254
4 Navigations from Ground to Space
network and multi-purpose”, the navigation network for the spacecrafts is planned
and designed to meet the needs of various spaceflight missions in near-Earth space.
The ground navigation network for the navigation constellations is a special
network for tracking, measuring and operating the navigation constellations, and
generally does not undertake the TT&C tasks for other spacecrafts. For example,
the GPS, GLONASS, BeiDou and Galileo constellations have their own navigation
networks, commonly referred to as the control segments or the ground control
networks. The special navigation frequency L-band is used to track and measure the
navigation satellites, while the TT&C frequency is S-band or C-band.
The ground navigation network for the deep-space explorations is a special
network designed for exploring the Moon, interplanetary space and interstellar space,
with the characteristics of continuous tracking, long navigation duration and far
distance for the measurement equipment to work. Consequently, it usually needs
to use a large diameter antenna of more than 25 m. Furthermore, considering the
influence of background noise in the Galaxy, the TT&C frequency should be transformed from L-band to S-band. For the navigation constellations and the deep-space
explorations, the deployments and tracking measurements of their ground navigation
networks will be discussed in the last two parts of this section, respectively.
4.8.2 Ground Control Networks of GNSS
It is well known that the Global Navigation Satellite System (GNSS) is composed of
the space constellation segment, ground control segment and user terminal segment,
where the ground control segment is implemented by a ground control network
worldwide, taking charges of tracking and measuring the operation status of the navigation satellites, monitoring their health status, generating the navigation message
and injecting the message to the navigation satellites. The network is essentially to
provide a navigation function for the space constellation. From the above section,
it is known that there are four major GNSSs, the GPS, GLONASS, BeiDou and
Galileo, whose control segments all have similar capability and function. Thereby,
as examples, the ground control networks represented by the GPS and GLONASS
system are introduced here in detail.
4.8.2.1 Ground Control Segment of GPS Constellation
The ground control network (or the ground segment) takes charge of the proper
operation for the GPS system, and its main tasks are: to monitor and control the
orbital parameters of the satellites, and their health and subsystem status, such as
the solar arrays, the battery power and the level of propellant used for maneuvers; to
activate the spare satellites; to update the navigation message like ephemeris, almanac
and clock correction parameters; to treat the satellite’s anomalies; to control the SA
and Anti-Spoofing (A/S); to track passively the satellites. The network consists of
4 Navigations from Ground to Space
network and multi-purpose”, the navigation network for the spacecrafts is planned
and designed to meet the needs of various spaceflight missions in near-Earth space.
The ground navigation network for the navigation constellations is a special
network for tracking, measuring and operating the navigation constellations, and
generally does not undertake the TT&C tasks for other spacecrafts. For example,
the GPS, GLONASS, BeiDou and Galileo constellations have their own navigation
networks, commonly referred to as the control segments or the ground control
networks. The special navigation frequency L-band is used to track and measure the
navigation satellites, while the TT&C frequency is S-band or C-band.
The ground navigation network for the deep-space explorations is a special
network designed for exploring the Moon, interplanetary space and interstellar space,
with the characteristics of continuous tracking, long navigation duration and far
distance for the measurement equipment to work. Consequently, it usually needs
to use a large diameter antenna of more than 25 m. Furthermore, considering the
influence of background noise in the Galaxy, the TT&C frequency should be transformed from L-band to S-band. For the navigation constellations and the deep-space
explorations, the deployments and tracking measurements of their ground navigation
networks will be discussed in the last two parts of this section, respectively.
4.8.2 Ground Control Networks of GNSS
It is well known that the Global Navigation Satellite System (GNSS) is composed of
the space constellation segment, ground control segment and user terminal segment,
where the ground control segment is implemented by a ground control network
worldwide, taking charges of tracking and measuring the operation status of the navigation satellites, monitoring their health status, generating the navigation message
and injecting the message to the navigation satellites. The network is essentially to
provide a navigation function for the space constellation. From the above section,
it is known that there are four major GNSSs, the GPS, GLONASS, BeiDou and
Galileo, whose control segments all have similar capability and function. Thereby,
as examples, the ground control networks represented by the GPS and GLONASS
system are introduced here in detail.
4.8.2.1 Ground Control Segment of GPS Constellation
The ground control network (or the ground segment) takes charge of the proper
operation for the GPS system, and its main tasks are: to monitor and control the
orbital parameters of the satellites, and their health and subsystem status, such as
the solar arrays, the battery power and the level of propellant used for maneuvers; to
activate the spare satellites; to update the navigation message like ephemeris, almanac
and clock correction parameters; to treat the satellite’s anomalies; to control the SA
and Anti-Spoofing (A/S); to track passively the satellites. The network consists of