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.)