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No. 143 - Fourth Pericentre Lowering Manoeuvre

No. 143 - Fourth Pericentre Lowering Manoeuvre

Report for Period 3 August to 9 August 2008 All operations have been nominal during the reporting period. The fourth and final pair of Orbit Control Manoeuvres (OCMs) to lower the pericenter altitude and to raise the apocentre altitude was executed. For the first time, there have been clear indications of a very low level of atmospheric drag causing an estimated reduction in apocentre altitude of 6-7 metres at each pericentre passage.

The table below shows a chronology of the main activities in the reporting period:

MET (Day) Date DOY Main Activity
999 03/08/08 216 Performance of apocentre raising OCM#4 just before Cebreros communication pass
1000 04/08/08 217 Performance of pericentre lowering OCM#4 during Cebreros communication pass, to bring pericentre altitude down to 185 km
1001 05/08/08 218 New Norcia pass, for tracking and to monitor the spacecraft status after pericentre manoeuvre.
Routine Operations at Cebreros pass and also reaction wheel offloading
1002 06/08/08 219

Routine Operations.
Atmospheric drag experiment with Deep Space Network ground station.
Reaction wheel offloading during Cebreros pass

1003 07/08/08 220 Routine Operations.
Reaction wheel offloading during Cebreros pass
1004 08/08/08 221

Routine Operations.
Atmospheric drag experiment with Deep Space Network ground station.
Reaction wheel offloading during Cebreros pass

1005 09/08/08 222 Routine Operations.
Atmospheric drag experiment with Deep Space Network ground station

At the end of the last Cebreros pass in the reporting period (DOY 222) Venus Express was orbiting Venus at 243.3 million km from the Earth. The one-way signal travel time was 811 seconds.

Pericentre Lowering Campaign

Between 13 July and 5 August 2008 a series of OCMs was performed to lower the pericentre altitude of Venus Express (see also the link on the right hand side for more details).

Apocentre raising OCM#4
The purpose of the OCM executed at pericentre on 3 August was to raise the apocentre altitude by 7.5 km. The manoeuvre had a nominal magnitude of 41.0 mms-1. The calibration within the orbit determination showed a slight under-performance of 1.26% (-0.51 mms-1) with a 1-sigma uncertainty of 0.05% (0.02 mms-1). The increase in apocentre altitude was about 95 m less than planned.

Pericentre lowering OCM#4
The purpose of the OCM executed at apocentre on 4 August was to lower the pericentre altitude by 5.5 km to 185 km. The manoeuvre had a nominal magnitude of 321.8 mms-1. The calibration within the orbit determination showed a slight under-performance of 0.47% (-1.52 mms-1) with a 1-sigma uncertainty of 0.11% (0.35 mms-1). The reduction in pericentre altitude was about 25 m less than planned.

Orbital period change
The combined effect of the two manoeuvres was foreseen to increase the orbital period by about 2.9 seconds. The actual increase in orbital period was about 0.1 seconds less than planned.

Atmospheric drag
During the interval when the pericentre altitude was at around 190 km, there are indications of a very low level of atmospheric drag. The effect is derived from the observed changes in the spacecraft's orbit as determined from tracking data. The estimated reduction in apocentre altitude, due to atmospheric drag on the spacecraft at each pericentre passage, is 6-7 metres per orbit. This corresponds to a reduction in orbital period at each pericentre passage of the order of 0.01 seconds caused by a decrease in orbital velocity of about 0.035 mms-1.

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 observations were made during the reporting period.

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

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

Future Milestones

  • High gain antenna (HGA1) S-band carrier power test is planned for 15 December 2008
  • Next quadrature phase will start on 19 December 2008

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Legal disclaimer
This report is based on the ESOC mission operations report, MOR #143. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.

Last Update: 1 September 2019
15-Nov-2019 23:02 UT

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