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No. 262 - Continuation of Earth occultation season, end of solar eclipse season, start of Atmospheric Drag Experiment campaign, and special operations due to extensive ground station maintenance

No. 262 - Continuation of Earth occultation season, end of solar eclipse season, start of Atmospheric Drag Experiment campaign, and special operations due to extensive ground station maintenance

Report for the period 23 June to 20 July 2013.This reporting period covers four weeks of Venus Express operations. It includes the continuation of the fifteenth Earth occultation season, end of the twenty-fourth solar eclipse season, the start of the twelfth Atmospheric Drag Experiment campaign, and special operational requirements due to extensive annual ground station maintenance.

Cebreros ground station

All Cebreros ground station activities were nominal during this reporting period. Part of this and the previous reporting period coincided with scheduled extensive annual maintenance on the ground station, from 17 June to 1 July. The Cebreros ground station was unavailable during this time, and Venus Express routine operations were performed temporarily with ESA's ground stations in Malargüe, Argentina, and New Norcia, Australia.

Malargüe ground station

During these annually scheduled maintenance periods at Cebreros, disruptive maintenance is performed and the ground station cannot be used for uplink or downlink. To accommodate daily uplinks and downlinks during the unavailability of Cebreros until 1 July, ESA's ground station in Malargüe, Argentina, was used to communicate with the spacecraft. As Mars Express was also scheduled to use the station each day, it shared station time with Venus Express. The communications windows in this planning period were shifted from the descending branch of the Venus Express orbit (during which the Cebreros ground station normally communicates with the spacecraft), to the ascending branch, when the spacecraft was in direct contact with the Malargüe ground station. The ascending branch of the Venus Express orbit is also the preferred period in which to obtain science data, so the modified communication windows resulted in reduced time available for some of science operations.

The Venus Express and Mars Express flight control teams arranged to use the Malargüe antenna by alternating long and short passes between the two missions from 17 to 30 June. Under this arrangement, on one day Mars Express would be scheduled for a long pass of about 6.5 hours, and Venus Express would be scheduled for about 2.75 hours. Then on the next day, Mars Express would be scheduled for a short pass of about 2.25 hours, and Venus Express would be scheduled for a longer pass of about 7 hours. The short passes do not allow much data dumping, but they allow time for command uplinks and telemetry downlinks to ensure safe operations. The short passes for Venus Express took place on 23, 25, 27 and 30 June. The long passes occurred on 22, 24, 26, 28 and 29 June.

New Norcia ground station

During this time, the ESA ground station in New Norcia was not booked for use on three days for a brief period when it had direct visibility of Venus Express. The spacecraft was already using this ground station for radio science observations; in those orbits where other missions were not immediately using the station after Venus Express, the operations team requested an extension of their use of the ground station to include data downlinks in the available time. This is unusual, and has only been done once before. The request was analysed and agreed to by the flight control team and the ground station scheduling office. On 23 June, 25 June and 27 June, Venus Express downlinked data via the New Norcia ground station.

High accuracy spacecraft ranging

ESA's Cebreros and New Norcia ground stations were used for a Delta Differential One-way Ranging (delta-DOR, or DDOR) measurement at the start of the Cebreros communications pass on 7 July.

These high accuracy ranging measurements are carried out with the Venus Express spacecraft on a regular basis to support the accurate determination of the ephemeris for the planet Venus that is maintained by NASA's Solar System Dynamics Group.

For more information about DDOR, see "Delta-DOR measurements".

End of the twenty-fourth eclipse season

Venus Express's twenty-fourth eclipse season ended during this planning period. The last eclipse occurred on 2 July 2013. The next eclipse season starts on 31 August 2013.

Particular science observations are carried out during eclipse seasons: for further details, see the Scientific Focus section below and 'Science observations with Venus Express during an eclipse'.

Battery charge reconfiguration and deep discharge test

The mission's twenty-fourth eclipse season ended on 2 July. The battery's end-of-charge (EOC) state, which had been at 100% for the eclipse season, was subsequently lowered to 80% on 8 July.

During solar eclipse seasons, the spacecraft is in complete darkness during a portion of each orbit when Venus blocks out the Sun. At this time, the spacecraft bus and payload are powered by the on-board battery, which must then be recharged again to 100% prior to the next eclipse. The battery (composed of three individual battery packs) is sized so that at the end of its life, the spacecraft can go through the longest eclipse and still retain enough stored power for the spacecraft to successfully complete a transition to 'safe mode' in the event of a spacecraft system anomaly.

Outside eclipse seasons, sufficient battery power must be maintained at all times for a transition to safe mode. However, a lower (than 100%) battery energy level (or end-of-charge state) can be maintained, as no provision is needed for eclipses. Lowering the battery's end-of-charge state prolongs its life.

In addition to the change in battery charge state, a battery deep discharge test was performed 8 July. This is a standard test that is repeated at intervals to determine the health of the battery. The battery is discharged very deeply, and its voltage is compared to the predicted values. The model describing the battery discharge is updated if necessary. In this case, the battery health was nominal.

Continuation of the fifteenth Earth occultation season

The fifteenth Earth occultation season continued during this entire planning period; occultation observations were performed in every other orbit. The spacecraft radio signal is received on Earth via the New Norcia antenna in western Australia, designated DSA-1. New Norcia is specifically used for the radio science because it has the best viewing angle to Venus Express orbit when the spacecraft is at pericentre (the Venus Express orbit is 24 hours long).

During this reporting period, Venus Radio science experiment (VeRa) occultation observations were alternated so that the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument could obtain measurements of the Nitrogen Oxide concentrations in the atmosphere during eclipses.

For more information, please see the Scientific Focus section (below) and 'Venus Express Earth occultation seasons'.

Twelfth Atmospheric Drag Experiment campaign

The twelfth Atmospheric Drag Experiment campaign began during this reporting period. Six drag passes were performed in this planning period, between 15 and 20 July; the campaign continued into the next reporting period.

Calibration passes (also known as pre-ADE passes) were carried out over a twenty-day period prior to the first pass on 15 July. Data from the pre-ADE measurements were calculated and stored on-board, then downlinked along with the spacecraft telemetry.

The ADE passes were performed at pericentre altitudes as low as 170 km. These ADE passes used radio tracking from ESA's New Norcia Ground station.

For more information on ADE campaigns, see the link in the right-hand menu.

Orbit control manoeuvres

Two orbit correction manoeuvres were carried out during this reporting period. The first was performed at pericentre on 30 June, to adjust the orbit period. The second manoeuvre was performed at apocentre on 1 July, for a very small adjustment to the pericentre altitude.

At this stage of the mission, with low fuel levels on the spacecraft, the orbit correction manoeuvres are carried out as a number of small burns – rather than fewer large burns – to ensure that they are performed accurately. An explanation for this can be found in Status Report no. 257.

Summary of main activities

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

Main activities during reporting period
ADE = Atmospheric Drag Experiment; AOS = Acquisition of Signal; CEB = Cebreros; DOR = Differential One-way Ranging; DOY = Day of year; EOC = End of Charge; MET = Mission elapsed time; MLG = Malargüe; NNO = New Norcia; OCM = Orbit Correction Manoeuvre
MET
(Day)
Date DOY Main Activity
2784 23-Jun-2013 174 NNO occultation pass; NNO communication pass; MLG communication pass; CEB shutdown for planned annual maintenance.
2785 24-Jun-2013 175 MLG communication pass; CEB shutdown for planned annual maintenance.
2786 25-Jun-2013 176 NNO occultation pass; NNO communication pass; MLG communication pass; CEB shutdown for planned annual maintenance.
2787 26-Jun-2013 177 Telemetry bitrate changed to 91kbps before AOS; MLG communication pass; pre-ADE calibration pass; CEB shutdown for planned annual maintenance.
2788 27-Jun-2013 178 NNO occultation pass; NNO communication pass; MLG communication pass; CEB shutdown for planned annual maintenance.
2789 28-Jun-2013 179 MLG communication pass; CEB shutdown for planned annual maintenance.
2790 29-Jun-2013 180 MLG communication pass; pre-ADE calibration pass; CEB shutdown for planned annual maintenance.
2791 30-Jun-2013 181 MLG communication pass; CEB under planned annual maintenance shutdown; OCM at pericentre.
2792 01-Jul-2013 182 NNO occultation pass; CEB communications passes resume after annual maintenance shutdown; OCM at apocentre.
2793 02-Jul-2013 183 CEB communication pass; end of the twenty-fourth eclipse season.
2794 03-Jul-2013 184 NNO occultation pass; CEB communication pass.
2795 04-Jul-2013 185 Pre-ADE calibration pass; CEB communication pass; CEB monthly maintenance.
2796 05-Jul-2013 186 NNO occultation pass; CEB communication pass; CEB monthly maintenance.
2797 06-Jul-2013 187 CEB communication pass.
2798 07-Jul-2013 188 NNO occultation pass; CEB communication pass; Delta-DOR with NNO and CEB.
2799 08-Jul-2013 189 Pre-ADE calibration pass; CEB communication pass; Battery deep discharge test; Battery EOC state lowered to 80%.
2800 09-Jul-2013 190 NNO occultation pass; CEB communication pass.
2801 10-Jul-2013 191 CEB communication pass.
2802 11-Jul-2013 192 NNO occultation pass; CEB communication pass.
2803 12-Jul-2013 193 Pre-ADE calibration pass; CEB communication pass.
2804 13-Jul-2013 194 NNO occultation pass; CEB communication pass.
2805 14-Jul-2013 195 CEB communication pass.
2806 15-Jul-2013 196 CEB communication pass; first pass of the twelfth ADE campaign.
2807 16-Jul-2013 197 CEB communication pass; ADE pass.
2808 17-Jul-2013 198 CEB communication pass; ADE pass.
2809 18-Jul-2013 199 CEB communication pass; ADE pass.
2810 19-Jul-2013 200 CEB communication pass; ADE pass.
2811 20-Jul-2013 201 CEB communication pass; ADE pass.

At the end of the reporting period on 20 July, Venus Express was 209 million kilometres from Earth. The one-way signal travel time was 699 seconds. The final oxidizer mass was 18.149 kg and the final fuel mass was 11.099 kg.

Scientific focus

This reporting period falls under the 94th medium term plan (MTP), which covered the period from 23 June to 20 July 2013. The fifteenth Earth occultation season continued in this MTP, while the twenty-fourth solar eclipse season ended on 2 July.

The twelfth ADE campaign had high priority during this 28-day period. The ADE passes started on 15 July and continued through this planning period, ending only on 27 July. Calibration passes (also known as pre-ADE passes) were carried out over a twenty-day period prior to the first pass on 15 July. Data from the pre-ADE measurements were calculated and stored on-board, then downlinked along with the spacecraft telemetry.

For short periods of time during Earth occultation seasons, the spacecraft's radio signal can pass through Venus' atmosphere before it is received on Earth. These periods are exploited for unique radio science measurements of Venus' atmosphere using the Venus Radio science experiment (VeRa).

While the spacecraft is in the shadow of the planet during solar eclipses, the Venus Monitoring Camera (VMC) can make use of an infrared 'window' in the clouds to obtain low resolution images of the surface.

The Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) Nitrogen Oxide mapping campaign continued to be a priority in this reporting period. VeRa occultation observations were alternated with SPICAV measurements of the Nitrogen Oxide concentrations in the atmosphere during eclipses; the latter were carried out in half of the orbits. VMC cloud tracking observations were prioritised at the end of the eclipse season to improve the global coverage at particular latitudes.

Change in Venus Express's pericentre altitude with time from 31 March 2013 to 20 July 2013. Credit: ESA Change in Venus Express's Local Time at Ascending Node from 31 March 2013 to 20 July 2013. Credit: ESA
Venus Express coverage of Venus from 23 June to 20 July 2013. Credit: ESA

Payload activities

All instruments performed nominally during this reporting period.

ASPERA The instrument was regularly operated nominally as part of the routine plan.
MAG The instrument was regularly operated nominally as part of the routine plan.
PFS The instrument was not operated.
SPICAV The instrument was regularly operated nominally as part of the routine plan.
VMC The instrument was regularly operated nominally as part of the routine plan.
VeRa The instrument was regularly operated nominally as part of the routine plan.
VIRTIS The instrument was regularly operated nominally as part of the routine plan.

Future milestones

  • End of the fifteenth Earth occultation season
  • Start of in-bound quadrature operations

Legal disclaimer

This report is based on four ESOC mission operations reports, MOR #395 through MOR #398, as well as the MTP94 Master Science Plan. Please see the copyright section in the Terms and Conditions for this site.

Last Update: 1 September 2019
15-Nov-2019 07:50 UT

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