ESA Venus Express Status Report No. 78 - Start of Quadrature Phase

Status Report From: ESA Venus Express Mission
Posted: Wednesday, May 23, 2007

image 16 May 2007 16:36 Report for Period 6 May to 12 May 2007

With the installation of AOCMS_SW patch 14 and the update of the on-board ephemeris, Venus Express was configured for the quadrature phase. This phase is defined as the period during which the Sun-Spacecraft-Earth angle is between 75* and 95*.

During the quadrature phase, revised operating constraints on the VMC lead to the necessity for changing the spacecraft attitude to prevent unacceptable illumination of the VMC. To this end, fake ephemerides on the positions of the spacecraft and the Earth are uploaded to Venus Express.

On 11 May 2007, for the first time, Earth pointing was achieved using fake ephemerides with a Sun illumination of ~10 degrees on the +Y spacecraft face. The first pass with a tilted attitude was closely monitored by the Flight Control Team (FCT). As part of quadrature operations, the delayed execution of TC files was also introduced. No anomalies related to quadrature operations were detected and the performances of the system were nominal.

Later in the quadrature phase a swap to High Gain Antenna 2 is required for Earth communications, as the spacecraft attitude for continuing the use of HGA 1 would result in illumination of spacecraft faces not designed to cope with such exposure.

As part of the investigation of the anomaly with the S-Band, a set of tests was performed on 8 May with the New Norcia ground station. The current indications suggest that the problem lies in the path between the entry to RFDU SW3 and the antenna.

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

MET (Day) Date DOY VPER# Main Activity
544 06/05/07 126 380 TM bitrate updated to 228 kbps before the pass
545 07/05/07 127 381 Routine Mission Operations
546 08/05/07 128 382 S-Band test
547 09/05/07 129 383 Installation of patch 14 in RAM and both EEPROM
548 10/05/07 130 384 Routine Mission Operations
549 11/05/07 131 385 Start of quadrature phase.
For the first time, fake ephemerides were used to compute guidance and commanding was uplinked via delayed TC files
550 12/05/07 132 386 Routine Mission Operations.

At the end of the last Cebreros pass in the reporting period (DOY 132, 18:00z) Venus Express was orbiting Venus at 139 million km from the Earth. The one-way signal travel time was 463 seconds.

Payload Activities

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

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

This instrument is OFF and was not operated.

The instrument was operated as part of the routine plan.

Occultation observations were performed over New Norcia on DoY 126, 128, 130 & 132 and over Canberra on DoY 127.

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

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

Ground Facilities

During the reporting period Venus Express has been supported by daily passes with Cebreros. Several TM frames were lost during two Cebreros passes on DoY 129 and 130. The missing TM packets were copied on-board for later retrieval and successfully dumped on DoY 132.

New Norcia supported radio science observations on DoY 126, 128, 130 and 132. The ground station provided support for the S-Band test on DoY 128.

Future Milestones

Swap from HGA 1 to HGA 2 will be performed on DoY 159.
The quadrature phase operations will extend up to mid June 2007 (DoY 167).

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