ESA Science & Technology - No. 236 - Start of eclipse season; Completion of Radio Science Investigations occultation campaign #11

Eclipse season

An eclipse season started on 29 June 2011. Two days before the start of the eclipse season, on 27 June, the batteries' end of charge levels were restored to 100%. These had been set to 80% on 27 April, shortly after the previous eclipse season had ended, to extend the battery lifetime.

VeRa Earth occultation campaign #11
The mission's eleventh Radio Science Investigations (RSI) Occultation Campaign, which started on 14 June 2011, was completed on 10 July 2011. These campaigns take place when the Earth is occulted by the disk of Venus; this occurs around the pericentre passages as seen from the spacecraft. Under these conditions unique measurements can be made 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 is used to generate a very stable signal which is sent to Earth over the HGA simultaneously 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 characteristics of the atmosphere (such as temperature, density and pressure) as a function of altitude.

RSI occultation measurements were performed around pericentre on fourteen 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 (NNO) and the NASA Deep Space Network ground station at Canberra (CAN).

VIRTIS cooler anomaly
The VIRTIS-H cooler remains out of service following a malfunction on 14 June 2011. During the VIRTIS-H observation on 21 June 2011, special precautions were taken; VIRTIS events were rerouted to a different event packet store, so that normal spacecraft event data would not be lost in the event of a large number of cooler failure packets. On the communications pass after the observation, the VIRTIS events were downlinked. The expected ‘cooler failure’ events were not present. Upon investigation of the registered events, it was discovered that the VIRTIS-H cooling process had failed. The VIRTIS-H cooler failure has now been confirmed and it will no longer be used; only those VIRTIS-H observations that do not require cooling will be performed.

Summary of main activities
During the reporting period, routine mission operations were conducted using the ESA Cebreros (CEB) ground station. Fourteen RSI occultation measurements were performed using the ESA New Norcia (NNO) (ten passes) and NASA Deep Space Network Canberra (CAN) (four passes) ground stations. Delta Differential One-way Ranging (DDOR) was performed on 25 June 2011, using the New Norcia and Canberra ground stations.

At the end of the reporting period on 16 July 2011, Venus Express was 255.6 million kilometres from Earth. The one-way signal travel time was 852 seconds.

At the end of the reporting period, the final oxidizer mass was estimated to be 32.391 kilograms, and the final fuel mass estimate was 20.178 kilograms.

Payload Activities

Future Milestones

Superior solar conjunction will start on 6 August 2011. Atmospheric Drag Campaign #6 will start on 23 August 2011.

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Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #293 through MOR #296. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.