222
4 Navigations from Ground to Space
Satellite (DORIS), a typical Doppler counting navigation system, was developed in
France by Centre National d’Etudes Spatiales (CNES) with cooperation of Grope de
Recherche en Géodésie Spatiale (GRGS) and Institut Géographique National (IGN)
in the mid-1980s. The system consists of more than 50 ground-based radio beacon
stations, a DORIS control center and a number of the onboard DORISreceivers.
The ground-based stations emit the radio signals to satellites at two central frequencies 401.25 and 2036.25 MHz, and then the double-frequency Doppler counts are
obtained with the DORISreceivers on board of the satellites. Thereby, the satellites
can autonomously determine its orbital parameters by using the Doppler counts. The
best known satellites equipped with the DORIS receivers are the ocean surface topography mapping satellite TOPEX/Poseidon, and the global ocean circulation monitoring satellites Jason-1 and Jason-2, which are used to observe the ocean surface as
well as currents or wave heights. The DORIScontributes to the two orbit accuracies
of about 2 cm. Moreover, the DORIS is also used for the orbit determinations of
other satellites, such as the Earth observation satellite series SPOT-2, SPOT-4 and
SPOT-5; the large geostationary Earth-observing satellite Envisat; the polar icecap
monitoring CryoSat-2; the ocean-observing satellite HY-2A; and so on. Apart from
the orbit determinations, the DORISobservations are used for positioning of ground
stations. Although the positioning accuracy of the DORIS is a bit lower than with
that of the GPS, it still contributes to maintain the International Terrestrial Reference
Frame (ITRF).
In the early 1980s, the European Space Agency (ESA) initiated a project for testing
extremely accurate orbit determination performance, called the Precision Range and
Range-rate Equipment (PRARE), which was developed in Germany. The PRARE
is a compact, space-borne, two-way, two-frequency microwave satellite tracking
system based on the measurement principle of determining the signal travel times and
Doppler shifts. The system is composed of the space-borne microwave transceivers,
ground microwave transmitting stations, ground master station and ground calibration stations. Its basic operation process is: firstly, the space-borne microwave transmitter sends the downlink signals of modulating the pseudo-random noise ranging
codes and data codes to the ground stations at two frequencies 8489 MHz and
2248 MHz, respectively; secondly, the ground stations forward the uplink signals of
carrying the modulated codes at the frequency of 7225.29 MHz; thirdly, the spaceborne receivers receive the uplink signals, getting the delays of the ranging codes
with Delay Locked Loop (DLL) and the Doppler shifts with Phase Locked Loop
(PLL), and demodulate the navigation data; finally, the satellites can autonomously
determine their orbital parameters by using the observables like the pseudoranges
and Doppler shifts, and the navigation data. Since 1991, the PRARE system has been
used for the precision orbit determination of the European Sensing Satellites ERS-1
and ERS-2, and the weather observation satellites from Meteor-3 to Meteor-7.
4 Navigations from Ground to Space
Satellite (DORIS), a typical Doppler counting navigation system, was developed in
France by Centre National d’Etudes Spatiales (CNES) with cooperation of Grope de
Recherche en Géodésie Spatiale (GRGS) and Institut Géographique National (IGN)
in the mid-1980s. The system consists of more than 50 ground-based radio beacon
stations, a DORIS control center and a number of the onboard DORISreceivers.
The ground-based stations emit the radio signals to satellites at two central frequencies 401.25 and 2036.25 MHz, and then the double-frequency Doppler counts are
obtained with the DORISreceivers on board of the satellites. Thereby, the satellites
can autonomously determine its orbital parameters by using the Doppler counts. The
best known satellites equipped with the DORIS receivers are the ocean surface topography mapping satellite TOPEX/Poseidon, and the global ocean circulation monitoring satellites Jason-1 and Jason-2, which are used to observe the ocean surface as
well as currents or wave heights. The DORIScontributes to the two orbit accuracies
of about 2 cm. Moreover, the DORIS is also used for the orbit determinations of
other satellites, such as the Earth observation satellite series SPOT-2, SPOT-4 and
SPOT-5; the large geostationary Earth-observing satellite Envisat; the polar icecap
monitoring CryoSat-2; the ocean-observing satellite HY-2A; and so on. Apart from
the orbit determinations, the DORISobservations are used for positioning of ground
stations. Although the positioning accuracy of the DORIS is a bit lower than with
that of the GPS, it still contributes to maintain the International Terrestrial Reference
Frame (ITRF).
In the early 1980s, the European Space Agency (ESA) initiated a project for testing
extremely accurate orbit determination performance, called the Precision Range and
Range-rate Equipment (PRARE), which was developed in Germany. The PRARE
is a compact, space-borne, two-way, two-frequency microwave satellite tracking
system based on the measurement principle of determining the signal travel times and
Doppler shifts. The system is composed of the space-borne microwave transceivers,
ground microwave transmitting stations, ground master station and ground calibration stations. Its basic operation process is: firstly, the space-borne microwave transmitter sends the downlink signals of modulating the pseudo-random noise ranging
codes and data codes to the ground stations at two frequencies 8489 MHz and
2248 MHz, respectively; secondly, the ground stations forward the uplink signals of
carrying the modulated codes at the frequency of 7225.29 MHz; thirdly, the spaceborne receivers receive the uplink signals, getting the delays of the ranging codes
with Delay Locked Loop (DLL) and the Doppler shifts with Phase Locked Loop
(PLL), and demodulate the navigation data; finally, the satellites can autonomously
determine their orbital parameters by using the observables like the pseudoranges
and Doppler shifts, and the navigation data. Since 1991, the PRARE system has been
used for the precision orbit determination of the European Sensing Satellites ERS-1
and ERS-2, and the weather observation satellites from Meteor-3 to Meteor-7.