ESA Science & Technology - Quadrature Operations Timeline

Timeline of first quadrature operations for Venus Express, with key events indicated:

The quadrature phase of the mission is defined as the period during which the Sun-spacecraft-Earth angle is between 75° and 95°. There are two points in Venus's orbit where the planet is in quadrature (see also related image) and consequently Venus Express is as well.

Around quadrature, operations involve:

• A tilt of 10° is required in the spacecraft attitude, to prevent unacceptable illumination of the VMC, the Visual Monitoring Camera
• To achieve and maintain the 10° tilt, fake ephemerides are uploaded to Venus Express
• A swap is performed between the two High Gain Antennae (HGAe). The time between the two quadrature points, and when Venus is between the Earth and the Sun, Venus Express uses the HGA2 for communications with Earth. During the remainder of Venus's orbit the HGA1 is used. The swap to HGA2 is required as the spacecraft attitude for continuing the use of HGA1 during Earth communications would result in illumination of spacecraft faces not designed to cope with such exposure
• In order to perform science during the quadrature phase, a 17 hour cooling is required before any spacecraft communication. This forces the missing of some of the passes at Cebreros, indicated with grey-hatched boxes in the figure
• Not having sufficient ground station passes to uplink all the commands, delayed TC files are used to store and call the commands on-board at a specific time

Explanation of acronyms: