No. 59 - Recharging Philae's Secondary Battery
Upon a request by the Lander Team, the Lander has been activated on 9 May to recharge the probe's secondary battery. This activity was required due to an unexpected high self-discharge of the Lander secondary battery observed since commissioning. The last monitoring performed during Passive Checkout 2 (3-7 March 2006) confirmed the need to recharge the battery before the next planned Payload operation slot.
On 10 May, the attitude guidance was changed as required for Near Sun Hibernation entry (X axis Earth pointing without bias, Y axis perpendicular to Sun-Spacecraft-Earth with South direction option). This resulted in particular in a change of the actual Y-axis direction, such that the Sun is shining on the +X/+Z spacecraft quadrant after the guidance change.
A total of 6 New Norcia passes were taken during the reporting period to recover solar conjunction telemetry. TM/TC links with the OCC have been established for all passes.
|794||02.05.06||122||Monitor pass - TM bit rate to 22 853 bps|
|801||09.05.06||129||Monitor pass - WOL|
At the end of the reporting period (DOY 132/2006) Rosetta was at 369.9 million km from Earth (2.47 AU; one-way signal travel time was 19 minutes 46 seconds). The distance to the Sun was 221.8 million km (1.48 AU).
The thermal behaviour of the spacecraft is nominal and stable. Its configuration is, since DOY 230/2005, ACM1, with tank gauge heater 7A switched off.
The spacecraft is slowly warming up as the spacecraft to Sun distance decreases.
The only instruments operated in the reporting period were SREM and the Lander. SREM remains active in the background for radiation monitoring. SREM's data collection rate is currently reduced to cope with the limited ground contacts during solar conjunction and the upcoming near Sun Hibernation period.
The Lander has been activated for 21 hours on DOY 128-129/2006 to recharge the probe's secondary battery. This activity was required in order to keep the battery state of charge above 10%. It had been originally scheduled during the first Active Checkout in December 2006, but telemetry from the last Passive Checkouts outlined a higher than expected level of self discharge for this battery. The Lander team therefore requested to advance this maintenance operation.
A total of 6 New Norcia passes were taken over the reporting period, to support spacecraft monitoring and intensive RF signal tracking during the solar conjunction. During the reporting period, a few incidents at the New Norcia ground station caused temporary degradation of the service.
On 23 May 2006, the spacecraft will be configured into Near Sun Hibernation Mode for a period of about 2 months, until end July 2006.
Operations for the Mars swing-by (February 2007) will start in August 2006, with another payload passive checkout (PC3), an intense tracking campaign around the Trajectory Correction Manoeuvre (DSM-2) in September, and the first payload Active Checkout (PC4) in November/December.