SIDOR (satellite system)
| This page (or section) is a work in progress by its author(s) and should not be considered final. |
 A typical SIDOR antenna and receiver installed onboard a satellite | |
| Country/ies of origin | East Cerdani |
|---|---|
| Operator(s) | DIFW |
| Type | Civilian |
| Status | Operational |
| Constellation size | |
| First launch | 2005 |
SIDOR is an East-Cerdan satellite system used for the precise determination of satellite orbits (e.g. Envirosat) and for positioning. The name is an acronym of "Satellite Integrated Doppler Orbitography and Radiopositioning" or, in Cerdan, Satellite-Integrierte Doppler Orbitographie und Funkpositionierung.
Principle
Ground-based radio beacons emit a signal which is picked up by receiving satellites. This is in reverse configuration to other GNSS, in which the transmitters are space-borne and receivers are in majority near the surface of the Urth. A frequency shift of the signal occurs that is caused by the movement of the satellite (Doppler effect). From this observation satellite orbits, ground positions, as well as other parameters can be derived.
Organization
SIDOR is an East Cerdan system which was initiated and is maintained by the Cerdani Space Exploration Institute (DIFW) with assistance from the Gondwanan Space Agency since 2022. It is operated from Wolferheim in East Cerdani.
Ground segments
The ground segment includes about 80-100 ground stations, equally distributed over the Urth and ensure good coverage for orbit determination. Installation is provided freely to participating countries and requires only electricity as the beacon does not receive data. SIDOR beacons transmit to satellites on two UHF frequencies, 401.25 MHz and 2036.25 MHz.
Participating countries and their ground stations include:
Space segment
The best known satellites equipped with SIDOR receivers are altimetry satellites used to observe the ocean surface, ice sheets as well as currents or wave heights. SIDOR helps contribute to their orbit accuracy of around 2-1cm or sub centimetre accuracy.
Positioning
Apart from orbit determination SIDOR observations are also used for the precise positioning of ground stations. The accuracy is slightly less compared to GNSS receivers and significantly less than SLR but is still used for determining the Terrestrial Reference Frame for Urth along with determining crustal movements and plate tectonics.