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
Any idea what might
have caused the spin rate to jump to 30.2 rpm? New razor?
Thanks,
Nigel
All,
We
completed the series of 3 USAK01 contacts for testing changes to
improve our tracking data. During the USAK01 contact 15Aug22 @18:00 I
set the spacecraft clock and the star
tracker spin rate jumped to 30.2 rpm. This value stayed there for the
duration of the pass. On the following USAK01 pass @20:30 we changed the
Kalman filter input to ground command and set the values to zero and
disabled the star tracker input. Using just
the static Z rate the spin rate started to come down but it never
settled out. On the final pass of the night USAK01 08/16/22@02:30 we
enabled the star tracker spin rate and disabled the static z rate and
the value stabilized at the 4.177 spin rate and residuals
were low. We changed the Kalman filter input back to STA_PCT_VAL and
the ACE looked nominal. We watched it for the duration of the pass and
it stayed solid.
Tasks Accomplished:
SSR Dump -> Dump New
Set Spacecraft Clock
Reset FDC Totals
Reset 18 Day timer
CAR # 1258 Orbit 579 ATS uplink
IBEX_2022_237_o0579a_v001 98
commands
CAR 1257 Redump Orbit 576 SSR Data – Dumped 17136 blocks of 26390 blocks
Will dump the rest on the next
orbit
Star tracker issue troubleshooting
Results from the Inertial Maneuver:
Q1 -0.48704600 ActNor.EstInrToBdy[0]
Q2 0.36519700 ActNor.EstInrToBdy[1]
Q3 0.79329000 ActNor.EstInrToBdy[2]
Q4 0.01037000 ActNor.EstInrToBdy[3]
GPS sec 1344617486 ActNor.EstTime
UTC time
08/15/2022 16:51:12 output
MPS Diff
0.800 deg
MPS Cmd Vector X -0.769676000
MPS Cmd Vector Y 0.589292000
MPS Cmd Vector Z 0.245629000
CSS Angle TLM 0.454134
CSS Sun-Pointing Angle 0.908268
11 Aug 22 @02:00:00
CSS Angle TLM 0.775817
CSS Sun-Pointing Angle 1.551634
15 Aug 22 @16:30:00
Pre-Burn
Thruster 1 3888 11 Aug 22 @02:00:00
Thruster 2 3792
Thruster 3 4416
Thruster 4 4512
Post-Burn
Thruster 1 4176 15 Aug 22 @16:30:00
Thruster 2 4080
Thruster 3 4720
Thruster 4 4816
Number of Pulses
Thruster 1 288
Thruster 2 288
Thruster 3 304
Thruster 4 304
Thruster Pairs
Thruster 1 & 2 576
Thruster 3 & 4 608