ESA Science & Technology - No. 185 - Start of Quadrature Operations

Outbound quadrature phase
The current quadrature phase is an outbound quadrature: it occurs after the inferior conjunction of Venus on 27 March 2009 and the distance between Venus and the Earth is increasing again. During the quadrature phase revised operating constraints on the VMC instrument lead to the necessity for changing the spacecraft attitude to prevent unacceptable illumination of the VMC. To achieve and maintain this attitude, with a 10° tilt, fake ephemerides on the positions of the spacecraft and the Earth are uploaded to Venus Express.

Later in this quadrature phase a swap to High Gain Antenna 1 (HGA1) is required for Earth communications, as the spacecraft attitude for continuing the use of its HGA2 would result in illumination of spacecraft faces not designed to cope with such exposure. The swap from HGA2 to HGA1 will be on 8 June 2009.

VeRa gravity observation campaign
The mission's eighth gravity observation campaign (GRA#8) was started this week. The campaign is 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 gravity observation campaign is set up to measure anomalies in the planet's gravitational field by analyzing the spacecraft's radio carrier signals received on ground, simultaneously in two radio bands. The detected anomalies provide insight into the properties of the crust and lithosphere of Venus.

The GRA#8 campaign is a set of four observations and is executed with the spacecraft's High Gain Antenna 2 (HGA2). The first three observations were completed in this reporting period, with the last observation planned for 31 May. After that, one more set of four gravity observations is planned before 1 July 2009, which will make use of HGA1 - the bigger dish with a higher signal to noise ratio.

The 70m NASA DSN ground station at Canberra, Australia, was used for receiving the spacecraft's radio signals in the gravity observation campaign.

The table below shows a chronology of the main activities:

At the end of the last Cebreros pass in the reporting period (DOY 150) Venus Express was orbiting Venus at 97.5 million km from the Earth. The one-way signal travel time was 325 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 measurements for gravity observation campaign #8 were carried out on 25, 27 and 29 May.

VIRTIS
VIRTIS-M was operated in the visual channels only.

VMC
The instrument was regularly operated as part of the routine plan.

Future Milestones

• Swap of high gain antenna (HGA) from HGA2 to HGA1 on 8 June 2009.

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Legal disclaimer
This report is based on the ESOC mission operations report, MOR #185. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.