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No. 128 - Test of the Deep Space Hibernation Mode

No. 128 - Test of the Deep Space Hibernation Mode

Report for Period 16 January to 29 January 2010The reporting period covers two weeks, which were fully dedicated to the test of the deep space hibernation mode (DSHM) for Rosetta. This is the hibernation mode in which the spacecraft will operate from June 2011 till January 2014 on its last long stretch of passive cruise to comet 67P/Churyumov-Gerasimenko.

The spacecraft was spin-stabilized on DoY 020 and commanded in the hibernation mode in the morning of DoY 021. The hibernation was completed on DoY 027 as planned by autonomous action of the on-board computer that triggered a safe mode. During the post-DSHM recovery another safe mode was triggered. The spacecraft was promptly recovered and restored to its normal mode.

The solid state mass memory (SSMM), which had been powered done on DoY021 and was off during the entire test, was fully re-configured as part of the nominal recovery activities following DSHM exit. The complete SSMM software was re-loaded in the Electrically Erasable Programmable Read Only Memory (EEPROM) of both memory controllers on DoY 027, as part of the EEPROM refresh campaign. The SSMM was fully reconfigured between DoY 027 and DoY 028; the reconfiguration included the re-uplink of all on-board control procedures (OBCPs).

During the reporting period, mission operations have been conducted with support of the ESA New Norcia (NNO) ground station. For the DSHM entry and exit operations additional support came from NASA DSN antennae at Madrid (DSS-65) and Goldstone (DSS-14, DSS-24).

DOY Date Pass Main Activity
018 18/01/10 NNO 2154

Monitoring pass

019 19/01/10 NNO 2155

Monitoring pass

020 20/01/10

DSS-24 2156
NNO 2156
DSS-65 2157

Go/no-go for spin-up
Spin-up
Monitoring pass

021 21/01/10

DSS-14 2157
NNO 2157

DSHM entry
DSHM monitoring

022 22/01/10

NNO 2158

DSHM monitoring

023 23/01/10

NNO 2159

DSHM monitoring

024 24/01/10 NNO 2160

DSHM monitoring

025 25/01/10 NNO 2161

DSHM monitoring

026 26/01/10

NNO 2162

DSHM monitoring

027 27/01/10 DSS-24 2163
NNO 2163
DSHM exit; spin down
SSMM EEPROM refresh and safe mode recovery
028 28/01/10 NNO 2164

SSMM EEPROM refresh and re-configuration

029 29/01/10

NNO 2165

SSMM re-configuration

At the end of the reporting period (DoY 029) Rosetta was at 56.9 million km from Earth (0.38 AU) and the one-way signal travel time was 190 seconds. The distance to the Sun was 200.5 million km (1.34 AU).

DSHM Test

The test of the deep space hibernation mode took place between 20 and 27 January and has been successfully completed. During this DSHM test the spacecraft was monitored daily for about 8 hours. The aim of the test was to validate the spacecraft behaviour and the operational scenario for this hibernation mode, including:

  • the spacecraft configuration for DSHM entry
  • the spacecraft spin-up manoeuvre
  • detection & processing of Rosetta's strobing signal on ground
  • commanding hibernation entry
  • the spacecraft in DSHM configuration for 1 week
  • the spacecraft's autonomous DSHM exit
  • the spacecraft spin-down
  • recovery of the spacecraft after DSHM exit

Rosetta spin-stabilized
When in deep space hibernation mode the spacecraft is spin-stabilized as opposed to being 3-axes stabilized. On 20 January the spin-up for the DSHM test was initiated, at 18:00 UT. The spacecraft's 10-Newton thrusters (only those on branch A of the reaction control subsystem) were used for the spin-up. These were also used again at the end of the DSHM test for the spacecraft spin-down.

Rosetta's spin rate was commanded to 4 degrees per second (or 2/3 rpm) and converged to a value of 3.93 degrees per second (deg/s), well within the thresholds of ±1 deg/s.

Strobing signal
Due to the spacecraft's spin a pulsed (strobing) signal could be observed on ground. After the spin-up on DoY 020, the spacecraft's downlink was switched a few times between modulated telemetry on the medium-gain antenna (MGA) and unmodulated carrier signal on the high-antenna (HGA). This was, respectively, to monitor the spacecraft and to test the signal acquisition of the strobing pulses from the spinning spacecraft.

Both at ESA and NASA the procedures and tools required for the detection and processing of the HGA strobing pulses on ground ran properly. The whole chain to the Rosetta Mission Operation Centre was exercised and worked flawlessly.

DSHM entry and exit
Following the successful spin-up, the detection of the strobing signal from the HGA and final checks, the entry in DHSM was authorized. On 21 January, at 02:00 UT, the onboard control procedure (OBCP) for the entry in deep space hibernation mode was started. Upon entry in DSHM the spacecraft switched OFF the subsystems for attitude and orbit control (AOCS) and for telemetry, tracking & command (TTC). The spacecraft transmitter was subsequently switched ON again for monitoring purposes during this test.

The timeline of activities during the DSHM entry and exit was as follows (all times are in UT):

DSHM entry
20 January 2010
17:00 Rosetta in thruster transition mode (TTM) with spin-up attitude and with reaction wheels OFF
17:35 Downlink on MGA
18:00 Transition to spin-up
18.01 End of spin-up, start of Nutation Damping Phase (NDP) to steady the spin axis
18:31 End of NDP, start of Principal Inertial Axis Estimation (PIAE) Phase
18:47 End of PIAE phase, HGA repositioning
20:00 Downlink on MGA for monitoring over DSS-65
23:00 Downlink on HGA (unmodulated carrier signal) - first detection of strobing pulses at NNO and later at DSS-65
21 January 2010
00:00 Configure for DSHM
02:00 Start DSHM entry OBCP (and 24 h time-out)
03:30 Downlink on HGA (unmodulated carrier signal) - detection of strobing pulses at DSS-14
05:15 Downlink on MGA for telecommand link test and last spacecraft configuration monitoring before DSHM entry
05:48 Downlink on HGA (unmodulated carrier signal) - final detection of strobing pulses at DSS-14
06:16 Hibernation Bits A and B set ON for DSHM entry
06:29 Loss of Rosetta's signal as expected, confirming DSHM entry
07:50 From ground: Rosetta's TX-2 transmitter switched ON for DSHM monitoring (via MGA at 148 bps)
DSHM exit
27 January 2010
05:37 Autonomous wake-up triggered by onboard software
12:03 Safe mode triggered by onboard software - Loss of signal as expected
12:30 Acquisition S-band carrier signal after spin-down
15:50 Attitude control based on reaction wheels again; spacecraft is 3-axes stabilized

Early results

  • Spin-stabilization
    During the seven-day DSHM test the spin rate was monitored and found to very slowly decrease over time with a rate of about 0.0002 deg/s/day. This is most likely due to solar radiation pressure acting on the large solar arrays and the high-gain antenna. Despite not a real concern for the mission's deep space hibernation phase during 2011-2014, this behaviour will be carefully studied.

    The principal inertial axis, or spin axis, which had been estimated beforehand to be at about 7° in the +X/+Z quadrant of the spacecraft's reference frame, converged to a value of 10.4°. The difference is well within the uncertainties, but will be carefully analysed.
     
  • Thermal
    The thermal subsystem was configured for DSHM between DoY 021 and DoY 027. Throughout the DSHM test the temperatures remained within limits and it was not necessary for the mission operations team to intervene on the configuration. The data collected on the heaters and thermostats activation will now be analysed in view of the mission's deep space hibernation phase for 2011-2014.

Spacecraft

Payload

ALICE

The instrument is currently OFF.

CONSERT
The instrument is currently OFF.

COSIMA
The instrument is currently OFF.

GIADA
The instrument is currently OFF.

MIDAS
The instrument is currently OFF.

MIRO
The instrument is currently OFF.

OSIRIS
The instrument is currently OFF.

ROSINA
The instrument is currently OFF.

RPC
The instrument is currently OFF.

RSI
The instrument was ON during the DSHM test. It was switched OFF by the DSHM exit on DoY 027. As part of the recovery actions following the DSHM test the RSI will again be switched ON.

VIRTIS
The instrument is currently OFF.

LANDER Philae
The instrument is currently OFF.

SREM
The instrument is currently OFF.

Future Milestones

Rosetta is now configured in normal mode with few activities remaining to be done after the successfully completed DSHM test. Re-lubrication of reaction wheel B is planned for DoY 034.

In the next weeks several activities in preparation of the 12th payload check-out (PC12) will be conducted, including a test of the Philae lander's solar generator, pending successful re-lubrication of reaction wheel B.

Rosetta is cruising towards asteroid Lutetia. The encounter with the asteroid will take place in July 2010.


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Legal disclaimer
This report is based on the ESOC mission operations report, WOR #128. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.

Last Update: 1 September 2019
10-Jul-2020 11:18 UT

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