ACE Weekly 05/15/2012 - 05/21/2012 All ACE spacecraft subsystems are performing as expected. ======================================================================== Orbit/Attitude: No maneuvers were completed this week. The next attitude maneuver and Station-Keeping #61 are scheduled for Friday 05/25/2012. ======================================================================= OCRs: None ======================================================================== Activities: Data Capture: 100% DOY 134-141 2012 WS1, the 18-meter antenna in White Sands, NM, is now getting range data consistent with DSN's Goldstones stations (+6.8 meter bias). There are still several outstanding issues, including: 1) during previous testing the MMOC needed to disconnect & reconnect in-between sending commands for them to be radiated, 2) WS1 handling of downlink data rate changes and 3) updating MMOC procedures and tools: clock calibration, schedule retrieval, TLM & CMD conversion tools, data forwarding to NOAA SWPC & ASC and pass procedures. Background Information on Downlink Data Rate Changes For normal operations, ACE transmits at 2 data rates. The low data rate (498bps) provides Real-Time Solar Wind (RTSW) data for NOAA SWPC's (Space Weather Prediction Center) network of ~12m antennas. During the ~3.5 hour DSN pass (34m antennas), the spacecraft is switched to the high data rate (87648bps) for the recorded science data. There are pros and cons for making the data rate change at the beginning of the pass via ground command or onboard time-tag command. Onboard Time-tag Command Using an onboard time-tag command to switch to the high data rate before the DSN pass means that the ground station only needs to configure for one data rate. This was done from 03/20/1998 to 11/02/2004. However, if there are station problems or if the DSN pass has been rescheduled, then NOAA SWPC wouldn't be receiving any ACE data (the network of ~12m antennas cannot process the high rate data). If the DSN pass had been rescheduled and the onboard timer was not reloaded, then the DSN station would need to configure for the low data rate at the beginning of the pass and then switch to the high data rate after the ground command had been sent. Ground Command Starting on 11/03/2004, each DSN pass started at the low data rate and was commanded from the ground to the high data rate. This provided more consistent operations and reduced data loss by NOAA SWPC (~5 hours/year). But, it also required a DSN operator to reconfigure the ground equipment and it delayed the science data playback by 2-4 minutes. Why Mention This Now? To WS1's credit, they are updating and testing their equipment so that it can determine which of the two data rates it is receiving. (DSN is also looking at reducing the work performed by the station operators which includes data rate changes and other activities.) Dealing with the data rate change is just one of many decisions that goes into configuring ACE for WS1. And the length to which it is discussed in this week's report shouldn't be used as a gauge of its importance. It just provides a little background information on ACE. Some other notes: In 2011, there were 9 DSN passes with problems at beginning of track that delayed activities from 13-120 minutes and 3 passes that were rescheduled at the last minute. This averages to only 1 problem per month where onboard data rate commands at the beginning of the DSN pass would have an impact. Also, in all scenarios, the command to switch from the high data rate to the low data rate at the end of the DSN pass is always done via onboard time-tag command. ======================================================================== Anomalies: Update on AR#S12-0001 S-ACE-0639 SWEPAM-E Overcount Alarm The SWEPAM-Electron Overcount Alarm has flagged continuously since DOY 135. The instrument team is working the next course of action, but their time is limited. IMPACT: The instrument automatically reduces voltages when the overcount alarm occurs.