lee%su-star@sri-unix.UUCP (10/28/84)
From: WOO IL LEE <lee@su-star> A question was raised recently about the remaining fuel in Palapa & Westar. Please note that the fuel-transfer experiment in the last Shuttle mission used liquids. That is because the idea is to refill the attitude control system tanks. Attitude control thrusters are always, as far as I know, liquid systems. That's due to the need to switch them on and off, which can't be done with solids. The Thiokol engine is a solid. Its igniters,which are one-shot affairs, have already been used up. Furthermore, the failure mode, as described in most reports, involves the structural failure of the nozzle throat area. The nozzle portion downstream of this point was blown away, so even if some other mechanism were to produce ignition condition, chamber pressure conditions would make it impossible to complete the ignition process and reach sustained combustion. As for the orbital mismatch between the Shuttle and the satellites, I understand that they are planning to use the attitude- control thrusters to reduce and circularize their orbits. Maybe they can use them to kill the spin too, as with the Orbiting Obsevatory? Does anybody have some accurate information? Emilio P. Calius Stanford Univ. ------