No. 223 - End of Earth occultation season #9
VeRa Earth occultation season #9
The mission's ninth Earth occultation season has lasted ten weeks, with the last three weeks falling in this reporting period and ending on 11 July (DOY 192). During ococultation seasons 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.
RSI occultation measurements were performed around pericentre on thirteen orbits in the reporting period. Two ground stations were used for receiving the spacecraft's radio signals on ground: the ESA deep space antenna at New Norcia, Australia, and the NASA Deep Space Station (DSS) at Canberra.
DDOR
On 24 June (DOY 175) delta differential one-way ranging (DDOR) was performed using two ground stations simultaneously to track the spacecraft. These measurements are performed regularly to support the accurate determination of the ephemeris for the planet Venus that is maintained by NASA's Solar System Dynamics Group.
The DDOR measurement principle uses a technique to highly accurately determine the position of a transmitter in space and relies on observing the time delay between reception of the signal from the transmitter by two ground stations at different positions on Earth. In this case the Venus Express spacecraft was the transmitter and the two ground stations were New Norcia in west Australia and Cebreros in Avila, Spain.
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. Two of these passes were shortened (one due to maintenance and one for the Rosetta flyby) and four passes were skipped. Additional passes for the RSI occultation campaign were performed around pericentre, with the New Norcia (NNO) and Canberra (CAN) ground stations.
The table below shows a chronology of the main activities:
| MET (Day) |
Date | DOY | Main Activity |
| 1685 | 20/06/10 | 171 | RSI occultation over NNO around pericentre |
| 1687 | 22/06/10 | 173 | RSI occultation over NNO around pericentre. Cebreros pass shortened because of planned ground station maintenance |
| 1689 | 24/06/10 | 175 | DDOR with Cebreros and NNO |
| 1691 | 26/06/10 | 177 | RSI occultation over CAN around pericentre |
| 1693 | 28/06/10 | 179 | Cebreros pass skipped |
| 1695 | 30/06/10 | 181 | Cebreros pass skipped |
| 1696 | 01/07/10 | 182 | RSI occultation over CAN around pericentre |
| 1697 | 02/07/10 | 183 | Cebreros pass skipped. RSI occultation over CAN around pericentre |
| 1698 | 03/07/10 | 184 | RSI occultation over CAN around pericentre |
| 1699 | 04/07/10 | 185 | RSI occultation over CAN around pericentre |
| 1700 | 05/07/10 | 186 | RSI occultation over CAN around pericentre |
| 1702 | 07/07/10 | 188 | RSI occultation over CAN around pericentre |
| 1703 | 08/07/10 | 189 | RSI occultation over CAN around pericentre |
| 1704 | 09/07/10 | 190 | Cebreros pass shortened for Rosetta flyby of asteroid Lutetia. RSI occultation over CAN around pericentre. The telemetry bit rate was increased from 114 kbps to 228 kbps |
| 1705 | 10/07/10 | 191 | Cebreros pass skipped for Rosetta flyby of asteroid Lutetia. RSI occultation over CAN around pericentre |
| 1706 | 11/07/10 | 192 | RSI occultation over CAN around pericentre |
|
MET = Mission elapsed time; DOY = Day of year | |||
At the end of the last Cebreros pass in the reporting period (DOY 198) Venus Express was orbiting Venus at 142 million km from the Earth. The one-way signal travel time was 473 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 thirteen orbits in the reporting period RSI experiments took place around pericentre as part of the Earth occultation campaign #9, with dedicated ground station passes. Two passes were over New Norcia, on DOY 171 and 173. Eleven passes were over Canberra, between DOY 177 and 192.
VIRTIS
VIRTIS-M was operated in the visual channels only.
VMC
The instrument was regularly operated as part of the routine plan.
Future Milestones
- 21 July 2010: Start of next quadrature phase (inbound)
- 28 July 2010: Restore battery end of charge levels from 80% to 100%
- 30 July 2010: Start of next eclipse season
- 15 August 2010: Swap from HGA1 to HGA2
- October 2010: Atmospheric drag experiment campaign #4
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Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #241 through #244. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.