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No. 181 - Gravity observation campaign

No. 181 - Gravity observation campaign

Report for Period 26 April to 2 May 2009The Venus Express spacecraft and instruments performed nominally during this week. An orbit control manoeuvre (OCM) was successfully carried out on 26 April (DOY 116) and the mission's seventh gravity observation campaign was completed.

Orbit Control Manoeuvre
The OCM executed on DOY 116 was a prograde manoeuvre at pericentre, with the intention of raising the apocentre altitude of the spacecraft's orbit by 113 km and increasing the orbital period by 187 seconds. The nominal magnitude of the manoeuvre was 605.0 mms-1.

The calibration within the orbit determination showed a slight over-performance of 0.60% (+3.7 mms-1) with a 1-sigma uncertainty of 0.03% (0.2 mms-1): the apocentre altitude was increased by 0.67 km more than planned and the orbital period was increased by 1.1 seconds more than planned.

VeRa gravity observation campaign
The mission's seventh gravity observation campaign (GRA#7) was performed 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#7 campaign was a set of three observations and was executed with the spacecraft's High Gain Antenna 2 (HGA2). Two more sets of gravity observations are planned before 1 July 2009. The HGA1 - the bigger dish with a higher signal to noise ratio - can only be used in defined geometrical constellations between Sun, Earth and Venus, because of thermal considerations that constrain the spacecraft's attitude. The swap from HGA2 to HGA1 will be on 8 June 2009, allowing the last set of gravity observations to be performed with HGA1.

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:

MET
(Day)
Date DOY Main Activity
1265 26/04/09 116 Orbit Control Manoeuvre, start at 02:17 UT.
Communications pass over Cebreros.
Tracking test with 15m dish at Perth
1266 27/04/09 117 Canberra RSI pass (GRA#7).
Communications pass over Cebreros
1267 28/04/09 118 Communications pass over Cebreros
1268 29/04/09 119 Canberra RSI pass (GRA#7).
Telemetry bit rate changed from 114 kbps to 91 kbps.
Communications pass over Cebreros
1269 30/04/09 120 Communications pass over Cebreros
1270 01/05/09 121 Canberra RSI pass (GRA#7).
Communications pass over Cebreros
1271 02/05/09 122 Communications pass over Cebreros

At the end of the last Cebreros pass in the reporting period (DOY 122) Venus Express was orbiting Venus at 65.3 million km from the Earth. The one-way signal travel time was 218 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 #7 were carried out on 27 and 29 April and on 1 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

  • Start of next (outbound) quadrature phase on 29 May 2009.
  • 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 #181. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.

Last Update: 1 September 2019
10-Jul-2020 01:16 UT

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