No. 196 - Earth Occultation Season #7
VeRa Earth occultation season #7
The mission's seventh season of Earth occultation experiments started on 16 July 2009 (DOY 197). These experiments effectively represent a sounding of the Venusian atmosphere and ionosphere. The measurements are made just before and after the spacecraft passes behind the disk of Venus as seen from Earth (occultation).
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 is pointed toward the Earth before the approach to occultation and a dual signal is sent in 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 composition and characteristics of the atmosphere as a function of altitude.
The 35m ESA deep space antenna at New Norcia (NNO), Australia, was used for receiving the spacecraft's radio signals on ground.
DDOR
On 12 August delta differential one-way ranging (DDOR) was performed using the New Norcia and Cebreros ground stations to track the spacecraft. These measurements are performed monthly 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.
The table below shows a chronology of the main activities:
| MET (Day) |
Date | DOY | Main Activity |
| 1370 | 09/08/09 | 221 |
Communications pass over Cebreros |
| 1371 | 10/08/09 | 222 |
Communications pass over Cebreros. |
| 1372 | 11/08/09 | 223 |
Shortened communications pass over Cebreros due to ground station maintenance |
| 1373 | 12/08/09 | 224 |
Communications pass over Cebreros. |
| 1374 | 13/08/09 | 225 |
Communications pass over Cebreros |
| 1375 | 14/08/09 | 226 |
Communications pass over Cebreros |
| 1376 | 15/08/09 | 227 |
Communications pass over Cebreros |
At the end of the last Cebreros pass in the reporting period (DOY 227) Venus Express was orbiting Venus at 184.3 million km from the Earth. The one-way signal travel time was 614 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
RSI occultation measurements were performed on DOY 222 and 225.
VIRTIS
VIRTIS-M was operated in the visual channels only.
VMC
The instrument was regularly operated as part of the routine plan.
Future Milestones
- Atmospheric drag measurements: 12 to 17 October 2009
- Superior conjunction: 29 December 2009 to 22 January 2010
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Legal disclaimer
This report is based on the ESOC mission operations report, MOR #196. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.