The DORIS instrument onboard Jason-2 provides real-time location and precise orbit determination. DORIS measurements are also used for geophysical studies, in particular through the International DORIS Service (IDS). DORIS is a dual-frequency instrument able to determine atmospheric electron content.
The main changes from the previous DORIS instruments are:
– the instrument will benefit from full redundancy;
– it will be possible to fully reload software without any mission interruption;
– platform attitude will be provided in real time to DORIS and used by Diode (the onboard DORIS navigator); and will also be downloaded by DORIS with the science telemetry dataflow;
– a dosimeter will be included in the electronics unit, to measure the total radiation dose received by DORIS;
– the onboard altimeter will receive information from DORIS for real-time tracking.
Real-time location: Diode
Precise orbit determination
Ionospheric electron content
By measuring and comparing the path delay of signals transmitted at two separate frequencies, DORIS is able to calculate the electron content in the atmosphere. This information is then used to determine perturbations on the altimeter’s radar signal.
This function complements the dual-frequency altimeter function.
DORIS orbitography beacons transmit signals at two separate frequencies (2,036.25 MHz and 401.25 MHz) to the satellite. The receiver onboard the satellite analyses the received signal frequencies to calculate its velocity relative to Earth. This velocity is fed into orbit determination models to derive the satellite’s position on orbit to within two centimetres on the radial component.