ACE Weekly 11/08/2011 - 11/15/2011 This week's report covers 8 days. Problems with the downlink during this week's Solar Exclusion Zone transit (SEZ) resulted in data loss. All ACE spacecraft subsystems are performing as expected. ======================================================================== Orbit/Attitude: Type Attitude Attitude Date 11/11/2011 11/14/2011 DOY 315 2011 318 2011 Thrusters 2R 4R+ 4R- 2R 4R+ 4R- Duration 22:07 min 3:40 min Start 20:35:56z 22:02:35z Stop 20:58:03z 22:06:15z HGAStart -7.93deg +5.84deg HGAStop +8.50deg +3.43deg SunStart 8.74deg 6.37deg SunStop 7.62deg 4.07deg SpinStart 5.0300rpm 5.0364rpm SpinStop 5.0364rpm 5.0372rpm Nutation 0.07deg 0.11deg Firing 112 pulses 19 pulses FuelUsed 0.34201lbs 0.0680lbs FuelRemain 125.7080lbs 125.6400lbs FinalSCMass 1359.968lbs 1359.900lbs A second maneuver was performed on Monday 11/14/2011 to align the spacecraft's antenna more closely with Earth. The HGA angle was moved from 5.84 to 3.43deg and the SNR increased by 3dB. This improved the chances of obtaining high-rate data on Tuesday 11/15/2011. The spacecraft will drift down to a sun angle of 3 degrees over the next few days (See MOCR 371). The next attitude maneuver is scheduled for Monday 11/21/2011. ======================================================================= OCRs: DOY 318 (11/14/2011) MOCR 371 - 4 degree sun constraint Approval was given to allow the spacecraft's sun angle to drift below the 4 degree sun constraint. When ACE is along the Sun-Earth line (small Sun-Earth-Vehicle angle), it is not possible to have the spacecraft antenna pointing directly back at earth AND have the sun angle be greater than 4 degrees. (see ascii figure below) Large SEV angle Small SEV angle Sun Sun \ | \ | ACE | \| \ | ACE \ | |\ \| | \ Earth Earth The known reason for maintaining the 4 degree sun constraint is that small sun angles cause spacecraft nutation to have a larger affect on the sun pulse timing by a factor of 1/tan(sun angle). Nutation affecting the sun pulse timing has the following impacts: (1) Maneuvers starting with a small sun angle have greater error in reaching the target. (2) Maneuvers ending with a small sun angle degrade the science data for a longer period. However, there are no known reasons for not allowing the spacecraft to drift through the 4 degree sun constraint when there is no nutation. ======================================================================== Activities: SOLAR EXCLUSION ZONE The following table provides the Sun-Earth-Vehicle (SEV) angles and the Signal to Noise Ratio (SNR) of the downlink signal. The solar activity was higher during this transit than in previous transits including the August 2011 transit. Date DOY DSS Time SEV angle hi-rate SNR hi-rate lock? --------- --- --- ---------- --------- ----------- ------------- Sat 11/12 316 D27 1455-1825z 0.82-0.76 -5 to +2dB after 1700z Sun 11/13 317 D34 0015-0115z 0.69-0.67 +1 to +2dB yes Sun 11/13 317 D27 1950-0000z 0.46-0.44 -11 to -3dB no Mon 11/14 318 D65 0820-0910z 0.42-0.42 -11dB no Mon 11/14 318 D27 2040-2320z 0.48-0.50 -9 to -6dB no Tue 11/15 319 D24 1955-2230z 0.77-0.80 +5 to +7dB yes The DOY 316 problems were unexpected and resulted in ~2.5 hours of data loss. DSN antenna availability has been reduced due to the GRAIL mission. Unfortunately, TDRSS 10 declared a spacecraft emergency and took the ACE pass on Tuesday 11/15. Fortunately, DSN Maintenance released DSS-24 and 25 out of 43 hours of data was recovered. Some of the data loss is covered by realtime ADC and Science data. The following table provides the data gaps for the week. Weekly Data Capture: 88.30% CRIS, EPAM, MAG, SWEPAM-Ion & SIS 89.78% SWEPAM-Electron, SWICS, SWIMS & ULEIS DOY Gaps seconds Notes --- ----------------- ------- ----------- 315 20:31:31-20:31:32 2 ADC covers 315 20:33:23-20:33:24 2 ADC covers 315 20:53:01-20:53:02 2 ADC covers 316 14:27:42-16:30:37 7376 no data 316 16:30:38-17:00:29 1792 ADC covers 316 17:00:30-17:12:11 702 intermittent data 316 17:12:12-17:15:10 179 ADC covers 317 17:16:15-19:58:36 9742 no data 317 19:58:37-20:21:02 1346 ADC covers 317 22:26:07-00:00:07 5641 ADC covers 318 00:00:08-12:12:49 43962 no data Total data loss 17 hrs 9 min 42 sec no data & intermittent data 2 hrs 29 min 24 sec ADC covers -------------------- 19 hrs 39 min 6 sec The ADC data format includes data from 4.5 of the 9 instruments CRIS, EPAM, MAG, SWEPAM-Ion & SIS. Not included are SWEPAM-Electron, SWICS, SWIMS, SEPICA & ULEIS. Additional antenna time is being scheduled for the Feb 2012 Solar Exclusion Zone transit. NOAA Space Weather Prediction Center (SWPC) started having gaps in coverage beginning on DOY 316 0700z. SWPC had very minimal data coverage from DOY 317 0700z to DOY 319 0700z. During these 48 hours, DSN provided 8 hours of coverage and WCDA (12m, Wallops) provided 5.5 hours of coverage. NICT (11m, Japan) and DLR (4.5m, Germany) were not able to provide coverage during this period (317-0700z to 319-0700z). ======================================================================== Anomalies: DOY 316 11/12/2011 S-ACE-0633 G11-0059 DSS-27 CMG problems "Lost Connection to User" problem (1509z) with the ground station's CMG (Command Modulation Generator) prevented commanding ACE to the medium data-rate. The problem was resolved at 1630z (DR#11209). The same problems also occurred on DOY 318, but was resolved within 5 minutes (DR#G112119). IMPACT: 35 minute delay in commanding to medium rate. 35 minute data loss to NOAA SWPC and Science teams.