My best guess is that it was just a matter of bad timing jumping us out of our spin rate “groove”.
It hasn’t been a problem to date, but every time we re-set the clock we see a jump in spin rate, maybe up to 4.3 rpm or something like that, as the estimator tries to make sense of the jump in timing between
the ACS time (which updates right when we set the clock) and star tracker time (which updates a minute or so later). Normally, this sort of thing cleans itself up within 10 minutes or so.
My hypothesis is that the estimator decided that the best explanation for what it saw, due to unfortunate timing, was that the spin rate had jumped significantly. And then once it got into that regime it got
stuck there, trying to fit all of the star tracker data into the context of that spin rate regime. So instead of assuming that the next star tracker reading was a fraction of a rotation away from the last it assumes it’s a few rotations plus a fraction of
a rotation away from the last.
Thus, once we got it back into the 4.17-ish rpm groove, it was able to latch back on and interpret the star tracker data correctly.
In some sense, I’m surprised this sort of thing hasn’t happened before given the time jump. Either repeating what we did or simply restarting the estimator should clear it up if it happens again.
-Ryan
From: NIgel Angold <nangold@princeton.edu>
Sent: Tuesday, August 16, 2022 11:00 AM
To: Perry, Timothy E [US] (SP) <Timothy.Perry@ngc.com>; Tyler, Ryan S [US] (SP) <Ryan.Tyler@ngc.com>
Cc: Carol Weaver <carol.weaver@unh.edu>; Ibex Mission Operations <ibexops@gmail.com>; ISOC at New Hampshire <isocops@lists.sr.unh.edu>; Ken Fairchild <fair-play@comcast.net>; Ken Fairchild UNH <Ken.Fairchild@unh.edu>; Nigel Angold <angoldconsulting@earthlink.net>;
Wesley, Sheral R [US] (SP) <Sheral.Wesley@ngc.com>; Wynn, Reese [US] (SP) <Reese.Wynn@ngc.com>
Subject: EXT :Re: IBEX Goat Herder for 15 & 16 August 2022
Any idea what might have caused the spin rate to jump to 30.2 rpm? New razor?
Thanks,
Nigel