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Mission Status 2009
Kevin V. Gilliland Stardust Spacecraft Team
December 2, 2009
All subsystems are nominal. At the start of the first pass in more than three weeks, we found the spacecraft in Safe Mode. The spacecraft team returned Stardust NExT to nominal operations yesterday afternoon, December 2.
Safe Mode entry was requested by the Attitude Control Fault Monitor. The attitude controller was correctly maintaining pointing control within the deadband of the Z-axis. The fault monitor, however, using an independent check, incorrectly determined the attitude was beyond the deadband limit. The fault monitor’s check is based on a small-angle approximation. While the controller was commanding the thrusters as designed, the approximation from the fault monitor requested a Safe Mode entry when none was required. In the future, this problem will not occur since contact periods will be more frequent, and smaller deadbands will be used. During Safe Mode, the IMU was powered on for less than 7 minutes. Sequence SN031 is now the active sequence, and the next contact is Monday, December 7.
December 9, 2009
All subsystems are nominal. The most recent contact was Tuesday, December 8. Propulsion and Navigation engineers are meeting Thursday, December 10, to discuss the results of the Mass Assessment Experiment (MAX). The objective of the experiment was to determine the remaining fuel mass. Using heaters on the spacecraft’s fuel tanks, the tank was heated and cooled while monitoring the tank’s response to changes in temperature. Nominally, tank temperatures are near 8 degC; during the experiment the temperature cycled around 21.5 degC. The estimate of remaining fuel mass is desired to allocate reserves for the remainder of the mission and determine a fuel budget for upcoming trajectory correction maneuvers. The next contact is Sunday, December 13.
December 21, 2009
All subsystems are nominal. Small forces data and thruster on-time trends show efficient control using string 2 thrusters. Star Camera solutions have been good, with few outages and low noise evident in the control responses. The spacecraft often settles in the +Y and +Z corners of the deadband. We have had three contact periods since the previous report. The most recent contact was today. The spacecraft’s distance to Earth is more than 218,000,000 miles (351,000,000 kilometers) and increasing. The range to the Sun is 159,300,000 miles (256,300,000 kilometers) and decreasing. The Sun-spacecraft-Earth angle is approximately 22 degrees and decreasing. A parameter used by safing has been updated to ensure power-safe Sun coning brings the antenna near Earth, in the event that the Star Camera is unable to provide an attitude solution. Background sequence SN031 is the active sequence. SN032 is on board, and will become active on Sunday, December 27. The next contact is Friday, December 18.
December 23, 2009
All subsystems are nominal. The most recent contact was Friday, December 18, and the next will be Wednesday, December 30. This week, the team completed a review of all telemetry alarms. The alarm review was the last step in a complete review and update of downlink processes, tools, procedures, and data. Propulsion and Navigation engineers have been working to plan the use of fuel for required comet approach and trajectory correction maneuvers. The team has also begun defining the encounter sequence parameters and timing. While the Tempel-1 encounter is more than a year away, the test program will begin early next year. The big event of 2009 was the Earth flyby, including Nav Camera calibrations and maneuvers on the cruise toward Earth. Because of the Earth-Spacecraft-Sun geometry, we spent months out of contact once we were beyond the range of the Low Gain Antenna. Attitude control using string 2 thrusters continues to perform well, after more than 8 months. The switch from string 1 to string 2 and some controller efficiency improvements were a highlight of the year. Systems and Real-Time Operations engineers successfully uplinked hundreds of commands during the year, and ensured successful downlink of telemetry. To date, a complete record of 68,358 small forces data packets have been received since the beginning of the year, with no gaps. Several of the team member families welcomed new additions throughout 2009. So ends 2009, with a healthy spacecraft and the team looking ahead to Tempel-1.
