No. 66 - Second Deep Space Manoeuvre
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.
|935||20.09.06||263||Monitor pass - WOL|
|941||26.09.06||269||Monitor pass - uplink DSM2 MTL|
|942||27.09.06||270||Monitor pass - WOL|
|943||28.09.06||271||Deep Space Manoeuvre 2|
|944||29.09.06||272||Monitor pass - IMP reconfiguration|
|949||04.10.06||277||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|
|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 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.
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.
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.