STARDUST Status Report
5 Oct 2001
(Source: Jet Propulsion Laboratory)
There were two Deep Space Network (DSN) tracking passes in the past week and all subsystems are performing normally.
Data sent back from the spacecraft showed that the large solar flare last week caused forty-four star camera outages of up to 25 seconds, compared to only one or two normal outages per week of less than 5 seconds. The on-board fault protection is designed to handle an outage of up to five minutes.
Stardust is currently at 2.35 AU from the Sun, the furthest any solar-powered spacecraft has flown. Next April, Stardust will be 2.72 AU from the Sun and the power subsystem was designed to have margin at this distance. The battery operating points of maximum state of charge and state (SOC) of charge level to trigger recharge were increased for the upcoming deep space operations. The pre-launch battery design value was 34 volts at full charge while we are now operating at about 32 volts, still providing margin at this large distance from the Sun.
Previously, when the battery SOC reached 100%, the battery was allowed to discharge until the SOC reached 95%. At 95% SOC the battery was then commanded to re-charge back to 100% using a trickle charge (0.125 amps). This 5% discharge helps keep the battery cells active and in good condition during normal cruise. The operating points of the battery were changed to provide additional capacity and voltage by increasing the upper SOC limit to 108%. The battery now cycles between 108% and 107%. The battery voltage increased to 32.1 volts and the SOC was at 107.3% by the end of the DSN pass. It is anticipated the average battery voltage will be 32 volts, providing additional power. The small depth of discharge is not a concern, as the battery will be heavily used to provide power during DSN passes for the next year. Next April when Stardust is at maximum distance from the Sun, the maximum communication time is expected to be just over two hours and will leave the battery SOC at 60%, keeping the battery cells alive and in good condition. On-board fault protection is design to take action only if the SOC reaches 50%.
There was an excellent collaboration between Stardust and Deep Space 1 as it successfully flew by the Comet Borrelly. Stardust shares the optical navigator and flight software being used aboard both spacecraft to track the comet nucleus during flyby. This worked exceptionally well, as the exciting images returned by DS1 showed. Also, Stardust's project scientist, responsible for computing the cometary dust environment and nucleus brightness for choosing camera exposure times, performed these functions for Borrelly, supporting the DS1 science and navigation team. Stardust has gained valuable flight experience from this collaboration and is now better prepared for its Comet Wild 2 encounter in 2004.
For more information on the Stardust mission - the first ever comet sample return mission - please visit the Stardust home page: