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American Institute of Aeronautics and Astronautics
1
The Terminator Tape™: A Cost-Effective De-Orbit Module
for End-of-Life Disposal of LEO Satellites
Robert P. Hoyt*, Ian M. Barnes†, Nestor R. Voronka,‡ Jeffrey T. Slostad§
Tethers Unlimited, Inc., Bothell, WA, 98011
The rapid growth of the orbital debris population poses an increasing threat to military,
commercial, and civilian science spacecraft in Earth orbit. NASA, the DoD, ESA, and other
organizations have begun to respond to this problem by imposing requirements for debris
mitigation upon new space systems. These requirements specify that spacecraft at end-of-
life be disposed of by either atmospheric re-entry within 25 years, maneuver to a higher
storage orbit, or direct retrieval. For most satellites operating in low Earth orbit (LEO),
atmospheric re-entry is the most viable option. To provide a cost-effective means for satellite
operators to comply with the 25-year post-mission orbital lifetime restriction, Tethers Un-
limited is developing a lightweight de-orbit module called the “Terminator Tape™”. The
Terminator Tape is a small module that bolts onto any side of a spacecraft during satellite
integration. At the completion of the satellite’s mission, the satellite will activate the Termi-
nator Tape module. The module will then deploy a several-hundred-meter length of thin
conducting tape. This tape will not only significantly enhance the aerodynamic drag experi-
enced by the system, but will also generate electrodynamic drag forces through passive in-
teractions with the Earth’s magnetic field and conducting ionospheric plasma, de-orbiting
the satellite within 25 years. Two modules are currently in development, one sized for mi-
crosatellites operating at altitudes of less than 900 km, and the other sized for CubeSats. In
this paper, we will present design overviews and concept of operations for both modules, as
well as analyses of deorbit of satellites using these modules.
Nomenclature
B
= magnetic field vector
I
= current vector
L = tether length
me,i = electron/ion mass
n∞
= ambient plasma density
v
= orbital velocity vector
V = tether voltage
w = tape width
I. Introduction
HE orbital debris population and its potential for continued rapid growth pose a significant threat to both DoD
space assets and civilian space systems. Studies of the interaction of satellite systems with the space debris envi-
ronment have concluded that unless debris mitigation measures are adopted, “the debris environment cannot sustain
the long-term operation of [large constellations but].... could sustain the long term operation of medium sized con-
stellations of up to 100.... provided that the constellations implement strict mitigation measures such as explosion
prevention and immediate satellite de-orbiting upon end-of-life and failure. These findings have proven that low
Earth orbit is not a limitless resource and must be managed carefully in the future.”1 Recent studies at NASA/JSC
have indicated that the population of debris in LEO is now so large that it will continue to increase for over 50 years
* President, CEO, & Chief Scientist, 11711 N. Creek Pkwy S., Bothell WA 98011, hoyt@tethers.com, Member AIAA.
† Lead Mechanisms Engineer.
‡ Chief Technologist, Member AIAA.
§ Chief Engineer.
T
American Institute of Aeronautics and Astronautics
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even if no new objects were to be launched into orbit.2 Other studies have indicated that unless strong mitigation
measures are adopted, the density of orbital debris particles in LEO will soon become large enough that collisions
between them will lead to exponential growth of the number of debris particles, which would pose a severe threat to
DoD and commercial space assets.3
Fortunately, NASA, the DoD, FCC, and other relevant authorities have begun to respond to the orbital debris prob-
lem by placing requirements for debris mitigation upon new space systems. Examples of these requirements are the
DoD Instruction 3100.12, Sec. 6.4, “Spacecraft End-of-Life” and NASA’s Safety Standard (NSS) 1740.14, “Guide-
lines and Assessment Procedures for Limiting Orbital Debris,” which specify that stages, spacecraft, and other pay-
loads should be disposed of at the end of mission life by one of three methods: atmospheric re-entry, maneuver to a
designated storage orbit, or direct retrieval. If these mitigation measures are implemented and adhered to over the
coming decades, the growth of the debris flux can be reduced from an exponential growth curve down to a logarith-
mic growth curve.3 If more aggressive actions such as active removal of existing large debris objects are under-
taken, the growth of the debris population could be halted and reversed within several decades.
A challenge to universal compliance with these regulations is the cost of meeting orbital lifetime restrictions using
current technologies. Relying upon chemical rocket-based propulsion to accomplish de-orbit will require a propel-
lant mass equal to 5-20% of the spacecraft mass, adding significantly to the satellite hardware and launch costs.
Even if higher specific impulse electric propulsion systems are used, many of the spacecraft’s systems, including
command and data handling, attitude control, guidance, telemetry, power, and the thruster systems themselves must
be designed with the robustness and redundancy needed to ensure operation at the satellite’s end-of-life. This addi-
tional redundancy can dramatically increase the cost of the satellite hardware, and even then the satellite operators
will eventually be forced into the unpleasant situation of having to de-orbit their spacecraft while they are still capa-
ble of performing revenue-generating operations.
1. Lessons Learned from Prior Work: The Terminator Tether™
Over a dozen years ago, Tethers Unlimited began working to address the orbital debris problem by developing a
device called the “Terminator Tether™” which utilizes electrodynamic drag generated by a several-kilometer-long
conducting tether to deorbit a spacecraft.4,5 Several lessons learned from developing and marketing the Terminator
Tether have guided our more recent efforts to develop the Terminator Tape, resulting in a very different end product.
The Terminator Tether module incorporated a tether deployment mecha-
nism, a multi-kilometer, multi-strand conducting tether, an active electron
emission device such as a Hollow Cathode Plasma Contactor (HCPC) or
Field Emission Array Cathode (FEAC), and control and power conversion
avionics. Under a NASA SBIR effort, we designed and built a Terminator
Tether brassboard prototype sized to deorbit 3-metric ton satellites from
mid-LEO altitudes with a deorbit time of less than a year. The prototype is
shown in Figure 1. The Terminator Tether unit would be integrated onto a
spacecraft prior to launch, and during the mission of the spacecraft the unit
would remain dormant. When the host spacecraft completed its mission,
or in the event of an unrecoverable malfunction of the host, the Terminator
Tether unit would activate itself, ejecting away from the host and deploy-
ing its conducting tether below the spacecraft. Voltages generated by the
motion of the conducting tether across the geomagnetic field would enable
the tether to collect electrons from the conducting ionospheric plasma.
These electrons would flow down the tether to the Terminator unit, where
they would be emitted back into the ionosphere. The flow of current along
the tether would generate a drag force through electrodynamic interactions
with the geomagnetic field, and this drag force would deorbit the tether and its host spacecraft over a period of sev-
eral months.
Several design objectives chosen early in the development of the Terminator Tether technology drove the system’s
complexity and cost. The first objective was to minimize the deorbit time achievable within a mass allocation of 2%
of the host spacecraft mass. This objective drove the system design to a very high-performance electrodynamic
tether system, requiring a relatively long tether length of 5-10 kilometers, as well as requiring active electron emis-
sion at one end of the tether. Both HCPC and FEAC electron emission devices have significant power, mass, and
cost impacts. A second objective was to enable the device to be autonomous, requiring no input power from the
Figure 1. The Terminator Tether
brassboard prototype developed in
prior efforts.
American Institute of Aeronautics and Astronautics
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host spacecraft, and enabling the device to deorbit the host spacecraft even if the host had malfunctioned and lost all
control and power. This autonomy requirement drove the design to incorporate power conversion electronics to
enable the system to power itself using the voltage and current generated by the electrodynamic tether. Furthermore,
it required inclusion of avionics to implement the autonomy. The need to ensure that these systems would all func-
tion with high reliability after up to a decade on-orbit resulted in system costs beyond that desired by spacecraft in-
tegrators.
2. Design Objectives for a Next Generation Deorbit Module
Recently, the DoD, NASA, FCC, and other agencies that regulate space activities have become more diligent about
enforcing end-of-mission disposal guidelines, driving a market need for a cost-effective satellite disposal technol-
ogy. Based upon the results of our prior work, we chose to develop a new generation of deorbit technologies, focus-
ing on a design approach that would seek to minimize complexity, technical risk, cost, and mass while enabling
spacecraft operators to comply with the 25-year orbital lifetime restriction. This design focus has resulted in a rather
different system concept.
The Terminator Tape Deorbit Module
To provide a significantly more cost-effective means for satellite operators to comply with the 25-year post-mission
orbital lifetime restriction, Tethers Unlimited is developing a lightweight de-orbit module called the “Terminator
Tape”. The Terminator Tape Deorbit Module is, essentially, a small, flat box that bolts onto any side of a spacecraft
during pre-launch integration. At the completion of the spacecraft’s mission, the spacecraft will activate the module
with a simple pyro signal. The module will then deploy a several-hundred meter length of thin conducting tape.
Regardless of what direction the tape is initially deployed in, gravity gradient forces will (eventually) orient the tape
along the local vertical direction, either above or below the spacecraft. This tape will not only significantly increase
the aerodynamic drag experienced by the system, reducing its ballistic coefficient, but will also generate electrody-
namic drag forces through passive interactions with the Earth’s magnetic field and conducting ionospheric plasma.
With proper selection of tape length, width, and conductivity, the enhanced aerodynamic drag and passive electro-
dynamic drag will be sufficient to de-orbit the satellite from orbits up to 900 km within 25 years. The Terminator
Tape technology is highly scalable to accommodate different satellite sizes. Tethers Unlimited is currently develop-
ing two Terminator Tape modules, one sized for 180-kg ESPA-secondary-payload class satellites, and the other
sized for 1-5 kg CubeSats and other pico- and nano-satellites.
Aerodynamic Drag Enhancement
Once the gravity gradient forces orient the tape roughly along the local vertical direction, the tape will increase the
system’s aerodynamic drag cross section by an amount approximately equal to
Adrag, tether ≈2πwL
, (1)
where the factor of 2/π results from the assumption that the tape either has some twist along its length, or that the
system rotates around the tape’s long axis.
Passive Electrodynamic Drag
The principal of passive electrodynamic drag generation by the Terminator Tape is illustrated in Figure 2. The or-
bital motion of the conducting tape across the Earth’s magnetic field will induce a voltage along the tape, equal to
V=
L ⋅
v ×
B
( )
, (2)
where V is the induced voltage,
v
is the orbital velocity of the system,
L
is the vector from one end of the tape to
the other, and
B
is the geomagnetic field vector. In a direct orbit, this voltage will bias the top of the tape positive
relative to the ambient environment, and the bottom of the tape negative. This voltage bias will enable the top por-
tion of the conducting tape to collect electrons from the ionospheric plasma, and the bottom portion of the tape will
collect ions, resulting in a small but significant flow of current up the tape. Note that this ‘passive’ current collec-
tion works regardless of whether the tape is deployed above or below the host spacecraft, and so the Terminator
Tape does not require specific placement on the spacecraft or deployment in a particular direction.
American Institute of Aeronautics and Astronautics
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This current exchange with the conducting plasma will result in a flow of current
I
up the tape, and this current will
interact back with the Earth’s magnetic field to induce a Lorentz force that will oppose the orbital motion of the
spacecraft, lowering its orbit:
F =
I ×
B
( )
0
L
∫d
, (3)
where the integral is performed along the length of the tape to account for variations in the current density along the
tape. Because ions are heavier and thus much less mobile than electrons, most of the length of the tape will be col-
lecting ions, balanced by a short electron-collecting length at the top of the tape. The collection of electron and ion
currents by the biased tape of width w can be approximated using the Orbit Motion Limit theory,6
dIelectron
d=−(2w) e n∞
π
2eΔV
( )
me
, dIion
d=(2w) e n∞
π
2e−ΔV
( )
mi
, (4)
where ∆V is the voltage difference between the metalized film and the local plasma potential, me and mi are the elec-
tron and ion masses, and n
∞
is the local plasma density. At an altitude of 700 km, where the plasma density is on the
order of 1.2x1011 m-3 at local noon, a 250 m long, 0.28 m wide Terminator Tape will collect an ion current density of
approximately 68 µA/m over most of its length, resulting in peak currents of approximately 10 mA. While this is a
small current, it will result in a drag force of approximately 15 µN. Thus at 700 km altitude, the passive electrody-
namic drag will roughly double the net drag on the tape. Because the ionospheric plasma density drops more slowly
with altitude than the neutral density, above about 700 km altitude the electrodynamic drag will exceed the neutral
density drag. Thus the Terminator Tape module will provide significantly lower deorbit times than aerodynamic-
drag-only systems, thereby dramatically increasing the altitude range over which satellites can meet the 25-year or-
bital lifetime requirement.
Figure 2. Illustration of the physics of passive electrodynamic drag on the Terminator Tape.
American Institute of Aeronautics and Astronautics
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Terminator Tape for ESPA-Class Microsatellites
Hardware Implementation
Under funding from the Air Force Research Laboratory Space Vehicles Directorate at Kirtland AFB, NM, Tethers
Unlimited is developing a Terminator Tape Module sized for ESPA-Class Microsatellites. The module’s configura-
tion is shown in Figure 3. The module has a square 8”x8” footprint, sized so that it will fit inside the Mark II Light-
band release clamp used for ESPA payloads, as shown in Figure 4. The module is designed to deploy a conducting
tape with a width of 17 cm and a length of 100-250 meters. Actuation of the Terminator Tape Module is accom-
plished using a single NEA Model 800 actuator, fired by a standard pyro signal from the host vehicle. If desired, the
module is designed to accommodate an additional NEA Model 800 actuator that can serve as a ‘safety’ to provide
redundant restraint of the module, ensuring the module deploys only when desired. An initial engineering model
prototype is shown in Figure 5. The mass of the module with a 150 m long, 17 cm wide tape is 1.5 kg.
The design of the tape must ensure that it will maintain electrical conductivity and tensile integrity over 25 years
deployed on orbit while minimizing the mass required for the tape. To accomplish these objectives, the tape will be
constructed of thin metalized films commonly used in multi-layer insulation with the addition of embedded metal-
ized aramid fibers intended to provide rip-stop characteristics, enhanced conductivity, and increased M/OD survivi-
ability.
Figure 3. Terminator Tape Deorbit Module design for
ESPA-class microsatellites.
Figure 4. The Terminator Tape Deorbit Module fits
within the keep-out zone of the motorized 15” Mark II
Lightband used for ESPA microsatellite payloads.
Figure 5. Engineering model prototype of the Terminator Tape module for ESPA-class microsatellites.
Predicted Performance
The amount of time required for a Terminator Tape Module to de-orbit a spacecraft will depend upon the spacecraft
mass, initial altitude and inclination, tape width, tape length, and tape linear resistivity. To evaluate these dependen-
cies, we utilized the TEMPEST code, an electrodynamic tether simulation code developed by the University of
American Institute of Aeronautics and Astronautics
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Michigan. TEMPEST includes models for electrodynamic drag, aerodynamic drag, and orbital mechanics, and util-
izes NASA-standard environment model codes such as the IRI-90 ionospheric plasma model and MSIS90 and
MSIS86 neutral density models. The TEMPEST code does not model tether dynamic behavior, but because the
electrodynamic forces in the Terminator Tape are very small compared to the gravity gradient forces, tether dynam-
ics can be neglected for this application, and simulations of several decades of operation can be conducted in a mat-
ter of hours.
Figure 6 shows plots of time versus altitude for four different several tape lengths. The four curves were generated
by simulating systems deorbiting from an initial altitude of 900 km, and plotting the resultant data with the time on
the y axis and the altitude on the x-axis. The higher-order oscillations on the curves at altitudes greater than 670 km
are the result of variations in aerodynamic and electrodynamic drag due to solar cycle impacts on neutral and iono-
spheric plasma densities during the deorbit period. Thus the deorbit time from a given altitude will vary depending
upon when in the solar cycle the Terminator Tape is deployed, with the longest deorbit times occurring when the
system is activated a few years after solar max. The figure indicates that for ESPA-class microsatellite payloads, a
150 meter long, 17 cm wide tape will suffice to deorbit satellites from orbits up to about 850 km within 25 years.
Figure 6. Deorbit time versus altitude for a 180 kg spacecraft in a 28.5 degree orbit, as a function of tape length, for
a 17 cm wide tape.
Figure 7 shows plots of deorbit time versus altitude for four different orbit inclinations. For initial altitudes above
about 670 km, deorbit times from polar and sun-synchronous orbits will be approximately 10 years longer than from
low-inclination orbits due to weaker electrodynamic coupling between the orbital motion and the geomagnetic field.
However, even in near-polar orbits, a 150 m long, 17 cm wide tape will suffice to deorbit ESPA-class microsatellites
from altitudes up to 850 km.
400 500 600 700 800 900
0
5
10
15
20
25
A ltitud e , (km )
D e orbit T im e (ye a r s )
18 0 k g Sp a cecra ft, 2 8 .5 ° In c lin atio n
100 m
150 m
200 m
250 m
American Institute of Aeronautics and Astronautics
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Figure 7. Deorbit time versus altitude for a 180 kg spacecraft with a 150 m Terminator Tape, as a function of inclina-
tion, for a 17 cm wide tape.
AREA TIME PRODUCT
To minimize the chances that a satellite will fragment and contribute to the growth of the space debris population, it
is necessary to not only reduce the orbital lifetime of the satellite, but also reduce its area-time-product, which de-
termines its probability of experiencing a collision with another space object. Deorbit devices which rely exclu-
sively upon drag enhancement may reduce the orbital lifetime of a system, but for these systems the orbit lifetime
scales as the inverse of the deployed area, so they offer little or no improvement in area-time-product. Because the
Terminator Tape induces both aerodynamic and electrodynamic drag to accelerate the deorbit of a spacecraft, it can
achieve a net reduction in area-time-product, and thus a reduction in the probability the object will experience a col-
lision. Figure 8 shows plots of deorbit time and area-time-product for 17 cm wide tapes of varying length. The plot
200 300 400 500 600 700 800 900
0
5
10
15
20
25
30
A lt it u d e, (km )
D e o rbit T im e (y ea rs )
180 kg S ate ll it e , 1 50 m Term ina tor T a pe
28.5
50
75
98.5
Figure 8. Variation of deorbit time and area-time-product with tape length, for a 180 kg spacecraft with a 1m2 cross
section, deorbiting from an 800 km initial orbit.
0
100
200
300
400
500
600
0
100
200
300
400
500
600
0 100 200 300 400 500 600
Area•Time Product (m2 yrs)
Deorbit Time (Years)
Tape Length (meters)
American Institute of Aeronautics and Astronautics
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indicates that the Terminator Tape module can roughly halve the area-time-product of the satellite. There appears to
be little advantage to using tape lengths in excess of 150 meters in terms of reducing area-time-product, so in de-
signing a Terminator Tape module for a given spacecraft, the tape length should be chosen as the minimum length at
which the system will meet the 25-year lifetime restriction.
nanoTerminator Tape for CubeSats
Nano- and pico-satellites such as CubeSats have developed as an attractive platform for conducting space flight mis-
sions rapidly and at low cost. A large number of organizations, including government agencies, universities, and
commercial companies, are taking advantage of the lower cost barrier to spaceflight afforded by the CubeSat pro-
gram, and even if only a small fractions of these programs make it all the way to flight they will contribute dozens of
new objects to the space catalogue per year. Because these spacecraft typically fly as secondary payloads, their op-
erational orbit is determined by the launch vehicle’s primary payload orbit, and as a result, most opportunities to fly
CubeSats are in orbits where the CubeSat will not meet the 25 year orbital lifetime restriction without use of a drag
enhancement device. Fortunately, the Terminator Tape technology is highly scalable, and so we have also imple-
mented the technology in a device suitable for use on CubeSats and other pico- and nano-satellites, shown in Figure
9. This “nanoTerminator Tape for CubeSats” is sized to mount on one face of a CubeSat. It can be mounted so that
it projects out into the ‘extra volume’ beyond the rail faces, as permitted by the CalPoly P-POD payload specifica-
tion, as illustrated in Figure 10. The module contains a 30-m length of conducting tape. The lid of the module is
restrained by a burn wire actuator, which can be activated by a small circuit board that must be integrated into the
CubeSat. The module design includes electrical feed-throughs so that solar cells can be mounted on the face of the
module. The mass of the module, including circuit board, but not including battery, is 80 grams.
Hardware Implementation
Figure 9. Photograph of a preliminary engineering model of the
nanoTerminator Tape for CubeSats.
Figure 10. Rendering of a nanoTerminator Tape
module integrated onto a 1U CubeSat.
Predicted Performance
Figure 11 shows graphs of deorbit time versus initial altitude for CubeSats with and without nanoTerminator Deor-
bit Modules. With no drag device, 1U CubeSats will exceed the 25 year orbital lifetime restriction if they are de-
ployed above about 650 km. The nanoTerminator Tape module, however, will enable even 3U CubeSats to meet the
25 year lifetime restriction in orbits up to 1000 km.
American Institute of Aeronautics and Astronautics
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Figure 11. Deorbit Time for 3U, 3kg CubeSats and 1U, 1 kg CubeSats, with nanoTerminator Tape modules, as a
function of initial orbit altitude. Deorbit times for a 1U CubeSat without a drag device is also shown. The shaded
regions illustrate (approximately) the variability of deorbit time as the tape deployment time is varied relative to the
phase of the solar cycle.
Conclusions
The Terminator Tape Deorbit Module has been developed to provide a means to enable satellite programs to comply
with orbital lifetime restrictions with minimum mass, cost, and risk impacts to the program. The technology is
highly scalable, and Tethers Unlimited is currently developing two modules, one sized for ESPA-class microsatel-
lites and the second sized for CubeSats. Analyses of the system’s performance indicate that this technology can
enable ESPA-class micosatellites to meet 25-year orbital lifetime restrictions in operational orbits as high as 850-
900 km, and CubeSats as high as 1000 km.
Acknowledgments
This work was supported in part by the Air Force Research Laboratory under contract FA9453-09-M-0099. The
authors wish to thank Prof. Brian Gilchrist of the University of Michigan for the use of the TEMPEST simulation
code.
References
1 Walker, Stokes, & Wilkinson, "Long Term Collision Risk Prediction for Low Earth Orbit Satellite Constellations", IAA Pa-
per 99-IAA.6.6.04.
2 de Selding, Peter, “Orbital Debris a Growing Problem with No End in Sight,” Space News, 31 July 2006.
3 Orbital Debris: A Technical Assessment, NRC Committee on Space Debris, 1995, p 169.
4 Forward, R.L., Hoyt, R.P., and Uphoff, C.W., “The Terminator Tether™: A Spacecraft Deorbit Device”, J. Spacecraft and
Rockets, 37(2) March-April 2000.
5 Hoyt, R.P., Forward, R.L., “The Terminator Tether™: Autonomous Deorbit of LEO Spacecraft for Space Debris Mitiga-
tion,” Paper AIAA-00-0329, 38thAerospace Sciences Meeting & Exhibit, 10-13 Jan 2000, Reno, NV.
6Sanmartín, J.R., Martínez-Sánchez, M., Ahedo, E., “Bare Wire Anodes for Electrodynamic Tethers,” J. Propulsion and
Power, 7(3), pp. 353-360, 1993
1100300 400 500 600 700 800 900 1000
30
5
10
15
20
25
Altitude
Deorbit Time (Yrs)
3U w/ TT
1U w/ TT
1U CubeSat
