ESA Science & Technology - No. 158 - Spin-up and entry into deep-space hibernation

During the reporting period Rosetta was successfully spun-up and commanded into Deep Space Hibernation Mode. The manoeuvre was executed as planned on 8 June without problems. The signal was lost on-ground at about 08:00:35 UTC when the spin-up manoeuvre was triggered on board the spacecraft. After the initial transient, the NASA Deep Space Network (DSN) DSS-43 70-metre antenna in Canberra detected an extremely weak strobing signal. This information was invaluable for the mission controllers in that they had confirmation that the spacecraft had successfully executed the most critical phase of the manoeuvre. About 50 minutes later, the on-board software repositioned the high-gain antenna after estimation of the actual principal inertia axis (that is, the real spin axis). The strength of the signal received on-ground increased sharply to the expected level (that is, the same level as was observed when the spacecraft was not spinning); this was visible at both DSS-43 and New Norcia. This confirmed that:

• All the autonomous pre-hibernation checks were successful, otherwise a safe mode would have been triggered;
• The difference between the estimated and the measured principal inertia axis was between 4.5 and 8 degrees, otherwise either a stronger signal would have been observed or a safe mode would have been triggered by the on-board software;
• The inertial pointing of the spacecraft was very good, otherwise the signal strength would not have been as strong as before the spin-up, when the spacecraft was perfectly pointing to Earth.

Once all the planned ground checks had been completed (strobing period and signal strength) the telecommand link was verified by switching the spacecraft telemetry modulation on and off twice and monitoring the change in signal strength. The pulsing signal received at DSS-43 at the time of the test confirmed that signal was transitioning to a lower level when the telemetry modulation was on.

The final telecommand to authorise hibernation entry was released at 12:57:40 UTC and confirmation of successful transition into hibernation mode came at 14:12:00 UTC when the last pulse from the spacecraft was received by the ground stations.

A passive monitoring phase of six days was then completed to ensure that the spacecraft had not aborted the operation due to multiple failures. The wake-up time has been set to 2014.020:10:00:00 UTC (20 January 2014 at 10:00 UTC) with a planned downlink signal a few hours later, following a warm-up phase and spin-down via Safe Mode.

During the reporting period, mission operations were conducted using the ESA New Norcia (NNO) and Cebreros (CEB) ground stations and the DSS-14 (Goldstone, 70 metres) and DSS-43 (Canberra, 70 metres) NASA DSN antennas.

At the end of the reporting period on 14 June, Rosetta was 562 million kilometres from Earth (3.75 AU); one-way signal travel time was 1875 seconds (31 minutes 15 seconds). The spacecraft distance from the Sun was 671 million kilometres (4.48 AU).

During the hibernation phase, Rosetta will reach the following record distances:

• 792 million kilometres (5.29 AU) from the Sun on 3 October 2012
• 937 million kilometres (6.26 AU) from Earth on 1 December 2012

Spacecraft

Future milestones

The spacecraft is now in Deep Space Hibernation Mode and will remain in this status until 20 January 2014, when it will initiate the hibernation exit sequence:

• 10:00:00 – 10:15:00 UTC: Wake-up time detected and start of star trackers warm-up phase
• 16:25:00 – 16:40:00 UTC: End of warm-up phase and spin-down via Safe Mode
• 17:35:00 – 17:50:00 UTC: Expected S-band downlink signal on-ground

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This report is based on the ESOC mission operations report, WOR #158. Please see the copyright section of the legal disclaimer (linked from the home page http://sci.esa.int) for terms of use.