No. 219 - Mission operations update
Atmospheric drag experiment campaign
The first day of this reporting period saw the completion of the latest Venus Express ADE campaign (#3a), which had started on 22 February 2010. (See status report no. 218, linked from the right-hand menu, for more details.) On 28 February, the spacecraft's arc around the pericentre was again devoted to a four-hour long spacecraft tracking-only pass with the NASA Canberra 70m ground station. The tracking data was used for accurate orbit determination, which allows determining any deviation from the expected orbit caused by atmospheric drag. During this last pericentre passage of the ADE campaign #3a, the pericentre altitude of Venus Express was around 182 km.
Solar array tilt experiment
An additional new method to detect the effect of Venus' upper atmosphere on the Venus Express spacecraft was recently introduced, as detailed in the previous status report, no. 218. Instead of studying deviations in the orbit caused by drag, this method involves flying Venus Express with an asymmetrical tilt on the solar arrays, to try to detect the effects of the atmosphere as a torque on the spacecraft. This torque can be identified from accumulated momentum on the reaction wheels.
On 25 March an experiment was performed using this method. During the pericentre passage the spacecraft flew with its solar arrays offset in an asymmetrical configuration. The effect of Venus' atmosphere, however, was much less visible in the reaction wheel data than during the test performed one month ago (see previous status report). This was due to a different spacecraft attitude and pointing with respect to the wind velocity.
DDOR
On 20 March delta differential one-way ranging (DDOR) was performed using the New Norcia and Cebreros ground stations 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 is the transmitter and the two ground stations are New Norcia in western Australia and Cebreros in Avila, Spain.
Summary of main activities
During the reporting period mission operations have been conducted with support of the ESA Cebreros ground station. Communication passes over Cebreros were performed daily. An additional tracking-only pass was performed with the NASA Canberra ground station on 28 February, as part of the ADE campaign #3a.
The table below shows a chronology of the main activities:
| MET (Day) |
Date | DOY | Main Activity |
| 1573 | 28/02/10 | 059 |
Canberra 70m tracking pass around pericentre as part of ADE campaign #3a |
| 1575 | 02/03/10 | 061 |
Cebreros pass started later due to planned ground station maintenance activities |
| 1576 | 03/03/10 | 062 |
Cebreros pass started later due to planned ground station maintenance activities |
| 1593 | 20/03/10 | 079 |
DDOR with the Cebreros and New Norcia ground stations |
| 1598 | 25/03/10 | 084 |
Solar array tilt experiment around pericentre |
|
MET = Mission elapsed time; DOY = Day of year | |||
At the end of the last Cebreros pass in the reporting period (DOY 086) Venus Express was orbiting Venus at 239.4 million km from the Earth. The one-way signal travel time was 798 seconds.
Spacecraft
Attitude and Orbit Control System (AOCS)
The AOCS subsystem is in its nominal configuration and performing nominally. Operations continue with all four reaction wheels.
The friction levels and bearing temperatures of the reaction wheels remained stable throughout the reporting period. The friction on reaction wheel 2 continued to show spikes, predominantly during the Earth pointing periods, but this behaviour has already been correlated to the higher bearing temperatures and has no impact on operations.
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
No radio science observations were made during the reporting period.
VIRTIS
VIRTIS-M was operated in the visual channels only.
VMC
The instrument was regularly operated as part of the routine plan.
Future Milestones
- April 2010: ADE campaign #3b
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Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #225 through #228. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.