Operation phases

There are two different phases of operations for Venus Express in its operational orbit: the Earth Pointing phase and the Observation phase. 

1) Earth Pointing phase

This phase is dedicated to communication with Earth and battery charging. It is used whenever the spacecraft is not in the observation phase. In the Earth pointing phase, one of the two High Gain Antennas is oriented towards Earth. The antenna is selected according to the season, so that the spacecraft's cold face remains always protected from illumination by the Sun:

  • The main High Gain Antenna HGA1 , derived from Mars Express but with a smaller diameter (1.3 m instead of 1.6 m), is used during three fourth of the mission, when the spacecraft is the most distant from Earth. In the middle of this period, Venus is in superior conjunction.
  • The second High Gain Antenna HGA2 , derived from Rosetta, is used during the remaining one fourth of the mission, when Venus is closer to Earth. In the middle of this period, Venus is in inferior conjunction.

The rotation angle around the Earth direction is optimised in order to avoid any entrance of Sun light on the side walls radiators.

Diagram of the Earth Pointing orientations
(credit: ESA)

High rate communication are performed 8 hours per day in X-band, in order to transmit to Earth all science data stored in the Solid State Mass Memory. An average of 2 Gbits of science data is downlinked every day to the new ESA ground station of Cebreros, Spain. 

2) Observation phase

There are several different modes of observation, depending on the payload configuration and spacecraft orientation:

  • Nadir pointing: preferably during pericentre pass, but possible on any portion of the orbit. VIRTIS, PFS, SPICAV and VMC may operate in this mode
  • Limb observation: VIRTIS, PFS, SPICAV and VMC may operate in this mode
  • Star occultation (SPICAV)
  • Star occultation (SPICAV/SOIR)
  • Radio science (VeRa)

During observation, the Sun can illuminate under transient conditions any spacecraft face, except for the cold face. The duration of observation is therefore limited by thermal constraints and by battery discharge. The maximum duration of an observation period depends on the Sun direction with respect to the orbit plane, which varies along the mission.

More info

 

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