No. 222 - End of eclipse season
End of eclipse season
During eclipse seasons, as Venus Express passes through the shadow of Venus during parts of its 24-hour orbit around the planet, the thermal and power requirements lead to increased demand on the spacecraft's batteries.
Following the end of the eclipse season on 30 May (DOY 150), a battery deep discharge test was performed on 7 June (DOY 158). The solar arrays were rotated away from the Sun and the batteries were allowed to discharge until they reached approximately 40% charge level. At that point the arrays were commanded autonomously back to Sun pointing and the batteries were recharged. As part of the test housekeeping telemetry was retrieved on ground for analysis.
Furthermore, on 8 June (DOY 159) the batteries were discharged for a short interval during the daily communication pass over Cebreros and the batteries' end of charge (EoC) level was reduced from 100% to 80%. This was done for all three batteries and is to extend their lifetime. The EoC level will be reset to 100% before the next eclipse season, which will start at the end of July 2010.
VeRa Earth occultation season #9
The mission's ninth season of Earth occultations, which started on 30 April 2010, is ongoing. During this season the Earth is occulted by the disk of Venus around the pericentre passages as seen from the spacecraft. This condition allows for unique measurements to investigate the fine structure of the neutral atmosphere and ionosphere of Venus.
The occultation measurements are part of the Venus Express Radio Science Investigations (RSI) performed under the Venus Radio Science experiment (VeRa). For these investigations the VeRa team makes use of the radio links of the spacecraft's communications system. The spacecraft's High Gain Antenna (HGA) is pointed toward the Earth before the approach to occultation. The on-board ultra-stable oscillator (USO) is used to generate a very stable signal which is sent to Earth over the HGA in simultaneously the S-band and X-band. Just before and after the occultation the transmitted radio signal passes through the ionosphere and atmosphere of Venus. The effect that this has on the received signal gives valuable information on the characteristics of the atmosphere (such as temperature, density and pressure) as a function of altitude.
During the reporting period two ground stations were used for receiving the spacecraft's radio signals on ground: the 35m ESA deep space antenna at New Norcia, Australia, and the 34m NASA Deep Space Station (DSS) at Canberra.
Summary of main activities
During the reporting period mission operations have been conducted with the support of the ESA Cebreros (CEB) ground station. The communication passes over Cebreros were performed daily. Additional passes for the RSI occultation campaign were performed around pericentre, with the New Norcia (NNO) and Canberra (DSS-34) ground stations.
The table below shows a chronology of the main activities:
| MET (Day) |
Date | DOY | Main Activity |
| 1660 | 26/05/10 | 146 | RSI occultation over NNO around pericentre |
| 1664 | 30/05/10 | 150 | End of Eclipse season |
| 1665 | 31/05/10 | 151 | RSI occultation over NNO around pericentre |
| 1667 | 02/06/10 | 153 | RSI occultation over NNO around pericentre |
| 1670 | 05/06/10 | 156 | RSI occultation over NNO around pericentre |
| 1672 | 07/06/10 | 158 | Deep discharge test during Cebreros communications pass |
| 1673 | 08/06/10 | 159 | Battery EoC lowered to 80% during Cebreros communications pass. RSI occultation over NNO around pericentre |
| 1677 | 12/06/10 | 163 | RSI occultation over NNO around pericentre |
| 1679 | 14/06/10 | 165 | RSI occultation over DSS-34 around pericentre |
| 1681 | 16/06/10 | 167 | RSI occultation over DSS-34 around pericentre. Telemetry bit rate increased to 152 Kbps |
|
MET = Mission elapsed time; DOY = Day of year | |||
At the end of the last Cebreros pass in the reporting period (DOY 170) Venus Express was orbiting Venus at 173.4 million km from the Earth. The one-way signal travel time was 578 seconds.
Payload Activities
ASPERA
The instrument was regularly operated as part of the routine plan.
MAG
The instrument was regularly operated as part of the routine plan.
PFS
The instrument was not operated during the reporting period.
SPICAV
The instrument was regularly operated as part of the routine plan.
VeRa
On eight orbits in the reporting period RSI experiments took place around pericentre as part of the Earth occultation campaign #9, with dedicated ground station passes. Six passes were over New Norcia, and two were over Canberra (DSS-34).
VIRTIS
VIRTIS-M was operated in the visual channels only.
VMC
The instrument was regularly operated as part of the routine plan.
Future Milestones
- 11 July 2010: End of Earth occultation season #9
- 21 July 2010: Start of next quadrature phase (inbound)
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Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #237 through #240. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.