Skip to main content

Full text of "NASA Technical Reports Server (NTRS) 20040111038: Plasma Interactions With a Negative Biased Electrodynamic Tether"

See other formats


PLASMA INTERACTIONS WITH A NEGATIVE BIASED 
ELECTRODYNAMIC TETHER 

Jason A. Vaughn 

George C. Marshall Space Flight Center 
Environmental Effects Group 
Mail Code: ED31 
MSFC, AL 35812 
Phone: (256) 544-9347 
Fax: (256) 544-5103 
Email: jason.a.vaughn@nasa.gov 

Leslie Curtis 
Ken J. Welzyn 

Space Transportation Directorate, MSFC 

Abstract 


The ProSEDS conductive tether design incorporates two distinct types of tethers from a 
plasma interaction viewpoint. The 200 m closest to the Delta II spacecraft is insulated from the 
plasma, and the remaining 4800 m is semi-bare. This latter portion is considered sc mi -bare 
because a conductive coating, which is designed to collect electrons from the plasma, was 
applied to the wires to regulate the overall tether temperature. Because the tether has both 
insulating and conductive tether sections, a transition point exists between the two that forms a 
triple point with the space plasma. Also, insulated tethers can arc to the space plasma if the 
insulation is weakened or breached by pinholes caused by either improper handling or small 
meteoroid and orbital debris strikes. Because electrodynamic tethers are typically long, they 
have a high probability of these impacts. The particles, which strike the tether, may not have 
sufficient size to severe the tether, but they can easily penetrate the tether insulation producing a 
plasma discharge to the ambient plasma. 

Samples of both the ProSEDS tether transition region and the insulated tether section with 
various size of pinholes were placed into the MSFC plasma chamber and biased to typical 
ProSEDS open circuit tether potentials (-500 V to -1600 V). The results of the testing showed 
that the transition region of the tether (i.e. the triple point) arced to the ambient plasma at -900 
V, and the tethers damaged by a pinhole or simulated debris strike arced to the plasma between - 
700 V and -900 V. Specific design steps were taken to eliminate the triple point issue in the 
ProSEDS tether design and make it ready for flight. To reduce the pinhole arcing risk, ProSEDS 
mission operations were changed to eliminate the high negative potential on the insulated tether. 
The results of the testing campaign and the design changes implemented to ensure a successful 
flight are described. 


Introduction 


ProSEDS is an electrodynamic (ED) tether mission designed to fly as a secondary payload on 
a DELTA II Global Positioning System (GPS) satellite, and demonstrate electrodynamic thrust 


as a potential propellant less propulsion application. After the primary GPS payload is placed in 
its orbit, the Delta II second stage fires to place ProSEDS in a near circular orbit with an altitude 
of about 275 km. The Delta II will then begin the ProSEDS mission by turning on the ProSEDS 
computer, which will control the payload for the remainder of the mission. The signal to release 
the endmass and deploy the tether comes from the Delta II once the stage has established the 
correct orientation. After the tether has been deployed ProSEDS will begin what is expected to 
be approximately a 1-day mission. 

ProSEDS consists of two separate hardware platforms, the Instrument Panel (IP) hardware 
and the Deployer side hardware. Both of these platforms are diametrically opposing each other 
around the Delta II bellyband. The IP hardware consists of a 10 A rated hollow cathode plasma 
contactor, primary battery, secondary battery, Power Distribution Box (PDB), a Langmuir Probe 
Spacecraft Potential (LPSP) electronics box, Differential Ion Flux Probe with Mass (DIFP/M) 
electronics box, and transmitter. The LPSP and DIFP/M probes are mounted on the Delta II 
struts 1 . The Deployer side hardware consists of an on-board computer called the Data System 
Electronic Box (DSEB), tether and deployer hardware, both a GPS receiver and antenna, and a 
student built endmass. The deployer hardware includes the tether canister, which housed the 
tether, brake mechanism, and the High Voltage Control and Monitor (HVCM) box to switch the 
tether in and out of the electrical circuit. The deployer side hardware closely resembles the 
design of the old Small Expendable Deployer System (SEDS) 2 . 

ProSEDS on orbit operation is to begin with the tether deployment and slowly bring the 
instruments on-line after tether deployment. Once the entire payload is operating, the primary 
mission would begin and last about five orbits due to primary battery life. These first five orbits 
ensure ProSEDS of at least five orbits of data, which is sufficient to meet all primary objectives 
established for the experiment. After the five orbits, the extended phase begins. The extended 
mission phase operates off the secondary battery, and during this time ProSEDS attempts to 
regulate the charge of the secondary battery using the current collected by the tether. During 
normal operation, the system is designed to both open and close the tether circuit to collect 
background plasma data. This data is needed for further model development of ED tether 
propulsion. 

The ProSEDS tether, shown in Figure 1, is a 15 km long tether, and consists of a non- 
conductive ballast tether and a conductive ED tether. The ballast tether is attached to the 
endmass using a 20 m Kevlar leader designed to withstand the exhaust plume of the Delta II 
motor firing. The Kevlar leader is attached to the 10 km non-conductive Dyneema section, 
which is designed with sufficient length to overcome the friction force generated by the ED 
tether as it exits the deployer canister. The non-conductive tether is attached to the conductive 
tether using a special Kevlar to Dyneema splice. This splice is designed to prevent the metallic 
wire of the conductive tether from coming in contact with the Dyneema due to its low melting 
point. 

The conductive tether has two distinct sections that have unique purposes during the mission. 
The conductive tether is designed to collect the ionospheric electrons on the semi-bare portion of 
the tether to evaluate the effectiveness of the bare tether current collection, which was proposed 
by San mart in . The insulating tether enables the ProSEDS scientists to open circuit the tether 



and measure the tether open circuit tether voltage. Computer simulations of the 5000 m ED 
tether, which include its late mission dynamics, have predicted the maximum open circuit tether 
voltage to be almost -1400 V. 4 This prediction is to be verified using on orbit data. 



Non-Conductive Ballast Tether Conductive Tether Section 

Section 


Dyneema T ether 


Bare C-COR 
Tether 


Figure 1. ProSEDS Overall Tether Design 


Insulated 



Deployer 

Canister 


The conductive tether consists of a 4800 m semi-bare tether and a 200 m insulated section. 
The entire conductive tether is made up of seven individually coated 28 AWG aluminum wires. 
The coating used for the semi-bare tether is an electrically conductive atomic oxygen resistant 
polymer, conductive colorless oxygen resistant (C-COR), specifically designed for the ProSEDS 
mission. The insulating coating consists of two distinct layers, triton oxygen resistant (TOR) and 
polyimide. 5 ' 6 TOR is an atomic oxygen resistant polymer, which protects the main dielectric 
layer, the polyimide. Finally, the insulated tether is then over braided with Kevlar for abrasion 
protection during tether deployment. 

An independent high voltage assessment of the entire ProSEDS system was performed early 
on in the program. 7 In that assessment two items of concern specifically related to the tether were 
identified. The items were: 1) The triple point at the junction between the bare and insulated 
tether, and 2) The triple point produced at the junction between the bare and the non-conducting 
tether interface. Also, early on in the ProSEDS tether design, the importance of maintaining the 
integrity of the insulating coating was recognized based on past history with TSS-1R where a 

o 

breach in the insulation led to an electrical discharge event which severed the tether. During all 
testing and handling with the flight tethers every effort was taken to maintain and verify the 
insulation integrity using a spark test. The two triple points identified in the high voltage 
assessment are located at two very different points on the tethers both physically and electrically. 
The first triple point, which is at the transition between the semi-bare tether and the insulated 
tether, is located very close to the Delta II, and it will see very high negative potentials during 
tether open circuit. Whereas the second triple point is located at the end farthest from the Delta 
II stage, and during open circuit it will experience mostly high positive voltages. 

The three potential tether interactions with the LEO plasma were investigated in plasma 
chamber testing at MSFC, and where problems existed design changes were implemented. The 


plasma chamber tests focused on the transition between the semi-bare conductive tether and the 
insulated tether and on the effects of pinholes in the insulated tether. The transition between the 
conductive tether and non-conductive tether does not experience negative potentials, so it was 
not tested at these potentials. However, a single test was done at positive potentials on the 
transition between the conductive and non-conductive tethers. The results of these investigations 
are discussed, and the required design changes described. 

Plasma Test Chamber Set-Up 

The ProSEDS tether sections were placed in a 1 .2 m diameter and 3 m long cryo-pumped 
vacuum system. The chamber was capable of a base pressure in the low 10 6 Torr, and mid 10 5 
Torr with the hollow cathode plasma source running. A photograph of the internal chamber set- 
up for these tests is shown in Figure 2. The hollow cathode source can operate on any noble gas, 
but for these tests argon was used except for one test that utilized nitrogen. The plasma source is 
designed to deliver cool diffuse plasma to the sample location with an electron temperature of 
0.5 to 2 eV and plasma density of 5xl0 5 to 2xl0 6 cm 3 . The plasma chamber contained a 
spherical Langmuir probe with an overall diameter of 2.5 cm to verify plasma conditions before 
and after testing. 

A 2 m long tether sample was placed in the plasma chamber diagonally across the vessel so 
that the center of the sample under test was directly in line with the hollow cathode plasma 
source about a meter away. Later a second sample was added to the setup by placing one sample 
eight inches below the other sample. In this case, both samples were equally spaced from the 
centerline of the hollow cathode source. One sample was allowed to float while not under test 
eliminating it from interacting with the other sample during testing. The 2 m long tether sample 
was supported by a specially designed sample holder, which was insulated from ground and 
allowed the tether to make electrical contact to a high voltage power supply. The electrical 
contact required a Faraday cage to prevent plasma from coming in contact with the connection 
because the electrical connection produced its own triple point with the plasma. 

The overall electrical circuit for studying the effects of the tether in a plasma is shown in 
Figure 3. The tether sample was connected to the high voltage power supply through a high 
power 250 Q load resistor. The load resistor was used to simulate the resistance of the tether. 
However, the load resistor was divided into five resistive segments of 50 Q each in an attempt to 
more closely simulate the distributed tether resistance. The power supply was controlled 
manually from the front panel, and a separate data acquisition computer recorded both tether 
current and voltage data during the test via the analog output on the back of the power supply. 

The procedure for testing each tether sample was the same with the ultimate goal of meeting 
the design requirement of -1800 V. The -1800 V limit was determined based on the worst case 
open circuit tether voltage (~ -1400 V) and providing a small 30% factor of safety. 




Figure 2. ProSEDS High Voltage Plasma Interactions Internal Chamber Set-Up 

The sample or samples were placed in the plasma chamber and pumped down overnight to 
ensure a good hard vacuum. Starting chamber pressures were typically around 1-2 xlO’ 6 Torr. 
Each test was stalled by turning on the plasma source and allowing it to come to thermal 
equilibrium. The voltage was set at -100 V and held for at least two minutes. The tether voltage 
was decreased in -100 V increments until the sample either arced to the plasma or passed the - 
1800 V limit. 

Triple Point at The Semi-Bare Conductive Tether and Insulated Tether Transition 

The most volatile triple point condition was found to be at the transition between the semi- 
bare (C-COR coated) conductive tether and insulated tether transition splice because this 
tranisition will experience the highest r rgtaive potentials. That particular transition is shown in 
the schematic in Figure 4. At this transition the tether is being transitioned from the conductive 
C-COR coated wire to the insulated wire by cold weldirg or butt welding the two diffent coated 
wires together and the central Kevlar core is changing size. The butt welding process is a 
process that joins two aluminum wires together without any heating. This is accomplished by 
using an off-the-shelf product that cold flows the aluminum wire together. This process worked 
extremely well because the coatings were relatively thin (-0.01 mm to 0.03 mm) compared to 
the wire diameter (0.32 mm), and the butt weld joints turned out to be stronger than the virgin 


aluminum wire. The butt welds were staggered over 7-10 cm to ensure that the butt welds would 
lay nicely in the tether volume. However, a by product of the cold welding process were sharp 
aluminum flanges that circled the butt welds. Every attempt was made to remove these flanges 
using a special cutting tool. Yet it was still difficult to make sure the joint was perfectly smooth. 
Also, a transition in the Kevlar core was necessitated by differences in the diameters of the two 
wire types (.i.e. 0.34 mm for the bare conductive wire and 0.39 mm for the insulated wire). This 
required a Kevlar coresplice which took place about 60-80 cm from the location of the butt 
welds. In order to protect the entire transition region the Kevlar overbraid, which was initally 
designed to protect the insulated wire, was extended over the region containing both the butt 
welds and the coresplice. 




evlar Over braid 


3 utt Welds 


Core splice 


6 Strand 
Kevlar Core 






//////////Zl 




1 




T 


8+1 Strand 
Kevlar Core 


Insulated Wire 


C-COR Wire 


Figure 4. ProSEDS as Designed Conductive Tether to Insulated Transition 




During the fabrication of the three ProSEDS flight tethers (FI, F2, and F3) extra conductive 
to insulated tether splices were made for post process testing. Some were used for strength 
testing while others were used for plasma testing. One of the samples created during the F2 
processing was specifically used for triple point evaluation. The F2 transition sample was placed 
into the plasma chamber and the standard procedure followed. At -900 V bias the sample 
initiated ~3.5 A discharge which sustained for about 20 s. At that point the tether separated and 
the charged end landed against the chamber wall and continued to discharge until the power 
supply was turned off. Figure 5 shows the data collected during this test. The blue circle data 
points represent the power supply voltage in kilovolts and the square red data points represent 
the current draw from the power supply. It is believe that the large current from the arc is being 
fed from the power supply in the lab, but is being limited by the power resistor in line with the 
supply. However, the electrical circuit as close to reality as possible and on-orbit currents of this 
magnitude with an operating plasma contactor were predicted. Post-test evaluation showed that 
the arc was initiated at the triple point caused by the plasma interface with the conductive tether 
transition region. Figure 6 is a photograph of the intense plasma discharge started and sustained 
when the triple point ignited in the plasma chamber. 

Once it was demonstrated the ProSEDS tether design had a triple point design problem, 
several materials and potential solutions were tested to find a solution that eliminated the 
problem. The solutions focused on two particular areas. The first area of concern was to 
eliminate the sharp electric field change at the triple point by adding semi-conductive materials 
over that transition region, and the second area of concern was to focus on the sharp butt weld 
flanges. Four different materials, Aracon (i.e. nickel plated Kevlar), carbon loaded Kapton®, 
carbon loaded cotton, and Aerodag-G graphite spray, were tested as potential semiconductor 
material candidates. These materials were chosen because they met the basic requirements 
which were the material had to be easy to apply to the tethers, it had to be conductive, and it 
could not react adversely with the existing tether materials. 

The results of the plasma chamber tests on the material design changes on the ProSEDS 
conductive tether triple point are detailed in Table 1. Of the materials detailed in Table 1 only 
one material, Aerodag-G, successfully passed the plasma chamber test at -1800 V. Aracon® did 
show surprising improvement over the initial transition design. The other materials did not show 
significant improvement or even made the situation worse. 

The second problem of softening the butt weld flanges was done by attempting to wrap 
Teflon tape around the butt welds then over wrapping the entire 7-10 cm long transition with a 
contiguous Teflon tape wrap. This type of design successfully passed initial plasma chamber 
testing. However, when the transition region was put through a simulated deployment test, the 
cold weld flanges punctured through the Teflon exacerbating the problem (see Table 1). The 
final solution was to add the Aerodag-G spray to both underneath and on top of the over braid 
and to shorten the length of the over braid. Then Aerodag-G was applied from the over braid 
beyond the butt welds into the C-COR region. Figure 7 depicts the new conductive tether 
transition region, which eliminated the triple point from the tether design. The integrity of the 
transition was verified by completing both five simulated tether deployments and exposure to 6 
days of on orbit atomic oxygen. Each of these samples was then subjected to a successful 
plasma chamber tests. 



Ai'bitray Scale 


4 

3.5 
3 

2.5 
2 

1.5 
1 

0.5 

0 

-0.5 

-1 












Art 
Pt = 

;on Plas 
= 3x1 O' 5 

ma 

Torr 









Ne 

Te 

- 2x10 
= 1.5 e3 

cm 

r 




Arc D 
Curr 

ischarg 
ent (A) 

e 



























































Tel 

her Bia 

s 








Vol 

Teth( 

tage (lc' 
;r Volta 

££ikV] 








19.1 19.2 19.3 


19.4 19.5 19.6 

Time (min) 


19.7 19. £ 


19.9 


Figure 5. Current and Voltage Data Due to ProSEDS 
Conductive Tether Triple Point Discharge 



Figure 6. Photograph of ProSEDS Conductive Tether Undergoing 
Plasma Discharge 



Table 1. ProSEDS Tether Triple Point Test Summary 


Sample Description 

Breakdow 

n 

Voltage 

(V) 

Chamb 

er 

Pressur 

e 

(Torr) 

Test Summary 

F2 Sample Transition 

-900 V 

4x1 0' 5 

The failure occurred at the 
intersection of the conductive C- 
COR and Kevlar over braid. 

F2 Simulated Tether Transition w/ 
Aracon® 

-1500 V 

5xl0" 5 

The sampled failed at -1500 V, 
about 1” from the end of the 
Metal clad Kevlar. 

F2 Simulated Tether Transition w/ 
carbon loaded cotton fibers 

-1000 V 

4x1 0’ 5 

The sample failed at -1000 V, but 
began arcing at -700 V. 

F2 Simulated Tether Transition w/ 
Teflon tape wrap on butt-welds 

-1400 

5xl0‘ 5 

The sample failed at -1400 V 

F2 Simulated Tether Transition w/ 
carbon loaded Kapton (resistance 
of 18 kQ). 

-500 

5xl0' 5 

The sample failed at -500 V 

F2 Simulated Tether Transition w/ 
Aerodag-G and Teflon Tape on 
Butt- Welds 

-1800+ 

6x1 0' 5 

The sample passed the design 
voltage at -1800 V 

F2 Simulated Tether Transition w/ 
Aerodag-G and Teflon Tape on 
Butt- Welds After simulated tether 
deployment 

-1000 

6xl0" 5 

The sample began arcing as early 
as -1000V. 

F2 Simulated Tether Transition 
w/Aerodag-G 

-1800+ 

6xl0" 5 

The sample passed the design 
voltage at -1800 V 

F2 Simulated Tether Transition 
w/Aerodag-G which had 
undergone 5 simulated 
deployments 

-1800+ 

6x1 0’ 5 

The sample passed the design 
voltage at -1800 V 

F2 Simulated Tether Transition 
w/Aerodag-G which had been 
exposed to 6 days atomic oxygen 
exposure 

-1800+ 

6x1 0’ 5 

The sample passed the design 
voltage at -1800 V 




Aerodag-G 




I I I I I I 1 1 1 1 I ITT 


i:ssssssss>^ 


isa 


Over Braid 

Figure 7. ProSEDS Tether Triple Point Mitigation Design 


N 

Butt Welds 


Plasma Interactions with Pinholes in ProSEDS Insulated Tether 


Several tests were conducted on the insulated ED tether to investigate the interactions 
between small nicks in the tether caused by either ground handling or micrometeoroid and orbital 
debris impacts and the ambient plasma. Various methods were used to try and simulate the 
damage caused by either ground handling or debris impacts. It was recognized from the start 
that if damage was caused on the ground, it would manifest itself as a tiny insulation nick either 
caused by a cut or cracking of the insulation. However, an orbital debris impact could potentially 
do more damage by exposing completely severed wire strands. Every attempt was made to 
quantify the effects of these two different scenarios. Plasma chamber testing was done on both 
samples with small cuts and samples with wires that have been intentionally cut. This range of 
damage should bound the potential problem for ProSEDS. During the plasma chamber testing 
only negative bias potentials were applied, because the insulated section is located in a region 
where high negative potentials are expected. 

The results of this investigation are detailed in Table 2. The main objective was to determine 
if the ProSEDS tether was at risk to an arcing event. A small cut was made in the insulation of a 
tether sample, which was verified with a digital multi meter (DMM) during the procedure. The 
sample was placed in the plasma chamber and biased using the standard procedure. The initial 
test did not show a problem, but there was some question as to weather the cut closed after the 
knife was removed, so a spark test at 3000 V was performed. The spark test is a standard test 
found in all electric cable manufacturers to look for holes in the insulation before shipping the 
product. During a spark test the wire is passed through a bead electrode, which is biased at the 
corresponding voltage. When a fault is present, an arc is produced. Because of the arc 
generated, the spark test is a destructive type test. The spark test verified the cut in the 
insulation. This sample was tested in the plasma chamber and a breakdown threshold of -900 V 
was measured. The difference between these two test results is likely the damage done by the 
spark test which likely enlarged the nick. The results of this tested verified that a nick in the 
tether insulation could cause a problem, but it did depend on the size of the nick. 

Several methods were attempted to simulate the effects of orbital debris impacts short of 
having an actual impact test done. The method that was repeated on various samples was simply 


cutting the wires and either leaving the wire inside the over braid or pulling the cut end outside. 
It was thought that during a debris strike the wire outside the over braid was a more plausible 
scenario as the over braid would likely be damaged during the impact. All simulated orbital 
debris tests where at least one wire was cut experienced electrical breakdown between -700 V 
and -1300 V. Because the insulated tether is expected to be at this potential during most open 
circuit periods, the ProSEDS tether has a design problem. Solutions to this problems could be 
design changes or to eliminate the open circuit period. Before any changes were made to either 
the tether design or ProSEDS operation, one last test was done to see if the chamber pressure of 
mid 10 3 Torr had a significant effect on the voltage breakdown thresholds. A test at mid 10 6 
Torr pressures was proposed to determine the overall effect. 

Table 2. ProSEDS Insulated Tether Pinhole Test Summary 


Sample Description 

Breakdown 
Voltage (V) 

Chamber 

Pressure 

(Torr) 

Test Summary 

Small Pinhole in Insulated 
Tether, verified with DMM. 

-1800+ 

5xl0' 5 

Sample passed the design 
voltage of -1800 V. 

Insulated tether with Small 
pinhole arced at 3000 V in the 
spark tester several times. 

-900 V 

5xl0' 5 

At -900 V the sample broke 
down and burned the tether in 
half. 

Insulated tether with knife cut; 
Aerodag applied along the 
length of the sample. 

-700 V 

5xl0' 5 

At -700 V the sample broke 
down and burned the tether in 
half. 

Simulated debris hit; two wires 
intentionally cut. 

-700 V 

5xl0' 5 

At -700 V the sample failed. 

A piece of insulated tether with 
two of the seven strands of wires 
intentionally cut. 

-800 V 

6x1 0' 6 

The sample discharged at -800 
V drawing a current of 1.5 A 
based on the supply current 
limit. 


A titanium sublimation pump was added to the chamber to add extra pumping capacity of the 
neutral gas. In order to make the most efficient use of the titanium pump, the plasma source 
working gas was switched to nitrogen. When a piece of insulated tether, which had two of the 
seven strands cut, was placed in the plasma chamber and tested, the sample broke down at -800 
V. When compared to the previous sample which had two wires cut yet the chamber pressure 
was mid 10 5 Torr, the breakdown voltage was only -100 V better. The results of this test 
indicated that a potential failure mode existed when an orbital debris hit the tether cutting at least 
one wire. A calculation of the probability that an orbital debris particle large enough to sever a 
single wire in the short 200 m insulated tether was done, and the probability that the insulated 
tether could sustain an arc inducing debris impact was about 13% per day 9 . This probability was 
higher than the accepted probability of 4 % per day that the entire tether will sustain a debris 
impact to sever the tether. 

The potential corrections to the insulated tether centered on either changing the overall tether 
design or the ProSEDS operational scenario. Because the changes to the tether design were 




going to be extremely costly in terms of cost and schedule, the operational timeline was changed. 
Initially, the tether was going to be in open circuit mode every 30 s the entire mission. Due to the 
potential debris induced arc event, the operational timeline was changed to allow open circuit 
mode every 30 s for only the first five orbits. After that point in time, the tether would no longer 
be allowed to enter the open circuit mode. The proposed operational change allowed scientists 
some time to collect needed data, though it reduced the total data set. The operational change 
reduced the probability of a debris particle impact large enough to cause an electrical breakdown 
to about 4% per day. This level of risk was equivalent to the risk accepted by the project early in 
the design phase. 

ProSEDS Conductive Tether to Non-Conductive Tether Transition 


The ProSEDS conductive tether to non-conductive tether transition did not show as volatile 
nature as the other transition. This is because this transition is biased at high positive potentials 
during open circuit. Because of the negative voltage potential did not exist, only a high positive 
potential was considered. The transition was placed into the plasma chamber and tested 
following the standard procedure, and it did not demonstrate any problems from 0 to +1500 V. 

Summary 


The ProSEDS tether design includes an insulated tether and a semi-bare conductive tether. 
The transition between the two creates a triple point with the ambient plasma. Plasma chamber 
testing of this transition region demonstrated electrical breakdown of -900 V, which was below 
the -1400 V design potential. Four semi-conductive materials were evaluated for use in reducing 
the electric field change at this point. Once the Aerodag-G spray was incorporated into the tether 
design, the tether passed all plasma chamber tests eliminating the triple point concern. The new 
tether design also passed both simulated deployment tests and six days on orbit of simulated 
atomic oxygen exposure. The ProSEDS insulated tether samples, which contained simulated 
orbital debris damage experienced plasma discharge between -700 V and -800 V. The cost of 
changing the tether design forced an operational change that eliminated the tether open circuit 
mode after the first five orbits. Finally, no plasma effects were measured at the remaining triple 
point at the conductive tether to non-conductive tether transition because it will only experience 
high positive tether potentials. 



References 


Leslie Curtis and Les Johnson, “Propulsive Small Expendable Deployer System (ProSEDS)”, 
Space Technology Applications International Forum (STAIF) 2002, February 3-6, 2002. 

'Joseph A. Carroll, "SEDS Deployer Design and Flight Performance", Proceedings of the 4th 
International Conference on Tethers in Space, April 10, 1995, Washington, D.C. 

Feslie Curtis, Jason Vaughn, Ken Welzyn, and Joe Carroll, “Development of the Flight Tether 
for ProSEDS”, Space Technology Applications International Forum (STAIF) 2002, February 
3-6,2002. 


4 J. A. Vaughn, M.M. Finckenor, R.R. Kamenetzky, Todd Schneider, and Pete Schuler, 
“Polymeric Coatings for Electrodynamic Tethers”, AIAA 2000-3614, 36 th 
AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Hunstville, AF, July 2000. 

5 J.R. San mart in, M. Martinez- Sanchez and E. Ahedo, "Bare Wire Anodes for Electrodynamic 
Tethers." Journal of Propulsion and Power, Vol. 9, No. 3, pp. 353-360, May-June 1993. 

6 Fes Johnson, R.D. Estes, E. Lorenzini, M. Martinez, J. San mail in, “Propulsive Small 

Expendable Deployer System Experiment,” J. Spacecraft and Rockets 37(2), 173-176 (2000). 

7 A.B.White, “ProSEDS High Voltage Assessment”, SDL/99-004, Feb. 1, 1999. 

8 Kenneth J Szalai, "TSS-1R Mission Failure Investigation Board, Final Report", 5/31/96. 

9 Bill Cook and Heather Lewis, ProSEDS Project Orbital Debris Assessment, Feb. 2002.