ACE Weekly 05/01/2013 - 05/07/2013 All ACE spacecraft subsystems are performing as expected. ======================================================================== Orbit/Attitude: Type Attitude Date 05/07/2013 DOY 127 2013 Thrusters 2R 4R+ 4R- Duration 17:37 min Start 14:13:40z Stop 14:31:17z HGAStart -7.85 deg HGAStop +8.57 deg SunStart 7.63 deg SunStop 13.15 deg SpinStart 5.0929 rpm SpinStop 5.0977 rpm Nutation 0.14 deg Firing 90 pulses FuelUsed 0.2653 lbm FuelRemain 114.3452 lbm FinalSCMass 1348.605 lbm The next attitude maneuver and a spin down maneuver are scheduled for Tuesday 05/14/2013. This week's attitude maneuver (0.27 lbm) is larger than usual (0.10-0.16 lbm). To maintain larger sun angles, the spacecraft is kept pointing away from the ecliptic plane, and the large maneuver is because the spacecraft crossed the ecliptic plane on Monday (5/6/2013; DOY 126). This will happen every 3 months (last occurrence 2/12/2013). Note, the size of the "ecliptic crossing attitude maneuvers" will decrease as the L1 orbit continues to open up. Spin Rate Background Information The spacecraft spin constraint is 4.9-5.1 rpm. Attitude maneuvers increase the spin rate and station keeping maneuvers decrease (to a lesser extent) the spin rate. Every 2-3 years, a spin down maneuver is performed (4/21/2006, 9/2/2008, 6/27/2011). Next week's spin down maneuver will target 4.95 rpm. The S3DPU is the documented driver for the 4.9-5.1 rpm spin constraint. The S3DPU (SWICS/SWIMS/SEPICA Data Processing Unit) captures the most data when the spin rate is 5.0 rpm. The S3DPU inserts dummy frames if the spin rate is less than 5.0 rpm and drops data if the spin rate is greater than 5.0 rpm. There may be more spin rate issues with other instruments that we are not aware of. The star scanner can work at a wider range of spin rates. But if the star scanner is started (or rebooted, which has never happened) and the spin rate is not within 4.9-5.1 rpm, then a "SetYRate" command is needed to acquire stars. ======================================================================== OCRs: None ======================================================================== Activities: Data Capture: 100% DOY 118-125 2013 On Tuesday 5/7/2013 (DOY 127), DSN performed scheduled maintenance on their Data Capture and Delivery (DCD) system. Telemetry to the MOC was delayed for 5 minutes (1501-1506z) and backfilled when the maintenance was completed. No problems were found. ======================================================================== Anomalies: None