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No. 224 - Start of quadrature operations

No. 224 - Start of quadrature operations

Report for Period 18 July to 14 August 2010 (week 29 - week 32)The reporting period, covering four weeks of Venus Express mission operations, was devoted to routine science activities. On 21 July the spacecraft entered a new quadrature phase that will last until 26 August. On 28 July a few anomalies were observed relating to the solid state mass memory (SSMM), which were solved by a warm restart of the SSMM. As part of the SSMM anomaly recovery a spacecraft safe mode was commanded on 30 July. After exit from the safe mode nominal operations were resumed. On 30 July another eclipse season started.

Inbound quadrature phase
Quadrature phases are periods of about 5 weeks during which the Sun-spacecraft-Earth angle is between 75° and 95°. They occur twice in every synodical period of Venus (584 days, or about 19 months), with an inbound quadrature phase ending 9 weeks before a Venus inferior conjunction and an outbound quadrature phase starting 9 weeks after the inferior conjunction.

The current quadrature phase is an inbound quadrature: it occurs before the inferior conjunction of Venus on 29 October 2010, and the distance between Venus and the Earth is decreasing.

During quadrature phases revised operating constraints on the VMC instrument lead to the necessity for changing the spacecraft attitude during Earth pointings to prevent unacceptable Sun illumination of the VMC. As part of the quadrature operations Venus Express therefore flies with a 10° tilt about its +X face during the Earth communication passes. To achieve and maintain this attitude, fake ephemerides on the positions of the spacecraft and the Earth are uploaded to Venus Express. The tilt, however, also leads to low-incident illumination on the spacecraft's +Y face. Because the +Y face carries several radiators, the spacecraft requires extended cool-down periods (about 17 hours) after the communication passes before resuming science observations. As a result, Cebreros passes are routinely skipped during the quadrature operations to allow more time for science observations. During this reporting period, ten passes were skipped. In addition, several passes were shortened to further increase the available time for science observations. With less Cebreros passes to upload commands, delayed telecommand (TC) files were used to store and call the commands on-board at a specific time.

Later in this quadrature phase, on 15 August 2010, a swap will be performed from high gain antenna 1 (HGA1) to HGA2 for use during Earth communication passes. A swap between the two high gain antennae is performed during each quadrature phase of the mission. This is to, during Earth pointings, avoid illumination of spacecraft faces that are not designed to cope with such exposure to the Sun. HGA1 can only be used for Earth communications during the periods when the Sun-spacecraft-Earth angle is smaller than 90°, while HGA2 is used when this angle is greater than 90° (see also "Earth Pointing Communication Phase" linked from the right-hand menu).

During the next quadrature phase, which starts at the end of December 2010 and is an outbound quadrature, a swap from HGA2 back to HGA1 will be made.

Eclipse season
On 30 July (DOY 211) another eclipse season started, which will last until 13 September 2010 (DOY 256). During eclipse seasons, as Venus Express passes through the shadow of Venus on parts of its 24-hour orbits around the planet, the thermal and power requirements lead to increased demand on the spacecraft's batteries.

Two days before the start of the eclipse season, on 28 July, the batteries' end of charge (EoC) levels were restored to 100%. These had been set to 80% on 8 June (DOY 159), about a week after the previous eclipse season had ended, to extend the battery lifetime.

Summary of main activities
During the reporting period mission operations have been conducted with the support of the ESA Cebreros ground station. The communication passes over Cebreros were performed daily up to the start of the quadrature operations. After that, Cebreros passes were regularly skipped and several communication passes were shortened to increase the available time for science observations. Two additional passes were performed with the New Norcia ground station, for checking the spacecraft status, for commanding a safe mode and performing the subsequent recovery to normal operations after the SSMM anomaly.

The table below shows a chronology of the main activities:

Date DOY Main Activity
1716 21/07/10 202 Quadrature phase entry
1717 22/07/10 203 Cebreros pass skipped
1718 23/07/10 204 Uplink delayed telecommand file
1720 25/07/10 206 Cebreros pass skipped
1722 27/07/10 208 Cebreros pass skipped
1723 28/07/10 209 Battery EoC levels restored to 100%.
Few SSMM anomalies observed
1724 29/07/10 210

New Norcia pass taken to check spacecraft status.
Cebreros pass skipped

1725 30/07/10 211 New Norcia pass taken to initiate a spacecraft safe mode, start safe mode recovery and recover the SSMM.
During the Cebreros pass recovery activities were completed and commands were uploaded for the next planning period.
Start of eclipse season
1727 01/08/10 213 Cebreros pass skipped
1728 02/08/10 214 Shortened Cebreros communications pass
1729 03/08/10 215 Cebreros pass skipped
1730 04/08/10 216 Shortened Cebreros communications pass
1731 05/08/10 217 Cebreros pass skipped
1733 07/08/10 219 Shortened Cebreros communications pass
1734 08/08/10 220 Cebreros pass skipped
1735 09/08/10 221 Shortened Cebreros communications pass
1736 10/08/10 222 Cebreros pass skipped
1737 11/08/10 223 Shortened Cebreros communications pass
1738 12/08/10 224 Cebreros pass skipped

MET = Mission elapsed time; DOY = Day of year

At the end of the reporting period (DOY 226) Venus Express was orbiting Venus at 108 million km from the Earth. The one-way signal travel time was 362 seconds.

Payload Activities

All instruments were switched OFF on 30 July (DOY 211) as part of the spacecraft safe mode. They were switched ON again on 31 July (DOY 212) according to the science routine plan, after the Cebreros communication pass (except for MAG, which had been switched ON already during that pass).

The instrument was regularly operated as part of the routine plan.

The instrument was regularly operated as part of the routine plan.

The instrument was not operated during the reporting period.

The instrument was regularly operated as part of the routine plan.

The instrument was regularly operated as part of the routine plan.

No radio science observations were made during the reporting period.

VIRTIS-M was operated in the visual channels only.

Future Milestones

  • 15 August 2010: Swap from HGA1 to HGA2
  • 26 August 2010: End of inbound quadrature phase
  • 13 September 2010: End of eclipse season
  • October 2010: Atmospheric drag experiment campaign #4
  • 29 October 2010: Venus at inferior conjunction
  • 31 December 2010: Start of outbound quadrature phase

Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #245 through #248. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.

Last Update: 1 September 2019
22-Feb-2020 10:13 UT

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