4.6 Navigation Satellite System
231
or Navigation System Using Timing and Ranging. With the individual satellite being
associated with the name of NAVSTAR, a more fully encompassing name was used
to identify the constellation of NAVSTAR satellites, NAVSTAR-Global Positioning
System (GPS), often simply referred to as GPS.
The GPS consists of three major parts: space segment, control segment and user
segment. The space segment is composed of 24−32 satellites in Medium Earth Orbit
(MEO), and also includes the payload adapters to the boosters required to launch them
into orbit. The control segment consists of a master control station, an alternate master
control station, four dedicated ground antennas and six dedicated monitor stations.
The user segment consists of hundreds of thousands of the U.S. and allied military
users, with secure GPS Precise Positioning Service (PPS), and tens of millions of
civilian, commercial and scientific users, with Standard Positioning Service (SPS).
The GPS satellites broadcast signals to the Earth, and the user receivers receive the
signals and calculate their three-dimensional locations including longitude, latitude
and altitude, as well as their positioning time. The implementation of GPS program
is divided into the following three phases:
(1) From 1973 to 1977 was the scheme demonstration phase. With the Air Force
named the Executive Service, then the TIMATION program merged with the
Project 621B to form the NAVSTAR−GPS program, the TIMATION-3 satellite originally developed by the NRL was re-designated Navigation Technology
Satellite 1 (NTS-1). In the summer of 1974, the NTS-1 with two rubidiumvapor frequency clocks onboard was launched to test the technologies, such
as the onboard atomic clocks, time-based ranging, range rate and 12-h orbit,
and to demonstrate the capability for pinpointing longitude, latitude and altitude throughout the world, leading directly to the first GPS technology. Three
years later, the NTS-2 was successfully sent into the orbit, to verify the earlier
technologies, such as cesium frequency standards, nickel–hydrogen battery,
radiation dosimeters and a worldwide network for data acquisition, and also
considered the first GPS prototype test satellite.
(2) From 1978 to 1985 was the phase that the GPS prototype satellites were
deployed. In February 1978, the first GPS prototype satellite, known as Block
I-1, was launched into the orbit, with an apogee of 20,308 km, a perigee of
20,095 km and an inclination of 63.3°. During this phase, there were a total of
11 Block I satellites launched, of which one was destroyed in a launch failure
and other ten formed a test constellation to validate the feasibility of the GPS
system. The Block I satellites weigh 845 kg each in final orbit, and with three
rechargeable nickel–cadmium batteries for power and 7.25 m
2 of single-degree
solar panels, and themselves, they could only store sufficient information for
3.5 days of independent operation. The Block I satellites emitted the navigation signals at two frequencies L1 (1575.42 MHz) and L2 (1227.60 MHz),
where the Coarse Acquisition Code (C/A-Code) signals were only emitted at
the L1 for civilian uses and the Precision Code (P-Code) signals emitted at
the L1 and L2 for military uses. The uploaded information from the Control
Segment was not encrypted for the Block I. The design life of the satellites
231
or Navigation System Using Timing and Ranging. With the individual satellite being
associated with the name of NAVSTAR, a more fully encompassing name was used
to identify the constellation of NAVSTAR satellites, NAVSTAR-Global Positioning
System (GPS), often simply referred to as GPS.
The GPS consists of three major parts: space segment, control segment and user
segment. The space segment is composed of 24−32 satellites in Medium Earth Orbit
(MEO), and also includes the payload adapters to the boosters required to launch them
into orbit. The control segment consists of a master control station, an alternate master
control station, four dedicated ground antennas and six dedicated monitor stations.
The user segment consists of hundreds of thousands of the U.S. and allied military
users, with secure GPS Precise Positioning Service (PPS), and tens of millions of
civilian, commercial and scientific users, with Standard Positioning Service (SPS).
The GPS satellites broadcast signals to the Earth, and the user receivers receive the
signals and calculate their three-dimensional locations including longitude, latitude
and altitude, as well as their positioning time. The implementation of GPS program
is divided into the following three phases:
(1) From 1973 to 1977 was the scheme demonstration phase. With the Air Force
named the Executive Service, then the TIMATION program merged with the
Project 621B to form the NAVSTAR−GPS program, the TIMATION-3 satellite originally developed by the NRL was re-designated Navigation Technology
Satellite 1 (NTS-1). In the summer of 1974, the NTS-1 with two rubidiumvapor frequency clocks onboard was launched to test the technologies, such
as the onboard atomic clocks, time-based ranging, range rate and 12-h orbit,
and to demonstrate the capability for pinpointing longitude, latitude and altitude throughout the world, leading directly to the first GPS technology. Three
years later, the NTS-2 was successfully sent into the orbit, to verify the earlier
technologies, such as cesium frequency standards, nickel–hydrogen battery,
radiation dosimeters and a worldwide network for data acquisition, and also
considered the first GPS prototype test satellite.
(2) From 1978 to 1985 was the phase that the GPS prototype satellites were
deployed. In February 1978, the first GPS prototype satellite, known as Block
I-1, was launched into the orbit, with an apogee of 20,308 km, a perigee of
20,095 km and an inclination of 63.3°. During this phase, there were a total of
11 Block I satellites launched, of which one was destroyed in a launch failure
and other ten formed a test constellation to validate the feasibility of the GPS
system. The Block I satellites weigh 845 kg each in final orbit, and with three
rechargeable nickel–cadmium batteries for power and 7.25 m
2 of single-degree
solar panels, and themselves, they could only store sufficient information for
3.5 days of independent operation. The Block I satellites emitted the navigation signals at two frequencies L1 (1575.42 MHz) and L2 (1227.60 MHz),
where the Coarse Acquisition Code (C/A-Code) signals were only emitted at
the L1 for civilian uses and the Precision Code (P-Code) signals emitted at
the L1 and L2 for military uses. The uploaded information from the Control
Segment was not encrypted for the Block I. The design life of the satellites