XPost: sci.space.shuttle
From: henry@spsystems.net
In article <5wNVb.1574$h44.295246@stones.force9.net>,
Ian Stirling wrote:
>> No, actually, "gyro" means "gyro" here. It's the high-precision sensors
>> that are giving trouble. The gyrodynes (I think) that actually produce
>> torque to rotate Hubble have been reliable.
>
>There seems to be talk on various pages about "2 gyro mode".
>How degraded is this?
I don't know quite enough about Hubble's guidance to be sure, but possibly
not at all, except for perhaps more headaches for the operations crew.
IUE was successively operated on two gyros, one, and none at all, although
that was an easy case because it was in GSO and hence in continuous contact
with the ground.
>Were the gyros brought down, and if so, did they all fail the same way?
They certainly brought the old ones down both times. I haven't seen a
detailed report; my understanding is that the analysis of the first batch
did conclude that they all died the same way and that the design has a
fundamental weakness.
>How long can the thing run open-loop? Are the gyrodynes "noisy", and this
>has to be nulled out over the short term.
>Might there be a way of just using star-tracking, although it
>probably would greatly restrict the target list.
I'm not sure how much the gyros are needed after locking onto a target.
The fine guidance sensors are optical in any case, and it may be just a
matter of having to get Hubble pointed in the right direction and more or
less motionless so they can lock on. *That* can probably be done with
limited assistance from the gyros, at the price of needing more help from
the ground and hence more TDRS time (to provide communications).
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. | henry@spsystems.net
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