20 

Using Lasers 

in Space 

Laser Orbital Debris 

Removal and Asteroid 

Deflection 

Jonathan W. Campbell, Colonel, USAFR

December 2000

Occasional Paper No. 20 

Center for Strategy and Technology 

Air War College

Air University 

Maxwell Air Force Base
Using Lasers in Space: 

Laser Orbital Debris Removal and 

Asteroid Deflection

by 

Jonathan W. Campbell. Colonel, USAER 

December 2000 

Occasional Paper No. 20 

Center for Strategy and Technology 

Air War College 

Air University 

Maxwell Air Force Base, Alabama 

Using Lasers in Space: 
Laser Orbital Debris Removal and

Asteroid Deflection 

Jonathan W. Campbell, Colonel. USAFR 

December 2000 

The Occasional Papers series as established by the Center for Strategy and 

Technology as a forum for research on topics that reflect long-term 

strategic thinking about technology and its implications for U.S. national 

security. Copies of No. 19 in this series are available from the Center for 

Strategy and Technology. Air War College. 325 Chennault Circle, 

Maxwell AFB, Montgomery, Alabama 36112. The fax number is (334) 

953-1988; phone (334) 953-2384. 

Occasional Paper No. 20 

Center for Strategy and Technology 

Air University 

Maxwell Air Force Base, Alabama 36112 

Contents 

Page 

Disclaimer i

The Author ii

Editorís Note iii

Abstract iv

I. Introduction 1 

II. Hazards from Orbital Debris 3 

III. Near Earth Asteroid Avoidance System 13 

IV. Conclusions 21 

References 25

Notes 27
Disclaimer 

The views expressed in this publication are those of the author and 

do not reflect the official policy or position of the Department of Defense, 

the United States Government, or of the Air University Center for Strategy

and Technology. 
The Author 

Jonathan W. Campbell, a Colonel in the United States Air Force

Reserve, is presently assigned as the Individual Mission Augmentee to the 

CADRE Commander at Air University. In civilian life, Dr. Campbell is a 

scientist and advanced projects manager in the Advanced Projects Office 

of the National Aeronautics and Space Administration (NASA) at the 

Marshall Space Flight Center in Alabama. In that capacity he has worked 

for over 20 years in the space program a number of advanced research

projects. He served as the project manager on Project ORION, which was

a NASA study published in 1997 that explored the feasibility of using 

lasers to remove orbital debris. He has published more than fifty scientific 

papers on various subjects, including laser orbital debris removal and laser 

asteroid, meteoroid, and comet deflection. He has a doctorate in 

astrophysics and space science from the University ofí Alabama in 

Huntsville; masters degrees in theoretical physics from the University of 

Alabama in Huntsville, in engineering management from the University of 

Alabama in Huntsville, and in experimental plasma physics from Auburn 

University; and a bachelorís degree in aerospace engineering from Auburn 

University. He is also a graduate of the Armyís Airborne School at Fort 

Benning, Georgia, the Air Command and Staff College and Air War

College at Maxwell Air Force Base in Montgomery. Alabama. 
Editorís Note 

The Center is devoted to publishing studies that examine the

relationship between technology and strategy and has been doing so since 

1997. While most of the studies published by the Center place a

significant emphasis on technological and policy problems, this study 

distinguishes itself because it places the emphasis on the scientific and 

technological challenges of using lasers to remove debris from earth orbit. 

This is an important idea that has gained prominence in recent years as a 

result of advances in directed energy, notably in the field of lasers. The 

second idea presented in this study is that defending the Earth against 

asteroids, as popularized in recent films, is an important, but admittedly 

far-reaching topic that the defense establishment must consider. The 

United States can proceed to tackle this latter issue on a more leisurely 

pace than the problem of man-made debris in earth orbit, which

increasingly limits our ability to place satellites in orbit. The Center is

pleased to publish this study in the hopes that it will stimulate further 

thought and discussion in the technological and policy communities as 

well as society at large about these problems. 
Abstract 

Orbital debris in tow-Earth orbit ranging in size from 1 to 10 

centimeters (cm) in diameter, poses a significant problem for space 

vehicles.1

 While this debris can he detected, it cannot he tracked with 

sufficient reliability to permit spacecraft to avoid these objects. Such 

debris can cause catastrophic damage even to a shielded spacecraft. Given 

the technological advances associated with adaptive optics, a groundbased pulsed laser could ablate or vaporize the surface of orbital debris, 

thereby producing enough cumulative thrust to cause debris to reenter the 

atmosphere. One laser facility could remove all of the one-ten centimeter 

debris in three years or less. This study proposes that the United States

develop a technology demonstration of this laser space propulsion in order

to implement a system for removing debris from earth orbit. The cost of 

this proposed demonstration is favorable in comparison with the typical

costs [or spacecraft operations. 

Orbital debris is not the only form of ìspace junkî that is deleterious

to the Earth.2

 Since collisions with asteroids have caused major havoc to 

the Earthís biosphere on several occasions in the geological past, the 

reality is that the Earth will probably experience another impact in the 

future. For this reason, this study also considers the possibilities of scaling 

up a system for removing orbital debris to a system that could prevent 

these catastrophic collisions if we have sufficient warning. 
Using Lasers in SpaceÖ.1 

I. Introduction 

Functional satellites represent only a small fraction of the estimated 

150,000 or more objects, which are larger than 1 centimeter in diameter, 

that are currently in low-Earth orbit (LEO) (Maethner 1994). Most of 

these objects are fragments of larger objects that have broken up in 

explosions and other events. Since the closing velocities of these objects 

are roughly 8 kilometers per second (km/s), a collision with any one of 

these objects is likely to cause catastrophic damage to a space vehicle or 

satellite, of which the Space Shuttle and International Space Stations (ISS)

are noteworthy examples. As the number of pieces of debris in orbit 

continues to rise so does the likelihood of collision. Maneuvers for

avoiding tracked debris have been undertaken by the Space Shuttle and are

planned for the International Space Station as well. Furthermore,

procedures for dealing with damage are being developed for the 155 in the 

event of a collision with orbital debris. 

Claude Phipps suggested the use of laser propulsion with a groundbased pulsed laser as a solution to the orbital debris problem in 1994 

(Phipps 1994). The Orion Project, which was a study conducted by NASA 

and the USAF in 1995-96, concluded that the concept of using groundbased lasers for removing orbital debris is feasible and cost effective 

relative to the cost of placing objects in orbit (Campbell 1996). This study 

presents an analysis of the debris removal concept, and a plan for 

developing the technology for removing orbital debris with near-Earth 

lasers. This study begins with an analysis of the cost of a laser orbital 

debris removal system as the first step toward establishing the costeffectiveness of this concept. This study then investigates the requirements 

for using laser propulsion for the diverse ensemble of debris particles in

orbit. The following section demonstrates that the adaptive optics

requirement for debris removal is within technological reach. After 

demonstrating that laser systems can effectively remove debris from orbit 

with the proper engagement strategy, the study concludes with a proposal 

to develop the technology for debris removal and advance that technology 

for laser space propulsion. 
Using Lasers in SpaceÖ.3 

II. Hazards from Orbital Debris 

The USAF Space Command maintains a catalog of space objects. 

Depending on the altitude and radar cross-section of these objects, it can 

reliably track objects that are larger than 10-30 cm in diameter in lowearth orbit. That catalog contained roughly 8000 objects in 1997. While 

roughly six percent of the cataloged objects were active payloads, the 

remainder consisted of inactive payloads, rocket bodies, and smaller 

fragments, many of which were produced during more than 100 breakups 

of space systems in orbit. Most of these breakups were caused by 

explosions, but collisions with other objects cannot he ruled out. For 

example, the breakup on July 24, 1996 of the French Cerise satellite has 

been linked to a collision with a cataloged object. 

Fragmentation generally produces large numbers of objects that are

too small to he tracked reliably. High-velocity impact tests have shown 

that shields that are designed to protect satellites can he effective against 

objects that are less than about 1-2 cm in diameter. Such shielding is part 

of the design for the International Space Stat ion. Depending on 

environmental requirements, satellites and space vehicles may require 

shielding, or active protection from impacts with small particles, notably 

orbital debris and micrometeoroids. For particles that are larger than 2 cm, 

the cost of shielding a space vehicle is prohibitive. 

There have been numerous surveys of debris in the 1-10 cm diameter 

range. Radar and optical surveys, when used in conjunction with computer 

models, reveal that there is roughly 150,000 objects in orbits below 1500 

kilometers. The problem is that each of these objects is quite capable of 

causing catastrophic damage to shielded spacecraft, and yet are too small 

to he tracked reliably by avoidance sensors. The likely composition of the

debris was considered by the Orion study. The debris was classified into 

five representative groups, with objects made of aluminum, steel, 

sodium/potassium metal, carbon phenolic, and multi- layer insulation

(MLI). 1

Based on the number of objects in low-earth orbit, and using the 

Iridium satellite system as an example, if we assume that the replacement 

cost of one of the 66 satellites in the $3.450 billion system is roughly $50 

million, then the total cost to LEO satellites from orbital debris is 
Using Lasers in SpaceÖ.4 

estimated to be roughly $40 million per year. Debris-related expenses that 

are on the order of tens of millions of dollars per year should he compared 

with estimates from the Orion study for debris removal. It estimated that

eliminating debris in orbits tip to 800 km in altitude within 3 years of

operation would not exceed $200 million. It was for this reason that the 

study team has proposed a technology demonstration project as a next 

step, which is estimated to cost roughly $13-28 million. 

Laser Propulsion of Uncooperative Debris. Laser propulsion is one 

technique for using radiant energy rather than fuel on space vehicles for 

the purpose of propulsion. In the case of removing orbital debris, the 

surface material of the debris becomes the propellant. In essence, the 

intensity of the laser must he sufficiently great to cause the material on the 

surface of the object to form a vapor, which as this hot vapor expands 

imparts a force or thrust to the object. For a given material and duration of 

a laser pulse there is an optimum intensity above which the ability to 

couple laser energy onto the material decreases.2

 This is because the 

resulting ionization of the vapor from the material effectively absorbs the 

energy of the laser: This means that a series of short pulses is the most

effective way to generate propulsion for orbit debris.3 

Since orbital debris consists of many materials, a debris removal 

system must be designed with this in mind. The Orion study considered 

laboratory experiments that were conducted with representative materials 

and found useful models for the coupling of metals and nonmetals, as 

shown in Figure 1. The optimum intensity is higher for metals than for 

nonmetals, since energy tends to he conducted to the interior of the metal. 

At higher intensities, however, the coupling is higher for metals than for

nonmetals because the onset of plasma formation above the optimum 

intensity for nonmetals occurs at lower intensities.4 This system would he 

effective against both metallic and nonmetallic targets in space, and could 

be effective against materials that arc at higher orbital altitudes. 

Adaptive Optics for Debris Removal. We have seen that useful laser 

propulsion of orbital debris results from placing an intensity on the order 

of l08

 W/cm

2 on the target. The angular beamwidth required to achieve this 

is given by 
Using Lasers in SpaceÖ.5 

α

π = 1

4

z

E

It

 , (1) 

where E is the pulse energy, I the required intensity. t the pulse duration, 

and z the target range. With a high pulse energy of 20 kJ, short pulse 

duration of 5 ns, and range of 1600 km for debris at an altitude of 800 km 

and zenith angle of 600

, the angular diameter required is 1.4 μrad. Without 

adaptive optics, small-scale turbulence in the atmosphere spreads the beam 

to an angular diameter on the order of 10 μrad. Also, turbulence on larger 

scales tends to tilt the wavefront and displace the emerging beam from its 

intended path. 

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

1.0E+07 1.0E+08 1.0E+09 1.0E+10

Irradiance (W/cm2)

Coupling coef. (N/W)

0

1

2

3

4

5

6

Coupling coef. (dyne/W)

Metals

Nonmetals

Orion system

example

FIGURE 1. Laser Coupling For 5 ns Pulse Duration. 
Using Lasers in SpaceÖ.6 

High-order correction for atmospheric turbulence has been 

demonstrated with laser guide stars and active optical correction. At the 

USAF Phillips Laboratory Starfire Optical Range (SOR) in Albuquerque, 

New Mexico, for example, resolution better than 1 μrad has been obtained 

at 0.85 μm with a 1.5 m aperture (Starfire Optical Range 1997). Sealing 

these results to 1.06 μm and a 3.5 m aperture would meet the requirements

of a laser system for orbital debris removal with existing technology. 

The image shift due to large-scale turbulence can be measured by the 

shift in the apparent position of a star from its expected position. It is 

impractical, however, to use stars for an orbital debris removal system, 

since there is not enough integration time available for faint stars, 

especially during daytime with competition from scattered sunlight. The 

light from a laser guide star traverses the same path as the original laser, 

and hence is not useful for determining the wavefront tilt. An alternative 

to the use of a field star to sense the wavefront tilt is to illuminate the 

debris particle, which should follow a predictable orbital path, and 

measure its apparent position (as affected by tilt) in the reflected light. 

Initial analysis of the debris removal strategy raised concerns that 

reflected light from the moving target, which can be up to 50 grad from 

the intended laser impact position because of the finite light-travel time, 

would he too far removed for effective tilt sensing. Recent astronomical 

results, however, have reduced this concern. At the Steward Observatory,

for example, tilt correction in the K band was accomplished for the 

Multiple-Mirror Telescope (MMT) with a field star 200 μrad from the 

laser guide star (Center for Astronomical Adaptive Optics 1997). 
Using Lasers in SpaceÖ.7 

Orion Adaptive

Optics

Astronomical Adaptive Optics

Laser

Guide

Star

Field Star

for Tilt

Faint

Star

Images

Laser Impact

Target at

Laser Launch

Target Images

400 Hz

illuminator

50 mrad

Target Motion

Figure 2. Comparison Of Adaptive Optics For Astronomical Imaging

And Orbital Debris Removal shows Orion well within the envelope for 

correcting tilt errors. 

Figure 2 is a comparison of adaptive for astronomical imaging and 

orbital debris removal. On the left, a field of dim stars is imaged with

high-order correction calculated on the basis of a laser guide star created

in the center of the field. A brighter field star to provide the tip/tilt 

correction is shown 200 μrad from the center. On the right, a series of 

solid circles shows the reflected signal from an object in a 500 km circular

orbit at a zenith angle of about 45 degrees. We have assumed a 400 Hz 

illuminating signal. The solid circle nearest the laser impact is the last

reflected signal, allowing 1 ms for data processing and moving the mirror 

actuators. The laser guide star must be created at the calculated position of 

the laser impact just before the pusher laser launch. The actual position of 

the target at the time of the pusher laser launch is shown as a cross. While 

the orbital debris removal scheme is shown as if it were imaged in a 

stationary telescope, however, in practice the debris will he tracked as it 

moves across the sky at up to 14 mrads/s. 
Using Lasers in SpaceÖ.8 

The assumption of a 500 km circular orbit in Figure 2 is not critical. In 

a higher orbit the time delay between the launching of a light pulse and the 

return of its reflection is greater, but the apparent angular speed of the 

target is less, with the result that the picture is nearly the same. Images

obtained at the Steward Observatory show that the field star may he as 

much as 200 μrad from the center and still he useful for correction ïThe 

orbital debris portion of the picture shows that reflection from the target in 

orbit provides wavefront tilt information quite close to the site of the

pusher laser launch in comparison with the astronomical imaging scenario.

Thus, the orbital debris removal by laser propulsion should he successful

in terms of the adaptive optics requirements. 

Two key points relative to the adaptive optics remain to be

investigated. First, since it is desirable to operate a future orbital debris 

removal or ground-based laser propulsion station at all times of the day, 

the requirements for adaptive correction during the daytime must be 

investigated. During the daytime, atmospheric turbulence increases and 

makes the adaptive optics more difficult. A laser technology 

demonstration will be able to determine to what extent the Fried scale of 

the turbulence decreases, and whether multiple guide stars will he needed 

for daytime operation. The second point to be investigated is how large the 

zenith angle can be while still maintaining good compensation. Answer 

discuss below, it is desirable to reach 60 degrees from the zenith. The 

smaller apparent angular speed of the target at larger zenith angles will 

work to an advantage. 

Debris Engagement Analysis. We have demonstrated in the laboratory 

that laser energy can he used for propulsion on a wide range of 

uncooperative debris surfaces, and that spreading of a laser related to

turbulence in the atmosphere can he overcome by adaptive optics. In this

section, we will examine strategies for removing orbital debris with an

ground-based pulsed laser. 

Let us assume a fairly difficult target, a 1-cm diameter Na/K sphere, of 

which there are believed to he tens of thousands from the leakage of a 

liquid metal reactor coolant in orbit. These targets are difficult because of 

their low area-to-mass ratios and the higher optimum intensity for a metal 

surface. The laser is taken to be a 1.06 μm, 20 kJ, 5 ns laser pulsed at 5 
Using Lasers in SpaceÖ.9 

Hz. We assume the target is in a 500 km x 600 km elliptical orbit, and 

passes over the laser as it is between apogee and perigee. The effects of 

individual hits are shown in Figure 3 as a function of zenith angle. The 

single pulse effects on the perigee, apogee, and lifetime are small but 

significant. The effects are generally beneficial at positive zenith angles 

(target approaching the laser). 

-400

-300

-200

-100

0

100

200

300

400

-80 -60 -40 -20 0 20 40 60 80

Zenith angle (degrees)

Change in altitude (m)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Lifetime change (day)

Apogee

Perigee

Lifetime

Rising

Setting

Figure 3. Effect Of Single Laser Pulse 

In Figure 3 we exhibit the cumulative effect on the lifetime of

engagements over zenith angle ranges. The final lifetime is plotted as a 

function of the starting zenith angle, assuming zero ending zenith angle. 

The initial lifetime of this target is about 171 days. An engagement that 

begins at 60 degrees reduces this to just 20 days and leaves the target in a 

317 km by 595 km orbit. The figure shows the importance of firing at

large zenith angles. At the larger angles, the apparent angular speed of the 

target is low, and there is time for more pulses than at smaller zenith 
Using Lasers in SpaceÖ.10 

angles. This and similar analyses show that all orbital debris in low earth 

orbit can he removed in one or more engagement.í consisting of pulses 

delivered by a single ground-based laser. The laser of this example is 

capable of removing debris up to 800 km in altitude in two or three years

of operation. 

Technology Demonstration. The serious international concern over the 

orbital debris problem, when coupled with the evident feasibility and costeffectiveness of debris removal by ground-based pulsed laser propulsion, 

has led to planning for the next step toward debris removal. The Orion 

report contained a suggestion for a technology demonstration in which a

120-J pulsed laser would he joined with a 3.5 m aperture telescope with 

tracking capability, such as the USAF Advanced Electro-Optical System 

(AEOS) under construction in Hawaii or the Starfire Optical Range (SOR) 

in New Mexico. Specially constructed targets, which would he deployed 

from the space shuttle, would have corner-cube reflectors or a UPS unit to 

return a strong signal for calibration tests. This demonstration would have

a number of goals.5

0

20

40

60

80

100

120

140

160

180

0 20 40 60 8

Starting zenith angle (deg)

Final lifetime (days)

0

Figure 4. Post-Engagement Lifetime For an Orbital Debris Object 

With Zero Final Zenith Angle. 
Using Lasers in SpaceÖ.11 

Cost estimates for the technology demonstration are in the range of 

$13-28 million, which is comparable with the cost of a single flight of the 

least expensive orbital launch vehicle (Pegasus). The potential benefits, if

the demonstration leads to an operational system, are saving tens of 

millions of dollars per year in expenses (increased shielding, damage 

control systems, and satellite replacements) related to orbital debris, and 

the accelerated development of other applications of laser space 

propulsion and laser power beaming. 
Using Lasers in SpaceÖ.13 

III. Near Earth Asteroid Avoidance System 

Astronomical telescopes and deep space radar systems have observed

the existence of at least 2000 Near Earth Objects (NEO), such as asteroids

and comets, which potentially could destroy most life on Earth. An 

asteroid with a diameter of 0.2 km would strike the Earth with a power

rivaling the strength of a multiple warhead attack with the most powerful 

hydrogen bombs. This strike would throwí up a cloud of dust rivaling the 

most powerful volcanic explosion, which would seriously affect climate

on the scale of two to three years. A strike by a larger asteroid, say 1 km, 

(especially in the ocean) would create a gigantic tsunami that would flood 

and obliterate coastal regions. More significantly it would eject a massive

dust cloud that would alter cur biosphere to the point that life as we know 

it would cease to exist with no chance of recovery within the near term. 

The consensus in the astronomical and astrophysics community was

that most of the known NEOs do not pose a near term threat, and therefore 

that these objects do not present any dancer to the Earth and its biosphere 

in the foreseeable future. However, the recent collision of a comet Iauki 

with Jupiter and the discovery of an uncatalogued asteroid, that passed 

near Earth without any advanced warning, have increased concerns. 

Several schemes have since been discussed for dealing with NEO on 

collision courses with the earth. ïThese include blowing them up with 

nuclear weapons or landing on them and using small, shaped nuclear 

detonations to steer the asteroid into a passing orbit. However, 

fragmentation may not be a solution because the center of mass of the 

resulting cloud of debris would continue on the original collision 

trajectory. Also, we presently do not have the lift capability to land and 

place nuclear devices on asteroids without extremely long lead times. The

research and development of a nuclear deflection system would cost 

billions and would still require sufficient warning of an impact to be

implemented. 

A better system would he one that is ìon stationî and could he used 

routinely to shape asteroid orbits over long periods of time so that they do 

not pose a potential threat. Phased Array Laser Systems (PALS) could he 

developed and orbited. Space-based laser constellations (SBL) are 

presently under development and will he flow-n during the next decade.
Using Lasers in SpaceÖ.14 

Coupling PALS with powerful telescopes, such as those being developed 

under the Next Generation Space Telescope (NGST) project, would 

provide long-term warning for implementation of an overall NEO 

avoidance system. The feasibility of this system is discussed below. 

The lasers that would he used in Project Orion have demonstrated 

sufficient capability for orbital debris removal for objects in the size range 

from 1-10 cm diameter. Ground based experimental data, using a 20 kW 

pulsed laser, show that the impulse imparted to aluminum targets due to 

the ejected plasma cloud gives an average surface pressure p = 6.5 x 10-4

N/cm2, or equivalently, an acceleration, a = l.25x 10-6 m/s

2

 With present 

technology, a laser phased array can be aimed at the asteroid with

sufficient power to ablate its surface. Assuming that a laser array can be 

scaled up to operate on a 1 km diameter iron asteroid, this would require a 

200 GW power grid. Several alternate potential power sources are 

available, including nuclear or electric generation and solar power arrays.

Let us assume that the asteroid is at infinity moving toward the Earth

with a velocity v0 and impact parameter R. The closest point of approach 

Re is given by 

R R g

R

v

e E

E ≅ +





 



 



 



1 2 

0

2

1

2

where RE is the radius of the Earth, and g is the gravitation acceleration at 

the surface of the Earth. There are two cases of interest: 

ï Head-on collision: v0 = 40km/s, → Re=l.04 RE

ï ìCatch-upî collision: v0 = 5km/s → Re=1.1 RE

The catch-up collision is the most dangerous. However, it is only 

necessary to move the asteroid laterally away from its original orbit by at 

most 1.1 RE, which is the worse case scenario. Table 1 gives several 

relevant times for irradiation. 
Using Lasers in SpaceÖ.15 

Table 1. Lateral displacement and final velocity of asteroid from

original orbit for perpendicular illumination of target. The final 

velocity is a linear change, but the displacement is quadratic. 

Note the change of units in the second and third columns. 

Table 1 shows that a minimum of 38.8 days of illuminating the target is 

necessary for the worse case of a head on collision, and in most cases 

would take much less time. The warning time of impending impact is of 

critical significance, which highlights the importance of deep space 

surveillance for NEOs, using the NGST for example, in addition to longterm monitoring and orbital calculations. Early orbit shaping would be 

extraordinarily effective. Also it is important that PALS be deployed at

positions, which are free from occluding (obstructing) the beam by the 

Earth or the Moon. The ability to see clearly, i.e., surveillance of small, 

dark objects such as asteroids requires freedom from Earth-and Moonshine, is essential for the NGST. However, it is obvious that the PALS 

must be located sufficiently near the Earth, which it is designed to protect.

A primary candidate is one of the Sun-Earth Lagrange points at which a 

spacecraft will maintain a fixed position with respect to the Earth.6

Figure 5. The five Lagrange points are shown as Ln, n=l-5. PALS is 

placed at L5 and NGST is placed at h. Note that nothing is to scale. 
Using Lasers in SpaceÖ.16 

In Figure 5, we pictorially describe an asteroid encounter with the Earth. 

Figure 5. The five Lagrange points are shown as Ln , n=1-5. PALS 

is placed at L5 and NGST is placed at L4. Note that nothing is to scale. 

This orbit, as depicted in Figure 5, lies between the orbits of Mars and

Venus, and is consistent with the recent news false alarm that an asteroid

would pass within 48.000 km of the Earth. Better data significantly altered 

the prediction of the closest point of approach to 1,000,000 km, and 

suggested that there is no significant threat in the foreseeable future. 

Nevertheless, the orbital period of an asteroid lying between Mars and 

Venus is roughly 0.9 yr. Thus, if the collision scenario depicted in Figure 

5 was correct, then with sufficient lead-time, then PALS firing with a good 
Using Lasers in SpaceÖ.17 

aspect from L5, as shown in the figure, would have had two-three months 

to move the asteroid away from a collision path with the Earth. Since, 

however, the original news report in this case, was very late, there 

probably would not have been sufficient time in advance, as shown in 

Table 1, for PALS to deflect the asteroid away from the Earth. This fact 

stresses the need for coupling with PALS an early warning system based 

on a technology similar to the NGST, in addition to deep space searches 

with radar. 

In another scenario, the undetected asteroid could he chaotically 

ejected from the asteroid belt. In this case it is possible to describe similar 

results as depicted in Figure 5. In this case, the calculation is simplified 

by assuming that the entire impulse to the asteroid is given in one instant.

It is necessary to set the stage for this event: 

ï ASTEROID ORBIT=.8 X3AU, POSIGRADE 

ï COPLANAR WITH ECLIPTIC 

ï BEGIN LASER IMPULSE WHEN 

- ASTEROID IS 2 AU FROM SUN 

- ASTEROID DESCEADS TO LAST PERIHELION BEFORE 

COLLISION 

ï LASER IMPULSE DIRECTED THROUGH ASTEROID CG 

ï IMPUSIVE ∆V INCREMENT 

This particular event can he calculated from the data given in the 

following figure. 
Using Lasers in SpaceÖ.18 

ORBITAL & IMPULSE GEOMETRY

COLLISION 

POINT @ t ~ 123 DAYS

( W/O DEFLECTION)

∆V 

2 AU 

1.6 AU 

ASTEROID

@ t = 0

ï

ï

EARTH

@ t = 0

ï

SUN 

1 AU

SEMIMAJOR

AXIS

APOHELION = 3 AU 

PERIHELION = .8 AU

LASER BEAM

Figure 6. The ∆V imparted to the asteroid causes the semi-major axis of

the asteroid to rotate clockwise and thereby reduces the period. As a 

result the asteroid will cross in front of the Earth. 

The ∆V of 5 m/s (as given in Table 1) is an obvious example of an

impulse that yields a ìmiss distance,î In this case the asteroid passes in

front of the Earth by 1.25 Earth diameters. The realistic case, however,

would be a gradual shift in the orbit by a long duration, low intensity 
Using Lasers in SpaceÖ.19 

impulse that gradually reshapes the orbit over long time period, perhaps 

over several orbits. Ideally, for the asteroidal orbit between Mars and 

Venus, it might conceivable to move the asteroid into an orbit that 

removes the threat to the solar system, On the positive side, it is 

interesting to contemplate orbit shaping for the purpose of asteroid 

mining. 
Using Lasers in SpaceÖ.21 

IV. Conclusions 

For several years, the Air Force and NASA have worked to 

characterize the implications for orbital debris for the risk to spacecraft.

While there is a continuing debate about the risk, there is agreement that

some risk exists and that these risks will increase as the use of space 

expands. A related question concerns the threshold at which the risk 

become too high. While we cannot answer complex questions here, there

are reasons for responding to this problem.

The use of space is vital for future economic and political power for

many reasons. Since an impact from a meteorite, asteroid, or comet 

would he an unimaginable catastrophe, we have little choice but to deal 

with this threat. On a lesser scale, the threat of orbital debris to 

spacecraft raises important economic questions. While there are many

risks with spaceflight, we must decide at what threshold the risks are too 

high and action s necessary. That threshold must balance the possible 

impact to the mission, resources available to accomplish that mission, 

and the technical arid cost feasibility of reducing that risk. In addition, 

that threshold must balance all of the risks that are associated with a

mission. In other words, if there is a practical way to reduce risk, then it

is probably prudent to do so. The purpose of this study is to describe one 

solution for reducing the risk posed by orbital debris. 

Presently, there are significant quantities of orbit debris in all sizes,

altitudes, and inclinations. However, the debris ranges in size from the

microscopic to several meters, including worn out satellites arid upper

stages of rockets, and fortunately there are many more small objects than

large ones. The typical closing velocities for a collision with orbital 

debris are on the order of 20,000 mph, which means that a collision with

a satellite would likely end its useful service life at costs that exceed one 

billion dollars. 

With the technological state of the art in orbital debris protection, 

satellites can he effectively shielded against hypervelocity objects that

are less than 1 cm in size. This shielding, however, is extremely

expensive. For example, the cost of increasing the protection for critical 

modules on the Space Station from 1 cm to 2 cm has been calculated to

be on the order of 100 million dollars for launch costs alone, not 
Using Lasers in SpaceÖ.22 

including research and development and manufacturing costs. 

For objects that are greater than 10-30 cm in size, the Space Station

will rely on the Space Command tracking network to provide early 

warning. If an object will come too close to the station, it will maneuver

to avoid it. But the total costs of this maneuvering system are

substantive, and we should note that it will not provide absolute 

protection, principally because the Space Command could have 

difficulties in continuously tracking objects that are less than 30 cm in 

size. In the event of a solar flare, the tracking system may lose objects 

for days at a time. 

The reality is that there is no system in to protect against the

approximately 150,000 objects that are in the range of 1-10 centimeters 

in size. Using the example of a ten n is ball that is approximately five 

centimeters; a hypervelocity collision between a tennis hall and a 

satellite will probably reduce that satellite into orbital debris. And it may 

have a cascading effect as many smaller objects produce orbital debris, 

which in turn increases the overall risk to objects in orbit. 

While the probability of a collision with an individual satellite is quite

low, the probability of a collision occurring with in the, entire population 

of space assets is not as remote. An analysis suggests that with the 

current level of orbital debris and the sizes of satellites, the probability is 

that there will be one collision per year. And that loss could amount to 

billions of dollars. This is a global problem and will involve an 

international effort that is coordinated by the United Nations. No one 

project cannot redress this problem. Nor is it economically practical to 

shield each spacecraft and give it maneuvering capabilities. 

An elegant, cost effective, and feasible approach is to use laser 

technology to solve this problem. It is estimated that a single. Groundbased laser facility that costs about $100 million and that operated near 

the equator could remove all orbital debris up to an altitude of 800 km in

two years Since satellites typically cost several hundred million and 

given the half billion price tags on shuttle and Titan launchers, this

investment is relatively small given the potential losses of rockets. 

Furthermore, the development of this technology will stimulate other

approaches, including laser power beaming, deflecting asteroids, 

meteoroids, and comets, and propulsion for interstellar missions. In 

closing, this study addressed a 
Using Lasers in SpaceÖ.23 

problem that the international community must resolve if we are to

reduce the risk to spaceflight, and hence to economic progress, that is 

caused by orbital debris. 
Using Lasers in SpaceÖ.25 

References 

Maethner. SR., A.E. Reinhardt. and LU. Anderson (1994) Report on 

USAF Space Debris Phase One Study. Phillips Laboratory Technical 

Report PL-RT-94-1042. 

Phipps. Claude R. and M. M. Michaelis (1994) ìNEO-LISP: 

Deflecting Near-Earth Objects Using High Average Power, Repetitively 

Pulsed Lasersî, 23rd European Conference on Laser Interaction with 

Matter, St. Johnís College, Oxford, England. September 19-23. 1994, 

LA-UR 94-3124. 

Campbell, J.W. et al (1996) ìProject ORION: Orbital Debris Removal 

Using Ground-Based Sensors and Laserî, NASA Technical 

Memorandum 108522, 

http//infinity.msfc.nasa.gov/Public/orion/default.html.

Cleghorn. George et al (1995) Orbital Debris: A Technical 

Assessment, National Academy Press. Washington, DC, 

http://www.nas.edu/cets/aseb/debrisl html. 

Starfire Optical Range (1997) http//wwwsor.plk.af.mil/. 

Center for Astronomical Adaptive Optics (1997) 

http ://athene.as.arizona.edu:8000/caao/.
Using Lasers in SpaceÖ.27 

Notes 

1. The 1994 USAE study (Maethner 1994) found a peak collision 

flux of about 0.0002 m-2 yr-1 for debris one cm or more in diameter at an 

altitude of 800 km and an inclination of 980. At an altitude of 500 km 

and an inclination of 280 the flux was estimated at 0.00001 m ñ2 

yr1

.

.

According to results cited in the 1995 National Research Council 

report on orbital debris (Cleghorn 1996)í there were then approximately 

400 spacecraft in the altitude range from 700 km to 1000 km. If we 

estimate that half of these are functional, and allow a typical crosssection of 20 m2

 for each satellite, then there is a total functional satellite 

cross-section of about 4000 m2

 near 800 km. The expected rate of 

collisions with orbital debris one cut or more in diameter is thus about 

0.8 yr-1

2. Coupling is strong when the intensity readies at least one tenth 

of the optimum intensity. The optimum intensity scales roughly as the

square root of the pulse duration. 

3. The reason is that a pulse with a modest energy may have a high 

intensityí if its duration is short, and at the same time the optimum

intensity is somewhat smaller for a short pulse. 

4. The peaks of the curves in Figure 1 are at the optimum

intensities for 5 ns pulses, and the optimum are at higher intensities for 

longer pulses. The vertical marks in the figure are the range of intensities 

calculated for a system with a 20 kJ, 5 ns pulsed laser at 1.06 μ directed 

by a 3.5 m aperture onto a target in a 500 km circular orbit as the zenith 

angle varies from 0-600

. 

5. These include the goals of accurately predicting the position of 

illuminated targets, correcting for wavefront tilt, performing high-order

correction for turbulence, correcting for atmospheric turbulence at large 

zenith angles- operating during daylight, determining whether target 

response to laser impact is within predictions, and locating and tracking 

small targets (with or without handoff from remote tracking station) 

quickly and often enough to provide pusher laser targets. 

6. Another advantage is that a slightly displaced spacecraft will 

orbit the Lagrange point. 
Center for Strategy and Technology 

The Center for Strategy and Technology was established at the Air 

War College in 1996. Its purpose is to engage in long-term strategic 

thinking about technology and its implications for U.S. national security. 

 The Center focuses on education, research, and publications that 

support the integration of technology into national strategy and policy. Its 

charter is to support faculty and student research, publish research through 

books, articles, and occasional papers, fund a regular program fo guest 

speakers, host conferences and symposia on these issues, and engage in 

collaborative research with U.S. and international academic institutions. 

As an outside funded activity, the Center enjoys the support of institutions 

in the strategic, scientific, and technological worlds. 

 An essential part of this program is to establish relationships with 

organizations in the Air Force as well as other Department of Defense 

agencies, and identify potential topics for research projects. Research 

conducted under the auspices of the Center is published as Occasional 

papers and disseminated to senior military and political officials, think 

tanks, educational institutions, and other interested parties. Through these 

publications, the Center hopes to promote the integration of technology 

and strategy in support of U.S. national security objectives. 

 For further information on the Center for Strategy and Technology, 

please contact: 

Grant T. Hammond, Director 

Theodore C. Hailes, Deputy Director 

John P. Geis II, Director of Operations 

Air War College 

325 Chennault Circle 

Maxwell Air Force Base, Alabama 36112 

(334) 953-6996/2985/5579 

(DSN 493-6996/2985/5579) 

Email: Grant.Hammond@maxwell.af.mil

 Ted.Hailes@maxwell.af.mil

John.Geis@maxwell.af.mil
Titles in the Occasional Papers Series 

1 

Reachback Operations for Air Campaign Planning and Execution

Scott M. Britten, September 1997 

2 

Lasers in Space: Technological Options for Enhancing U.S. Military 

Capabilities 

Mark E. Rogers, November 1997 

3 

Non-Lethal Technologies: Implications for Military Strategy 

Joseph Siniscalchi, March 1998 

4 

Perils of Reasoning by Historical Analogy: Munich, Vietnam, and the 

American Use of Force Since 1945 

Jeffrey Record, March 1998 

5 

Lasers and Missile Defense: New Concepts for Space-Based and GroundBased Laser Weapons 

William H. Possel, July 1998 

6 

Weaponization of Space: Understanding Strategic and Technological 

Inevitables

Thomas D. Bell, January 1999 

7

Legal Constraints or Information Warfare

Mark Russell Shulmann, March 1999 

8 

Serbia and Vietnam: A Preliminary Comparison of U.S. Decisions to Use 

Force 

Jeffrey Record, May 1999 
9 

Airborne and Space-Based Lasers: An Analysis of Technological and 

Operational Compatibility 

Kenneth W. Barker, June 1999 

10 

Directed Energy and Fleet Defense: Implications for Naval Warfare

William J. McCarthy, February 2000 

11 

High Power Microwaves: Strategic and Operational Implications for 

Warfare

Eileen M. Walling, March 2000 

12 

Reusable Launch Vehicles and Space Operations 

John E. Ward, Jr., March 2000 

13 

Cruise Missiles and Modern War: Strategic and Technological 

Implications 

David J. Nicholls, March 2000 

14 

Deeply Buried Facilities: Implications for Military Operations 

Eric M. Sepp, March 2000 

15 

Technology and Command: Implications for Military Operations in the 

Twenty-First Century 

William B. McClure, July 2000 

16 

Unmanned Aerial Vehicles: Implications for Military Operations 

David Glade, July 2000 
17 

Computer Networks and Information Warfare: Implications for Military 

Operations 

David J. Gruber, July 2000 

18 

Failed States and Casualty Phobia: Implications for Force Structure and 

Technology Choices 

Jeffrey Record, December 2000 

19 

War as We Knew It: The Real Revolution in Military 

Affairs/Understanding Paralysis in Military Operations

Jan S. Breemer, December 2000