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Monday 2 August 1999 7.00am EST
| The Chandra mission continues to proceed nominally.
The following is an overview of the events that occurred over the last 24 hours. Completed On-Orbit software load of IU-A, dump and compare verified it OK. Continued characterization tests of ISIM flexure over temperature at spacecraft attitudes near the solar avoidance limit (45). The objective is to determine temperatures as Chandra approached the solar avoidance-limiting attitude and evaluate workarounds. Continued ACIS calibration using internal sources. Attempted to turn on HRC high voltage, but the pressure in the instrument remains too high to allow full turn on of high voltage. The Optical Bench Vacuum Gauge reading is 9.7 x 10EE-6 torr. The Chandra operations team has studied the results of Integral Propulsion System (IPS) burn #3 (conducted on Liquid Apogee Engine (LAE) #1 and #3) and discovered that the RCS attitude control response was greater then expected. That, coupled with a post burn performance analysis indicates that LAE #3 developed approximately 2.5 pounds lower thrust than LAE #1. This is consistent with the lower (but acceptable) apogee attitude. Given that the root cause of the lower thrust is unknown, and to enhance a safe completion of the Chandra transfer orbit phase, it was decided to perform the remaining IPS burns on LAEs #2 and #4. To allow controllers time to develop and rehearse procedures and develop software patches to safely perform the IPS burns on these different engines, IPS burn # 4 will be performed at 12:36 am EDT Wednesday, August 4. Since this will be the first burn on these LAEs, IPS burn 4 will be a five-minute trim burn to calibrate the performance of these engines. IPS burn 5 is planned to be a 6 minute burn to raise the perigee to the target apogee and is scheduled for the next apogee pass on Saturday, August 7. Events scheduled for the next 24 hours
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Revised: July 08, 2022