From: lip@s1.gov (Loren I. Petrich)
Subject: What Progress in Opening Up Galileo's Antenna? (was Re: Galileo Update - 01/08/93)
Keywords: Galileo, JPL
Organization: LLNL
Date: Mon, 11 Jan 1993 03:20:17 GMT

In article <9JAN199318252344@kelvin.jpl.nasa.gov> baalke@kelvin.jpl.nasa.gov (Ron Baalke) writes:

>10. On December 29, after approximately 20 hours at the warming attitude, the
>DDA-5 windup/hammering activities commenced at 1455 UTC.  A total of 2160
>hammer pulses were executed along with three 20 second windup sequences. Data
>analysis indicated the ballscrew rotated approximately 360 degrees for a total
>ballscrew rotation beginning with the initial deployment attempt of
>approximately 6.4 rotations.  There was no indication of a rib release
>(see Special Topic No. 2).

	1 rotation added to 6.4 rotations.

	Not bad.

>11. On December 30, the spacecraft, under stored sequence control, was
>commanded back to a 5 degree off-sun attitude at approximately 1048 UTC.
>After the sun acquisition, sun gate data was collected to determine if an
>antenna rib is still obscuring the sun gate signal.  Preliminary data
>analysis indicates that the sun gate field of view is still obscured although
>the signature appears to have changed.  Initial analysis indicates that rib
>No. 2 may have moved out to a 43 degree angle.  Also, preliminary results may
>indicate that the antenna mesh is covering the sun gate field of view.

	"Rib No. 2"? What rib it is does not have much meaning unless
one knows which are the stuck ones.

	It was reported that 2 or 3 ribs had been stuck. If one of
them is now unstuck, then it's 1 or 2 to go, I suppose.

	Moving out to a 43-degree angle? Is that the angle that the
already-open ones are out to?

	"Signature appears to have changed" -- what's that?

>     Additionally, real-time commands were sent to open the star scanner (SS)
>shutter, reacquire celestial reference, and select scan type 6 to perform
>precise wobble estimation.  The wobble estimate indicated a change of 0.3
>milliradians which collaborated the motor current data indicating that no
>ribs released (see Special Topic No. 2).

	This change of 0.3 milliradians would presumably mean that the
ellipsoid of inertia has changed by some comparable fraction. I'm not
sure about Galileo's weight and dimensions, but I would presume that
if the spacecraft weighs 1 ton, then this wobble change corresponds to
a motion of a mass of about 300 grams across the dimensions of the
spacecraft.

>     After approximately two hours at the warming attitude, hammering of the
>HGA (High Gain Antenna) motors commenced.  Five 180 hammer pulse sequences
>were sent beginning at 2225 UTC and ending at 0442 UTC.  The motor hammering
>sequences were executed with the HGA motor temperature at 19.3 degrees C,
>29.8 degrees C, 34.4 degrees C, 36.2 degrees C, and 40.6 degrees C.
>Preliminary analysis indicated that the ballscrew was stalled with no
>appreciable ballscrew rotation.  There was some suggestion of minor rotation
>with the HGA motor temperature at 29.8 degrees C.  There was no indication of
>a rib release (see Special Topic No. 3).

	Disappointing.

	[Later such HGA motor hammering mentioned...]

	Any further results?

-- 
/Loren Petrich, the Master Blaster
/lip@s1.gov
Newsgroups: sci.space