An experimental optical link between an earth remote sensing satellite, SPOT 4, and a European data relay satellite

The implementation of an experimental optical link between a low earth orbit spacecraft (SPOT 4) and a geostationary satellite (for which ESA is responsible) is described. This optical link is to be used for transmitting the SPOT 4 payload data stream at a rate of 50 Mb/s. These data will be relayed to a ground station through a feeder link in the Ka or Ku band. This first model, on SPOT 4, will demonstrate the feasibility and performance of optical communications and will be used on a preoperational basis to relay image data. The second model, on SPOT 5, could be used on an operational basis in connection with the European Data Relay satellite. The optical terminal uses a 20-cm-diameter telescope with Ritchey-Chretien optics, a 30 mW GaAlAs laser diode, and a silicon avalanche photodiode, the total weight being around 80 kg, and the power consumption 120 W.