ESA Science & Technology - No. 237 - Superior Solar Conjunction

Summary of main activities

The reporting period began with routine science activities and was nominal on the spacecraft side.

Orbit Change Manoeuvres (OCM) were executed on 17 July (at pericentre) and 18 July (apocentre) 2011.

The solid-state mass memory (SSMM) had a re-occurrence of an anomaly on 25 July 2011 causing the telecommand file transfer to be aborted. The unit was recovered by executing a warm reset.

The Earth-spacecraft-Sun alignment approached Solar Conjunction, when the Sun is almost directly between the spacecraft and the Earth. The angle, from the Earth to Venus to the Sun, is between 3 degrees and 6 degrees. This places a powerful energy source (the Sun) almost directly in the line from the Earth to the spacecraft, with the result that it can be harder to detect the spacecraft downlink signal, and harder to get a clear signal to the spacecraft from Earth. To offset the problems caused by this situation, the Telemetry and Telecommand bit rates (TLM BR and TC BR) were decreased on 26 July before entering the Solar Conjunction operations. As a general rule, reducing the amount of information in the signal increases the signal clarity. The Cebreros ground station also switched from the usual downlink power amplifier (the X-Band Low Power Amplifier, or XLPA) to the High Power Amplifier (XHPA), to improve the raw signal strength, and therefore the ease of signal detection on the spacecraft.

On 05 August 2011, all science operations were stopped due to the upcoming loss of communications (during Solar Conjunction). On 06 August, Venus Express entered Superior Solar Conjunction; this lasted until 26 August. Science operations were resumed on 28 August.

The spacecraft functioned autonomously without ground control from 08 August to 22 August to allow maintenance at the Cebreros (CEB) ground station. During this period, two short passes, on 10 August and 18 August and each of 3 hours duration, were held with the New Norcia (NNO) ground station, to check the spacecraft status. Daily passes resumed on 22 August through the nominal ground station at Cebreros.

At the end of the reporting period on 27 August 2011, Venus Express was at 258.09 million kilometres from Earth. The one-way signal travel time was 860 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

• Atmospheric Drag Experiment (ADE) #6 will start on 13 September 2011.
• Atmospheric Radio Occultation (OCC) season #12 begins on 15 November 2011

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Legal disclaimer
This report is based on four ESOC mission operations reports, MOR #297 through MOR #300. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.