Factitos concerning TiPS

Allen Thomson (thomsona@netcom.com)
Tue, 2 Jul 1996 12:05:01 -0700

Here some factoids concerning the new tethered satellite.


   News Release
   Naval Research Laboratory
   Public Affairs Branch, Code 1230
   (202) 767-2541 (voice)
   (202) 767-6991 (fax)
   [EXCERPTS]
   
   Small Tether Satellite Deployed by NRL
   
      The TiPS satellite was deployed today into a circular orbit, 
   at an altitude of 1022 km and an inclination of 63.4 deg. A 
   deployment sequence jettisoned the TiPS satellite from a host 
   vehicle and then separated its two end masses from each other. 
   When fully deployed, the 53.5 kg tethered system consisting of 
   two small end-masses is connected by a 4 km  nonconductive 
   braided tether. 
   
      NRL, NASA and an international network of Satellite Laser 
   Ranging (SLR) stations are tracking the position of each end-
   mass to study the dynamics and survivabiity of tethered systems. 
   Telemetry generated during the separation of the two end-masses 
   was received by the United States Air Force. 
   
      The National Reconnaissance Office (NRO) is a sponsor of the 
   TiPs program.  Research and funding for this low-cost, passive 
   experiment began in 1995.  The NRO helped fund this project to 
   increase understanding of gravity gradient tether dynamics for 
   space operations.  In addition, NRO engineers hope the research 
   will assist the scientific community in evaluating survivability 
   of future tethered vehicles in low-earth orbit. 
   
      The tether, roughly 2 mm in diameter, can be severed by a 
   particle as small as 1 mm [sic] travelling at a relative 
   velocity of 14 km/s [no kidding!]. 
   
      Mr. William Purdy, NRL's TiPS program Manager says, "The TiPS 
   end-masses are similar in size and weight, which dictates that 
   both will undergo significant dynamic motion with respect to the 
   center of mass of the system.  The heaviest end mass, 
   affectionately dubbed 'Ralph,' weighs 37.7 kg. Ralph contains 
   all of the electronic components, which include the telemetry 
   system, turn-count recorder, and temperature sensors. The 
   telemetry system, supplied by NASA, is powered by a 
   nonrechargeable battery, which operated for the first eight 
   hours of the satellite's life.  The lighter end-mass dubbed 
   'Norton' weighs 10.3 kg. The tether weighs 5.5 kg, and was 
   coiled on a spool inside Ralph, much like a spinning reel. 
   
      Ralph and Norton separated at a relative velocity of 
   approximately 5.1 m/s.  The passive deployment scheme utilized a 
   small Marman clamp and ten spring-loaded cartridges. The initial 
   separation energy was designed to deploy about 2 km of the 
   tether, at which time gravity-gradient forces assisted to unwind 
   the remainder. 
   
      The TiPS satellite orbits the Earth with a nominal vertical 
   orientation, Ralph being closest to the earth. 
   
      Retroreflectors are mounted on the exterior surfaces of both 
   Ralph and Norton...  End-mass discrimination is accomplished by 
   coating the retroreflectors on Ralph to reflect only one of the 
   two transmitted laser wavelengths.  The uncoated retroreflectors 
   on Norton reflect both transmitted wavelengths. 
   
   
   
   NRO Orbiting Spacecraft Studies Tether Survivability
   by Joseph Anselmo
   Aviaiton Week and Space Technology
   July 1, 1996, p.24
   [EXCERPTS]
   
   TiPS was designed to complement the NASA/Italian Space Agency 
   Tethered Satellite System 1-R... that had the primary goal of 
   studying the generation of electrical power in space. [It flew 
   in February 1996 on the shuttle.] 
   
   TiPS was jettisoned from its host satellite on June 20... [The] 
   tether deployed to its full length of 2.15 naut. mi. in 42 min. 
   
   Col. Pedro Rustan, director of the NRO's small satellite office, 
   said he believes operational tethers will be in use on 
   "somebody's spacecraft" within the next 10 years.  He said the 
   [Feb. 1996] shuttle tether experiment was important because 
   spacecraft are becoming more power hungry and advances in power 
   generation are not keeping up with those in other subsystems, 
   such as antennas. 
   
   "If we could power from other sources such as the tether, that 
   would be a significant reduction to a spacecraft's weight and 
   would increase capability," Rustan said.  Rustan said TiPS will 
   explore two "basic conditions" for operating tethers in space 
   that the shuttle experiment did not address. "It has to be 
   survivable and controllable," he said. "The purpose of this type 
   of tether is to put something out there and leave it for years. 
   It's a very thin type, and we want to know if it's going to last 
   for weeks, months or years. 
   
   Rustan said the experiment's $4-million price tag includes $1.9 
   million for two years of tracking. 
   


    A random thought: it's interesting that the 
TiPS deployment took place from the NOSS 2-3 bus, as NRL is 
believed to the lab responsible for the NOSSes.  Also, as the 
NOSSes apparently use some sort of propulsion to fly in 
formation in order to do their supposed TDOA emitter location 
trick, it's not implausible that NRL would be interested in 
investigating other ways to keep them together.

   The arithmetic of the tether's cross section is instructive: 
two mm across and 4 km long gives 8 square meters exposed to 
micrometeorite/debris flux, not a small amount. (This is also, 
of course, related to the reason why the tether is visible.)