizing

Sector

orAccording to the Outer Space Treaty of

1967, to which the United States is party, each

nation is responsible for regulating the activities of its nationals in outer space. The private

sector, including the launch vehicle industry

and the spacecraft industry, will be affected

by any international agreements entered into

by the U.S. Government.

Several U.S. Government agencies regulate

private sector space activities in accordance

with several U.S. laws (app. C). Whatever policies the United States adopts for regulating

private sector activities should take into account the needs and concerns of the private

sector. In particular, government agencies

charged with regulating space activities

should not unnecessarily prejudice the ability

of the U.S. private sector to compete with

firms in other countries. However, the government should also assure itself that private

firms are instituting appropriate controls on

the generation of orbital debris.

Firms that own space assets have already

benefited from government-sponsored research on the extent of orbital debris, mitigation strategies, and protective technologies. In

the long run, privately owned space assets will

experience a safer environment as a result of

this research. However, some debris-reduction strategies that could be required by the

government may be costly. The Department

I=J.J. Butts and W. G. WgINJOIO, “$at,e]lit.e Collisions in the Geosynchronous Belt,” contract no. FfM7014WC-00S2t The Aemspa@

Corp., Jan. 15, 19S2.

1-N. Ja~ntuliyan% “Envimnmen~ Impact of Space Activities: An International Law Perspective,” American Institute of AerG

nautics and Astronautics, 27th Colloquium on the Lao of Outer Space, 19S4, p. 391.

l~~er) op. c~t., f~tnote92, pp. 21.22; R Bridge, “International Law and M.ili~Activities in Outer Space,” VO1. 13, fimnkw

Review, 1980, p. 649.
Orbiting Debris: A Space Environmental Problem . 43

of Transportation is investigating the costs of space debris should draw upon all of the

and benefits of controlling debris generation. best talent available. As commercial space acThe expertise on detailed vehicle and space- tivities grow in importance, government

craft design in the United States is shared be- should continue to involve the private sector

tween highly specialized government research in developing debris reduction strategies and

facilities, the universities, and the aerospace in determining which ones are most costindustry. A national appraisal of the problem effective.
Appendixes
Appendix A

Collision Probabilities for Satellites

The probability of collision (PC) between a

satellite and debris during a mission of duration T is represented by

PC =

1- e (-SPD*

VREL*AC*T

) (1)

where SPD = spatial density, objects

per km3

VREL = relative velocity, km/s

AC = cross-sectional area, km2

T = mission duration, sec

When the probability of collision is very

small, less than 0.190, the equation above may

be approximated by

PC = SPD * VREL * AC * T. (2)

Table A-1 summarizes typical values of the

terms in the PC equation for LEO and GEO

orbits over a mission period of 1 year.

Table A-1 - Probability of Collision

LEO GEO

SPD 1 0 -

10 to 1 0- 7

1 0

-11 to 1 0- 7

VREL 6 to 14 km/s 0.1 to 0.8 km/s

AC 10 m2

10 m2

T year 1 year

PC 1 0

-7 to 10-4 per year 1 0-12 to 10-7 per year

NOTES: For the GEO calculations the maximum values for SPD and VREL

cannot be used simultaneously to arrive at a maximum PC.

The PC for a GEO satellite is clearly orders of magnitude smaller than

for a LEO satellite

SOURCE: Darren S McKnight

47
Appendix B

U.S. Statutes Governing Outer Space

The National Aeronautics and Space Act1

does not refer specifically to “space debris;”

rather its provisions for environmental protection are based upon the National Environmental Policy Act (NEPA)2 and its pertinent

regulations. 3 This means that whenever

NASA’s actions may affect the quality of the

environment it must either have an environmental assessment (EA)4 or submit an environmental impact statement (EIS).5 Both

U.S. and ESA reports rely upon the international legal definition of ‘(global commons,”

which are those territories outside the jurisdiction of any states. This definition provides

the broadest, most general basis for including

outer space within those “global commons, ”

and would provide a mandate for protection

of the space environment. Such a mandate

would necessitate recognition and prioritization of some of the legal issues which involve

mitigation and control of space debris.6 This

definition is also the basis for the Outer Space

Treaty’s provision that no state shall claim

sovereignty over outer space, the Moon, or

other celestial bodies.7 However, NASA regulations that provide for environmental protection appear to characterize the global commons much more narrowly, and it is argued

that NASA regulations do not mandate protection of the outer space environment, per

sea For example, NASA regulation 14 CFR

1216.321(a) (1988) states that the analysis by

the Headquarters Official of actions under

his/her supervision shall include consideration of the environmental effects abroad as

well as potential effects upon the global commons (i.e., “oceans and the upper atmosphere”) (emphasis added). That argument

might be stronger if the agency created by the

Act was simply the “National Aeronautics Administration,” but the title includes SPACE;

therefore the regulations appear to have been

constructed in ways to leave U.S. obligations

to the outer space environment in the internatational forum, rather than expanding domestic

regulations. Consequently, an environmental

assessment or environmental impact statement is not a legal requirement for space activities in outer space, which could produce

space debris.

The application of the National Environmental Protection Act. according to the U.S.

report, has been stated by various government agencies as legally inappropriate for application to space debris problems because

neither civil nor military regulatory law provide standards SPECIFIC to space law.9 Such

agencies may choose to conduct environmental assessments for their activities involving space transportation and communication

as a matter of policy, but do not consider such

INation~ Aeronautics ~d Space Act,, 72 Stat. 426 (1958) (codified at 42 U.S.C. 2451 [1978 & suPP. 19871).

242 U.S.C. 4321-4370 (1978& supp. 1987). NEPA fites that ~] Feder~ a~ncies must Comp]y with its requirements. (42 U.S.C.

4321).

s40 Cm 15~- 1517 (1987). The N~A re~]ations imp]ement the di~ives of NEPA to “prot~ ~d enhance the quality of the

environment . . . (from) actions which may have an impact on it.” 14 CFR 1216.102(a) (d) (1984).

4E~me generd]y rf@rd ‘or”“ “specific spacecraft development and flight projects in space and terrestrial applications; reimbursable launches of nonNASA spacecraft or payload;. . . and actions to alter ongoing operations at a NASA installation which could lead

either directly or indirectly to natural or physical environmental effects. ” 14 C!FR 1216.306(c)(2) (1984).

5A tw of ~Fi~c a~ion that Wou]cj recpire NASA to do a more formal E~ would ~. “. . . development and operation of space

vehicles likely to release substantial amounts of foreign materials into the Earth’s atmosphere, or into space. ” Ibid. (c)(2).

eNation~ hfity Counci], Re~rt on Oi+ital Debris by Interagency Group (space), Februwl~gt P“ 43-

T@ter Space Treaty, Article ~.

eHow~ ~er, SPW ~bris: ~~ ~d Po]iq Implications (~rdr~ht: M~,lnus NijhOff publishers, 198$)), p. 70.

9Nation~ ~rity Council, op. cit., footnote 6) P. 43

49
50 . Orbiting Debris: A Space Environmental Problem

assessments to be required, under essentially

the same argument as that stated above for

the NASA environmental protection regulations. A similar decision has been made with

regard to Executive Order 12114 for certain

Federal actions that may affect the “global

commons outside the jurisdiction of any nation (e.g., the oceans or Antarctica)”: the

specification of examples is interpreted as an

intention to narrow the environmental considerations. 10

The Commercial Space Launch Act of 1984,

as amended 11 establishes a licensing process

that addresses hazards from space debris generated by commercial launch activities.12 In

addition, for certain payloads, the Office of

Commercial Space Transportation must determine whether the launch of these payloads

would jeopardize public health and safety,

safety of property, and U.S. national security

and foreign policy interests.13

The Lund Remote Sensing Commercialization Act of 198414 provides that licensed entities must dispose of any satellites in space

when the license terminates, and disposal

must be made ”... in a manner satisfactory to

the President.”15 Presumably this would

mean that a defunct spacecraft would not be

left where it would contribute to the creation

of more space debris.

I“Ibid.

1149 U.S.C. app. 2601-2623, Public Law 96-575, 1(M)-667, (Iw and ~PP. 1~).

1214 Cm Ch. III.

ls~id. (14 cm 415.27).

ld~b]ic hW 96-366, !)8 Sht. *1, Jdy 1’7, 1~.

15Nation~ Security Council, op. cit., fmtnot.e 6.
Appendix C

U.S. Commercial Regulatory Programs

The three U.S. governmental agencies most

involved in the regulation of commercial activities in outer space are the National Oceanic and Atmospheric Administration

(NOAA) of the Department of Commerce1,

the Federal Communications Commission

(FCC)2, and the Department of Transportation (DOT).3 Each of these agencies is involved

in promulgating regulations that fulfill three

principal regulatory aims of the Federal Government: direct control of commerce and

trade; protection of public health and the environment; and proper management and control of Federal funds and property.4 National

Space Policy recommends a certain amount of

regulatory restraint, in order not to “. . . unnecessarily prejudice the development and international competitiveness of the U.S. commercial space industry.”5

Federal Communications Commission. The

role of FCC in regulating commercial space

activities is connected to its authority to allocate radio frequencies and to manage their

use.

6 Because FCC authorizes construction,

launch, and operations of U.S. commercial

communications satellites, it is necessarily involved in activities to promote orbital safety

for the purposes of maintaining communications capabilities in GEO as well as to promote general safety of life and property. President Bush’s National Space Policy

(November, 1989) includes a mandate to all

governmental and private-sector entities involved in outer space activities to reduce and

control space debris. By implication, FCC licensing of communication satellite activities

should address debris control and prevention

through both design and operational stages.

The U.S. report, Orbital Debris suggests that

in the same way the FCC coordinates its regulations with the Federal Aviation Administration, so it should coordinate with DOT to address on-orbit safety and space debris issues.7

National Oceanic and Atmospheric Administation. NOAA is responsible for licensing

private land remote sensing systems8 in order

to phase-in commercial land remote sensing

while providing up-to-date information to the

Federal Government and advancing its commitment to international obligations and national security. The U.S. Report on Orbital Debris states that NOAA has the specific

authority to control the disposition of the entire spacecraft, and this authority should include directing reasonable conditions for

keeping a spacecraft in one piece during its operations. NOAA’s authority does not extend to

activities of the launch itself.

Department of Transportation. The DOT involvement in space debris issues is by far the

most comprehensive, as it attempts to address the orbital debris problem in commercial space launch activities through licensing

and enforcement, research and standards

INOAA’s authority Wth respecttocommemi~ spsce activities derives from Title IVofthe Land @mote-*nsingCommercialization Act of 1984.

me authority of the FCC is derived fmm the Communications Act of 1934.

3~T)s authofity is ~anted to the Secre~ of Transportation under the Commercial Space Launch Act of lm.

qNation~ Security Council, Report on Witcd@bris kYIn~~ Gmup($pace) (Washington, DC: National Security Council, February 19s9).

SNatio~ -O CO W@ P. 49”

sNation~ %mrity Councfi, p. 47.

?Tbid.

Whe Land Remote-Sensing Commercialization Act of 19S4, Title IV, 402(b)(3).

51
52 . Orbiting Debris: A Space Environmental Problem

development, and setting financial responsibility and risk allocation requirements.9 Under the Commercial Space Launch Act of

1984,10 DOT’s authority as a safety and regulatory agency covers all nongovernmental

launches made by U.S. citizens or from U.S.

territory, including the safety at prelaunch,

launch, and in-space transportation stages of

these operations. The U.S. Report on Orbital

Debris suggests that Federal regulations toreduce and control space debris should be a direct result of DOT’s Safety Review and Mission Review procedures.11 As part of the

launch license application evaluation, DOT

examines proposed commercial launches to

ensure no other activities in space are directly

at risk. The interagency review of the application, which includes input from NASA and

DOD, assists in this process.

$DOT’S f-s as t. ~ety ~d trmsP~tion for remote-sensing systems is combined with the economic fas of NOAA nd the

regulatory fxus of the FCC.

1049 U.S.C. 2601-2623 (19S4 & supp. l-)

1 INation~ $ecurity Counci], op. cit., fmtnote 4, PP. *-49.

U.S. GOVERNMENT PRINTING OFFICE : 1990 0 - 21-701 : QL 3