4.8 Ground Navigation Networks for Spacecrafts
257
Fig. 4.11 Ground control network of GPS constellation
in New Zealand. The purpose of deploying the 16 monitoring stations is to ensure
that each GPS satellite can be tracked and measured by more than three stations at
the same time, to compute more precise orbit and ephemeris parameters and further
improve the system accuracy. There are four of the twelve injection stations colocated with monitor stations, respectively, at Cape Canaveral, Ascension Island,
Diego Garcia Island and Kwajalei Atoll, which are specially designed and configured for operating the GPS constellation. The other eight injection stations are the
remote tracking stations worldwide, which are subordinated to the Air Force Satellite Control Network (AFSCN), respectively, located at Schriever AFB in Colorado
Springs, Vandenberg AFB in California, Hawaii and New Hampshire within the US,
as well as Greenland Island in the North Pole region, Hermitage in the UK, Diego
Garcia Island in the central Indian Ocean and Guam in the western Pacific Ocean,
to increase the visibility, flexibility and robustness for commanding and controlling
the GPS satellites. The ground antennas equipped at the monitor stations uplink the
commands and data codes to the GPS satellites via S-band radio signals and collect
the telemetry. The information can be uploaded to each satellite three times per day,
i.e., every 8 h, and nevertheless, it is usually updated just once a day. Moreover, using
the S-band ranging data from the injection stations, the 2SOPS is allowed to provide
anomaly resolution and early orbit support.
4.8.2.2 Ground Control Segment of GLONASS Constellation
Like the GPS, the GLONASS ground segment takes charges of tracking, monitoring, operating and managing its constellation, determining the satellite ephemeris
257
Fig. 4.11 Ground control network of GPS constellation
in New Zealand. The purpose of deploying the 16 monitoring stations is to ensure
that each GPS satellite can be tracked and measured by more than three stations at
the same time, to compute more precise orbit and ephemeris parameters and further
improve the system accuracy. There are four of the twelve injection stations colocated with monitor stations, respectively, at Cape Canaveral, Ascension Island,
Diego Garcia Island and Kwajalei Atoll, which are specially designed and configured for operating the GPS constellation. The other eight injection stations are the
remote tracking stations worldwide, which are subordinated to the Air Force Satellite Control Network (AFSCN), respectively, located at Schriever AFB in Colorado
Springs, Vandenberg AFB in California, Hawaii and New Hampshire within the US,
as well as Greenland Island in the North Pole region, Hermitage in the UK, Diego
Garcia Island in the central Indian Ocean and Guam in the western Pacific Ocean,
to increase the visibility, flexibility and robustness for commanding and controlling
the GPS satellites. The ground antennas equipped at the monitor stations uplink the
commands and data codes to the GPS satellites via S-band radio signals and collect
the telemetry. The information can be uploaded to each satellite three times per day,
i.e., every 8 h, and nevertheless, it is usually updated just once a day. Moreover, using
the S-band ranging data from the injection stations, the 2SOPS is allowed to provide
anomaly resolution and early orbit support.
4.8.2.2 Ground Control Segment of GLONASS Constellation
Like the GPS, the GLONASS ground segment takes charges of tracking, monitoring, operating and managing its constellation, determining the satellite ephemeris