karn@mouton.UUCP (Phil Karn) (05/13/84)
Since the Apollo days, NASA manned spacecraft have used something called the "Unified S-Band Tracking and Telemetry System". This is a coherent two-way transponder system in which the ground tracking station sends up a phase-modulated carrier on 2106.4063 mhz. The shuttle carries a phase-locked-loop synthesizer which multiplies the received carrier frequency by 240/221 and transmits the resulting 2287.5 mhz signal. The ground can now lock onto this carrier and regenerate its original uplink frequency, which will of course be doppler shifted. In fact, if the system stays locked, the ground can count individual wave fronts as the shuttle moves, much like a police radar (but much more reliable). The phase modulation on both the uplink and the downlink can go on simultaneously with the doppler measurement, but it can also contain pseudo-random data sequences to provide range information as well as velocity. Take these numbers and put them into a least-squares nonlinear curve fitting program with an orbit model, and you get the shuttle's orbital elements. Phil
chris@proper.UUCP (Chris Hayes ) (05/16/84)
<> A question..... As to the tracking cameras that NASA uses to track the shuttle after liftoff, etc.... Does the shuttle have any type of transponder for identification/tracking purposes, or is it all done by ground radar? Also, I was idly wondering how practical it might have been to put a ram/scramjet engine on the shuttle. The former type has no moving parts, will *ONLY* work well at mach > 2 velocities, and consumes relatively little fuel/thrust. It would seem like a good idea..... Tnx in advance... Chris Hayes ucbvax!dual!proper!chris