No. 188 - Quadrature Operations
24 June 2009 17:13
Report for Period 14 June to 20 June 2009
The Venus Express spacecraft and instruments performed nominally during this week of quadrature operations. As part of the quadrature operations the Venus Express spacecraft is flying a tilted attitude during Earth contact with the Cebreros ground station. The 10° attitude tilt with respect to the non-quadrature Earth pointing attitude requires an extended cool-down period for the spacecraft afterwards, before resuming with science pointings. As a result, Cebreros passes - each lasting about 8 hours and nominally performed once every 24-hour orbit - are routinely skipped to allow more time for science pointings. Only three passes were performed in this reporting period as opposed to the usual seven daily passes.
With less passes available to uplink all the required commands, Venus Express is using delayed telecommand files to store and call the commands on-board at a specific time.
The DDOR measurement principle uses a technique to highly accurately determine the position of a transmitter in space and relies on observing the time delay between reception of the signal from the transmitter by two ground stations at different positions on Earth. In this case the Venus Express spacecraft is the transmitter and the two ground stations are New Norcia in western Australia and Cebreros in Avila, Spain.
The table below shows a chronology of the main activities:
At the end of the last Cebreros pass in the reporting period (DOY 171) Venus Express was orbiting Venus at 122.7 million km from the Earth. The one-way signal travel time was 409 seconds.