Tether Physics and Survivability (TiPS) 

Fact Sheet

20 November 1996

Purpose: The Tether Physics and Survivability (TiPS) experiment consists of two small end 

masses (dubbed "Ralph" and "Norton") connected by a 4 km tether. TiPS has been designed as a 

quick reaction, low cost experiment to research on-orbit tether motion and survivability 

characteristics. Radar and optical ground sensors tracking TiPS provide data on long term tether 

dynamics to validate existing tether dynamics models. As the longest lasting tether system to 

date, TiPS will also provide data on space tethers' long term survivability. Confidence in these 

models is necessary to reduce the risk for future operational tether applications and focused 

tether experiments.

TiPS Sponsor: National Reconnaissance Office (NRO). TiPS is the NRO's first unclassified, onorbit spacecraft.

TiPS Design and Integration: Naval Research Laboratory (NRL).

Physical Characteristics: 

Tether: 4 km Spectra 1000 braid over acrylic yarn. 

Attitude Control: Gravity gradient stabilized. No active measures. 

Orbit: 

Weight Dimensions

Ralph 93 lbs 27 in x 14 in x 7 in

Norton 22 lbs 27 in x 14 in x 7 in

Tether 12 lbs 2-3 mm diameter, 4 km long

Total 127 lbs
• Altitude - 552 nm circular 

• Inclination - 63.4 deg 

• Period - 105 min 

Launch and Jettison: TiPS was jettisoned from a host vehicle on June 20, 1996 into a 552 nm, 

63.44 deg circular orbit. The TiPS jettison occurred in the positive velocity vector using a 

separation nut/jettison bolt mechanism and four spring cartridges designed to impart a 3 ft/sec 

separation velocity. 

Tether Deployment: Almost 3 hours after TiPS was jettisoned, the two TiPS endbodies were 

separated using a bolt cutter, Marman clamp mechanism, and ten spring cartridges designed to 

impart a 16.5 ft/sec separation velocity. Because of drag in the tether reel, gravity gradient forces 

were relied upon to fully deploy the 4 km tether. Complete deployment of the tether took 42 

minutes and occurred within view of the AF Phillips Laboratory's Starfire Optical Range (SOR) 

and NASA's laser ranging sites. Deployment halted for 2.5 minutes as libration swung the two 

end masses close to a horizontal position. When the libration abated and the endmasses returned 

to a more vertical orientation, gravity gradient forces again dominated and the tether deployment 

concluded. The tether deployment interruption was expected. 

Ralph contains a transmitter and a Small, Expendable Tether Deployer System (SEDS) box 

provided by NASA. The SEDS box counted the turns of the tether spool as the tether 

deployed. This information was transmitted to Air Force Space Control Network until the battery 

ran down, and forwarded to NASA and NRL for further analysis. The transmitter and the SEDS 

box were powered for several hours by a Lithium-Thionyl Chloride battery. Once the battery 

died, TiPS became completely passive. 

Position Determination: There are 18, one-inch diameter laser retro-reflectors mounted on each 

end body for use by worldwide Satellite Laser Range (SLR) sites to determine the TiPS inertial 

position and tether attitude. The laser retro-reflectors mounted on Norton are uncoated while the 

laser retro-reflectors mounted on Ralph are coated with TiO2 and SiO2. The coatings allow the 

end bodies to be distinguished since both sets of retro-reflectors will reflect green laser sources 

(.532 microns) but only the retro-reflectors on Norton will reflect infrared laser sources (1.064 

microns). At TiPS altitude of 552 nm, the Space Laser Range allow TiPS' end bodies to be 

determined to an accuracy of approximately 15 centimeters (1 sigma). 

In addition to the Space Laser Range, TiPS is tracked by highly accurate ground based radars. 

These radars are not limited by illumination constraints currently imposed on the SLR sites. 

Until the tether model can generate very precise pointing vectors, the SLR sites can only track 

TiPS when the spacecraft is illuminated by the sun and the laser site is in darkness. This 

condition is called "terminator" mode. In terminator mode, the brightly illuminated spacecraft 

can be easily acquired by the laser sites regardless of prediction errors. The principle radar that 

will augment laser observations is the HAVESTAREX-band radar located at Vanderberg AFB. 

As more observations are processed, it is hoped that the tether prediction models will generate 

more accurate pointing predictions. 
TiPS is also tracked by the USSPACECOM Space Surveillance Network (SSN). The system 

tracks each end mass independently, and occasionally returns tracks from a UHF dipole 

imbedded in the tether at the system's center of mass. Element sets obtained from 

USSPACECOM form the basis for tether position predictions. Unfortunately, the UHF radars 

forming the mainstay of the SSN can not provide precise enough observations to accurately 

model tether dynamics. 

Space Laser Range: NASA provides access to the worldwide Space Laser Range consisting of 

both NASA and international optical ranging facilities. In support of TiPS operations, Allied 

Signal in Greenbelt, MD generates and distributes the interrange vectors required for these sites 

to acquire and track the end masses. Allied Signal will also consolidate the data sets collected by 

the SLR sites, and to make the data available to scientists and the public through the Internet. All 

data consolidated by Allied Signal will also be passed to NRL for analysis and archiving. 

Results to Date: Observed TiPS motion confirm anticipated results. Maximum in-plane libration 

angle is based upon three events; the rate the tether is extended, the amount of friction realized 

from the tether spool during release, and the angle relative to the Earth in which the tether is 

released. A maximum in-plan libration angle of about 40 degrees was expected, which generally 

agreed with observed value of 30 degrees a week after release. Libration in the plane 

perpendicular to the plane of motion, called cross-plane libration, was measured at this time to be 

about 15 degrees. 

Two interesting characteristics were observed shortly after tether deployment. First, the tether 

quickly became bowed. This abnormality was later confirmed by Space Laser Range data which 

NASA SLR Sites

• Monument Peak, CA 

• ASTC, Greenbelt, MD 

• Haleakala, HI 

• Yarragadee, 

Australia 

• Arequipa, Peru 

• Reno, CA 

• MacDonald Obs, TX 

• Santiago, Chile

International SLR Sites

• Hertmonceux, 

England 

• Wettzell, Germany 

• Graz, Austria 

• Grasse, France 

• Orroral, Australia 

• Riga, Latvia 

• Postdam, Germany 

• Borowiec, Poland 

• Cagliari, Italy

Other Participating Laser 

Sites

• Starfire Optical 

Range, NM 

• AF Maui Optical 

Station (AMOS), HI
indicated the two end masses were 80 meters closer together than if the tether was straight and 

rigid. Secondly, the bow appears to be rotating in a "skip rope" manner about an imaginary line 

connecting both endmasses. 

These two characteristics are probably due to the large amount of rotational momentum 

transferred from the endmasses at deployment. TiPS was deployed from its host spacecraft 

spinning at 4 revolutions per second. With a combined moment of inertia in the spin axis of 

approximately 5920lbm*in2, the host vehicle imparted an extra 0.1 foot pound force of rotational 

energy into the TiPS system. 

The spacecraft's overall system energy appears to be dampening with time. Libration has 

decreased in both in-plane and cross-plane directions. Visual observations taken at the Air Force 

Maui Optical Site (AMOS) during the last week of September, 1996, show in-plane libration has 

decreased to about 12 degrees while cross-plane libration has decayed to about 8 degrees. 

Libration periods have remained relatively stable at about 65 minutes and 56 minutes for inplane and cross-plane libration periods, respectively. Furthermore, recent observations indicate 

that the tether bow has decreased significantly. The reduction in vertical length between the two 

end masses was 80 meters a week after deployment and 15-20 meters after three months. The 

period of the bow rotation is estimated to be several hours long. Finally, the endmasses appear to 

be slowing down as well from their initial spin rate of 4 rev/min to about 0.5 rev/min. 

A Week After Deployment 3 Months From Deployment

In-Plane Libration 30 deg, 65 min period 12 deg, 64 min period

Cross-Plane Libration 15 deg, 56 min period 8 deg, 58 min period

Bow (reduction in vertical length) 2% 0.4%

Endmass Rotations 4 rev/min 0.5 rev/min

The tether dampening appears to be caused by several effects. The most important effects are the 

bending of the tether, the torsional waves, the skip rope effect, and the frictional forces. The 

continuing small but finite bending of the tether as it rotates around the Earth would release 

energy causing dampening of the tether especially along the velocity vector. This factor would 

explain the larger reduction of the in-plane libration. The torsional waves would cause friction 
between the fibers in the tether, releasing energy, and dampening the system. As the tether's 

motion follows a skip rope effect, the variation of the gravity gradient and the centrifugal forces 

of the bow effect would cause the tether to stretch and retract. This hysterisis effect will make the 

fibers work against each other releasing energy and dampening the system. Finally, there would 

be some dampening due to frictional forces of the rarefied atmosphere at this altitude, further 

taking energy out of the TiPS system. 

Changes in TiPS orbit characteristics, such as eccentricity, inclination, and altitude, have been 

typical of equivalently sized non-tethered spacecraft in similar orbits 

Internet Address: Spacecraft details and orbit ephemeris are available to both international 

researchers and the public through the TiPS Internet home page at 

http://hyperspace.nrl.navy.mil/TiPS. 

Any questions should be directed to NRO Public Affairs at (703) 808-1015.