Z
d

I
The First Mission of the

Tethered Satellite System

Table of Contents

A Line To The Universe 1

The First Tethered Satellite System Mission 2

Major Tethered Satellite System Elements 6

Tether Dynamics 10

TSS-1 Science Background 14

TSS-1 Science Investigations 23

Mission Scenario 28

TSS-1 Crew 30

A Line To The Future 32

Quick Reference To Experiments And Investigators

For Further Reading 36

Glossary Of Abbreviations And Acronyms 37

35

N/ A

National Aeronautics and

Space Administration

ORIGINAL PAGE

PHQTOGRAPH,
il
A Line To

The Universe

The first Tethered Satellite System (TSS-1) will soon

be launched aboard the Space Shuttle. Circling Earth at

an altitude of 296 kilometers (kin), the reusable tether

system will be well within the tenuous, electrically

charged layer of the atmosphere known as the ionosphere. There, a satellite attached to the orbiter by a

thin conducting cord, or tether, will be reeled from the

Shuttle payload bay. This will grant scientists experimental capabilities never before possible.

On this mission, the satellite will be deployed 20 km

above the Shuttle. The conducting tether will generate

high voltage and electrical currents as it moves through

the ionosphere and allow scientists to examine the

electrodynamics of a conducting tether system. These

studies will not only increase our understanding of

physical processes in the near-Earth space environment

but will also help provide an explanation for events

witnessed elsewhere in the solar system. In addition, the

mission will explore the mechanical dynamics of tethered systems, providing information that will improve

future missions and possibly lead to a variety of future

tether applications.

Tethered spacecraft can be deployed toward or away

from Earth. Downward deployment (toward Earth) on

future missions could place the satellite in regions of

the atmosphere that have been difficult to study because

they lie above the range of high-altitude balloons and

below the minimum altitude of free-flying satellites.

A series of Tethered Satellite System flights, exploring

in both directions from the Shuttle, could gather data

previously impossible to obtain. Each flight would

allow scientists and engineers to conduct new experiments, explore phenomena discovered through previous

missions, and develop new uses for tethers in space

exploration.

Deployment of the Tethered Satellite System upward

from the Shuttle On TSS-I allows scientists to gather

data on performance, while providing an excellent

platform for a variety of plasma physics and electro@-

=.....

namics investigations.

MIllilllAL ".... ""

The Tethered Satellite

System has the potential

to be deployed toward the

Earth. On such a future

mission, large-scale

investigations of previously inaccessible regions

of the atmosphere could

be performed.
The First Tethered

Satellite System Mission

Launc 

i "

_%____ Mission Objectives _,

_;_._r n The era of space-age tethered operations moves ._, _ $_

_ - _/7..-_._ _---_y toward reality with the launch of TSS-I. The C "_P_"_'_ _

/ primary objective of this m_ss,on ts to demon- _ A_:._,_,_ _ i

[ strate the technology of long tethered systems e_ efrtevat ._

in space and to demonstrate, through scien- ---_ ._i.i._ _ _,:"! " :

useful for research. Speeding through _ _

tific investigations, that such systems are Science Goals _%_ _

the magnetized ionoEngineering Goals spheric plasma at almost 8 km

Manipulating a satellite on a tether from the per second, a 20-kin long

orbiter is a unique engineering challenge, conducting

• " and tether :i_%ii_y:_'_t///, t

Because gravity, cenmfugal force, atmo- !_'_'a_/i_l _/

spheric drag vary with altitude, each of the should _ .. _i_: _ ,

two bodies in a tethered system, one orbiting create __--'____yar_ah/-_

: above the:other:is subject to different influ __: :avari= r -'='_r. __

encesi_Consequently, the primary engineering .....ety ofvery :" " " ' _ ........

goalofrss-i is to demonstrate that a satellite interesting ptasma- ii'.i,_-_i: _ -..:

can be deployed, stabilized, and retrieved on a electrodynamic phenomena. These are -

long tether in space and that an electrically expected to provide a variety of unique experconducting system can be operated success- imental capabilities, including the ability to

fully. Tether dynamics and control are not collect an electrical charge and drive a large

intuitive; while reeling out a satellite on a current system within the ionosphere, to

tether is somewhat analogous to flying a kite, generate high voltages [on the order of

the analogy breaks down when the environ- 5 kilovolts (kV)] across the tether at full

ments in which the systems operate are com- deployment, to control the satellite potential

pared. Unlike a kite in the atmosphere, the and the satellite's plasma sheath, and to genertethered satellite is in an_electrically charged ate low-frequency electrostatic and electroenvironment and is controlled by gravity magnetic waves. It is believed that these

gradient rather than aerodynamic forces. TSS-1 capabilities can be used to conduct controlled

will improve our understanding of tether experimental studies of phenomena and

dynamics and allow scientists and engineers processes that occur naturally in plasmas

to develop more sophisticated tether control throughout the solar system, including Earth's

models for future tethered missions, magnetosphere.

2
Anecessary first step toward these studies

--and the primary science goal of TSS-1 --

is to characterize the electrodynamic behavior of the satellite-tether-orbiter system.

Of particular interest is the interaction of the

system with the charged particles and electric

and magnetic fields in the ionosphere, including the nature of the external current loop

within the ionosphere and the processes by

which current closure occurs at the satellite

and the orbiter. This will be investigated by a

series of experiments conducted with electron

accelerators and tether current-control

hardware, along with a set of interdependent

diagnostic instruments provided by the

TSS- 1 investigators.

Organization

The Tethered Satellite System is a joint

venture of the United States' National

Aeronautics and Space Administration

(NASA) and Italy's Agenzia Spaziale Italiana

(ASI, the Italian Space Agency). Based on

a 1984 Memorandum of Understanding

between NASA and ASI, the Italian agency

has responsibility for developing the reusable

satellite, while NASA has responsibility

for developing the deployer system and the

tether, integrating the payload, and providing

transportation into space. In addition, the

U.S. Air Force Phillips Laboratory, by agreement with NASA, is participating in the

program by providing an experiment that

supports the TSS-I mission as well as Air

Force research interests. The deployer system

and the tether were developed by the Martin

Marietta Astronautics Group in Denver,

Colorado, and the satellite by the Alenia

Space Systems Group in Turin, Italy.

Both NASA and ASI are sponsoring

experiments to address the goals of the TSS-I

mission. Research guidelines specify that

experiments study Tethered Satellite System

electrodynamics and plasma interactions.

The experiments selected are compatible with

the engineering objectives and yield complementary data.

NASA's Marshall Space Flight Center,

Huntsville, Alabama, is providing the overall

management of the Tethered Satellite System

project for NASA Headquarters. Johnson

Space Center, Houston, Texas, and Kennedy

Space Center, Florida, are also integral parts

.Liiiiiiiiiz

of the Tethered Satel!i!e System mission.

Flight and science operations are controlled

from Johnson Space Center, while Kennedy

Space Center is responsible for integrating

payloads into the orbiter and launching

the Shuttle.

An Investigator Working Group, composed of TSS-I Principal Investigators and

Associate Investigators, advises NASA and

ASI in the design, development, and operation of TSS-1. This group develops and

reviews all science requirements for the

mission, recommends mission profiles and

experiment sequence_; and specifies how data

should be acquired, processed, handled, and

distributed. The Investigator Working Group

also oversees science activities during

the flight.

Mission Profile

The Shuttle will carry TSS-1 in its payload

bay to a circular orbit where the satellite will

be deployed spaceward on a conducting

tether. Thus begins an adventure that could

revolutionize the architecture of space structures and expand the PoSsibilities for space

investigations.

The deployed mission begins when a

crew member unlatche_s the satellite and the

deployer boom extends. Then the satellite's

tether-aligned thrusters fire, gently lifting it

away from the boom and the Shuttle. At

a distance of 6 km fro_mthe Shuttle, other

thrusters will spin the satellite so that it rotates

a quarter turn each minute, allowing data to

be collected as the satellite sensors rotate

through different electric and magnetic fields.

Approximately 6 hours later, the satellite

is fully deployed 20 km from the Shuttle. Ten

hours of on-station operations begin with the

satellite's spin being stopped for an orbit as

data on tether system dynamics are collected.

After this orbit, thrusters will spin the satellite

so that it rotates at slightly less than one full

turn each minute. As the Tethered Satellite

System stimulates and interacts with the

ionosphere, instruments in the satellite and the

Shuttle's payload bay measure the response,

determine how the Tethered Satellite System

collects an electrical current from the ionosphere, study the power generation properties

of the entire tether system, and characterize

the surrounding environment.

Retrieval operations begin with the reel

assembly winding in the tether. The satellite

approaches to within 2.4 km of the orbiter,

where it stops for 5 hours to gather additional

data and stabilize the system for final

retrieval. Retrieval resumes and crewmembers

take manual control for final approach

and docking.

.... .÷_

3
L

kk __

Regions of the Atmosphere

Earth'selectricallyneutralatmosphereis composedof fourprimary

layers.The|owestlayer,lhe onewelivein onEarth'ssurface,Js

knownasthetroposphereandextendsashighas16kmabove

sealevel.Extendingfromabout16to 48 kmis thestratosphere.

Ninety-ninepercentof theair intheatmosphereis locatedin these

tworegions.Abovethe stratosphere,from48to 85 kmis the mesosphere.Theuppermostlayeristhethermosphere,whichextendsto

approximately1,000 km.

Theupperthermosphereis alsocharacterizedbythe presenceof

electricallychargedgases,orplasma.Thisregion,whichextends

from85to approximatelyt,000 km, is alsoknownasthe ionosphere.

Theboundariesof the ionospherevaryaccording1osolaractivity.

Overlappingtheionosphereisthe magnetosphere, whichextends

fromapproximatelyS_Oto 60,000kmonthes_e towardstheSun,and

trailsoutmorethan300,000kmawayfromtheSun.Themagnetosphereis theregionof spacesurroundingEarthinwhichthe geomagneticfield playsa dominantroleinthe behaviorof chargedparticles.

TSS-1will allowscientiststostudya varietyofionosphericprocesses.

Forexample,it will generatelarge-scaleelectricalcurrentloopsin

theionosphere.Thesecurrentloopsmaybesimilarto currentsthat

occurinthe polarregionsof theatmosphereassociatedwithauroras.

Conductingtethersmayalsoprovidean alternatesourceof powerfor

futurespacecraft.Thismissionwill helpquantifytheamountof electricalpowerthatcanbeproducedbyconductingtethers.

Thelowerregionofthe thermosphere,fromapproximately130to

180km, hasbeenverydifficulttoexplore.Satellitescannotorbilin

thisregionbecausetheywouldrapidlyfallfromorbitandburnup

fromatmosphericfriction.Balloonscannolreachthisaltitude,and

soundingrocketspassthroughtheregiontooquicklytoobtainmore

thana quickverticalprofileofa particularspot.WhileTSS-1will be

deployedawayfromEarth,futuremissionscanbe deployeddownward.ThesefutureTetheredSatelliteSystemmissionscanspenddays

atthesealtitudes,gatheringvaluabledataina previouslyinaccess_le regionofouratmosphere.

_:'_ "___" -: "--_7 .....

Layers of the Atmosphere
Justasthebarmagnet produces

field!ines,so t#o does Earth. You

can Visualiz_ thcse field lines by

thinkin_'_f _e Earth as having

a bar ma_n_runningfrom the

North to S_h-poles.

, , . , ,_

Earth'sMagnetic Field and HowTSS-1Will ProducePower ..........

I

TSS-1makesuseof Earth'smagneticfieldandelectricallycharged--

ionosphereto producea currentthroughthetetherforavariety

ofexperiments.Tounderstandsomeof thediscussionsaboutthe _

mission,a basick_edge ofEarth'smagneticfield is helpful, - _-_

All magneticobjectsproduceinvisiblelinesof force,extending =

betweenthe polesofthe object.Aneasywaytovisualizethisisto _--

...... spreadironfilingsona sheetof paperandplacea barmagnetunder

:...... the paper.Theironfilings-w_Farrangethemselvesaroundthe

_-_.......... andalongthe magnetficfieldllnes. -_

Inthesimplestterms,Earthcanbethoughtof asa dipole

fii_ggfiet.Magneticfield linesradiatebetweenEarth'snorthandsouth

_ magneticpoles,justastheydobetweenthepolesofa barma

ofa batterybeforea currentcan

flow.Inthe caseof TSS-1,the

circuitmustbeclosedbythe

conductingionosphere.Theelectronscollectedbythesatellite

will flowthroughthe tethertothe

orbiter,whereelectronacceleratorswill returnthemtothe ionosphere.AtthealtitudeofTSS-1,

currentsnormallycanonlyflow

alongEarth'smagneticfield

lines.Asa result,regionsof

positiveandnegativecharge

createdat theendsof thetether Chargedparticlesanda]-mosphericmoleculesbecometrappedon TSSPower Production

............thesefi_eldI!nes(justastheTronfilingsare trapped),formingthe streamoutalongthe geomagnetic

magnetosphere. Earth'sfield linesare notas symmetricalasthoseof _jeld lines.Thesearecalledfield-alignedcurrents.However,when

thebarmagnet._l'heimpacto_e solarwindcausesthe compression the currentsreachthe loweranddenserpartof theionosphere,

ofthelinesfacingsunward,whilethe fieldlinesfacingawayfrom .... _knownastheE-region,collisionsbetweenthe chargedandneutral

theSunstreambackto formEarth'smagnetotail, particleswilleffectivelyscatterelectricchargesacrossthefield

lines,formingwhatare knownascrossfieldcurrentbranches.These TheTetheredSatelliteSystemcanproducepowerbecausea high

__,;.._ branchesplayan importantroleinTSS-1powerproductionbyallow- potentialisgeneratedacrossthe tetherasa resultof itsrapid,,o,u,

acrossEarth'smagneticfield lines.Thiseffectis analogousto the --............. ingthe circuittobe closed.

waypoweris genera[edbyan automobilealternator.Theelectric

potentialattraclsfreee_ctrons to the satelliteasit passesthrough

theIonosphericplasma.Fora current(aflowofchargedparticles)to ORIGfNAL ,_A_.._

be produced,thecircuitmustbecompleted-- justasa wiremust

closethe circuitbetweentwopoTes COLOR PHOTOGRAPH

5
Major Tethered Satellite

System Elements

- Satellite

Dep4oyer

Reel Mechanism

SPREE t' : __ :

Hardware

SETS

Hardware

Satellite

Support

Core Equipment

Eq_pme_

Support Structure

The Tethered Satellite System The Tethered Satellite System

has five major components:

the deployer system, the tether,

the satellite, the carriers on which

the system is mounted, and the

science instruments. These specific elements are supported by

the standard capabilities of the

Space Shuttle orbiter, payload bay

mounting equipment, and control

and command facilities on

the ground.

The Tethered Satellite System is

seen here undergoing integration

at the Kennedy Space Center.

6

The TSS-1 hardware is

mounted on two carriers in the

payload bay. The deployer rides

on a Spacelab Enhanced

Multiplexer Demultiplexer Pallet

(called an EMP), a general-purpose unpressurized platform. The

pallet provides both functional

and structural support to the

deployer, and its enhanced features include temperature control,

power distribution, and command

and data transmission capabilities.

The second carrier is the MultiPurpose Equipment Support

Structure, an inverted A-frame

truss located immediately aft of

the enhanced pallet. This structure holds deployer core equipment and two of the mission's

experiments.

The Deployer System

The deployer system includes the

satellite support structure, the

deployment boom, the tether reel

mechanism, a system that distributes power to the satellite

before deployment, and a data

acquisition and control assembly.

Umbilical cables woven

through the deployment structure

provide power and data lines to

the satellite before deployment.

When the umbilicals are disconnected after checkout, the satellite operates on its internal

battery power. If the safety of the

orbiter becomes a concern, the

tether can be cut and the boom

and satellite jettisoned.

When fully extended, the

boom is a 12-meter (m) foursided framework resembling a

ORIGINAL PAGE

COLOR PHOTOGRAPH

short broadcasting tower. Like a

bolt forced upward by a rotating

nut, the boom unfolds and

extends slowly out of the turning

canister on rollers that follow

four tracks. As the canister

rotates, fiberglass battens, similar

to ones that give strength to sails,

are released from their stowed,

bent-in-half positions, to act as

horizontal crossmembers to hold

the longerons, or vertical members, erect. Diagonal tension

cables further strengthen the

boom, and flat ribbon-like cables

provide the connection for electrical functions at the boom tip.

During retrieval, the canister

rotation is reversed. Tracks guide

the rollers back, forcing the

battens into their original bent

position, and the longerons fold

smoothly into the boom canister.

The tether reel mechanism, which

controls the length, rate, and

tension of the tether, is critical to

tether control. This assembly

consists of the tether reel and the

reel motor. It is controlled by

The TSS-I deployer system has

undergone many tests to ensure

proper operations during the

mission.
the motor control assembly and

a data acquisition and control

assembly. The reel mechanism

is capable of letting out the tether

at 16 km per hour; during the

TSS-1 mission, however, the

tether will be reeled out at a much

slower rate.

The Tether

The tether's length and electrical

properties affect all aspects of

tethered operations. With its

satellite fully deployed, the

TSS-1/orbiter combination is

100 times longer than any previous spacecraft, and when the

tether's current is pulsed by

electron accelerators, it becomes

the longest and lowest frequency

antenna ever placed in orbit.

Also, for the first time, scientists

can measure the charges collected

by spacecraft with high electrical

potentials. All these capabilities

are directly related to the structure of the shoe lace-thick tether,

a conducting cord designed to

anchor a satellite miles above

the orbiter.

The TSS-1 tether is 22-kin

long and is expected to develop a

5,000 volt (V) potential and carry

a current of up to 1ampere (A).

Manufactured for Martin-Marietta

by the Cortland Cable Company

of New York, the tether has a

center of Nomex TM that is wrapped

with copper wire which acts as

the electrical conductor. The layer

of wire is insulated with Teflon",

which is then covered with braided

Kevlar" 29 to give strength to the

tether. The outer jacket of the

tether is braided Nomex" which

protects the tether against the

corrosive effects of atomic oxygen

and mechanism-induced abrasion.

The different layers of the tether

can be seen in this photograph.

TSS-1 Tether Characteristics

Diameter (outer): 2.54 mm

Deployed length: 20 km

Breakstrength: 1,780 N

Maximum allowable tension: 700 N

Maximum expected load: 53 N

Maximum allowable mass: 8.2 g/m

Temperature range: -I00 to +125 °C

Electrical characteristics:

current (maximum) - 1 A at 10 kV

dc resistance - 0.12 ohms/m

nominal operating voltage - 5,000 Vdc

Maximum expected operational current: 500 to 750 mA

Mission life." 1 mission

7

Deployer System Characteristics

• Deployer System

Total mass: 2,027 kg

Thermal control: 4 coldplates, Multi-Layer Insulation (MLI), thermal

tent covering pallet

Power."500 to 1,000 W (average); 1,500 W (peak)

Data: 16 kbps (telemetry); 2 kbps (command)

• Tether Reel Assembly

Capacity: 22-km conducting tether; llO-km nonconducting tether

• Boom

Extended length: 12 m

The Deployer System

ORIGINAL PAG-E

COLOR PHOTOGRAPH
The Satellite

Before it is deployed, the satellite

is located on a satellite support

structure where six latches hold it

in place. Once removed from this

structure, the satellite rests on a

Teflon'-coated docking ring at

the tip of the deployment boom.

A l-m fixed instrument boom

extends out of the satellite's skin

at the equator; a short mast opposite the boom carries the S-band

antenna. For TSS-1, the satellite

will have two deployable/

retrievable instrument booms.

Aluminum-alloy panels covered

with electrically conductive paint

The TSS-I satellite is seen here

undergoing final checkout in Italy,

before being shipped to the U.S.

form the outer skin of the satellite. These panels contain the

connectors for the umbilical

cables from the deployer; windows for Sun, Earth, and charged

particle sensors; and access doors

for installation or replacement of

each satellite battery. At the base

of the satellite, a bayonet pin

attaches the tether to the satellite

structure, and a connector routes

the tether conductor to an ammeter and then to the satellite's skin.

The satellite is divided into

two hemispheres: science instruments are located in the Payload

Module, or upper half (opposite

from the tether), and the support

subsystems (power distribution,

data handling, telemetry, and

navigational equipment) are

housed in the Service Module, or

lower half. A pressurized tank

containing gaseous nitrogen for

the cold gas thrusters is located in

the center of the satellite. This

tank, along with the various

thrusters and associated plumbing, form the Auxiliary

Propulsion Module. Separating

the science instruments and support equipment into three modules that can be integrated into

the satellite independently allows

the satellite to be refurbished,

reconfigured, and readied for

subsequent flights.

The components of the

Payload Module will change

from mission to mission. For

TSS-1, the module houses three

experiments (Research on

Electrodynamic Tether Effects,

Research on Orbital Plasma

Electrodynamics, and Magnetic

Field Experiment for Tethered

Satellite System Missions), the

satellite core science equipment

(a triaxial accelerometer and a

current meter), and the deployable/retrievable instrument

booms, which have a maximum

extension of 2.4 m. The experiSatellite Characteristics for TSS-1

Diameter: 1.6 m

Actual mass: 518 kg

Payload mass: 68 kg

Deployable booms: 2

Fixed boom length: I m

Thermal control: white conductive paint on outer skin; black paint on

internal skin; multilayer insulation blankets covering portions of

the internal skin; heaters in payload and service modules and on

batteries and sensors

Propellant: cold gas nitrogen

Lifetime: at least 3 missions

ORIGINAL PAGE

COLOR PHOTOGRAPH

8
ment electronics are located on

the floor and internal side panels

of the module. Experiment sensors are mounted on the deployable/retrievable booms, the fixed

boom, and the surface of the

Payload Module.

The Auxiliary Propulsion

Module, in conjunction with the

tether reel and motor, controls the

motion of the tethered satellite.

This module also initiates, maintains, and controls the satellite

spin at up to 0.7 rotations per

minute upon command from the

Shuttle. Most components, such

as the spherical high-pressure gas

tank, pipes, valves, and mounting handling, attitude measurement

hardware, occupy the equatorial and control, telemetry and comfloor of the satellite. A set of mand, thermal control, support

thrusters near the tether attach- structures, and the tether attachment can provide extra tension on ment are located at various points

the tether, while a set of thrusters on satellite shell sections and the

around the equator can be used to internal panels, permitting easy

reduce or eliminate pendulum- access to the components.

type motions in the satellite. A

final set of thrusters, also on the

equator but directed off to one

side, will be used to spin and

despin the satellite.

The Service Module contains

all the satellite support subsystems, except the propulsion system. Power distribution, data

Within the Service Module are

the gyros, Sun sensors, and Earth

sensors that measure and control

satellite attitude. Thermal control

is primarily passive, but there are

some active heaters. An S-band

antenna provides a communications link between the satellite

and the orbiter.

O

An exploded view of the TSS satellite

Dlr, ' ! ,_ Or_'_lt_',,"_L PACE

COLOR PHOTO_RAI.:'_

In this photograph of the payload

module, it is possible to see the

internal structure, wiring, and the

electronics packages for various

experiments.

.q

This photograph of the service

module shows some of the sensors

and instruments located in this

half of the satellite. It also shows

the tank and piping for the auxiliary propulsion system, the tether

attachment point, and in-line

thrusters (upper left).

9
Tether Dynamics

\

\

\

\

While space-based tethers have

been studied theoretically since

early in the century and later

modeled extensively on computers, the TSS-I investigations of

electrical generation and plasma

physics in the upper atmosphere

will be the first time such a large,

electrodynamic tethered system

has ever been flown. In many

respects, this mission is like the

first test flight of a new airplane:

the lessons learned will improve

both scientific theory and future

operations on tether missions.

The use of tethers in space is

not new, but the applications

have been extremely limited. The

application most people remember are the tethers that connected

spacewalking astronauts to their

spacecraft; these were used until

the advent of the Manned

Maneuvering Units used on the

Shuttle. These applications,

however, used very short tethers

that were not stabilized by gravitational forces and, therefore,

have little relation to the

Tethered

10
SatelliteSystem. TheTSS-1

missionwillbeusinga20-km

longtetherthatwillbestabilized

bygravitational forces.Since

thedynamicsoftheTethered

SatelliteSystemarecomplexand

canonlybetestedfullyinorbit,it

isimpossibletopredictbeforethe

missionexactlyhowthesystem

willact.Whilethedynamics have

beenextensively testedandsimulated,it ispossiblethatheactual

dynamicswillbesomewhat

different frompredictions. In

additiontothenormal mechanicaldynamicstherearealsothe

complexities ofawidelyseparated,multi-component system

andtheforcescreatedbytheflow

of current through the system.

Deployment

A satellite is maintained in its

orbit around Earth by a balance

between the force of gravity,

which pulls it toward Earth, and a

centrifugal force, which pushes it

away from Earth. The centrifugal

force results from the motion of

the satellite around its circular

orbit. This is the same force that

one can experience by swinging a

ball around on the end of a string.

At the orbital altitude for

TSS-1, a speed of approximately

7.6 km per second is required to

create sufficient centrifugal force

to balance gravitational attraction.

If the altitude is changed, however, the two opposing forces will

no longer be in balance unless the

Shuttle's speed is also changed.

Going higher requires a slightly

greater speed, although it will

take longer to complete an orbit

because increasing the altitude

makes the orbit a larger circle and

significantly increases the dis- ......... experience libration, or back

tance around it. As a result, a .............. and forth movement of the tether.

higher satellite will move at a If the satellite were stopped

slightly higher speed but will take suddenly, the gravity gradient

longer to travel around its orbit ..... Would bring the tether back to

than a satellite below it. If the the vertical orientation.

two satellites are tied together - However, the tether would overwith a tether, they will be forced shoot and go out in the forward

to travel at a higher speed than ......................... direction, and then come back

required for its orbit and, there- ......... again. The satellite would be

fore, its centrifugal force will be ............. moving in much the same backgreater than the pull of gravity. If................... and-forth movement as a penduthe tether were cut, it would lure in a clock but without the

move to a higher orbit where the friction needed to stop the

two forces would, again, be in -motion. Indeed, to dampen this

balance. With the tether in place_..... pendulous motion, or libration,

however, the net effect of the .......would require much more time

unbalanced forces is to create than a typical Shuttle mission.

tension in the tether. This is the Libration will be controlled

force that causes the Tethered ............. -i_y varying the speed at which

Satellite System satellite to rise the tether is reeled. By avoiding

above the orbiter as the tether is .............. :'sudden stops and decreasing the

reeled out. Very close to the .... reel-rate slowly, the rate at which

orbiter, there is little difference ifi..................... the gravity gradient brings the

the two orbits and the tension ..... tether closer to the vertical is also

force is insufficient to overcome ..... Slowed. If the motion is slowed

friction in the deployer mecha- just right, the tether will come to

nism. Therefore, until the satellite a halt in a stable, vertical posireaches a separation of approxi- tion, with no residual libration.

mately 1,000 m, the tension is --

augmented by small tether-aligned ...............

thrusters on the satellite. Beyond

this point, the tension in the

tether is the only force required.

But deployment of the satellite is not quite as smooth as it

might seem. While the process is ..............

inherently stable, the system can ..............

\ ,

Libration

11
\

Longitudinal

Oscillation

"Sklprope" '_ _ /

/

Trans

Oscillation

Pendulous

Motion

t2

Tether Oscillations

By experimenting with a ball

hung on a piece of elastic cord

(a paddle ball, for example)

it is possible to simulate all the

different types of oscillation that

are possible on a space-based

tether system. The elastic cord,

representing the tether, may

compress and stretch causing

the ball to bounce up and down

(referred to as longitudinal oscillation). It may also develop

wave-like motions (transverse

oscillation), or even move in a

circular, or "skiprope" motion.

Even if the string itself is not

moving much, it is possible to

get the ball rocking back and

forth about its attachment point

(pendulous motion).

Each type of motion occurs

with a particular frequency, which

depends on the length and tension

of the tether. When the frequencies are different, the motions do

not interact. However, at some

tether lengths, the frequencies of

two or more types of oscillation

can become very close. At this

point, energy can be transferred

from one type of motion to

another, a phenomenon known

as resonance. For instance, the

transverse oscillations in the

tether may cause the satellite to

rock back and forth in pendulous

motion.

Many different factors may

cause oscillations; the movements

of the satellite or Shuttle are but

two of these. On TSS-1, one

potential cause of oscillation will

be of particular interest. As the

system produces an electrical

current, it also produces a magnetic field around the tether. This

magnetic field will interact with

Earth's magnetic field resulting

in a force expected to produce

skiprope oscillations.

Because it is necessary to

maintain control of the satellite,

much study has gone into identifying the different types of possible motions and methods to

control them. Dynamicists hope

to observe all these types of

oscillations during TSS-1 to see

how real-world tether behavior

compares to the mathematical

simulations done over many

years. This will increase the

knowledge and understanding

of tethered systems.

-z

Retrieval

While deployment is an inherently stable process, retrieval of

the tethered satellite is inherently

unstable. As it comes toward the

Shuttle, the satellite is also moving towards Earth's axis of rotation and so moves "east" or

ahead of the orbiter. Any libration

produced by this movement will

tend to grow as the satellite and

orbiter get closer to each other,

because of the conservation of

angular momentum.

Retrieval will, therefore, be

very carefully controlled. The

retrieval rate is programmed into

the deployer system computer to

keep the libration angle under

control. The gravity gradient will

be used to keep the tether taut

until the satellite is approximately

200 m from the orbiter, when the

satellite's thrusters will be turned

on. At this point, the crew will

take manual control of the last

stages of retrieval. Then, using

the tether reel rate, satellite

thrusters, and movement of the

orbiter itself, the crew will

keep the satellite lined up as it

is returned to its docking ring on

the deployer.

ORfGINAL PAGE

COL_#, PHOTOGP-.APH
ii ii!!i _i!!i_I

_ . The-Conservationof AngularMomentum

:- - Many ollhe dynamicstheories affecting, or-Se[ngi-e-st-e-don, TSS--1

arequite complex. While theconservation of angular momentqgLmay

seem_.'om_plex,_ilTs quffe easy to visualize_

Take__a-b_l|attached to the endofa_s|r[n0 ...... and moveit in a steady

m_and lorth, like a pendulum. Once a steady swing has

:............ been:es_blis_, take the thumb and forefinger of your other hand

!. _ and make a circle aroundthe top of the string. This will not interfere

:_ ...... _.... wilh_wing, so no changewill be noticed.

i .............. - - - " Whil_ keepingyour swing steady, slowly begin to raise the hand_

_;_-;................. _-_ . ..... ;_ :..:i__. _._ .....hoid[ng_Se string. As your handgoes higher,the string begins_L]lit

:_i_........ ._--_- .- _: ._-__-__.. tS_he circle made byyou fingers. As this happensthe

frequen_of the balls movementincreases. The shorterthe string,

............. thefasTer_e ball travels and the furtherfrom the vertical it tries_to

..... go. Asyou IoweY_hestring backdown, the ball will eventually _re_turn

- to its original motion.

...... _ _ _ The_ forJhls is that th_ene,,gyin the system remains the

_ same. As-the length of the stringgrows shorter, the same amonnt

of ene_is preenS. This producesa longer and faster arc.

O__!_JNAL PA_

i _tlllliil_'_!_'

13
TSS-1 Science

Background

To prepare for the mission, numerous tests using scale models of

the TSS satellite, such as this one

in the Frascati (Italy) Plasma

Chamber, were conducted to test

instruments, paints, and materials.

14

The TSS-1 mission will study the

electrodynamic properties of a

tethered satellite system and its

interaction with Earth's ionospheric environment of charged

gas and magnetic and electric

fields. These studies will help

demonstrate the Tethered Satellite

System's capabilities as a

research facility for investigations in electrodynamics and

space plasma physics. Most of

the TSS- 1 experiments require

essentially the same set of measurements, with instrumentation

from each investigation providing

different parts of the total set.

While some instruments measure

magnetic fields, others record

particle energies and spectra,

and others map electric fields.

A complete set of data on the

plasma and field conditions is

The spiral path of an electron

beam around magnetic field lines

can be seen clearly in this photograph taken in a plasma research

chamber.

required to characterize this

environment and Tethered

Satellite System perturbations

accurately and completely. The

TSS-1 science investigations are

interdependent; they must share

information to achieve their

objectives. In fact, these investigations may be considered to be

different parts of a single complex experiment.

The motion of the Tethered

Satellite System through Earth's

magnetic field generates a voltage across the conductive tether.

As a result, it is able to extract an

electrical current from the ionospheric plasma at the satellite and

emit that current by means of

electron accelerators in the payload bay. Investigators will use

the ability to vary this current and

control the electrical potential of

the satellite to create and study a

variety of phenomena and processes. These include electric

power generation, wave generation and propagation, neutral gas

ionization, and basic physical

processes that occur naturally in

plasmas surrounding Earth and

other planets, moons, and comets.

Although some of these phenomena have been studied in laboratories, very small scale-size,

chamber wall effects, unnatural

plasma distributions, and other

problems hamper the groundbased experimenter. For the

Tethered Satellite System, Earth's

ionosphere is a vast, unbounded

laboratory for space plasma

experiments that can be conducted in no other way.

ORIGrNAL PAGE

CI:]I_R PHOTOGRAPH
/

/

_-_ Lightning is a commonly

1 seen form ofplasma.

TheFourthStateof Matter-

_re-a-re threeclassi_statesof matter:solid,liquidandgas.Then, Piasm_is foundbothin ordinaryandexoticplaces.Whenan electric

splasma,which_me scientistsconsiderto hethefourth curren|is passedlhroughneongas,it producesbothplasmaand

tt-er_1'beplasmastateof matteris notrelatedto blood __. Li-ght_ng_rlcal discil-a-rgeintheatmosphere _'-

_asma, themostcommonusageoftheword.Rather,theterm thatcreatesa jaggedcolumnof ionizedair, orplasma.Partofa

plasmahasbeenusedinphysicssincethe1920sto representan _met's streamingtail is plasmafromgasionizedbysunlightand

ionizedoas,andspaceplasmaphysicsbecamean importantscien- otherunknownprecesse-s. TheSunis a 1.5-million-kilometerball of

nl-'T'_[_r_pline in theearly1950swiththe discoveryoftheVanAllen plasma,heatedby nuclearfusion.

--: radiationbelts. _-.....

..... _ Scientistsstudyplasmaforpracticalpurposes.Inan effortto har-

"---:_-Matter changesstateas it is exposedto differentphysicalcondi- n_s fusionenergyhereonEarth,physicistsare studyingdevices

-- tions.Ice is a solidwjthhydrogen(H) andoxygen(0) molecules that cre-aieandconfineveryhotplasmasin magneticfields.In

_arra_ge--d-in regula_patterns,butif theice melts,the H2Oentersa space, plasmaprocessesare largelyresponsibleforshieldingEarth

news_E_e!liquidwater.Asthewatermoleculesarewarmedmore, fromcosmicradiation,andmuchoftheSun'sinfluenceonEarth

eccursbyenergy_oug_l the ionizedlayersof theupper

a_osphere.

_____ o!all|lle-electronsorbitingaroundit sothatthe netchargeis zero.

_tom ISelec|ficallyneutral.

_enough energyto escapeits atom. "_is atomis e one

an ion. In-asufficJent!y_eaeI gas, onza;ion appensmany

__-------ereaUngErowdsoffreee ecrons ogeL:erwl ons. owever,not

---_ all theatomsare necessarilyionized;somemayremaincompletely

__ Intactwithnonet_ _s_onzzedgasmnxture',

ions,electrons,

plasnlainciuJd-eslec[ronsandiOhS_,_selectri_

_, it Is macio-scopicallyneutral:in measurablequantitiesthe

---- nt ionsare ever

particlesareaffectedbyelectricandmagnelicTie_dsappliedto

m

th-eplasma, andthemotionsoftheparticlesinthe plasmagenerate

fieldsandelectriccurrentsfromw_tthin.Thiscomplexsetof

interactionsmakesplasmaaunlque,

of matter.

m

The Sun, seen

here in a Solar Max

image of the corona,

is a plasma heated

by nuclear fusion.

15

#
Earth's Magnetosphere.

18

The Plasma Universe

More than 99 percent of matter

in the Universe exists in the

plasma state -- that is, as a mixture of ionized and neutral gases.

Although nature rarely produces

plasma on Earth's surface, it is

common elsewhere. The electrically neutral environment to

which we are accustomed is a

rare exception. Plasma processes

are important factors in the

behavior of stars, interstellar

clouds, comets, the aurora, and

even in our upper atmosphere.

Our understanding of astrophysical and many geophysical phenomena depends on our

knowledge of how matter

behaves in the plasma state.

Even before the space era, an

unexpected discovery was made

through ground-based radio wave

observations: a region of plasma

that exists above Earth's electrically neutral atmosphere. Plasma

begins to dominate Earth's environment in the ionosphere, which

extends upwards from about 85 km

above the ground. The ionosphere

has distinctive layers that differ

in composition and density: the

F1 layer (around 200 km) and

F2 layer (around 300 to 400 kin).

The plasma in these layers,

consisting mainly of electrons

and atomic oxygen ions, is sustained by the ionizing action of

solar ultraviolet radiation on the

neutral atmospheric gas. All

ionospheric layers tend to merge

at night.

Ionospheric plasma is very

tenuous. In the F2 layer, where

the plasma is the most dense,

there are rarely more than

1 million electron-ion pairs in a

cubic centimeter (cc), or thimbleful, of space. In comparison,

the neutral gas density for the

same region is typically l billion

particles per cc, while neutral

gas density at Earth's surface is

approximately 100 billion billion

particles per cc. Never the less,

the ionosphere effectively reflects

most radio waves back to Earth,

and it is this process that led to

its discovery.

With the advent of man-made

satellites, it became possible to

measure the characteristics of the

space environment near Earth

directly -- and it was discovered

that Earth's ionized atmosphere

extends much higher than

originally thought. The region

between the ionospheric E-layer

_ (approximately 140 km) and the

boundary between Earth's magnetic field and interplanetary

magnetic fields (approximately

64,000 km on the sunward side),

known as the magnetopause,

contains minute quantities of

Earth's ionized atmosphere. The

behavior of the gas in this region

is controlled by the geomagnetic

field, and the region is, therefore,

referred to as the magnetosphere.

On the night side of Earth, the

magnetopause trails away from

the Sun forming the magnetotail,

which has been found to extend

more than 384,000 km, the distance from Earth to the moon,

forming a shape similar to a

comet's tail.

ORIGINAL PAGE

COLOR PHOTOGRAPH
Plasma is strongly influenced

by magnetic and electric forces,

and in turn, plasma particles

affect the distribution of magnetic

and electric fields. Beyond the

magnetopause, energetic plasma

from the Sun, called the solar

wind, rushes past Earth at speeds

ranging from 300- to 1,000-km

per second. While most of this

solar wind goes around Earth,

some of it penetrates the magnetosphere. The interaction between

the solar wind and the magnetospheric plasma acts like an electric generator [called the magnetospheric MagnetoHydroDynamic

(MHD) generator], creating

electric fields deep inside the

magnetopause. These fields in

turn give rise to a general circulation of the plasma, or a current

system, and accelerate some

electrons and ions to higher

energies.

The visible manifestation of

the high-energy electrons are

seen in the aurora, the colorful

Northern and Southern Lights

that appear at 90 to 160 km above

Earth. The auroral colors are

determined by the nature of the

atoms that are struck by magnetospheric electrons and the energies

of the collisions: the night sky is

painted with the reds and greens

of oxygen and hydrogen and the

purples and pinks of nitrogen.

A typical 3-hour aurora, covering

By characterizing the magnetic and plasma environments

in our own neighborhood, we are

able to recognize and understand

plasma processes in the rest of

the Universe. Already, auroras

have been spotted on Jupiter,

and the same types of phenomena

appear to occur in the magnetospheres of Saturn and Uranus.

Many high-energy X-rays

and gamma rays detected by

astronomical observations come

from magnetized plasmas near

stars, galaxies, and other objects.

A visual image of our Universe

reveals only the superficial

a million square kilometers, appearances, but plasma studies

discharges approximately 100 will show us the invisible strucmillion kilowatt hours of electric ture of space and the processes

energy into Earth's immediate that may have formed the solar

environment, system from dust and plasma.

Mission Science

Objectives

One of the most important TSS- 1

science objectives is to measure

the plasma and field environment

of the electrodynamic tether

system. These measurements will

be obtained over a wide range of

conditions, since the ionospheric

density varies naturally along an

orbit from day to night and with

the inclination of the geomagnetic field, causing the voltage

across the tether to change by

a factor of two or more during

a complete orbit. This results in

increases and decreases in the

maximum current the Tethered

Satellite System can collect.

In addition to natural variations, the Shuttle alters the space

plasma when it dumps water,

fires thrusters, or changes attitudes. In fact, some scientists

have compared the Shuttle to a

comet enclosed by a halo of

water vapor and other ions that

interact with the natural plasma.

The environment near the Shuttle

will be thoroughly characterized

before, during, and after the

satellite is deployed. In this way,

investigators can separate natural

variations and disturbances

caused by the Shuttle from interactions between the Tethered

Satellite System and the plasma.

While the Shuttle and tether

are monitored by instruments in

the payload bay, instruments on

the satellite simultaneously measure the space plasma and fields

around the satellite. The physical

processes in the region around

the satellite determine how many

particles it collects and, hence,

the magnitude of the current in

the tether.

Colorful auroral displays, such as this view of

the Aurora Austrialis photographed from the

Shuttle, are the result of collisions between

electrons and magnetospheric plasma. A typical

3-hour display can discharge I00 million

kilowatt hours of electric energy into Earth's

immediate environment. ORiG!NAL PAGE

COLOR PHOTOGRAPH

'lid
The ideal goal for each experiment would be to cover all ranges

of electromotive force and

plasma conditions experienced

by the Tethered Satellite System

during both the day and night

portions of an orbit at all tether

lengths. Since TSS-1 is the test

flight of a new, reusable system,

most measurements during the

mission will be made at a single

tether deployment distance.

Wakes and Sheaths

Some special features are likely

to develop in the vicinity of the

satellite as it actively perturbs the

space plasma. Traveling at high

speed (around 27,200 km per

hour), the satellite affects the

density, temperature, and electrical properties of the surrounding

plasma. A plasma sheath containing an electric field develops

around the satellite, while a

wake, in some respects resembling the wake left by a boat in

water, trails behind.

Sizable voltage drops are

predicted to occur across the

plasma sheath surrounding the

positively biased satellite. The

physics of a high-voltage sheath

of this type is largely unknown,

and its effects on the current

flowing to the satellite and on the

ambient neutral and charged

particJes are uncertain.

As the electrons accelerated

by the electrically biased satellite

collide with the neutral particles

in the vicinity of the satellite,

some of these particles may be

ionized, releasing more electrons

that will then be attracted to the

positive surface of the satellite

and may add significantly to the

current collected by the tether

system. This process should be

enhanced when the satellite

thrusters release more neutral

gas, which can become ionized in

the sheath.

The plasma sheath around the

satellite is predicted to be unstable and to change in size and

shape with variations in ionospheric density, magnetic field

alignment, and the voltage developed across the tether. As the

sheath changes, it may produce

instabilities in the plasma that

result in an unsteady tether current and voltage. Electron heating

in the sheath would also affect

the plasma processes taking place

_ff: • :

Wo/er

near the satellite. For example,

the character of the satellite's

plasma sheath and wake will be

affected, and the type and amplitude of waves excited may

change. These changes can in

turn affect the current and voltage

of the tether.

In addition to mapping the

sheath and wake, investigators

will attempt to change the

sheath's structure and study the

resulting processes. Laboratory

investigations have shown that

the satellite potential can be set

to determine the dominant mechanism involved in the plasma

sheath and the near- and midwake regions. For example, if the

satellite is maintained at a few

tens of volts negative, a plasma

sheath will exist, and the electric

field within the sheath will focus

ions into the wake. If the satellite

is maintained at the ambient

plasma potential, however, no

plasma sheath develops and the

plasma rapidly expands from

denser regions to fill the void.

If the satellite is maintained a few

tens of volts positive, it will repel

the ambient ions while attracting'

electrons. Higher positive volt-

- ,(\!.,,,./. ;.......:=::........\/ -\

= _!_,_,:_ii_  ̧

: ;i' i,'*_:;V!iil

_d,o

ages will expel ions, ionize neutral particles, and possibly generate instabilities in the plasma near

the satellite. In the majority of

TSS-] operations, the satellite

will vary from electrically neutral

to positively charged. Wakefilling processes are of interest

because they can affect the tether

current and voltage and because

the same processes affect the

environments, and, therefore,

the measurements made from all

spacecraft. These processes may

also occur in the environments of

some natural celestial bodies --

such as the Moon or asteroids.

Antennas and Waves

Waves are large-scale coordinated disturbances. While the

medium in which a wave travels

does not necessarily move as a

whole in the direction of the

wave, the wave creates smallscale motion in the medium.

This motion varies with the type

of wave: a wave on the surface of

a lake moves molecules in small

circles, and sound waves move

air molecules back and forth.

Just as a water wave lifts swimmers up and sets them down as

it passes, plasma waves can shift

a net electrical charge in a plasma

from one ionospheric region

to another.

Waves of every kind carry

energy and momentum obtained

from their source, which may

be transferred to objects they

impact: ocean waves transform

the shore, sound waves crack

glass, and electromagnetic

(infrared and ultraviolet) waves

heat Earth. Similarly, plasma and

electromagnetic waves transfer

energy between electrons, ions,

and neutral particles. Scientists

are very interested in how energy

is exchanged between ionospheric and atmospheric layers,

and waves (and wave- particle

20
interactions) are partially responsible for this transfer.

One TSS-1 goal is to study

how waves are generated naturally in the ionosphere. The ionosphere supports a variety of

plasma waves from many sources,

including whistle-like noises

triggered by magnetic storms and

lightning, which can be heard on

a radio. In a plasma, the particles

vibrate and oscillate in unison,

and the plasma waves, when

converted to sound by a radio

receiver, form a symphony of

sound. TSS-1 instruments on the

satellite and in the payload bay

can measure the generation and

propagation of naturally occurring plasma waves.

A plasma may also emit and

absorb light, radio, and other

electromagnetic waves created

by shifting electric and magnetic

fields. Radio signals of the right

frequency are able to pass through

the ionosphere and travel up into

the magnetosphere, where they

grow and trigger a noisy chorus

of signals at different frequencies.

By injecting known amounts of

radio waves into the space plasma,

scientists can study the composition, distribution, and motion of

the plasma. Since the speed and

pattern of waves are influenced

by the medium in which they

travel, the way in which the ionosphere affects radio wave propagation can tell us much about the

ionospheric plasma.

The TSS-1 tether will be the

longest antenna ever placed in

orbit. It can either be used passively, for receiving radio waves

from other sources, or actively,

as a transmitting antenna. To

transmit, the current passing

system that may be generated in

the ionosphere by the Tethered

Satellite System.

When the field-aligned

branches of the auroral currents

exceed the capacity of the plasma

to carry a charge, a drop in electhrough the tether may be modu- trical potential occurs. This may

lated by pulsing it on and off at take the form of electric double

the required frequency. The layers -- plasma structures in

longer the tether, the lower the which two layers of excess elecfrequency at which it can radiate tric charge, one positive and the

waves efficiently. This unique other negative -- exist in close

ability to produce low-frequency proximity. Between the two, there

waves makes a number of active

experiments possible.

Currents in Space

Currents are created in the polar

regions of the magnetosphere

by the magnetospheric

MagnetoHydroDynamic generator. The generator is driven by

the motion of the plasma at the

boundary of the magnetosphere.

These auroral current systems

are aligned with Earth's magnetic

field in the magnetosphere but

have cross-field branches in the

lower ionosphere. This is very

is an electric field that can accelerate charged particles. Plasma

theory and laboratory experiments have shown that double

layers can form when currents are

driven along magnetic fields in a

plasma. There is some evidence

that weak double layers exist

naturally in the ionosphere, but

because they are so thin, they

are difficult, if not impossible, to

observe directly. Their effects on

charged particle distributions can

be measured, however, and

Tethered Satellite System instruments should be able to detect the

similar to the type of current presence and motion of double

layers by measuring electrons

beamed from below the satellite

and energetic ions created by the

collapse of double layers near

the satellite.

Simulating Phenomena

of the Plasma Universe

Immersed in the ionospheric

plasma, the Tethered Satellite

System will allow scientists to

study many space plasma phenomena first hand. The electrodynamics of the satellite system

involve a number of phenomena,

such as wakes, sheaths, and

currents, that will be carefully

studied throughout the mission.

Once the basic phenomena of the

Tethered Satellite System are

characterized, some experimental

parameters, such as satellite

potential and tether current, can

be varied to model important

basic processes that occur naturally in our magnetosphere, solar

system, and beyond.

Because of the difficulty,

expense, and time required to

send probes to other parts of the

solar system, scientists want to

A tethered satellite research facility can be used to duplicate electrodynamic phenomena observed

elsewhere, such as the interaction

of Jupiter and Io, the small orange

moon in the upper left.

ORIGINAL PAGE

COLOR PHOTOGRAPH
TSS-I may help scientists better understand both the processes occurring

in comets as they travel and how they were formed.

model plasma environments

around other celestial objects

accurately. Observations to date

reveal that plasma may interact

with the surface of a body

(the Moon or artificial satellites),

with the gaseous atmosphere of

the object (comets or Venus), or

with the intrinsic magnetic field

of the body (Earth or Jupiter).

These interactions affect both the

space plasma and the electrodynamic characteristics of the body.

Shock waves occur in front of

planets, waves are generated and

interact with charged particles,

and wakes and sheaths may form.

Not enough on-site data has been

collected to understand these

processes fully, and laboratories

are not large enough to model the

vast size of the processes created

by the movement of planets

through space. The Tethered

Satellite System, however, may

bridge the gap between these two

extremes, allowing scientists to

investigate actively such largescale plasma phenomena.

Jupiter and Io

Scientists have detected intense,

naturally occurring, radiofrequency emissions from Jupiter.

These emissions may last more

than an hour at a time and consist

of bursts of extremely intense lto 2-second pulses. The radiated

energy from a single pulse may

be as great as 100 thousand million joules, the equivalent of the

energy released from 25 tons of

dynamite.

These emissions have been

correlated with the motion of

Jupiter's moon, Io. Unlike Earth's

moon, Io orbits deep inside the

Jovian magnetosphere, where it

moves at hypersonic speeds

through the magnetic field and

magnetospheric plasma. Volcanic

activity on Io ejects gases, forming an atmosphere, which is

ionized to form a region similar to

Earth's ionosphere. As Io sweeps

through the Jovian magnetic field,

a potential of approximately

400,000 volts is created across its

conducting atmosphere, and

massive currents on the order of

5 million amperes flow along the

22

field lines between Io and Jupiter

into the lower Jovian ionosphere.

The current that will be

created by the tether's motion

through Earth's ionosphere is

predicted by some scientists to

be similar to the current system

generated by the motion of Io.

In this scaled-down model of the

Jovian system, the Tethered

Satellite System serves as the

conducting moon, and Earth with

its ionosphere and magnetic fields

mimics Jupiter. Parameters to be

measured include field-aligned

currents, turbulence, radio frequency emissions, and waveparticle interactions.

Comets

Comets are essentially balls of ice

and dust that streak through the

solar system. When they approach

the Sun, the intense radiation

converts some of the ice to gas

which ionizes very rapidly --

apparently as a result of several

processes. The solar wind and the

interplanetary magnetic field

force the ionized gas to stream

behind the comet, forming the

familiar cometary tail. It is

thought that one of the ionization

processes results from the rapid

motion of the neutral cometary

gas through the interplanetary

medium. This ionization mechanism is known as "critical velocity ionization."

This effect, hypothesized by

Nobel Prize winning Swedish

plasma physicist Hannes Alfv6n

and subsequently observed in

laboratories, may explain the

rapid ionization in comets and

may also help explain how

comets and planets formed in

the solar system. According to

Alfv6n's theory, the gravitational

field of the ionized core of a

primordial dust cloud attracted

the surrounding dust and gas,

and as the atoms fell toward the

core, they became ionized and

subject to the effects of the core's

magnetic field. Alfv6n hypothesized that when the falling neutral

gas reached a certain "critical"

velocity, massive ionization

occurred, and the gas was

trapped, suspended in space some

distance from the core by its

magnetic field. This velocity

was assumed to be related to the

energy required to ionize the gas.

Since the energy required to

ionize different elements varies,

clouds of gases would become

trapped at various distances from

the evolving Sun based on the

composition of the cloud. The

ionized particles were concentrated in the plane of the solar

equator, eventually coalescing

into planetary bodies.

Scientists, therefore, want to

study how a high-speed cloud of

neutral gas interacts with a magnetized plasma. The motion of

the Tethered Satellite System

through the geomagnetic field

offers this opportunity. It provides

the essential ability to control

spacecraft potential, combined

with the ability to release controlled amounts of neutral gas

from the satellite thrusters.

In particular, the system can be

used to establish the conditions

necessary for the ignition of

critical velocity ionization. Local

measurements can be made to

study the creation and growth of

plasma instabilities, the heating

of electrons, the conditions at

which critical velocity ionization

becomes self-sustaining in space,

and its effect on the ambient

ionospheric medium.

ORIQ_NA!. PAGE

COLOR Pi-.I,OTOGRAPH
TSS-1 Science Investigations

TSS-1 is comprised of 12 investigations. Seven investigations address

the science goals of the TSS- 1 mission, using equipment that either

stimulates or monitors the tether system and its environment. Two

investigators will use ground-based instruments to measure electromagnetic emissions from the Tethered Satellite System as it passes

overhead, and three investigators were selected to provide theoretical

support in the areas of dynamics and electrodynamics.

[] Indicates instrument(s) located in orbiter

[] Indicates instrument(s) located on ground

I Indicates instrument(s) located on deployer

Indicates instrument(s) located on satellite

TSS Deployer Core Equipment and Satellite Core

Equipment (DCORE/SCORE}

Carlo Bonifazi, Principal Investigator

Agenzia Spaziale Italiana

The Tethered Satellite System Core Equipment will demonstrate the

capability of a tether system to produce electrical energy and allow studies to be made of the electrodynamic interaction with the ionosphere. It

does this by controlling the current flowing through the tether between

the satellite and the orbiter, and by making a number of basic electrical

and physical measurements of the Tethered Satellite System.

B Deployer Core Equipment consists of several instruments and

sensors on a pallet aft of the deployer in the cargo bay. A master

switch connects the tether conductor to science equipment in the orbiter;

a power distribution and electronic control unit provides basic power,

command, and data interfaces for all deployer core equipment except the

master switch; and

a volt meter measures the tether potential with respect to the orbiter

structure. The Core Electron accelerator has two electron beam emitters

that can eject up to 500 milliamperes of current from the system. Two

other instruments complement the electron accelerator's operations: a

vacuum gauge to measure ambient gas pressure and prevent operation if

pressure conditions might cause arcing and a device to electrically connect either generator head to the tether.

Satellite Core Equipment consists of a linear three-axis accelerometer and an ammeter. The accelerometer (along with the satellite's

gyroscope) will measure satellite dynamics, while the ammeter will

provide a slow sampling monitor of the current collected on the skin of

the TSS-I satellite.

The DCORE

equipment can

be seen in the two

boxes below and

to the right of the

satellite in this

photograph taken

during payload

integration at the

Kennedy Space

Center.

Research on Orbital Plasma Electrodynamics

(ROPE)

Noble Stone, Principal Investigator

NASA Marshall Space Flight Center

I This investigation is designed to study the behavior of the ambient

B ionospheric charged particle populations and of ionized neutral

particles around the TSS-1 satellite under a variety of conditions. Since

the collection of free electrons from the surrounding plasma produces

current in the tether, knowledge of the behavior of charged particles is

essential to understanding the physics of tether current production.

From its location on the l-m fixed boom, the Differential Ion Flux Probe

measures the energy, temperature, density, and direction of ambient ions

that flow around the satellite and neutral panicles that have been ionized

in the satellite's plasma sheath and accelerated radially outward. In this

instrument, an electrostatic deflection system, which determines the

charged panicle direction of motion over a range of 100 degrees, routes

particles to a retarding potential analyzer, which determines the energy of

the ion stream, measuring particle energies from 0- to 100-electronvolts

(eV). The directional discrimination of the Differential Ion Flux Probe

will allow scientists to differentiate between the ionospheric ions flowing

around the satellite from ions that are created in the satellite's plasma

sheath and accelerated outward by the sheath's electric field.

The Soft Particle Energy Spectrometer instrument is a collection of five

electrostatic analyzers that measure electron and ion energies from 1- to

10,000-eV. Three analyzer modules provide measurements at different

locations on the surface of the satellite's hemispherical payload module.

These sensors determine the potential of the satellite and the distribution

of charged panicles flowing to its surface. Two other Soft Panicle Energy

Spectrometer sensors, mounted with the Differential Ion Flux Probe on

the end of the boom, measure ions and electrons flowing both inward and

outward from the satellite. These measurements can be used to calculate

the local potential of the plasma sheath.

The sensor package on the boom is electrically isolated from the satellite

and its potential is controlled by the floating power supply. For satellite

potentials up to 500 volts, the sensor package will be maintained near the

local plasma potential to allow unambiguous measurements to be

obtained. The potential of the sensor package can also be swept, allowing

the package itself to serve as a diagnostic probe.

0,,, _,,.-d. P/_.GE

COLOR PHOTOGR/_H

The ROPE

experiment

will gather

data around

the TSS-I

satellite similar to these

spectrograms

obtained

during a

previous

space plasma

experiment.

23
TSS-I Science Investigations

Research on Electrodynamic Tether Effects

(RETE)

Marino Dobrowolny, Principal Investigator

Consiglio Nazionale delle Ricerche/Instituto Fisica Spazio

Interplanetario

I The behavior of electrostatic waves and plasma in the region

B around a tethered satellite affects the ability of that satellite to

collect ions or electrons and, consequently, the ability of the tether to

conduct an electric current.This investigation provides a profile of the

electrical potential in the plasma sheath and identifies waves excited by

this potential in the region around the satellite. Probes, placed directly

into the plasma in the vicinity of the satellite, map alternating (ac) and

direct current (dc) electric and ac magnetic fields produced as the current

in the tether is changed by instabilities in the plasma sheath or as the

Fast-Pulse Electron accelerator or Core Electron accelerator are fired in

the payload bay.

The instruments are mounted in two canisters at the end of a pair of

2.4-m extendible booms. As the satellite spins, the booms are extended

and sensors measure electric and magnetic fields, particle density, and

temperature at various angles and distances in the equatorial plane of the

satellite. To produce a profile of the plasma sheath, measurements of

dc potential and electron characteristics are made both while the boom is

fully extended and as it is being extended or retracted. The same measurements, taken at only one distance from the spinning satellite, produce

a map of the angular structure of the sheath.

One boom carries a wave sensor canister, which contains a three-axis

alternating current electric field meter and a two-axis search coil ac

magnetometer to identify electric fields and electrostatic waves and

characterize the intensity of surrounding magnetic fields. Highly sensitive radio receivers and electric field preamplifiers within the canister

complement the operations of the probes.

On the opposite boom, a plasma package determines electron density,

plasma potential and low-frequency fluctuations in electric fields around

the satellite. A Langmuir probe with two metallic sensors samples the

plasma current; from this measurement, plasma density, electron temperature, and plasma potential may be determined. This potential is then

compared to that of the satellite. Two other probes measure low-frequency electric fields.

Magnetic Field Experiment for TSS Missions

(TEMAG)

Franco Mariani, Principal Investigator

Second University of Rome

The primary goal of this investigation is to map the magnetic

fields around the satellite. If the magnetic disturbances produced

by satellite interference, attitude changes, and the tether current can be

removed from measurements of the ambient magnetic fields, then the

Tethered Satellite System will prove an appropriate tool for magnetic

field studies.

Two triaxial fluxgate magnetometers, very accurate devices designed to

measure magnetic field fluctuations, are located on the fixed boom. One

sensor at the tip of the boom and another at midboom characterize ionospheric conditions at two distances from the satellite, determining the

magnetic signature produced as the satellite moves rapidly through the

ionosphere. Combining measurements from the two magnetometers

allows realtime estimates to be made of the magnetic fields produced by

the presence of satellite batteries, power systems, gyros, motors, relays,

and permanent magnets. The environment at the tip of the boom should

be less affected by the spacecraft subsystems. After the mission, the

variable effects of switching satellite subsystems on and off, of thruster

firings, and of other operations that introduce magnetic disturbances will

be modeled on the ground in an attempt to remove these spurious signals

from the data.

The two magnetometers will make magnetic field vector readings

16 times per second to obtain the geographic and temporal resolution

needed to locate short-lived or thin magnetic structures, and twice per

second to allow discrimination between satellite-induced magnetic noise,

the magnetic signals produced by the tether current, and the ambient

environment. The magnetometers will alternate these rates: while the one

on the tip of the boom operates 16 times per second, the midpoint magnetometer will operate twice per second, and vice versa. Data gathering

begins as soon as possible after the satellite is switched on in the payload

bay and continues as long as possible during satellite retrieval.

24
/

TSS-1 Science Investigations

Shuttle Electrodynamlc Tether System (SETS)

Peter Banks, Principal Investigator

University of Michigan

i,_ This investigation is designed to study the ability of the tethered

satellite to collect electrons by determining the current and voltage

of the tethered system and measuring the resistance to current flow in the

tether itself. The experiment also explores how tether current can be

controlled by the emission of electrons at the orbiter end of the system

and characterizes the charge that the orbiter acquires as the tether system

produces power, broadcasts low-frequency radio waves, and creates

instabilities in the surrounding plasma.

The hardware is located on the Multi-Purpose Equipment Support

Structure near the center of the payload bay and adjacent to the deployer

pallet. A Spherical Retarding Potential Analyzer, mounted on a stem at

one corner of the support structure, records ion current density, temperature, and energy and determines the potential of the orbiter. The potential

of the surrounding plasma and charged particle density and temperature

are measured by a Spherical Langmuir Probe, also mounted on the tower.

At the center of the support structure, the Charge and Current Probe

measures the return current to the orbiter, recording large and rapid

changes in orbiter potential, such as those produced when electrons are

conducted from the tether to the orbiter frame or when an electron beam

is emitted.

A Fast-Pulse Electron accelerator emits electron beams of 50 and 100

milliamperes (mA) at 1 kiloelectronvolt (keV), stimulating wave activity

over a wide range of frequencies. These beams discharge the orbiter

and produce electrical changes in the system and can be pulsed with

on/off times ranging from 105 to 106 nanoseconds. The Fast-Pulse

Electron accelerator is located as close to the Core Electron accelerator

as possible and aligned so that the beams of both instruments are adjacent

and parallel.

For the Fast-Pulse Electron accelerator beam to be aimed with precision

for several experiments, a three-axis fluxgate magnetometer will measure

the magnetic fields in the payload bay. These measurements will map the

magnetic field lines in the payload bay, which is crucial since electron

beams spiral in response to these fields. Using this information, the electron beam can be aimed at various targets, including orbiter surfaces to

study the fluorescing that occurs.

Shuttle Potential and Return Electron Experiment

(SPREE)

Marylin Oberhardt, Associate Investigator

Department of the Air Force, Phillips Laboratory

The SPREE will measure the charged particle populations around

the orbiter for ambient space conditions and during active TSS-1

operations. SPREE supports the TSS-1 electrodynamic mission by determining the level of orbiter charging with respect to the ambient space

plasma, by characterizing the particles returning to the orbiter as a result

of TSS- I electron beam operation and by investigating local wave particle interactions produced by TSS-1 operations.

SPREE is mounted on the portside of the Mission Peculiar Experiment

Support Structure (MPESS). The sensors for SPREE are two pairs of

Electrostatic Analyzers, each pair mounted on a Rotary Table Motor

Drive. The sensors measure the flux of all electrons and ions in the orbiter

at the SPREE location. The energy range is sampled either once or eight

times per second. The sensors measure the electrons and ions simultaneously over an angular field-of-view of 100 degrees x 10 degrees.

This field-of-view combined with the motion of the rotary tables allows

SPREE measurements over all angles out of the payload bay.

The Data Processing Unit (DPU) performs all SPREE command and

control functions and handles all data and power interfaces to the orbiter.

In addition, the DPU processes SPREE data for use by the crew and the

ground support team. A portion of the SPREE data is downlinked realtime and the full data set is stored on two SPREE Flight Data Recorders

(FDR). Each FDR holds up to 2 Gigabytes of data for post flight analysis.

The SPREE hardware is

located on the left side of the

Mission Peculiar Equipment

Support Structure in this

view of the tether payload.

The SETS hardware can be seen in the center of this

photograph of the Tether System.

50000

30000

2000,0

1000'0 1 J

0.0 ._ .... _., = .... t .... i

0.0 50 10.0 15.0 200 25.0 30.0 35.0 40.0

elapsed time from satellite release (hours}

OR!GIN,_d_ Pb._E

COLOR Pi-tOTOGRAPH

This graph is a premission prediction

of the voltage generated across the

tether over time. The SETS and

DCORE experiments will make

detailed measurements of tether

generated potential

25
TSS-1ScienceInvestigations

Tether Optical Phenomena Experiment (TOP)

Stephen Mende, Associate Investigator

Lockheed

_ Using a hand-held camera system aboard the orbiter with image intensifiers and special filters, this investigation will provide

visual data that may allow scientists to answer a variety of questions

concerning tether dynamics and optical effects generated by TSS-1. In

particular, this experiment will examine the high voltage plasma sheath

surrounding the satellite, by which the electron accelerators return current

to the plasma.

In place of the image-intensified conventional photographic experiment

package, that has flown on nine previous Shuttle missions, a chargecoupled device electronic system will replace the film back. This new

system combines the image intensifier and the charge-coupled device in

the same package. The advantage of charge-coupled devices over film is

that they allow realtime observation of the image, unlike film, which has

to be processed after the mission. It also provides higher resolution in

low-light situations than conventional video cameras.

The imaging system will operate in four configurations: filtered, interferometer, spectrographic, and filtered with telephoto lens. The basic system

consists of a 55 mm F/1.2 or 135 mm F/2.0 lens attached to the chargecoupled device equipment. Various slide mounted filters, an airspaced

Fabry Perot interferometer, and spectrographic equipment will be attached

to the equipment so that the crew can perform various observations.

For a current to be developed by the Tethered Satellite System, electron

accelerators have to return electrons to the plasma surrounding the

orbiter. The interaction between these electron beams and the plasma is

not well understood. By using the charge-coupled device to make visual,

spectrographic, and interferometer measurements, this process, and how

it affects both the spacecraft and the plasma, can be better understood.

Thruster gases may also play a critical role in Tethered Satellite System

operations. By observing optical emissions during the build-up of the

system-induced electromotive force and during gas discharges, scientists

can gain a better understanding of the interaction between a charged

spacecraft and the plasma environment and how the current system closes

at the poles of the voltage source.

. l.i 6 I ,.

26

Investigation of Electromagnetic Emissions

for Electrodynamic Tether (EMET)

Robert Estes, Principal Investigator

Smithsonian Astrophysical Observatory

Observations at the Earth's Surface of

Electromagnetic Emissions by TSS (OESEE)

Giorgio Tacconi, Principal Investigator

University of Genoa

One goal of these investigations is to determine the extent that

waves generated by the tether interact with trapped particles and

precipitate them. Wave-particle interactions are thought to occur in the

Van Allen radiation belts where waves transmitted from Earth jar regions

of energetic plasma and cause particles to rain into the lower atmosphere.

Although poorly understood, wave-induced precipitation is important

because it may affect activity in the atmosphere closer to Earth. Various

wave phenomena that need to be evaluated are: discrete emissions, lightning-generated whistlers, and sustained waves such as plasma hiss. Wave

receivers on the satellite detect and measure the characteristics of the

waves, and particle detectors sense wave-particle interactions, including

those that resemble natural interactions in radiation belts. Ground stations

may also be able to detect faint optical emissions produced as waves

disturb particles and enhance ionization.

Another goal is to determine how well the Tethered Satellite System can

broadcast from space. Ground-based transmissions, especially below

15 kHz, suffer from inefficiency. Most of the power supplied to the antenna,

large portions of which are buried, is absorbed by the ground. Because of

the large antenna size and consequent high cost, very few ground-based

transmitters operate at frequencies below 10kHz. Since the Tethered

Satellite System operates in the ionosphere, it should radiate waves more

efficiently. For frequencies less than 15 kHz, the radiated signals from a

1-kW space transmitter may equal that from a 100-kW ground transmitter.

Waves generated by the tether will move in a complex pattern within the

ionosphere and into the magnetosphere. Magnetometers at several locations in the chain of worldwide geomagnetic observatories and extremely

low-frequency receivers at the Arecibo Radio Telescope facility, Puerto

Rico, will try to measure the emissions produced and track the direction

of the waves when electron accelerators in the orbiter payload bay pulse

the tether current over specific land reference points. An Italian ocean

surface and ocean bottom observational facility also provides remote

measurements of TSS-1 emissions. These instruments measure emissions

in the frequency range from dc to about 3 kHz.

(Far Left) Ground stations

around the world will attempt

to detect and measure the

different types of electromagnetic waves generated by the

TSS.

The Arecibo Radio

Observatory will be the focus

of Caribbean operations

during TSS-I.

O_G_NAL PAOE

COLOR P_qOTOGRAPH
TSS-1 Science Investigations

The Investigation and Measurement of Dynamic

Noise in the TSS (IMDN)

Gordon Gullahorn, Principal Investigator

Smithsonian Astrophysical Observatory

Theoretical and Experimental Investigation of

TSS Dynamics (TEID)

Silvio Bergamaschi, Principal Investigator

Institute of Applied Mechanics

I TSS-1 will be the longest structure ever flown in space, and its

B dynamic behavior will involve oscillations over a wide range of

frequencies. Although the major dynamic characteristics are readily

predicted, future applications of long tethers demand verification of the

theoretical models. Moreover, higher frequency -- essentially random --

oscillations are more difficult to predict. This seemingly random behavior

is called "dynamic noise" by analogy to radio static, and an understanding

of its nature is needed for possible future uses of tethered platforms for

microgravity facilities and for studying variation in the small scale structure of Earth's gravitational and magnetic fields, caused by variations in

the composition and structure of Earth's crust. These gravitational variations may be related to mineral sources.

These two investigations will analyze data from a variety of instruments

to investigate Tethered Satellite System dynamics. Primary instruments

Theory and Modeling in Support of Tethered

Satellite Applications _I'MST)

Adam Drobot, Principal Investigator

Science Applications International Corporation

This investigation will develop numerical models of the tether system's overall current and voltage characteristics, of the plasma

sheaths that surround the satellite and the orbiter, and of the system's

response to the operation of the electron accelerators. Also of interest are

the plasma waves generated as the tether current is modulated. All data

collected on the mission will be combined to refine these models.

Two- and three-dimensional mathematical models of the electrodynamics

of the tether system will be developed to provide an understanding of the

behavior of the electric and magnetic fields, and the charged particles,

surrounding the satellite. These studies are expected to model the plasma

sheath surrounding the satellite under a variety of conditions. This

includes those in which the motion of the tether and neutral gas emissions from thrusters are not considered, those that incorporate the effects

of tether motion, and those that factor in the gas emissions.

The sheath surrounding the orbiter has several unique features that are

related to the ability of the electron accelerators to control the orbiter's

potential. Models of the orbiter's sheath when small currents are flowing

in the tether will consider the potential of the orbiter to be negative; for

will be accelerometers and gyros on board the satellite; tether tension and large currents, models will be developed assuming a positive orbiter

length measurements and magnetic field measurements will also be used. potential. In this way, the sheath structures and impedance characteristics

The dynamics will be observed realtime at the Science Operations Center of the orbiter/plasma interface can be studied.

and subjected to detailed postflight analysis. Basic models and simula- The response of plasma to the electromotive force produced by the

tions will be verified (and extended or corrected as needed); these can motion of the tether system through the geomagnetic field is another

then be used confidently in the design of future tethered missions, both of focus of this investigation. Using data from other studies, kinetic plasma

Tethered Satellite System and of other designs. The dynamic noise inherprocesses will be analyzed or numerically simulated by computer to

ent to the system will be analyzed to determine the suitability of tethered

systems to serve as platforms for sensitive observations of the geomagnetic and gravitational fields, and if required, to develop possible damping methods.

model the reaction of the ionosphere to the passage of TSS- 1.

This investigation also models the relationship between the efficiency of

wave generation and the amount of current flowing through the tether to

examine how the tether antenna couples to the ionosphere, and how ultraand very-low-frequency waves propagate through the ionosphere. These

models will complement the information gathered by TSS-1 instruments

with emissions recorded at ground stations.

The TMST experiment has developed numerical

models of the TSS current and voltage characteristics.

Graphic displays of data during the mission will be

similar to this premission prediction that examined

a case where the satellite was biased to 200 volts.

27
Mission

Scenario

Twenty-four hours before deployment, a crew member at a console

in the aft flight deck activates

the Tethered Satellite System, to

check the different systems.

The satellite systems are checked

electronically through two cables,

called "

umbilicals, _

whichpro- _ _ • _: _

vide electri- ="=i_ ...... _.;

caI power

and link the

satellite and

orbiter instruments. Portions of

the pallet-mounted science payload gather data during different

orbital phases and attitudes to

establish basic operating characteristics and obtain general

measurements of the Shuttle's

electrical and optical environment.

Engineers and scientists compare

these baseline data with measurements made later in the mission to

determine the effects of the system on the surrounding plasma.

J

t t ,.=f J

When these

operations are

complete, satellite

internal power is

switched on, and a

crew member

releases the latches

and the first umbilical cable.

The 12-m satellite deployment boom slowly extends

from its housing, lifting the

satellite out of the payload

bay. Once the boom is

extended, a second umbilical

is used for a last-minute checkout

of the satellite's support systems at

the boom tip and disconnected.

The satellite is then sent on its way

as its thrusters fire, gently lifting

it away from the docking ring.

Using a tether reel assembly,

the crew reels the satellite out

slowly and carefully, as they and

ground controllers monitor status

and develop a sense for tether

control. A sensor at the tip of the

deployment boom continuously

measures tether tension, while a

second sensor at the base of the

boom measures the speed of the

tether. This information is fed to

_i the deployer cornSatellite puter that controls

_ Release the reel assembly.

'_ ..... _._ Once it passes 6

_:_:i!_'. kin, the satellite is

.- ___ ...__spun at 0.25 rpm

so that sensing

instruments in the satellite and the

orbiter can measure the response

of the system as it travels through

the electrical and magnetic fields

in the ionosphere.

Six hours pass as the satellite

steadily and gradually approaches

Station 1, its fully deployed position 20 km from the Shuttle. Ten

hours of operations begin with the

satellite's rotation being stopped

so that investigations can be performed on tether dynamics over

the course of an orbit. After these

investigations, gas-jet thrusters

spin the satellite, so it rotates

0.7 revolutions each minute. The

Deployable/Retrievable Booms

extend to their first stopping point

to measure the satellite's particle

and field environment. The booms

remain at this first point for an

entire orbit, and then move further

out to a second stopping point

to repeat the process. The third

and final measuring point is at

full extension.

Instruments in the satellite and

the payload bay stimulate the

ionosphere, measure the resulting

response, determine the power

generation properties of the entire

tether system, and characterize the

surrounding environment at three

electrodynamic configurations.

Direct current operations will

permit the study of the most

fundamental state of the electrodynamic Tethered Satellite

System, allowing the tether current to determine its own behavior. During current-voltage

operations the tether current will

_II_Y

_ On-Station " Operations

\

be stepped rapidly through several different levels m let the

relationship between the tether

current and the magnitude of the

tether's motional electromotive

force to be studied. Alternating

current operations will permit the

investigation of low-frequency

radio and plasma waves excited

by modulating the tether current.

In addition, several variations of

these configurations will be used

for particular experiments and the

overflight of ground stations

looking for Tethered Satellite

System-induced radio emissions.

Approximately halfway through

these operations, the satellite's

rotation is reversed so that the

tether will not be twisted when

retrieval begins. However, the

tether can be retrieved twisted

if necessary.

After Station 1operations,

retrieval operations begin with

the reel assembly winding in

the tether. The satellite, under

computer control, approaches to

within 2.4 km of the orbiter, a

position known as Station 2,

where it stops for 5 hours to

dampen dynamic perturbations

and gather additional engineering

and science data. Many of the

same experiments conducted at
Station1willberepeated, includingtheboommeasurements at

threedifferent distances fromthe

satellite. Whilestopped, any

oscillations thathavedeveloped

inthesystemwillbedampedto

anacceptable level.

Retrieval resumessothathe

finalstagesofretrievalnddockingtakeplaceindaylight. When

thesatelliteis200mfromthe

orbiter, crewmembers takeover

tethercontrol.Usingradar,

closed-circuit televisionimages,

computer displays, andlooking

outtheorbiter'swindowsto

monitorthesatellite'sposition

andspeed, crewmembers graduallyeasethesatellitebackinto

thedockingringontheboomby

controllingthetetherreeltake-up

rateandfiringtheShuttle's

maneuvering thrusters. After

docking, thedeployer boomis

retractedintoitscanister, andthe

satelliterelatchedtothesatellite

support sructure. Themission

timelineprovidesforpostretrieval operations atthistime,

allowingscientiststomakefurthermeasurements withthesatelliteinstruments. Oncethese

operations arecomplete, satellite

electrical poweristurnedoff.

Retrieval

\

Science instruments mounted Science Operations Center

in the cargo bay may continue located at Johnson Space Center.

to take readings of the Shuttle In the operations center, they will

environment after docking, be able to evaluate the quality of

When these final measurements .........clata obtained, replan science

are completed, the instruments

are turned off, and the Tethered

Satellite System enters a quiet

state until the Shuttle returns

to Earth.

During the TSS-I mission,

activities as needed, and direct

adjustments to the instruments.

After the flight, the Science

Operations Center will support

......data distribution and analysis.

Deployer and satellite systems

principal investigators and their will be monitored by the Payload

support teams will monitor and Operations Control Center at

direct science activities from the Johnson Space Center.

Investigators in the Science Operations Center

2g
The TSS-1 Crew

With a number of experiments sharing equipment,

the crew of TSS-I will work

closely with the principal

investigators to monitor

results, initiate changes,

and control satellite operations. The crew member

controlling this process will

have to rapidly analyze and

synthesize data from such

sources as radar, computer

displays, and direct visual

observation.

The crew for the first

Tethered Satellite System

mission brings to it a variety of experience which

allow them to readily meet

these challenges. The TSS-I

crew has trained extensively

for the mission and will

work closely with the principal investigators during

the mission.

The Science Grew

Three scientists--Jeffrey A.

Hoffman, Franklin R. Chang-Diaz,

and Claude Nicollier--will be

the mission specialists for TSS- 1.

Mission specialists are career

astronauts who have been trained

to operate orbiter hardware,

as well as specific mission

experiments.

Jeffrey A. Hoffman, the

Payload Commander, will be on

his third mission. He was selected

by NASA in January 1978 and

became a mission specialist in

August 1979. He graduated from

Amherst College in 1966 with

a B.A. degree in astronomy

(summa cum laude), earned

a Ph.D. in 1971 from Harvard

University in astrophysics, and

in 1988 earned an M.S. degree

in materials science from Rice

University. He made the first

Space Transportation System

contingency spacewalk in 1985 in

an attempt to rescue a malfunctioning satellite. His research

interest lies in high-energy astrophysics and his second spaceflight was the Astro-1 ultraviolet

and X-ray observatory mission.

Franklin R. Chang-Diaz was

selected in May 1980 as an astronaut candidate and became a

mission specialist in August

1981. He earned his B.S. degree

in mechanical engineering in

1973 from the University of

Connecticut and his Ph.D. in

applied plasma physics in 1977

from the Massachusetts Institute

of Technology. He has been

heavily involved with the United

States controlled fusion program

and has helped design new concepts in rocket propulsion based

on high-temperature plasmas. His

previous spaceflights were STS

61-C in January 1986 and STS 34

in October 1989.

Claude Nicollier is a research

scientist selected in July 1978 by

the European Space Agency

(ESA) to be one of three

Europeans to train as payload

specialists for the Spacelab 1

mission. Under an agreement

between ESA and NASA, he

joined the NASA astronaut candidates selected in July 1980 for

astronaut training as a mission

specialist. He earned a B.S.

degree in physics from the

University of Lausanne,

Switzerland, in 1970 and an M.S.

degree in astrophysics in 1975

from the University of Geneva.

He has helped develop retrieval

techniques for the Tethered

Satellite System, taken part in

infrared astronomy programs, is

a certified test pilot, and is a captain in the Swiss Air Force. This

will be his first space mission.

Two Italian scientists--Franco

Malerba and Umberto Guidoni--

will be the prime and alternate

payload specialists for the mission. Payload specialists are

astronauts provided by a payload

sponsor, who have been trained to

perform specific science duties.

Franco Malerba earned his

B.S. in electronics engineering

in 1970 (cure laude) and his

Ph.D. in physics, specializing

in biophysics, in 1974 from the

University of Genoa, Italy. He

was selected as one of the

European payload specialist

candidates for the first Spacelab

mission and served as a staff

member at the European Space

Agency Technical Center Space

I

Dr. Jeffrey A. Hoffman

30

Dr. Franklin R. Chang-Diaz Capt. Claude Nicollier Dr. Franco Malerba

Ot_,, ,., PLGE

COLOR PHOTOGRAPH
Science Department, where he

participated in a space plasma

experiment that flew on Spacelab

1. He has performed research in

membrane biophysics at the U.S.

National Institutes of Health and

the Italian National Research

Council (CNR) and served as a

consultant to Digital Equipment

Corporation, Europe, for more

than a decade. He has also performed research on signal detection methodologies for sonar data

systems. Dr. Malerba will be the

first Italian national in space.

Umberto Guidoni is a coinvestigator on the Research on

Electrodynamic Tether Effects

experiment and was appointed

the Project Scientist for it in

1989. In this capacity, he was

responsible for integration of the

experiment into the TSS-1 satellite. He earned his Ph.D in astrophysics from the University of

Rome, Italy, in 1978. He has

served as a staff scientist in the

solar energy division of ENEA

(National Council for Renewable

Energy) and became senior

researcher at the CNR Space

Physics Institute in 1984. He

received a CNEN (the Italian

Nuclear Energy National

Committee) post-doctoral fellowship for 1979-80 in the thermonuclear fusion field.

Dr. Umberto Guidoni

The Orbiter Crew

The commander, pilot, and flight

engineer complete the TSS- 1

crew. Veteran NASA astronaut

Loren J. Shriver serves as the

mission commander, Andrew

M. Allen serves as the pilot, and

Marsha S. Ivins as the flight

engineer. The mission commander has responsibility for all

operations during the flight,

while the pilot and flight engineer

assist in these efforts.

Col. Loren J. Shriver (USAF), the

Mission Commander, will be on

his third mission. He graduated

from the U.S. Air Force Academy

in 1967 with a B.S. in aeronautical engineering and earned an

M.S. in astronautical engineering

from Purdue in 1968. Selected as

an astronaut candidate in January

_i9:/8 and completing training as

a pilot in August 1979, Shriver

served as pilot on STS-51C, a

Department of Defense Mission,

and as mission commander on

STS-31 for the deployment of the

Hubble Space Telescope.

Major Andrew M. Allen

(USMC),the Pilot, will be on his

first mission. He was selected as

an astronaut candidate in June

1987 and qualified as a pilot in

August 1988. He graduated from

Villanova University in 1977

with a B.S. in mechanical engineering and graduated from the

Marine Weapons and Tactics

Instructor Course, the U.S. Navy

Test Pilot School and the Naval

Fighter Weapons School (Top

Gun). He has logged more than

3,000 flight hours in some 30

different aircraft.

Marsha S. Ivins, the flight

engineer, will be on her second

mission. She was selected as an

astronaut candidate in May 1984,

qualified as a mission specialist

in June 1985 and served as a

mission specialist on STS-32,

which retrieved the Long

Duration Exposure Facility. She

graduated from the University of

Colorado in 1973 with a B.S. in

aerospace engineering and holds

a multi-engine Airline Transport

Pilot License, a single engine

airplane, land, sea and commercial licenses, and instrument,

multi-engine and glider flight

instructor ratings. She has logged

more than 4,500 hours in civilian

and NASA aircraft.

CoL Loren J. Shriver

Maj. Andrew M. Allen

Marsha S. lvins

OR',Gi,..d_ PLGE

COLOR P._OTOG.,APH 31
Atether cuts across magnetic

fields in low-Earth orbit, converting some of the spacecraft's

orbital energy into electrical

power. Another tether is a giant

antenna, transmitting electromagnetic waves that carry messages

to Earth. An instrumented, aerodynamic model is being towed by

a tether through the only wind

tunnel that can provide exact

high-altitude hypersonic flight

conditions -- the upper atmosphere. At a space station, a robot

craft on its way to capture a

satellite is released from a tether

and propelled into a higher orbit,

and later, the Shuttle is released

on a tether from a remote docking

port and lowered to the right

altitude for return to Earth; no

fuel is expended for either

32

maneuver. Still farther away, a

tethered probe retrieves samples

from the dusty, red Martian landscape and returns them to the

parent spacecraft for analysis.

Tethers may make these scenarios possible. Many ideas for

using tethers in space are being

advanced, but before the scenarios become realities, the concepts

behind them must be proven.

Several steps are being taken to

bring the ideas to fruition. The

TSS-1 mission is crucial for

demonstrating that satellites on

very long tethers can be successfully deployed and retrieved

in space. It may also determine

whether conducting tethers can

generate high electrical potentials

and drive currents, possibly leading to the production of power for

future spacecraft. Successful

Tethered Satellite System flights

may lead to the following possible uses for tethers.

Generating

Electrical Power

A tether system could supply

power to an orbiting spacecraft,

supplementing solar arrays and

batteries or serving as a backup

emergency power system. The

longer the tether, the higher the

electrical voltage it will produce.

The 20-kin long tether used in the

TSS-1 mission will generate up to

approximately 5,000 volts, while

a 96-kin long tether could generate as much as 15,000 volts. The

total amount of power produced

by the system will depend on

conditions in the ionosphere and

the capabilities of the satellite to

collect electrons. One of the

questions TSS- 1 may help to

answer is how much current can

be extracted from the ionosphere.

Spacecraft

Propulsion

Active Spacecraft Propulsion

After TSS-I characterizes the

electrodynamic properties of

conductive tethers, future missions may be used to demonstrate

tether propulsion. If the direction

of the current in the tether is

reversed, the force caused by its

interaction with Earth's magnetic

field changes from drag to

propulsion. If an onboard power

supply, such as a solar array,

pumps electricity into the tether,

the current direction is reversed,

making the tether into an electric

motor. The electrical energy

flowing into the tether is transformed into motional energy for

the spacecraft, causing it to gain

altitude; thus, the spacecraft's

orbit is boosted without using

precious fuel.

COLOR PHOTOGRAPH
Passive Spacecraft Propulsion

Non-conducting tethers can also

propel spacecraft. A tether transfer system could place objects to

higher or lower orbits without

excessive use of rocket engines

and fuel consumption. For example, if a satellite tethered above a

space station is released, it gains

momentum and moves into a

higher orbit while the station's

orbit is lowered. Conversely,

if the Shuttle is lowered from

a space station on a tether and

released, it loses altitude and

the station is boosted into a

higher orbit.

A tethered elevator could be

used for many transportation

needs: moving payloads up and

down between a space station and

remote laboratories or platforms;

taking laboratories to different

gravity levels along a tether;

and returning materials to Earth

for analysis.

Broadcasting Studying the

from Space Atmosphere

Wave generation and propagation In an atmospheric mission, the

are the focus of some TSS-1 Shuttle payload bay would face

experiments. Travelling through Earth, and the satellite could be

the ionospheric plasma, the cur, lowered to a fringe area of the

rent-carrying tether radiates atmosphere about 130 km above

electromagnetic waves from its Earth's surface on tethers up to

whole length, and especially 100 km long. Sounding rockets

from its two ends. By modulating have provided vertical profiles of

the current (turning it on and off this atmospheric region in a few

at desired frequencies in the same isolated spots, but it has not been

manner that a radio station oper- studied on a global basis because

ates), it may be possible to use atmospheric drag prevents satelthe waves for communicationS. : lites from orbiting below approxiA 20- to 100-km long tether mately 180 km.

deployed from the Space Shuttle With the Tethered Satellite

could produce ultra-low- System, the region down to

frequency (ULF) waves from 130 km can be surveyed for days

3 to 30 hertz (Hz); extremely- at a time because the large inertial

low- frequency (ELF) waves mass of the orbiter overcomes

from 30 to 300 Hz; and very-low- the satellite's relatively small

frequency (VLF) waves from drag. Satellite instruments

300 to 3,000 Hz. Ground-based immersed in the atmosphere can

antennas, especially below

15,000 Hz, are extremely inefficient as most of the power pushed

into them goes into heating the

ground. Broadcasting from space

in these bands could not only

prove to be much more efficient

but also extend the radio frequen- __

cies available.

measure chemical constituents,

map global current systems and

magnetic and electric fields, track

winds, and monitor pollution and

ozone depletion. Measurements

from this previously inaccessible

region will improve models

of atmospheric chemistry

and dynamics.

The TSS-1 hardware can be

reconfigured for follow-on atmospheric missions. The satellite can

be outfitted with additional insulation to control heating, atmospheric instruments, and

aerodynamic stabilizers so that

most instruments can face forward. Five times longer than

on TSS-1, the tether would be

nonconducting. More advanced

missions may string probes downward to different points along a

tether to collect data simultaneously at different altitudes.

0i_ii -\- _- ..........

O_,r,,,','_1pP_.GE

COLOR [sisOTOGP'A£ H

Movable platforms on an atmospheric tether could allow

scientists to gather extensive, global data about the upper

atmosphere simultaneously at a variety of altitudes,

possibly leading to an understanding of phenomena

such as the ozone hole over the South Pole.

33
• \ \

Wind tunnels can only partially simulate flight conditions in the upper atmosphere. By using tethers to place

instrumented models in this region, engineers could

gather true performance data on proposed designs for

aerospace craft.

=

= i

A movable laboratory on a tether could be positioned at

the exact level of gra_qty required by an experimenter.

Using the Atmosphere

as a Wind Tunnel

Wind tunnels on Earth are used

to test the effects of aerodynamic

flow around objects, including

the thermal stability of structures

and materials. Tethers can give

engineers access to the largest,

open, continuous wind tunnel --

the atmosphere. A tether

anchored to the Space Shuttle can

lower an instrumented aerodynamic model 100- to 150-km into

the outer atmosphere. Here, it can

be exposed to ranges of conditions that are impossible to reproduce in wind tunnels: heat

transfer, drag, strong air flows,

and turbulence. Data gathered

from these tests can be used to

improve spacecraft reentry and

develop aerobraking techniques

that take advantage of the atmosphere to slow a spacecraft's

speed. A Shuttle tethered aerothermodynamic research facility

is being studied for demonstration on a future mission.

Tether-Controlled

Microgravity

When a tethered satellite is

deployed from a spacecraft, the

center of mass for the total system shifts to a point between the

two objects. At some point near

this center of mass, an object

attached to the tether will experience no relative acceleration, or

zero-gravity. By changing the

object's position on the tether,

different accelerations, or gravities, can be obtained. A portable

laboratory that can crawl to different positions along the tether

can be exposed to various levels

of microgravity; experiments

exploring the effects of gravity on

materials and biological samples

will benefit from such a facility.

Conversely, a tethered ballast

could be used to "tune" a space

station microgravity lab. By

changing the length of the tether,

the lab's center of gravity could

be changed to account for such

things as the use of consumables,

area movement, and other factors

affecting microgravity conditions.

Tethers could also be used to

simulate gravity in space. By

attaching a tether between two

objects, such as a living module

and an automated processing

facility, and then rotating the two

around a common point at the

center of the tether, the "artificial

gravity" of centrifugal force can

be created.

COLOR p:-:OT,-,n-,_ ^ P_.,J J I ,J I '._'_Mgl_l&l r]

34
Quick Reference ToExperiments

Acronym

EMET

IMDN

OESEE

RETE

ROPE

SETS

SPREE

TEiD

TEMAG

TMST

TOP

DCORE

SCORE

Title

Investigationof ElectromagneticEmissionsby theElectrodynamicTether

InvestigationandMeasurementof DynamicNoisein theTSS

Observationsat theEarth'sSurfaceof ElectromagneticEmissionsby TSS

ResearchonElectrodynamicTetherEffects

ResearchonOrbitalPlasmaElectrodynamics

ShuttleElectrodynamicTetherSystem

ShuttlePotentialandElectronReturnExperiment

TheoreticalandExperimentalInvestigationof TSSDynamics

MagneticFieldExperimentfor TSSMissions

TheoryandModellingin Supportof Tether

TetherOpticalPhenomenaExperiment

DeployerCoreEquipment

SatelliteCoreEquipment

Investigator/Organization PageNo.

R. Estes,PI/SAO p. 26

G.Gullahorn,PI/SAO p. 27

G.Tacconi,PI/U.of Genoa p. 26

M Dobrowolny,PI/CNR p. 24

N. Stone,PI/MSFC p. 23

P.Banks,PI/U.of Michigan p. 25

M.Oberhardt,N/Phillips Laboratory p. 25

S.Bergamaschi,PI/Inst.ofAppliedMechanics p. 27

F.Mariani,PI/U.of Rome p. 24

A. Drobot,PI/SAIC p. 27

S. Mende,AI/Lockheed p. 26

C.Bonifazi,PI/ASI p. 23

C.Bonifazi,PI/ASI p. 23

35
Further Reading

1. "Applicationsof TethersinSpace,"Proceedingsof firstworkshopon

applicationsof tethersin space,NASACP-2364,2365,2366, March

1985.

2. "TheProcessof SpaceStationDevelopmentUsingExternalTanks,"

Reportby theExternalTankWorkingGroupof the CaliforniaSpace

Institute,LaJolla,California,11 March1983.

3. "ShuttleTetheredSatelliteSystemDesignStudy,"

NASATM X-73365,MarshallSpaceFlightCenter,December1976.

4. "TheTetheredSatelliteSystem,"FinalReportfromthe Facility

RequirementsDefinitionTeam;sponsoredby MSFCunderNASA

ContractNAS8-33383to theCenterfor AtmosphericandSpace

Sciences,UtahStateUniversity,May1980.

5. Alfv_n,H.,"SpacecraftPropulsion;NewMethods."Science,

Vol. 176,pp. 167-168, 14April 1972.

6.Artsutanov,Y.,"V KosmosBezRaket(Into SpaceWithout Rockets)."

ReportNo.ADA084507,Air ForceSystemsCommand,Wright

PattersonAFB,Ohio,lp69.

7.Artsutanov,Y.,"V kosmosnaelektrovoze."KomsomolskayaPravda,

31, July 1960.

8.Banks,PeterM, P.R.Williamson,andK. L. Oyama,"ShuttleOrbiter

TetheredSubsatellitefor ExploringandTappingSpacePlasmas."

AeronauticsandAstronautics,February1981.

9. Clarke,Arthur C.,"TheSpaceElevator;'ThoughtExperiment,'or Key

to the Universe?"AdvancedEarthOrientedApplicationsof Space

Technology,Vol. 1, pp. 39-48,1981.

10. Collar,A. R.,andJ. W.Flower,"A (Relatively)LowAltitude24-Hour

Satellite."Journalof the BritishInterplanetarySociety,Vol. 22, pp.

785-799,1969.

11. Colombo,Giuseppe,E.M.Gaposchkin,M D.Grossi,"Shuttle-Borne

'Skyhook;'A NewToolfor Low-Orbital-AltitudeResearch."

SmithsonianInstitutionAstrophysicalObservatory,1974.

12. Colombo,Giuseppe,et al.,"Useof tethersfor PayloadOrbitaltransfer." SmithsonianAstrophysicalObservatory,NAS8-33691,March

1982.

13. Dobrowolny,M., G.ColombolandM. D,Grossi,"Electrodynamicsof

LongConductingTethersin theNear-EarthEnvironment."

SmithsonianInstitutionAstrophysicalObservatory,NAS8-31678

October1976.

14. Drell,S. D., H.M. Foley,andM.A. Ruderman,"DragandPropulsion

of LargeSatellitesin the Ionosphere:AnAIfv6nPropulsionEngine

inSpace."Journalof GeophysicalResearch,Vol.70, no. 13,

pp.313!-3145, July1965.

15. Hunter,MaxwellW.,"AdvancedSpaceTransportationOptions."

Lockheed,August1982.

16. Isaacs,John D.,et al.,"SatelliteElongationIntoaTrue'Skyhook'."

Science,Vol. 151,pp. 682-683,1966.

17. Moore,R.D.,"TheGeomagneticThruster- A HighPerformance

'Alfv_nWave'PropulsionSystemUtilizingPlasmaContacts."

AIAAPaperNo.66-257.

18.Moore,R.D.,"TheSolarWindEngine,ASystemUtilizingthe Energy

in theSolarWindfor Powerand Propulsion."

AIAAPaperNo.66-596.

19. Moravec,Hans,"A Non-SynchronousOrbitalSkyhook."Journalof

theAstronauticalSciences,XXV,No.4, pp.307-322,1977.

20.Pearson,Jerome,"AnchoredLunarSatellitesfor Cislunar

transportationandCommunication."Journalof theAstronautical

Sciences,XXVII,No.1, pp. 39-62, 1979.

21.Pearson,Jerome,"TheOrbitalTower;A SpacecraftLauncherUsing

theEarth'sRotationalEnergy."ActaAstronautica2 (9/10),

pp. 785-799,1975.

22.Polyakov,G.,"Kosmicheskoye'Ozherel'ye'Zemli(A Space

'Necklace'AbouttheEarth)."TeknikaMolodezhi,No.4,

pp.41-43, 1977.Translation:NASATM-75174.

23. Rupp,C.C.,andJ. H. Laue,"Shuttle/TetheredSatelliteSystem."

Journalof theAstronauticalSciences,XXVI-I,January-March1978.

24. Rupp,C.C.,"A TetherTensionControlLawfor TetheredSubsatellites

DeployedAlongthe LocalVertical."NASATMX-64963,

September1975.

25.Shoddy,W.C.,"ScientificandTechnicalApplicationsof aTethered

SatelliteSystem."175thAIAAAerospaceSciencesMeeting,

NewOrleans,Louisiana,15-17January1979.

26. Tsiolkovsky,KonstantinE.,"Grezio zemlei nebe(Speculations

betweenEarthandSky)." Moscow,Isd-voANSSSR,1959.

First publishedin 1895.

27. vonTeisenhausen,Georg,"Tethersin Space-BirthandGrowthof a

NewAvenueto SpaceUtilization.NASATM-82571,February1984.

28. Williamson,P.Roger,P.M. Banks,andK. Oyama,

"TheElectrodynamicTether."NASAContractNAS5-23837,

UtahStateUniversity,1978.

Suggested Terms for Database Searches

AdvancedPlanetaryExploration

AdvancedPropulsion;AdvancedLaunchSystems

Alfv_n

Beanstalk

ElectrodynamicInteractions

ElectrodynamicTethers

Funiculars

OrbiterMonitorTransfer

Skyhook

SolarSails

Tether(s):History,Constellations,andSpace

36
Glossary

A:

ac;

Ah:

AI:

AMPS:

bps:

CEA:

cm:

CNR:

dc:

DCORE:

deg:

degC:

deg/sec:

ELF:

EMET:

eV:

FPEA:

g:

Hz:

IMDN:

IWG:

JSC:

K:

kbps:

keV:

kg:

kHz:

KSC:

kV:

kW:

m:

mA:

MHz:

MOU:

MPESS:

MSFC:

of Abbreviations and Acronyms

Amperes NASA:

AlternatingCurrent

Amperehours nT:

AssociateInvestigator OESEE:

Atmospheresand

MagnetospheresandPlasmas

(NASAworkinggroup) PI:

Bitspersecond POCC:

CoreElectronAccelerator PSN:

Centimeters

ConsiglioNazionaledelleRicerche RETE:

-- ItalianNationalResearchCouncil

DirectCurrent ROPE:

DeployerCoreEquipment

Degrees SAO:

DegreesCentigrade

Degreespersecond

ExtremelyLow Frequency SCORE:

Investigationof SETS:

ElectromagneticEmissions

bytheElectrodynamicTether SPREE:

ElectronVolt

FastPulseElectronAccelerator STS:

Gravity

Hertz

InvestigationandMeasurement T:

of DynamicNoisein theTSS

InvestigatorWorkingGroup TAG:

JohnsonSpaceCenter TEMAG:

DegreeKelvin

Kilobitspersecond TEID:

Thousand(Kilo) ElectronVolts

Kilogram TMST:

Kilohertz

KennedySpaceCenter TOP:

Kilovolt

Kilowatt TSS:

Meter TSS-I:

Milliamperes

Megahertz

MemorandumOfUnderstanding

Multi-PurposeEquipment ULF:

SupportStructure VLF:

MarshallSpaceFlightCenter W:

NationalAeronautics

andSpaceAdministration

Nanotesla

Observationsat theEarth'sSurface

of ElectromagneticEmissions

by TSS

PrincipalInvestigator

PayloadOperationsControlCenter

PianoSpazialeNazionaleItalianNationalSpacePlan

ResearchonElectrodynamic

TetherEffects

ResearchonOrbitalPlasma

Electrodynamics

SmithsonianAstrophysical

Observatory

(Cambridge,Massachusetts)

SatelliteCoreEquipment

ShuttleElectrodynamic

TetherSystem

ShuttlePotentialandReturn

ElectronExperiment

SpaceTransportationSystem

(Numericdesignationindicates

specificmission)

Tesla(unit of measurefor

magneticflux density)

Three-axisAccelerometerGyro

MagneticFieldExperimentfor

TSSMissions

TheoreticalandExperimental

InvestigationonTSSDynamics

TheoryandModelingin Support

of Tether

TetherOpticalPhenomena

Experiment

TetheredSatelliteSystem

FirstTetheredSatelliteSystem

Mission.TSSdeployedspaceward

andelectrodynamictests

conducted

UltraLow Frequency

VeryLow Frequency

Watt

37
Acknowledgements

ThisbrochurewasdevelopedbytheTetheredSatelliteSystemProjectOffice,

NASA/Marshall SpaceFlightCenter(MSFC),Huntsville,Alabama.

Authors: C.BlakePowers,CharlotteShea,andTracyMcMahan,

allof EssexCorporation

Editor: C.BlakePowers,EssexCorporation

EditorialAssistants:ChrisScantland,JulieCoolidge,ValerieNeal,

SandraMurphree,LynnFinger,SarahMorgan,andDeniseAccardi,

allofEssexCorporation

SPREEwrite-upby CaptainWilliamE.Slutter,U.S.Air Force,PhillipsLaboratory

EditorialReviewTeam

Mr.BillyW. Nunley,TSS-1ProjectManager,MSFC

Mr.MurrayCastleman,TSS-I DeputyProjectManager,MSFC

Dr.NobieStone,TSS-1MissionScientist,MSFC

Mr.TomShaner,TSS-1ChiefEngineer,MSFC

Mr.TomStuart,TSS-1ProgramManager,NASAHeadquarters

Mr. RickHoward,TSS-1SciencePayloadProgramManager,NASAHeadquarters

Ms.PaulaCleggett-Haleim,PublicAffairsOffice,NASAHeadquarters

Ms.DebraRahn,PublicAffairsOffice,NASAHeadquarters

Mr. MarkHess,PublicAffairsOffice,NASAHeadquarters

Dr.JeffreyA.Hoffman,TSS-1PayloadCommander,JSC

Dr.FranklinChang-Diaz,TSS-1MissionSpecialist,JSC

Mr.ClaudeNicollier,TSS-1MissionSpecialist,JSC

Dr.GianfrancoManarini,TSSProgramManager,AgenziaSpazialeItaliana

Withappreciationfor theirContributions:theTSS'i principalinvestigators,the

payloadexperimentdevelopers,andtheengineersandscientistsontheirteams;

theTSS-I crew;MartinMariettaAstronauticsGroupandAleniaSpaceSystems

Group,thedevelopersof thedeployerandsatellitehardware;andotherparticipantsintheTSS-1missionwho providedinformationandillustrationsand/or

reviewedthis document.

GraphicDesigner:BrienO'Brien,O'BrienGraphicDesign,Huntsville,Alabama

Coverpaintingandcenterfoldartby DavidW. Johnston,Huntsville,Alabama

Illustrationsonpagesiv,2,4, 10,tl, 12,13,28,& 29byDavidW.Johnston

Illustrationsonpages33& 34courtesyofAlenia

Illustrationsonpages1 & 6 courtesyof MartinMarietta

Photographsonpage7 by PatCorkery,MartinMarietta

Photographof cometonpage22courtesyof R.RoyerandS.Padilla

Photographonpage14courtesyof ChristianoCosmovici,CNR

Allotherphotographsandillustrationscourtesyof NASA

'_ U.S. GOVERNMENT PRINTING OFFICE: 1992-324-999

38

LIMITED

REPRODUCIBILITY

MORE THAN 20% OF THIS

DOCUMENT MAY BE

AFFECTED BY:

D FAINT OR BROKEN TYPE

_COLOR PHOTOGRAPHS

El] BLACK AND WHITE PHOTOGRAPHS

[_ FOLDOUTS

DOT MATRIX PRINT

D CHARTS/GRAPHS with SCRIPT NOTATION

D NON-ROMAN ALPHABET

D OTHER (specify)