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No. 196 - Earth Occultation Season #7

No. 196 - Earth Occultation Season #7

Report for Period 9 August to 15 August 2009The Venus Express spacecraft and instruments performed nominally during this week. The seventh Earth occultation season is ongoing, with two observations carried out in this reporting period. On DOY 224 the regular DDOR measurements were performed.

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.

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:

Date DOY Main Activity
1370 09/08/09 221

Communications pass over Cebreros

1371 10/08/09 222

Communications pass over Cebreros.
Telemetry bitrate decreased to 114 kbps.
RSI occultation measurements with NNO

1372 11/08/09 223

Shortened communications pass over Cebreros due to ground station maintenance

1373 12/08/09 224

Communications pass over Cebreros.
RSI occultation measurements with NNO.
DDOR with the Cebreros and New Norcia ground stations

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

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.

RSI occultation measurements were performed on DOY 222 and 225.

VIRTIS-M was operated in the visual channels only.

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

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.

Last Update: 1 September 2019
28-Feb-2020 20:57 UT

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