No. 78 - Start of Quadrature Phase
16 May 2007 16:36Report 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:
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.