Earth Pointing Communication Phase
Diagram of Venus's orbit around the Sun, with the orientation of the Venus Express spacecraft during Earth pointing indicated at different positions. For communications with Earth, Venus Express uses either of its two High Gain Antennae (HGAe) depending on the Sun-Venus-Earth angle.
There are two points in the orbit where the Sun-Venus-Earth angle is 90°. Around these points, or more precisely, when the Sun-spacecraft-Earth angle is between 75° and 95°, Venus Express operations are in the quadrature phase.
Around the quadrature phase a swap is made between Venus Express's two HGAe, which is necessary to maintain the spacecraft's cold face pointed away from the Sun at all times. This is indicated in the figure with the 180° flip around the spacecraft Z-axis.
During the part of the orbit where the Sun-Venus-Earth angle is less than 90° (with the Earth and Sun at conjunction as seen from Venus in the middle of this period) the 1.3m HGA1 is used for communications. When the Sun-Venus-Earth angle lies between 90 and 180° (with the Earth and Sun in opposition as seen from Venus in the middle of this period) the smaller HGA2, with a diameter of 0.3m, is used instead.