ESA Science & Technology - No. 147 - RF test for deep-space hibernation mode entry

During the reporting period mission operations have been conducted using the ESA New Norcia (NNO) ground station and the DSS-26 (Goldstone. 34 metres), DSS-43 (Canberra, 70 metres), DSS-54 (Madrid, 34 metres), DSS-55 (Madrid, 34 metres) and DSS-63 (Madrid, 70 metres) NASA Deep Space Network (DSN) antennas.

The ESA New Norcia ground station and the NASA DSN DSS-43 70-metre antenna in Canberra supported the DSHM entry RF test on 19 November.

At the end of the reporting period on 26 November, Rosetta was 662.8 million km from Earth (4.43 AU); the one-way signal travel time was 36 min 50 sec (2210 sec). The spacecraft's distance from the Sun was 538 million km (3.59 AU).

DSHM entry RF test

During the hibernation entry window next year, Rosetta will be between 3.7 and 4.4 AU from Earth. At those distances, and once Rosetta is spinning, it will be necessary to be able to command Rosetta using the low-gain antenna (LGA) and to detect the strobing signal coming from the high-gain antenna (HGA).

On 19 November, a test similar to the one conducted on 20 August was repeated to validate the RF activities and performance to be expected at the end of the DSHM entry window in July 2011 at a geocentric distance of about 4.4 AU. The tested elements were as follows:

1. reception of HGA S-band strobing signal by DSN 70-metre dish (DSS-43, Canberra)
2. reception of HGA S-band strobing signal by ESA 35-metre dish (New Norcia)
3. viability of LGA-F S-band telecommand link (7.8 bps) from DSN 70-metre dish (DSS-43, Canberra) with 95 kW uplink power
4. viability of LGA-F S-band telecommand link (7.8 bps) from DSN 70-metre dish (DSS-43, Canberra) with 20 kW uplink power
5. viability of LGA-F S-band telecommand link (7.8 bps) from ESA 35-metre dish (New Norcia) with 20 kW uplink power

All the elements were successfully validated, even though elements 4 and 5 are well beyond the expected spacecraft performance; for this reason the nominal uplink configuration for DSHM entry will be a DSN 70-metre dish with 95 kW uplink power, with options 4 and 5 available as backups.

Spacecraft

Attitude and orbit control system
The behaviour of reaction wheel C was judged unsatisfactory after the first relubrication, performed on 13 November, and a second relubrication was performed on 24 November; the wheel is now in its run-in phase and its behaviour will be assessed over the next few weeks.

Future milestones

Payload checkout activities will now begin and cover the next two weeks of operations. The plan for the payload checkout is as follows:

• week 48: final RPC activities; Lander test part one and passive checkout of payload complement
• week 49: Lander test part two and ROSINA software update

The activities scheduled for the OSIRIS instrument have been postponed until the conclusion of the relevant Material Review Board (MRB) is available. The instrument will be activated after the first rendezvous manoeuvre, at a time compatible with the spacecraft operations plan.

The first rendezvous manoeuvre is planned for the second half of January 2011, with the first burn leg on 17 January. Due to its magnitude, this manoeuvre has been split into five nominal burns plus an optional extra one in the event that a final correction is needed. Detailed definition of the burn sequence is ongoing.

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Legal disclaimer
This report is based on the ESOC mission operations report, WOR #147. Please see the copyright section of the legal disclaimer (linked from the home page http://sci.esa.int) for terms of use.