https://ntrs.nasa.gov/search.jsp?R=19980203952 2017-09-13T19:48:04+00:00Z

NASA

/ TP--1998

-208475

Electrodynamic Tether and Power Generation D.L.

Gallagher

Marshall

and L. Johnson

Space

Flight

Center,

Marshall

J. Moore SRS

Technologies,

Huntsville,

Alabama

F. Bagenal University

National

Boulder,

and

Administration

Marshall

June

of Colorado,

Aeronautics

Space

Space

1998

Propulsion at Jupiter

Flight

Center

Colorado

Space

Flight

Center,

Alabama

Available

NASA Center for AeroSpace Information 800 Elkridge Landing Road Linthicum Heights, MD 21090-2934 (301 ) 621-0390

from:

National Technical

Information

Service

5285 Port Royal Road Springfield, VA 22161 (703) 487-4650

TABLE

.

INTRODUCTION

.......................................................................................................................

1

.........................................................................................................................

2

2.

BACKGROUND

3.

TETHER

PHYSICS

4.

TETHER

PROPULSION

5.

JOVIAN

CAPTURE

6.

JOVIAN

ELECTRODYNAMIC

AND

.

°

9.

MANEUVERING

MISSION-SPECIFIC

7.1 7.2

Gravity Gradient Micrometeoroid

SUMMARY

AT JUPITER AND

ANALYSIS

.............................................................................................. POWER

....................................................................

............................................................................................... TETHER

CAPABILITY ISSUES

MODEL

POWER

3 11 !2

GENERATION

.....................................................................................

16

....................................................................................................

!9

Forces ....................................................................................................... Threat ........................................................................................................

19 20

.................................................................................................................................

RECOMMENDATIONS

REFERENCES

OF CONTENTS

.............................................................................................................

.....................................................................................................................................

111

21 23 24

LIST

1.

Total electron and 6,000

density

with constant

OF FIGURES

density

contours

at 10, 100, 500,

1,000,

3,000,

cm -3 ..........................................................................................................................

2.

Spacecraft

speed

3.

Induced

4.

Tether current contours

5.

Force

6.

Total power

7.

Orbit

8.

Tether propulsive

9.

Tether current and voltage

during capture maneuver

10.

Orbit

capture

11.

Power

generation

12.

Effect

of tether

13.

Tether

orbital

maneuvering

capability

for changing

14.

Tether

orbital

manuevering

capability

for plane

15.

A rotating

16.

The probability

of survival

17.

Artist's

of an electrodynamic

EMF

relative

to the Jovian magnetic

4

field ..............................................................

in a 10-km tether at Jupiter .................................................................................

experienced

by the tether

developed

footprint

................................................................................................

capability power

spacecraft

with 11.009-km

during capture maneuver

tether

for 5-day

generation

and tether

bare-wire

forces

10

tether ................................

...................................................

................................................................

..................................................................................

elliptic

orbit

............................................................

apojove

change

....................................................

...........................................................

system

could

be used to maintain

for a single

strand

tether

tether-augmented

V

in near-Jovian spacecraft

tether space

tension

....................

..............................

at Jupiter

13 13 14 15

orbit ..................................................................

on polar

7 9

..........................................................................................

orbit capture

force magnitude

using

6

1, 5, 10, and 20 A .............................................................

in the tether

for Jovian

circularization

concept

for 0.1,0.5,

5

.........................

16 17 18 18 19 20 21

TECHNICAL

PUBLICATION

ELECTRODYNAMIC AND

POWER

TETHER

PROPULSION

GENERATION

AT JUPITER

1. INTRODUCTION

This report an electrodynamic The environment EDT.

the planet

velocities

which,

velocities

between

propulsive

forces

Jovian tempt generic

of a study performed

has a strong

combined

the magnetic are found

were

to evaluate

the feasibility

intended

rapid

rotation

the spacecraft.

to simulate once

a tether

tether

established

design

to demonstrate

For all cases,

is specified

and

The simulation

maneuvering

scenarios

field and the mass

with the planet's field

developed

is made to optimize

magnetic

as an input

the tether

and merits

of using

mission.

the potential is assumed

can produce orbit

and power

orbit,

close

very

high orbital large

relative

to the planet,

tether

performance

in the

generation

the use of an EDT for Jovian

and spacecraft Instead,

power

the model

of an EDT for future

to be uninsulated

and it is assumed

dictates

as high as 1 MW.

code was used to evaluate

for a specific

to the simulation

rate,

levels

propulsion

in Jovian

of the planet

In a circular

to be as high as 50 N and power

environment.

orbital

sion planning. length

when

planetary

insertion,

the results

tether (EDT) for propulsion and power generation for a spacecraft in the Jovian system. of the Jovian system has properties which are particularly favorable for utilization of an

Specifically,

Models

discusses

was exercised

engineering

and to have

that the tether

generation. studies

orbit No at-

in several and mis-

a 1-mm

diameter.

is deployed

radially.

The

2. BACKGROUND

In recent

years,

tethers

cations.

Conducting

systems.

1 Conducting

moving

wire in a magnetic

tethers

useful in any planetary closure can occur.

niques (RTG's)

have

plutonium

used

solar panels

for electrical however,

rapidly

degrade

planet,

also typically

high "wet" the strong

magnetic

power

require

specifically

generation

field,

power

generation

in all past deep

space

has improved to high levels

use of an expendable and/or

lifetime

rotation,

Stion 3 reports the tether's

in recent

Tethers

through

which

larger

tech-

generators

risk of releasing of using

Even with improvements system

tethers

of the assessment applications.

in this

are expected

system,

or around

to any

This may lead to

on orbit. It is for these reasons,

use for spacecraft

current

than that at

The possibility

maneuvering.

a

may be

and propulsion

The finite

in the Jovian

that electromagnetic

the results

through

thermoelectric

in the Jovian

for orbital

flowing

much

missions.

years.

operations

propellant

limited

missions.

on future

of radiation

Extended

radioactive

orbit appli-

and propulsion

medium.

and a plasma

magnetic

for alternative

low-Earth power

of the current

or conducting

field

is the large Jovian

of solar arrays.

address

of a plasma a magnetic

may rule out RTG's

field and rapid planetary

Stions

2

power

exposure

mass at launch

magnetosphere.

more

exists

in many

for electrical

as a result

to low solar luminosity,

environment

extended

opportunities considered

their properties

is the need

Due

for electrical

use in the Jovian 4-6

there

however,

the effectiveness

spacecraft

derive

where

to Jupiter.

into the terrestrial

technology,

are being

The first inducement

missions

been

tethers

field and in the presence

The real motivation,

for future

come to offer significant

or EDT's

system

But why Jupiter? the Earth.

have

and nonconducting

are being

from a physics

and because

of

considered

for

perspective.

3. TETHER

This stion

of the report

Jovian

planetary

Parker

and

system.

current

and resulting

Murphy

discusses

Tether

2 and power

the initial

modeling

Sanmartin.

PHYSICS

is based

3 The

estimates.

AT JUPITER

results

of analyzing

on results

computed

The Jovian

the performance

from the TSS-I

tether

magnetic

R mission

performance

of a spherically

assumptions. sumed

The

of this distance,

distance,

therefore,

field model

(1965)

coordinate

system,

are defined

axis is along

the planetary

orient

the x axis

reference

which

1 shows

and outside

linear

interpolations

varies

is accomplished with the Jovian system.

coordinate

the torus,

4 con-

on several

to the tether

will be somewhat

with the square length

is as-

volts

and

high inside

this

root of the thermal

electron

of 10 km has been

assumed,

magnetic nature

toward

with constant

profile.

Both the magnetic

point

and show

density

inside

One is the System

coordinate of Aries

constant

contours

the Io torus, Inside

level

the torus,

The torus falls off exponentially

other

the z

contours

system. of various

1,000,

and outside

the density

to

inertial

coordinate

at 10, 100, 500,

the Io torus,

where

has been made

or any

inertial

III

field and den-

system,

of this study, no effort

the first

falls off exponentially.

radial

field.

systems.

in the x-z plane of this work's

components:

the density

of a measured

also depend

current

is only a few electron

current

in two coordinate

the x and z axes

density

up of three

The results

The sond is an inertial

system

graphically

+8 Rj along

total electron

Khurana,

and an Euler potential formuof that presented by Bagenal 5

the thermal

to it. A tether

from

of

limiting

diameter.

rotates

are shown

extend

cm -3. It is made

Inside

current sensitive

maximum

is obtained

temperature

the estimated

spin axis. Due to the preliminary

of this inertial

Each of the displays quantities. Figure

of l-mm

in this coordinate

point. All results

and 6,000

Tether

of EDT performance

sity models

to estimate

radii (Rj), the electron

this distance. tether

plus an Io toms.

is used

eV. This means

it is not tremendously

with a cylindrical The analysis

which

of 5 Jovian

it is 10-50

and low outside

temperature,

distribution,

temperature,

to be 10 eV. Inside

outside

along

symmetric

electron

and the theories

represents

sisting of the Goddard Space Flight Center (GSFC) 06 internal field model, lation for the external field. The plasma density model is a simplified version and consists

of an EDT in the

3,000,

the torus.

is derived

from

away from the magnetic

equator. Induced magnetic

tether

current

will depend

field. That speed will depend

upon the speed

on spacecraft

motion

with which around

the tether the planet,

Fj. For the purpose of initially exploring tether behavior, the spacecraft circular orbit at each radial distance and latitude where the calculations

VSC

=

moves

through

the Jovian

_sc, and planetary

motion is assumed are made:

to result

rotation, from a

(1)

3

where relative

0 is the latitude to planetary

and _ is the longitude. rotation,

given

This velocity

is added

to the velocity

of a stationary

location

by

Fj = -1.7585"

10 -4.

rcos(0)_

.

(2)

Density(cm-3) 10

i

i

I

I

I

i

i

i

I

I -5

i

i

i

i

I

i

L

i

t

i

i

i

I

i

r

i

i

I

i

I 5

i

L

L

L

5 --

.-_

0

-5

-Io -10

Figure

1. Total

i

electron

density

at 10, 100, 500,

Jupiter

is assumed

to rotate

relative

to the planetary

plotted

in figure

with a period

magnetic

2. Constant

field,

velocity

t

with constant

1,000,

3,000,

contours

density

and 6,000

of 9 hr 55 min 29.70333 Vrel, which

=

_sc

cm

10

contours -3

s. The resulting

is the sum of spacecraft

are shown

Vrel

4

I i 0 x_iS (hi)

speed

of the spacecraft

speed and planetary

rotation,

is

for 1, 2, 4, 6, 8, 10, 20, and 40 km/s

+ Vj

•

(3)

Relative Velocity (km/s)

10

I

_

i

I

i

l

i

f

L

I

i

i

]

I

I ,

t [

__'

i

i

I

I

I

i

I

I

1

iI

i II i

,,Ill

5 --

,,

/" 'l, ",,, I,

,,,"

'II

/

I, It

tI

.,,n 0 )4 I N

iI ,iII ,,," ,,,"

--5

-/

',, "ll

I I

I

-10

J

i

-10

I

i

L

i

i

I

-5

I

i

i

i

0

]

I

5

10

xAxis (Rj)

Figure

2. Spacecraft

You can see that for most increases

with increasing

the planetary contribute

distance.

At 90 degrees,

to induced

electromagnetic

3 shows

induced

locations, Close

rotation.

Figure

speed

relative

to the Jovian

the planetary

to the planet,

the planetary force (EMF)

EMF in the 10-km

1, and 10 kV values. Induced voltage depends netic field, Vrel, and the vector magnetic field,

upon B

rotation

the orbital

motion

magnetic

field.

dominates

spacecraft

is not a factor,

the plotted

speed

leaving

begins

speed,

to dominate

only the orbital

i.e.,

it

over

motion

to

in the tether. tether.

Contours

the tether

V = ['$;rel

x/_

are shown

length,

for-50,

[, the velocity

-10,-1,-0. relative

l, 0. l,

to the mag-

(4)

Voltage(V) 10

I

I

I

i

i

I

I

I

i

I

I

I

I

I

\

%

J j-J

\

\

/ /

.-_ 0

! ,/ /

/

/

-5

/

I,

/

"I

//

\,

/•

-1o

i

J

i

I

I

-10

/

l

i

I

I

I

-5

I

I

l

0

t

I

i

I

i

i

5

10

xAxis (Rj) Figure Tether on Parker times surface

is plotted

and Murphy,

a factor.

magnetic

current

field

2 current

The factor strength,

sity, Jo, is a function electron, e,

in figure

EMF

4. Here,

in a 10-km contours

into a conductor

is a function B. The

and the component

3. Induced

current

of the thermal

of the density,

are shown

in a magnetic

of induced

thermal

tether

voltage, density

ne, the mean

Jo -

4

1, 5, 10, and 20 A. Based

field is equal

to the thermal

of the cross-stional

along

thermal

ene VTe

for 0.1,0.5,

V; the area of the conducting

is a function

current

at Jupiter.

the magnetic

electron

velocity,

current,

surface,

Io,

a, and the

area of the conducting

field.

Thermal

current

VTe, and the charge

denof an

(5)

Current (A) 10

5

I

I

I

I

I

I

l

I

I

f

i

I

I

I

I

I

t

I

I

I

I

I

I

t

i

L I

I

l

i

l

[

I

i

i

J

i

--

A

.on 0

--5

--

-10 -10

I

-5

0

10

5

x Axis (Rj)

Figure The component the total thermal projected

current

onto a plane

4. Tether

current

of the current density. transverse

contours

density

The

along

for 0.1, 0.5, the magnetic

area of the conducting

to the magnetic

d is the diameter

radial

tether

of the tether

and the vector

magnetic

(0.001 field.

field is obtained

surface

is taken

by taking

to be the area

one-fourth

of

of the tether

field

a = d'l"

where

1, 5, 10, and 20 A.

sin(a)

m), l is the tether length This angle

is obtained

o_ = cos-l l _ )

(6)

,

,

( 10 4 m), and a is the angle between

the

from

(7)

where

Br is the radial component

of 2 to take into account magnetic

of the Jovian

the collection

magnetic

of current

field. The thermal

from both the parallel

current

is multiplied

and antiparallel

by a factor

directions

along

field

I,, = 2.,,-jo

found

Finally, the current is multiplied by factors to be a factor of 2-3 times greater than Parker

is the source

of the first factor. The sond factor

is thought to enhance the current in the TSS and TSS-1R missions

collection 6

(8)

of 2.5 and 30. The limiting current and Murphy 2 in the TSS and TSS-1R

results

from the analysis

by a factor

of bare tether

of at least 30 over the spherical

into a tether was missions, which

performance,

which

end-collector

used

vo,ol,s)

The 0.01,0.05, magnetic

force, 0.1,0.5,

field,

/_, a current-carrying 1,5,

tether

would

experience

10, 25, and 50 N. The force is obtained

Figure from

(9)

is shown

in figure

from the tether

length,

5, with contours l; current,

at

I'; and the

/_,

P= # x

decades current

the

6 shows

the power

1 W to l0 MW.

developed

Power

is simply

distance

of Europa

that tether performance will be limited presence of a Europa atmosphere. 7

(10)

in a current-carrying obtained

P=V.I The orbital

.

puts it beyond

from

tether. the product

Contours

are drawn

of the induced

for even

EMF

and the

. the distance

at that distance

unless

(11) treated plasma

in this report; density

however,

is enhanced

it is clear

locally

by the

Force(N) 10

5

I

I

I

I

I

i

i

i

i

I

i

i

i

i

I

I

I

1

I

-m

\

\

v

._-

d

0 --

t_

-5

m

I

I

I

I

I

i

I

-5

i

i

I

i

I

i

i

0 x Axis (aj)

Figure

5. Force

experienced

I 5

by the

tether.

i

I

I

I 10

10

f

,

i

I

I

I

I

i

i

f

Power(W) i I i

I

I

i

i

i

l

i

i

I

I

i

I

i

i

i

!

I

I

I

I

h

i

.in 0 m

--5

--

-10 -10

J

-5

I

I

0

5

xAxis (Ri) Figure

10

6. Total

power

developed

in the tether.

10

4. TETHER

The simulation trajectory

model

user-specified

developed

coupled

initial

PROPULSION

for this study

with an EDT model.

conditions,

by solving

AND

consists

MODEL

of a fifth-order,

The trajectory the two-body

d2r/dt

POWER

model

propagates

equations

2=-mr/r

3+a

3 degrees

of motion

of freedom

spacecraft

the spacecraft's

state, from

in the following

form:

t ,

(12)

where

r = spacecraft

constant

at = acceleration

caused

passed

vectors

Runge-Kutta

The tether

the motion

model

spacecraft.

The simulation

are output

at user-specified current,

are specified

algorithm

model continues

the current

the electrodynamic

tether

relative

over the user-specified as are tether

inertial

stepsize

control

state vector voltage,

to the Jovian

and used to calculate

time increments

in a Cartesian

with automatic

code passes

then calculates

of the conducting

back to the trajectory

sive forces,

forces.

At each time step, the trajectory

model.

ing from

by tether

and acceleration

uses a fifth-order

of motion. tether

vector

m = gravitational t = time

The position model

position

to integrate

current,

and force The

( 1) by dividing

time period.

system.

The

the equations

(x, y, z, Vx, Vy, Vz, t) to the

magnetosphere.

at in equation performance

coordinate

Spacecraft

parameters

vector force

by the mass

position including

result-

vector

is

of the

and velocity tether

propul-

and voltage.

11

5. JOVIAN

The tether to chemical craft.

The

simulation

propulsion mass

tionally,

used to evaluate

the feasibility

for initial

to perform

is completed.

Jovian

appealing

when

using

to be used for on-orbit

Thus, the weight

of using an EDT as an alternative

orbit insertion

is particularly

this maneuver

has the potential

maneuver

ANALYSIS

for this function

required

the tether

capture

or aerobraking

use of a tether

spacecraft

was initially

CAPTURE

(JOI)

of an interplanetary

because

of the large

conventional

maneuvering

propulsion

and/or

of the tether can be traded

power

against

space-

percentage systems.

generation

multiple

of Addi-

once the

systems

of the

spacecraft. For the purpose and mission. ments

Typical

outlined

provides

spacecraft

utilizes

missions

of 1.05 Rj and

consistent hyperbolic

launch

excess

spacecraft

from

constraint

orbit.

along

metrically

was initialized were evaluated.

orbit.

Once

drops

rapidly

at a distance approaches,

days).

force

that the tether

approaches

as the spacecraft

assumed

at Jupiter,

once

trajectory

This

report

around

The

Jupi-

first mission

utilizes

an orbit with

to be 340 kg, which would

is

be launched

the spacecraft

has a predicted

the feasibility

of capturing

Figure

the spacecraft

the planet, away

stated

during

the planet.

builds

rapidly

tether, The

trajec-

simulation

is

into the desired

maneuver

is illustrated

of time during

in

the initial flyby.

2.5 Rj from

to a peak

radially

simulation

approach

it. The

is captured

the capture

on a para-

be established

bare wire

decelerating

benefit

a retrograde

was varied

trajectory.

a

The

of the spacecraft

orbit could

is more than approximately force

to enter

on the hyperbolic

over a short period

the tether

from

center

increase,

orbit.

the maximum

length

assumptions;

that the spacecraft

by the tether

force is applied

Tether

of the spacecraft's

forces

7 shows

conditions

that the desired

the planet's

tether

to utilize

the planet.

It was found

by a 100-day

was targeted

the initial

toward

the footprint

generated

moves

to allow the spacecraft

of 6 Rj from

shows

off rapidly

the require-

orbits

that the spacecraft

used to evaluate

to the previously

the planet

propulsive

the tether

was

into a 1.05 Rj perijove

inbound

7 shows

x 106 s (100

force drops

center.

12

The

8. The figure

km (subject

Figure

was

by specifying

orbits

of 11.009

mass

The arrival

and the resulting

for 8.64

The tether

code

trajectory

diameter).

in polar Observer.

The sond mission

It was assumed

in order

The simulation

length

spacecraft

orbit directly

magnetosphere.

with the spacecraft

continued figure

transfer

of the planet's

tory. As the spacecraft elliptic

the simulation

approach

l-mm

by reviewing

Studies ''8 report.

spacecraft

in 2006. On arrival

the hyperbolic

a tether

deployed,

evaluated

and the Auroral

of 100 days.

the spacecraft

km/s.

for a polar orbit was not enforced

equatorial

begins

analysis,

regarding

Mission

involving

Observer

The

assumptions

were

Preliminary

spacecraft.

occurring

of 6.854

an Earth-Jupiter

from the rotation

using

Science

of 5 days.

some

requirements

Orbiters:

for two missions

polar orbiter

opportunity

velocity

to make

of 1.01 Rj and a period

a period

For the capture

point

planning

with the proposed

in the low energy

Polar

are the Radio

an orbit with perijove

perijove

and orbital

Close

mission

proposed

it was necessary

size

in the "Jupiter

preliminary

ter. The

of this study,

the planet's

of 107 N and then

Spacecraft Trajectory in Jovian Equatorial Plane (Capture Orbit Footprint)

_lIJlrIIIZllllllllllllIFIfflrll

14

v

LtlltJllLLlllJ0

2.10 6

4,,106 6.10 6 8,,106

x(km)

Figure

7. Orbit

footprint

for Jovian

orbit capture

with 11.009-km

bare-wire

tether.

TotalForce Reactedon SpacecraftDuring Maneuver 120

_l

I rl

I II

II

i I

I

I

!

I

I

I

I

I _

100

8O

:

/

A Z

6O O t_

40--

/

2O --

0

. m

-20 5,000

I

llllll

_llll 1.10 4

1.5°10 4

t Ill

I II

2°10 4

2.5*10 4

Time (s)

Figure

8. Tether

propulsive

force magnitude

during

capture

maneuver.

13

Tether proximately

voltage

approximately generated

6.6 MW. These tethers

by the tether

assumed

radial

possible;

in most

targeting

mission

density

during

stability

ting the spacecraft

mass

tions to the high power possible

to justify

requirement

levels

estimate

which

would

analysis

be addressed

have

would

large power

the large propulsive

of the tether, tension

probably

the system

identified.

engineered

for stability

in this

using

and power

a tether

somewhat

this possibility.

it should

be noted

power

levels

by

electron

The tether

for spin stabilization tension.

is

for orbit

the peak

to produce

However, for these

forces by the

time and reduce

the spacecraft

is

of reason-

the use of a tether

forces

at ap-

is implied

capture,

preclude

the peak

which

required

to fully investigate

and spinning

system

Additionally,

the fly-by

is required

peaks

the encounter

capabilities

of tether

to reduce

increase

voltage

during

on the physics-orbit

by designing

not been readily

of a tether

9. The

generation

the power-carrying

materials.

that based

problems

into two endmasses

the weight

for a very

indicate

Additional

probably

in figure

stabilization

It may be possible

radius

exceed

of conventional

results

scenarios.

could

levels

gravity-gradient

that engineering

the encounter.

problem

and power

preclude

perijove

are shown

at 26.5 A. The peak power

of the tether. A first-order

it seems

for a higher

the encounter

peaks

constructed

is 130 N. These

however,

capture

current

would

orientation

encounter

during

V and the current

ably sized (diameter)

fly-by

and current

290,000

by split-

Practical

solu-

that it might be

if the spacecraft

had a

supply.

3O 2.5ol05 25 20

15

= CID

10

Time (s)

Figure Some power

interesting

during

the fly-by

at a lower

the 100-day orbital

additional

produced

utilized

discharge

and power

of the capture

tether

by. The orbit can be circularized no propellant

14

required

current

and voltage

observations could

resulted

be captured

rate, an average

initial orbit period.

maneuvering

capability

9. Tether

power

It was also noted generation ( 11.009

for circularizing.

capture

from the capture

with some

capabilities

maneuver. analysis.

form of rapid

of 1,731 W could

that a tether

km ) to circularize

to a radius

during

It was noted

charge

be supplied

the spacecraft

of 1.05 Rj approximately

rate device

and then

to the spacecraft

sized for orbit capture

for use in subsequent

that, if the

orbits.

would

have

Figure

during

significant

10 shows

the

(340 kg) orbit after the initial

fly-

120 days after the initial fly-by

with

Circularization of Jovian Orbit Using Baseline Capture Tether 1'4"107Li 1,2.107

_

i II

itlJ

li

I I II

II

II

I I I I

I_

b_

8"1061E-

O_ 0

/

_"

20

40

60

80

--

100

120

Time (Days) Figure

10. Orbit

circularization

using

capture

tether.

15

6. JOVIAN

ELECTRODYNAMIC AND

The Jovian orbital

tether

maneuvering

requirements

model

once

of a mission

similar

of 180 W over the 5-day meet this requirement. generation However,

profile The

power

for use over

the entire

required

orbit would

equatorial.

the spacecraft

Observer.

radius

similar

a high charge

of the tether

of the tether

requirements

for other

in a polar

× 1-mm tether

more

power

maneuver.

manageable

peak of the

device.

shorter

could

is 140 kW. Storage Figure

11 shows

different

(<4.75

the

orbit inclina-

as the orbit inclination

that a much orbital

supply

in an impulsive

above for various

significantly

power

for the capture

in much above

rate storage

described

increases

was modeled

of this orbit result results

and

the power

a time-averaged

shown

generation

to address

that a 4.75-km

described

The figure demonstrates

power

The spacecraft

to the profiles

for this application require

for power

was sized

was sized to provide

rate for the tether

capability

capability

orbit. A tether

It was determined

period

generation

generation

generation

Science A tether

Whr/orbit).

GENERATION

the use of EDT's

Jovian

orbit and low perijove

length

power

from polar to retrograde used to meet

orbit (21,600

tether

peak

power

tions. The power

to the Radio

and 5-day period.

The elliptic

the shorter

levels.

time-averaged

in a specified

with a high rate and short

power

POWER

CAPABILITY

was also used to investigate

established

orbit with a 1.01 Rj perijove

TETHER

MANEUVERING

is varied

km) tether could

be

inclinations.

JovianTether PowerGenerationCapability '4.75-km Tether,1.01 Rj x 5-Day RetrogradeOrbit 500.103

_l i i i_ll 400-103

:-I

_

ii

i ill

i i i i II_l

I_owerGeneration/

I I_

////

Orb t/W br/ j // /--

300ol03

-_

J Equatorial

C o

Orbit

_ 200.10a

_

- Polar _ 100o103

Q.

i I I L I II i I i I I I I I I I 10 -L_i'll 8o 100 120 140 160 180 200 Inclination(deg)

Figure The sensitivity the tether

(radial)

lized it would

16

of power

with respect

be possible

to meet the spacecraft

11. Power

generation the tether

requirement

capability

for 5-day

to orbit inclination

to the planet's

to orient

power

generation

magnetic

field.

in any inertial

with a tether

elliptic

is primarily It was noted

plane desired.

much

shorter

orbit.

a function

of the orientation

that if the tether In that case,

than indicated

of

was spin stabi-

it might

be possible

by this analysis.

Typically, spacecraft.

EDT power

12 shows

of tether

tives. Figure

ing of the apojove varied

different

results

force can be desirable

the effect

used to size the power decay

generation

The propulsive

generation

radius

over

tether

power

the 100-day

with the rotation

drag force,

or undesirable

depending

generation

described

above.

period

from orbit to orbit. This is possibly

orbit passes

in a propulsive

over

affects

the motion

on the specific

forces

resulted

It was also noted

due to the inclination

of the

mission

time on the 1.01 Rj x 5-day

The tether

simulated.

which

objec-

polar

orbit

in only a slight lower-

that the amount

of apojove

of the pole and the time phasing

of

of the planet.

Effectof Tether Forceson Polar Orbit 25

20

15 ,m

re-

10

.m

5

0 0

2.10 6

4.10 6

6.10 6

8"10 6

1"10 7

Time(s)

Figure The rapid the potential the tether

rotation

high altitudes,

the simulation

results

895 kW. Figure

in the power The

peak

generation

A maximum power

the plane change

that broadens

orbit the direction

velocity

maneuvering.

14. These

study. Figure

and, conversely,

The orbital

figures

13 shows

rate generated

rate corresponding by the 4.75-km

maneuver

were generated

the rate of apojove

rate of 1.15 Rj per orbit is predicted

generation

tether

high spacecraft

more effective

velocities

for plane

changes

near perigee

in the elliptic

in a low circular

orbits

studied.

The

on the 340-kg

tether

would

from change

for the case of

to this maneuvering

rate is

spacecraft.

A maximum plane change rate of 0.041 degree per orbit is predicted. Thus, for the cases studied, that the tether is much more effective in performing in-plane orbital maneuvers. This is probably very

of

of the orbit. At

velocity.

13 and

in figures

system

on the altitude

the relative

for orbital

are illustrated

orbit.

in a posigrade

depending

field dominates the relative

on polar

of the Jovian

For example,

from the EDT can be exploited

orbit.

14 shows

properties

as 180 degrees,

dominates

of orbit inclination.

equatorial

forces

tether

generated

as a function

a retrograde

missions.

of the magnetic

velocity

generation

is one of the unique

for Jovian

velocity

resulting

of the 4.75-km

power

can vary by as much

the spacecraft

The forces

predicted

of EDT's

force

the rotational

at low altitudes,

of tether

rate of Jupiter

applications

propulsive

capabilities

12. Effect

it appears due to the

probably

be

orbit.

17

Jovian Tether Orbital Maneuvering Capability 4.75-km Tether, 1.01 Rj x 5-Day Retrograde Orbit) 1.2 b_

_l

I I t i I I ] I I I I I I I I t/I

1,0 _

Maximum Apojove

/

I I_ /

0,8 I

g _

ChangeRate (Rj)

I

/

Eqo_O_ial

0.6

O

E _ E N "_ E

Polar

0.4

0.2

a I_t

0 8O

IJl, 100

ItJ

Ill

120

II _

IIlllJll

140

160

180

200

Inclination (deg)

Figure

13. Tether

orbital

maneuvering

capability

for changing

apojove.

Jovian Tether Plane Change Capability (4.75-km Tether, 1.01 Rj × 5-Day Retrograde Orbit)

0.04

-£

m

0.03

= = = r.-

\

Orbit

.E=

_

0.02

_= =E

--

l

e___e Maximum Plane I Change Rate (deg

\

-

._E O.Ol E=

Equatorial Orbit-_

OI I I I J I, 80

100

J h

\ \

_ _ I J i J I J i_--.,_l

120

140

160

J

180

200

Inclination(deg)

Figure

18

14. Tether

orbital

maneuvering

capability

for plane

change.

7. MISSION-SPECIFIC

7.1 In order dous forces

to maintain

experienced

tion must be used. be attained Jupiter,

One

such forces

approach

after deployment. integral

part of the design

science

measurements

option

This approach in two places

using

Figure

would

a rotating in figure

also increase

simultaneously,

15. A rotating

would

spacecraft

Forces to keep

it vertical

mechanism sufficient

and endmass

other to keep

under

the potentially

than gravity the tether

weights.

Due

tremen-

gradient

stabiliza-

vertical

and stable

can

to the mass

distribution

of

too weak. vertical

would

be to reevaluate expanding tether

system

and tether

scope

rotation return

because

could

to rigidize

approach,

making

of a mission

spacecraft.

keeps

and spatially-varying

system

a stiffener

mission

and two small

science

time-varying

be to include

the entire

the science

15. The system's

the potential

providing

some forces

lengths

the tether

and potentially

like that illustrated

gradient

tether

are simply

to keeping

Another

sufficient

near Jupiter,

gravity,

modest

Gradient

in the tether

by operation

In Earth-orbit

with relatively

however,

something

tension

Gravity

ISSUES

to include

Such

the tether measurements

a system

from

could

tether

an

multipoint might

developing

time-coordinated

be used to maintain

the tether the tether

look slack.

now be made observations.

tension.

19

7.2

The threat all tethers

operating

of severing in Earth

the tether orbit.

Micrometeoroid

by collision

With an impactor

Threat

with a micrometeoroid of one-third

is very real, as is the case with

the tether

cut, the probability of survival for tethers of 1- and 10-mm diameter diameters of one-third and one-fifth the tether diameter were assessed.

diameter

is shown

assumed

in figure

16.

JovianTetherExamples

P

m ¢o

a.

Time (yr)

Figure

20

16. The probability

of survival

for a single

strand

tether

in near-Jovian

space.

to cause Impactor

a

8. SUMMARY

The use of EDT's in the Jovian system, as shown in the artist's concept (fig. 17)' presents entirely new challenges and opportunities. In a circular orbit near the planet, it appears that induced tether voltages can reach as high as 50,000 V, currents can become greater than 20 A, power levels can reach over a million watts, and propulsive forces can reach higher than 50 N. Utilizing this tremendous power is clearly beyond current engineering capabilities.

Figure 17. Artist's concept of an electrodynamic tether-augmented spacecraft at Jupiter. EDT's appear, on the basis of plasma physics, to be feasible for use in the Jovian magnetosphere. They also appear to present significant engineering challenges including: High levels of tether current mean that managing a spacecraft system's thermal budget is not simple. The complex geometry of forces that a tether would experience around Jupiter means that sophisticated control of tether current will be required in order to achieve specific mission orbital characteristics. The capture analysis illustrates the potential for reasonably sized tethers to generate significant propulsive forces and tremendous, megawatt-level power generation. The huge power levels predicted for the capture maneuver would require a relatively heavy tether system to handle the load. However, the weight of such a system could be justified for missions with very large power requirements.

22

•

It alsoappearsfeasiblethatvery shorttethers(- 1km) couldbeutilized for generatingsubstantial power andorbital maneuveringcapabilities.Powergenerationvia tethermay provide a realisticalternativeto RTG's.

•

The issueof tetherstabilityremainsopen.Gravity gradientforcesat Jupiterareinsufficientto maintain tetherorientationandtensionunderthesepropulsiveloads.Alternative configurations, includinga rotatingsystem,shouldbeconsidered.

•

Additional analysesshouldbe performedto evaluatethe behaviorof a tethersystemin lower altitude,morecircularorbits.In thesetypesof orbitsit wouldbepossibleto providecontinuous power andpropulsiveforceswithout the requirementto deal with the very largepeaklevels generatedin highly elliptic orbits.

9.

Based and power

•

•

on the study performed

generation

A more

A rotating

system

with two spacecraft

Power

•

This should

both the tether management

A detailed

and the power dynamic

namic

environment

Better

physics

integrated

using

and merits

of EDT

mission-specific

coordinated

be examined

an EDT for propulsion

are as follows:

performance

for propulsion

and power

requirements.

by a small-to-modest with the science

and the enhanced

should

of using

recommendations

connected

be closely

engineering options

system,

characterization

be performed

the tether •

and detailed

should

mize

the feasibility

in the Jovian

generation

investigated.

•

to evaluate

for a spacecraft

specific

RECOMMENDATIONS

science

length investigation

tether

should

be

team

to opti-

the limits

of both

return.

in more detail

to determine

system.

simulation

should

be developed

to thoroughly

understand

the unique

dy-

at Jupiter.

models

describing

the plasma

environment

at Jupiter

should

be obtained

and

into the simulations.

23

REFERENCES

I°

Johnson,

L., et al.: "Electrodynamic

craft Propulsion,"

AIAA-96-4250,

ville, AL, September 2.

3.

L.W.;

Journal

of Geophysical

5.

F.: "Empirical

Shiah,

and Power,

Kliore,

Spilker,

A.J.; Galileo

Potential

Model

Models

Hinson, Radio

T.: "Jupiter Meeting

Space

and Space-

Conference,

Hunts-

Polar

Summary,

Wire Anodes

Satellite,"

for Electrodynamic

Teth-

1993.

Magnetospheric

Field,"

Journal

of Geophysical

Torus:

EM.;

Voyager

Measurements,"

Journal

of Geophysi-

1994. N.H.:

"Three-Dimensional

Sci., Vol. 45, pp. 475-482,

Occultations,"

Ionospheric

1967.

E.: "Bare

of Jupiter's

of the Io Plasma

D.P.; Flasar,

Close

and Technologies

Station

1997.

K.S.; Wu, S.T.; and Stone,

Planet.

Space

of an Electron-Emitting

Vol. 9, pp. 353-360,

Vol. 99, pp. 11043-11062,

A.; Hwang,

Program

Buildup

M.; and Ahedo,

Vol. 102, pp. 11295-11306,

Bagenal,

Space

of the International

Vol. 72, pp. 1631-1636,

K.K.:

ing Group

24

Research,

Research,

From 8.

"Potential

Khurana,

tion in Space," 7.

1996 AIAA

B.L.:

of Propulsion

cal Research, 6.

and Murphy,

"Euler

for Reboost

1996.

J.R.; Martinez-Sanchez,

ers," Journal 4.

24-26,

Parker,

Sanmartin,

Tethers

Nagy,

Science,

A.E;

Orbiters:

Preliminary 26, 1995.

of Current

Collec-

1997. and Cravens,

Vol. 277, pp. 355-358,

September

Simulation

Mission

T.E.: "The

Ionosphere

of Europa

1977.

Studies,"

Outer

Planets

Science

Work-

REPORT

DOCUMENTATION

PAGE

FormApp,'oved OMBNo.0704-0188

Pubhc reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Informalion Operation and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Prolect (0704-0188), Washington. DC 20503 1. AGENCY

USE ONLY

(Leave

Blank)

2. REPORT

DATE

3. REPORT

June 1998 4. TITLE

AND

TYPE

Technical

SUBTITLE

Electrodynamic

AND

DATES

COVERED

Publication 5. FUNDING

Tether Propulsion

and Power Generation

NUMBERS

at Jupiter

6. AUTHORS

D.L. Gallagher, 7. PERFORMING

L. Johnson,

ORGANIZATION

J. Moore,*

NAMES(S)

AND

and F. Bagenal** 8. PERFORMING

ADDRESS(ES)

REPORT

George C. Marshall Space Flight Center Marshall Space Flight Center 35812

ORGANIZATION

NUMBER

M-876

9.SPONSORING/MONITORING AGENCY NAME(S) ANDADDRESS(ES) National Aeronautics and Space Administration Washington, DC 20546-0001

10. SPONSORING/MONITORING AGENCY REPORT NUMBER

NASA/TP--

! 998-208475

11. SUPPLEMENTARY NOTES

Prepared by Program Development Directorate *SRS Technologies, **University of Colorado 12a.

DISTRIBUTION/AVAILABILITY

STATEMENT

12b.

DISTRIBUTION

CODE

Unclassified-Unlimited Subject Category 20 Standard Distribution 13.

ABSTRACT

(Maximum

200 words)

The results of a study performed to evaluate the feasibility and merits of using an electrodynamic tether for propulsion and power generation for a spacecraft in the Jovian system are presented. The environment of the Jovian system has properties which are particularly favorable for utilization of an electrodynamic tether. Specifically, the planet has a strong magnetic field and the mass of the planet dictates high orbital velocities which, when combined with the planet's rapid rotation rate, can produce very large relative velocities between the magnetic field and the spacecraft. In a circular orbit close to the planet, tether propulsive forces are found to be as high as 50 N and power levels as high as i MW.

14.

SUBJECT

TERMS

tethers, electrodynamic in-space transportation 17.

SECURITY

CLASSIFICATION

OF REPORT

Unclassified NSN 7540-01-280-5500

15. NUMBER

propulsion,

OF PAGES

32

orbit transfer, power generation, 16. PRICE

CODE

A03 18. SECURITY

CLASSIFICATION

OF THIS PAGE

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