Re: Tethered sat with NOSS 2-3

Neil Clifford (n.clifford1@physics.oxford.ac.uk)
Mon, 24 Jun 1996 20:22:43 +0100 (BST)

TETHER PHYSICS AND SURVIVABILITY EXPERIMENT (TiPS)

A. Peltzer, W. Purdy, and S. Coffey/NRL

The Tether (i) Physics and Survivability (TiPS) experiment is intended to be
the first long term tethered satellite flight experiment. Two end bodies,
shown in Figure 1 [1], weighing 90 and 20 pounds respectively, will be connected
by a four kilometer long tether. The system will be placed in a 550 nautical
mile circular orbit with an inclination of 63.40ree;. The tethered system
will be jettisoned from a host spacecraft. The tether will be deployed after
a period of separation from the host spacecraft. The TiPS experiment is
presently planned to be operational in the spring of 1996.

There are two primary objectives to the TiPS experiment:

  1. Evaluate the long term gravity gradient dynamics of a tethered system.
  2. Gather data on the survivability of the tether in the space
     environment.

No tether experiment to date has been on orbit longer than about one month.
As such, there is relatively little data on the long term dynamics of these
systems. The dynamics of particular interest include in-plane and out of
plane libration, system damping, orbital perturbations and environmental
effects. The TiPS experiment is the first designed to maximize the
survivability of the tether. The tether is predicted to have a mean life of
5 years before it is cut by orbital debris. The observed life of TiPS will
help understand and validate these theoretical predictions. A schematic of
the tether dynamics experiment is shown in Figure 2 [2].

The TiPS experiment will have its dynamics measured by Satellite Laser
Ranging (SLR) and ground based radars. The SLR will provide very accurate
measurements of the positions of each end body. The length and libration
angles of the system will be determined repeatedly over a long period of
time from these measurements. Analysis of this data will be compared to
theory to improve the understanding of tether dynamics. The SLR data will be
available over Internet. Each end body will be covered with 18 uniformly
spaced laser retroreflectors to enable the ground based laser ranging. The
retroreflectors on one body will be coated to reflect light from 420 nm to
850 nm. The retroreflectors on the other body will be uncoated. These two
types of retros will enable differentiation between the two end bodies. The
laser ranging operations are planned to last for a period of at least 6
months after TiPS deployment. The U.S. Space Command network of radars will
be utilized to support the laser ranging and to provide continuing
observation of the system for the duration of the TiPS lifetime to determine
if or when the tether has been cut.

[1] http://cddis.gsfc.nasa.gov/920_1/pubs/SLRNEWS/9506/tips.gif

[2] http://cddis.gsfc.nasa.gov/920_1/pubs/SLRNEWS/9506/tips2.gif