To:sot_shift from: Dan Schwartz date: 24 July 99, 1120 EDT Subject: SOT shift report, Shift A2 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii -------- Shift A-2. 205:04:00 GMT 1201am 24 July 99 SOT Lead DAS Spac/Aspect WAP FOT/Sci liason EM HRC MVZ,AR ACIS PPP (Times will be given in GMT on day 205) PLAN Review/approve/upload/execute IPS-0 Dry run burn. Decide on an IPS burn scenario to recover from low IUS injection apogee. Carry out earth scan #1. Troubleshoot Diego Commanding problems. (In progress at end of shift) Monitor ACIS focal plane temperatures. (45min at 04:30; 5min at 12:31) Perform battery trickle charge adjustment. (Done ~0500) EVENTS We had a discussion to plan the IPS burns scenarios. Change in burn sequence was caused by the decreased period (24h 17m 18s) at our decreased apogee of 72065 km. This alters our ground station coverage times, and forces delay of the IPS-3 burn (the first burn at perigee) in order to obtain coverage. Four generic options were discussed: a) Delay three revs, get an optimum IPS-3 burn b) Delay two revs, burn slightly non-optimal, i.e., not centered exactly at perigee c) Increase IPS-1 duration, decrease IPS-2 duration to try to increase the perigee for the optimum IPS-3 case d) Combine IPS-1 and IPS-2 burns to increase apogee earlier. Option d) was deemed risky since we don't yet know the actual IPS performance. Option c) gave negligible performance enhancement (few hundred km of perigee, ~0.03% increase in time above 60,000km). An option b) has been selected, which gives a final 140,000 x 10134km orbit, and final IPS burn at MET 12/15:58, for a -15degree off perigee burn. This compares to an option a) perigee of 10255km and final IPS burn at MET 13/17:39. (The "baseline" plan had been for 11097km perigee and final burn at MET 10/18:18). So events will be about 2 days later than listed in the baselined Phase 1 timeline. (Note: PET is about 9hrs 18min less than MET). All IPS burn scenarios used the same amount of fuel, with 140# expected to be left for possible MUPS use late in the mission. IPS burn dry run at ~0730. Complete 0839. MUPS thrusters 1 & 4 have an apparent underperformance. See Flight note 031. Executed CAP 37A at ~0900 to combine test of those thrusters with a test of the auto-unloading of momentum. Needed to do this to be sure auto-unload works, before perigee. SSR dump, completes about 0910. No CRC errors. LGA swap at ~10:45. Good data from Earth Sensor scans, both sensors see earth. NOTES/ISSUES/PROBLEMS We can communicate with the duty scientists via black phone at 6-7003. As of now, they don't have voice mail setup, so if they are on the phone we'll just get a "voicemail not connected" message. Also note that email should be addressed just to dutysci and NOT to dutysci@cfa although that address is given on the sot webpage http://asc.harvard.edu/mta/sot.html Call 496-7030 for a Chandra Status message. This number will report updated SHIFT CHANGE times! Planned momentum dump at PET 0/14 won't be done because such a small momentum has accumulated. We had some questions on whether the ACIS focal plane temp has stabilized, since we do not directly see any data from the control heaters. The temperature is holding at -118.9 C. The setpoint is -120.6 C However the cold radiator is also holding at -127.9 deg C. SO this may be indicating that we have "bottomed out" the cooling capability. The implications need investigation: we may want to operate the focal plane slightly warmer, to maintain active control. We may anticipate even warmer operation in the out-years due to degradation of the radiator surfaces over the life of the mission. We may need to experiment to see if we are as cold as possible: set ACIS focal plane to -130 deg C -- then the temperature will decrease, unless we are already as cold as possible. Attitude error and rate monitor safing was disabled, discovered ~0925. It will be investigated why. RCS thruster valve temperatures are running too hot with the cat bed heaters on continuously. Need to keep them off, and turn ON 60 minutes before RCS thruster modes. See CAP 38 and flight note 42. A new tool, wheel_momentum, was built and installed in the ACA EGSE station coot. It rotates 6 wheel speeds into angular momentum (ft-lb-sec) in the 3 principal axes. SOT LEAD workstation is to be upgraded to an Ultra 5 during the upcoming shift change. ------------------------------------------------------- Dan Schwartz, MS #3 das@head-cfa.harvard.edu phone: (617)495-7232 FAX: (617)495-7356 cell phone: (617)512-5627 pager: 800-759-8352 PIN 1636502 or e-mail 1636502@skytel.com -------------------------------------------------------