An instrument used on satellites to indicate their precise trajectory. It employs the Doppler effect, in which a frequency is higher between a transmitter and receiver moving towards one another and lower if they are moving apart. DORIS is a receiver that measures the Doppler shift of radio signals continuously transmitted by 50 ground beacons. Designed and developed by four French groups, among them the Centre National d'Etudes Spatiales, DORIS has flown on several spacecraft, including the European Space Agency's Envisat.
Subjects: Astronomy and Astrophysics.