Second Deep Space Manoeuvre for Rosetta
Report for Period 15 September to 6 October 2006
The reporting period covers three weeks of active cruise and was dedicated to the preparation and execution of the second Deep Space Manoeuvre (DSM2).
The manoeuvre was executed on 29 September at 02:00 UTC. Its planned magnitude was 31.791 ms-1, which corresponds to an overall burn duration of about 52 minutes. In the manoeuvre attitude, the high gain antenna could not be kept pointing at the Earth during the burn because it was in the plume zone. The high gain antenna therefore had to be moved away shortly before the start of the manoeuvre, and was pointed back after the completion of the burn. The manoeuvre was thus performed without ground contact.
The manoeuvre performance was outstanding: the last orbit determination performed by Flight Dynamics using tracking data collected until 4 October indicated an over-performance of 0.279% (+88.7 mms-1) with a 1 sigma uncertainty of 0.026% (8.3 mms-1). The best estimate for the manoeuvre direction error is 0.14??, with a quite large uncertainty between 0.08 and 0.25??.
SREM was kept continuously active in the background for the entire reporting period. All other instruments remained OFF.
A total of 16 New Norcia passes of 4 to 10 hours commanding were taken during the reporting period. Ten of these passes were scheduled for tracking only. During the remaining 6, TM/TC links were connected to the control centre. In addition, 11 tracking passes of 4 hours have been taken with DSN.
NNO
Pass DOY Date Main Activity 935 263 20.09.06 Monitor pass - WOL 941 269 26.09.06 Monitor pass - uplink DSM2 MTL 942 270 27.09.06 Monitor pass - WOL 943 271 28.09.06 Deep Space Manoeuvre 2 944 272 29.09.06 Monitor pass - IMP reconfiguration 949 277 04.10.06 Monitor pass - WOL - Uplink AOCS Checkout MTL
At the end of the reporting period (DOY 279) Rosetta was at 282.5 million km from Earth (1.89 AU; one-way signal travel time was 15 minutes 6 seconds). The distance to the Sun was 148.2 million km (0.99 AU).
Deep Space Manoeuvre
- Start of manoeuvre DOY 272, 02:00 UTC
- Manoeuvre magnitude 31.791 ms-1
- Fuel consumption 33.7 kg (from telemetry)
- Thrusters pulse counter Within prediction: 0.5% lower than predicted value of 92686.6 Ns
- Duration 3128 seconds
- TTM duration after manoeuvre 100 seconds
As part of the manoeuvre preparation, the accelerometer biases were calibrated. During the manoeuvre itself, the antenna was repositioned at -150 elevation and -180?? azimuth. As a result, ground contact was interrupted from 272.01.46 to 272.03.36.
The delta-v measured by the accelerometers during DSM2. The measurement is reset when the delta-v value reaches 20 ms-1
Spacecraft
Thermal
The thermal behaviour of the spacecraft is nominal and stable. It remains configured for Active Near Sun cruise (ACM1 since DOY 207/2006).
On DOY 263, the TCT lines which had been spuriously declared failed on DOY 257/258 during the first thermal characterisation were manually reset to Prime software control.
The temperature of the thrusters and of the high gain antenna mechanism was monitored closely during the Deep Space Manoeuvre. All temperatures remained well within their defined limits.
There was some concern on the temperature of the high gain antenna mechanism during the manoeuvre because the motor was to remain active for two hours at a Sun distance of 1 AU. However, the observed temperature variations remained very moderate. The temperature of the elevation mechanism only increased from 51.6 to 53.3 ??C, whereas the temperature of the azimuth motor increased from 45 to 51.7 ??C.
Payload
SREM remains active in the background for radiation monitoring with accumulation parameters configured for active cruise. All other instruments remained OFF during the reporting period.
Future Milestones
The Mars Swingby Phase formally started on 28 July. The phase includes the first payload Active Checkout (PC4) in November/December 2006, while the actual swingby will take place on 25 February 2007, followed by a Deep Space Manoeuvre in April 2007.
The next short-term activity is an AOCS checkout on 11/12 October.
