SummaryObsid 4977 is a 79 ksec ACIS-S imaging observation of Abell 2029 that began at 2004:008:12:57:38 (start of KALMAN interval). In this observation there appears to be an anomaly in the star acquisition sequence: the ACA acquired a star in slot 7 which is inconsistent with the commanded star catalog parameters. This is the first such case to be identified. The incorrect star led to the ACA tracking two ACQ stars for 8 seconds in the KALMAN interval, at which point the OBC intervened and sent commands to acquire the correct guide stars. The 8 seconds of unexpected data prevent proper completion of automatic aspect pipeline processing and force manual processing.DetailsThe starcheck output for this catalog is shown below (but note that the entries for slots 4 and 7 have been highlighted in red for visual clarity). The key information is that for slot 7 the acquisition box for the BOT star is centered at (Yag,Zag) = -541,478 arcsec, with a box half-width of 120 arcsec. However, from PCAD engineering telemetry, the actual acquired star in slot 7 is at (Yag,Zag) = -1045,-1554. This coincides with the commanded position for slot 4. The other star acquisition slots show no unusual behavior.In slot 4 the ACA acquired a spoiler star of comparable magnitude which is very near the edge of the search box. This star is clearly seen as the point on the lower-left side of the box labeled with index 5 on the star field plot below. This corroborates the picture from engineering telemetry that the ACA was tracking in slot 7 the ACQ star which was intended for slot 4. The position of the acquired star was verified in a way independent of the OBC telemetry by inspecting the ACA image telemetry. This confirmed that the ACQ star in slot 7 is centered near (-1045,-1554) arcsec, and so the problem is not in the OBC telemetry. We directly confirmed that the starcheck output which gives the search box angles matches the values in the Backstop output. No previous instances have been identified where the ACA acquired a star at a position outside of the nominal commanded search box. As part of the study on acquisition star success rates, we have compared the expected position with the actual position for all acquisition stars since the year 2001. No cases of a large offset were seen. The anomaly occurred at a time approximately 24 hours before the radiation shutdown by SCS107 at 2004:009:14:29:11. However, inpsection of the ACE rates at the time of the acquisition anomaly shows no sign of excessive rates. ExplanationAt this time we have no meaningful explanation for the anomaly. Examining the chain of events, possibilities include:
Star catalogOBSID: 4977 Abell 2029 ACIS-S SIM Z offset: 0 Grating: NONE RA, Dec, Roll (deg): 227.746478 5.734288 62.487652 Dither: ON Y_amp= 8.0 Z_amp= 8.0 Y_period=1000.0 Z_period= 707.1 BACKSTOP GUIDE_SUMM OR MANVR DOT MAKE_STARS MP_TARGQUAT at 2004:008:12:45:34.974 (VCDU count = 9176235) Q1,Q2,Q3,Q4: 0.17054824 -0.49101853 -0.77034055 0.36930954 MANVR: Angle= 10.45 deg Duration= 641 sec Slew err= 25.8 arcsec MP_STARCAT at 2004:008:12:45:36.617 (VCDU count = 9176242) ---------------------------------------------------------------------------------------- IDX SLOT ID TYPE SZ MINMAG MAG MAXMAG YANG ZANG DIM RES HALFW NOTES ---------------------------------------------------------------------------------------- [ 1] 0 1 FID 8x8 5.797 7.000 8.000 940 -1722 1 1 25 [ 2] 1 4 FID 8x8 5.797 7.000 8.000 2158 181 1 1 25 [ 3] 2 5 FID 8x8 5.797 7.000 8.000 -1808 175 1 1 25 [ 4] 3 44959056 BOT 6x6 5.797 9.682 12.406 -1880 467 20 1 120 2 [ 5] 4 44959728 BOT 6x6 5.797 10.242 13.000 -1037 -1553 20 1 120 2 [ 6] 5 44961784 BOT 6x6 5.797 10.342 11.844 -594 -1834 20 1 120 2 [ 7] 6 44966344 BOT 6x6 5.797 5.924 7.422 -2123 2241 20 1 120 2 [ 8] 7 45482024 BOT 8x8 5.797 10.421 13.172 -541 478 20 1 120 2 [ 9] 0 44961248 ACQ 6x6 5.797 10.589 12.641 -1565 1458 20 1 120 3 [10] 1 44957744 ACQ 6x6 5.797 10.645 12.156 -1948 1120 20 1 120 2 cp [11] 2 45490016 ACQ 8x8 5.797 10.027 12.781 376 -234 20 1 120 1 >> WARNING: Magnitude. [ 7]: 5.924 >> WARNING: Magnitude. [ 5]: 10.242 >> WARNING: Search spoiler. [ 5]- 44960208: Y,Z,Radial,Mag seps: 117 71 137 -0.4 >> WARNING: Magnitude. [ 6]: 10.342 >> WARNING: Magnitude. [ 8]: 10.421 >> WARNING: Magnitude. [ 9]: 10.589 >> WARNING: Marginal star. [10]: B-V = 0.700, Mag_Err = 0.41, Pos_Err = 0.30 >> WARNING: Magnitude. [10]: 10.645 Figure of Merit : -5.62 Stars Expected : 6.28 Engineering telemetryEngineering telemetry reveals that during acquisition, slot 7 acquired the star which had been intended for slot 4, and that slot 4 acquired a spoiler star near the edge of its search box. The detailed data and timeline are shown below. The Time is in seconds, where 189953884 is 2004:008:12:57:00.Slot 4 Slot 7 Cmd = -1037 -1553 (yag,zag) Cmd = -541 478 Comment Time Slt 4 Slt 7 Yag Zag Yag Zaz AOACASEQ --------- ---- ---- --------- ---------- ---------- --------- ----- ------ 189953883 SRCH SRCH -3276.80 -3276.80 -3276.80 -3276.80 AQXN 189953884 SRCH SRCH -3276.80 -3276.80 -3276.80 -3276.80 AQXN 189953885 SRCH TRAK -3276.80 -3276.80 -1044.60 -1553.650 AQXN 1 189953886 SRCH TRAK -3276.80 -3276.80 -1044.60 -1553.650 AQXN 189953887 TRAK TRAK -1163.2250 -1633.4250 -1044.750 -1553.80 AQXN 2 189953888 TRAK TRAK -1163.2250 -1633.4250 -1044.750 -1553.80 AQXN ... 189953927 TRAK TRAK -1163.350 -1634.30 -1045.20 -1556.5250 KALM 189953928 TRAK TRAK -1163.450 -1634.6250 -1045.550 -1556.70 KALM 189953929 TRAK TRAK -1163.450 -1634.6250 -1045.550 -1556.70 KALM 189953930 SRCH SRCH -3276.80 -3276.80 -3276.80 -3276.80 KALM 3 ... 189953937 SRCH SRCH -3276.80 -3276.80 -3276.80 -3276.80 KALM 189953938 TRAK TRAK -1045.350 -1557.3750 -549.40 472.90 KALM 4 189953939 TRAK TRAK -1045.350 -1557.3750 -549.40 472.90 KALM 189953940 TRAK TRAK -1045.350 -1557.7250 -549.1250 472.7250 KALM 189953941 TRAK TRAK -1045.350 -1557.7250 -549.1250 472.7250 KALM Comments: 1. Star which should have been acquired in slot 4 is instead acquired in slot 7. This is NOT compatible with commanded search box for slot 7. 2. A spoiler star near the edge of the slot 4 search box is acquired 3. OBC has set the KALMAN flag, but the star positions in slots 4 and 7 are wrong, so it commands a new guide search 4. Correct stars acquired Aspect Information main page Comments or questions: Aspect Help Last modified:12/27/13 |