Rosetta conducted a manoeuvre today – a thruster burn that lasted 82 seconds – and it was completed as planned, Spacecraft Operations Manager Sylvain Lodiot has confirmed.
“The burn looks OK from telemetry, and the spacecraft is in good health,” wrote Sylvain in an email.
The burn got underway at 12:59 UTC (13:59 CET), ended at 13:01 UTC (14:01 CET) and, based on an initial analysis of post-burn telemetry, delivered a change in velocity – ‘delta-v’ – of 0.081 meters/sec. This pushed the spacecraft to leave the 10-km-altitude circular orbit (following the terminator line) – the so-called ‘Close Observation Phase’ (COP) orbit – where it’s been since 15 October.
The COP orbit enabled high-resolution images of the landing site in order to best prepare for Philae’s challenging touch-down.
Today’s manoeuvre is important as it means Rosetta has now started the transition from the COP to the pre-lander-delivery orbit.
Specifically, today’s burn has put Rosetta on a very elliptical trajectory rapidly moving the spacecraft away from the 10-km orbit. In three days, on 31 October, the mission control team will perform another manoeuvre to enter onto the pre-delivery orbit proper.
This is a slightly elliptical orbit at approximately 30 km distance from the comet centre (see the animation above).
After another orbital change taking place about two hours before separation, the spacecraft will finally deploy Philae from a distance of 22.5 km from the comet centre, at 08:35 UT on 12 November.