ESA Science & Technology - No. 205 - Atmospheric drag experiments

Venus Express is in a highly eccentric orbit that takes it out to about 66 000 km from the planet when at apocentre, but much closer to the planet's surface when the spacecraft is at pericentre. The altitude at the pericentre passages naturally evolves to as low 175 km. After reaching this lowest value the orbit's pericentre altitude is raised again by mission operations to keep it in the allowed range.

Around the lowest pericentre passages the spacecraft is expected to experience small levels of drag from the upper atmosphere of Venus. The atmospheric drag experiments are set up to detect this drag by its integrated effect on the spacecraft's orbit. Using spacecraft tracking data, accurate orbit determinations are performed to keep track of any drag effect that would show up as a deviation from the expected orbit.

Six experiments were successfully carried out from 12 to 17 October. The spacecraft tracking data was gathered with the support of the New Norcia ground station (NNO) and the regular Cebreros communication passes were also used to record close loop data. Preliminary analysis by the flight dynamics team showed no clear drag effect, but the drag science team have yet to release their analysis results.

The table below shows a chronology of the main activities:

At the end of the last Cebreros pass in the reporting period (DOY 290) Venus Express was orbiting Venus at 232.3 million km from the Earth. The one-way signal travel time was 774.4 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
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

• 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 #205. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.