Monday 22 May 2000 8.30am EDT
|During the last week, Chandra completed the observing schedule as planned.
This week's loads were rebuilt on 5/15 after noting a failure to acquire 3 of the 5 acquisition stars for an observation (Q0059-2735) on 5/15. Acquisition Stars had also been dropped by the Aspect Camera on a number of other observations over the weekend. If the number of stars acquired falls below 2 then the spacecraft will stop the daily load and transition to bright star hold. Engineering assessment indicated that the aspect camera performance had not changed, and that the likely cause was a recent change to the parameters used by the OFLS in determining the faint limit for acquisition stars. The change was made in conjunction with the installation of a new star catalog and was based on analysis of prior on-orbit data. The loads for the remaining part of the week were rebuilt using an increased error term to avoid the possibility of a bright star hold. The loads were uplinked without impact to spacecraft operations, and the remaining acquisitions for the week were made as expected. Further analysis is underway to determine the optimal error terms for use by the OFLS.
The first HETG insertion and retraction commanded from the daily load using the B-side MCE was completed successfully for the 5/18 observation of Ex Hya. Telemetry indicated that both the insertion and retraction were nominal. Operations will continue using the B-side MCE while other approaches for returning A-side redundancy are assessed.
Preparations were completed for the 4th ACIS Squeegee mode test scheduled for 5.30pm EDT on 5/22. This test will include initial flushes of the CCD to remove charge built up while the CCD is not being clocked in order to remove a bias instability seen during the earlier on-orbit tests. Two runs will be performed: a 16 row squeegee with a 32 row exclude window, and a control run.
The planned observations for the coming week are as follows.
PSS 1435+3057 ACIS-S May 21 Cen Cluster ACIS-S BHXB (Outburst Decay) ACIS-S/HETG May 22 Radiation Belts NGC 6652 HRC-I NGC 6441 HRC-I Ophiuchi Mosaic #4 ACIS-I May 23 1735-269 ACIS-S G21.5-0.9 (a series) ACIS-S NGC 5846 ACIS-S May 24 Radiation Belts Abell 2104 ACIS-S May 25 1217+301 HRC-I May 26 Cygnus A ACIS-S M31 (N, S, Center) HRC-I Q2345+007 ACIS-S AXAF Southern Deep Fld ACIS-I Radiation Belts May 27 E0102-72.3 ACIS-S May 28 Q1127-145 ACIS-S
All spacecraft subsystems continued to operate nominally.
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