4.6 Navigation Satellite System
233
eventually, allowing civilian users to receive a non-degraded GPS signals globally,
the SPS accuracy had been improved from 110 to 20 m available. The GPS is owned
and operated by the U.S. Government as the national asset, while the DoD is the
steward of GPS. From 1996 to 2004, the IGEB oversaw the GPS policy matters. In
2004, the U.S. President George W. Bush updated the national policy directive, and
then the IGEB was replaced by the national executive committee for space-based
Positioning, Navigation and Timing (PNT) to advise and coordinate federal departments and agencies on matters concerning the GPS and related navigation systems.
The PNT executive committee is chaired jointly by the deputy secretaries of defense
and transportation, and its membership includes equivalent-level officials from the
departments of state, commerce and homeland security, as well as the joint chief of
staff and the NASA. Furthermore, components of the executive office of the president participate as observers of the executive committee, and the chairman of Federal
Communication Commission (FCC) participates as a liaison.
Since the GPS deployment, the improvements of the system performance have
been implemented consistently, including the added new signals; updated ground
stations; improved navigation accuracy and increased continuity, integrity, availability, anti-jam and autonomous survivability. Meanwhile, all of the improvements
maintained compatibility with existing GPS equipment. Modernization of the GPS
satellites has been an ongoing by the DoD through a series of satellite acquisitions to
meet the growing needs of the military, civilian and commercial markets. Between
1997 and 2004, a total of 12 GPS replenishment satellites called Block IIR were
launched, of which the first launch was unsuccessful due to the rocket’s failure and
the other 11 satellites successfully entered into the orbits. There are two significant
advancements for the Block IIR satellites. One is with the autonomous navigation
capability by using the inter-satellite crosslink ranging, known as AutoNav, and the
other is to use the onboard reprogrammable processors to do their own fixes in flight.
Moreover, the Block IIR also demonstrated the concept of Distress Alerting Satellite System (DASS). Between 2005 and 2009, a total of eight GPS replenished and
modernized satellites were successfully sent into the orbits, known as Block IIR-M.
The Block IIR-M satellites emitted the added signals of two codes, the M-code as a
new military code and the L2C code as a new civilian code. Between 2010 and 2016,
a total of 12 GPS follow-on satellites called Block IIF were put into the constellation. Compared with the Block IIR-M, the improvements of the Block IIF include
the third civil signal L5 (1176.45 MHz), 12-year design lifetime, improved rubidium
frequency standards, direct orbit insertion and operational DASS repeaters. The third
civil signal and the L2C signal, with double carrier frequencies, are very helpful for
ionosphere modeling, to further improve the positioning accuracy for civilian users.
It was reported that the SPS horizontal accuracy was better than 3.5 m in 2015, using
the high-quality GPS receivers with Federal Aviation Administration (FAA) grade.
Of course, there would be many factors affecting this accuracy, such as receiver
noise, atmospheric issues and multi-path delay.
In December 2018, the new generation GPS satellite Block III-1 was launched
successfully, with the design lifetime of 15 years, and by 2023, a total of ten Block
III will be deployed to the constellation to meet higher demands of both military and
233
eventually, allowing civilian users to receive a non-degraded GPS signals globally,
the SPS accuracy had been improved from 110 to 20 m available. The GPS is owned
and operated by the U.S. Government as the national asset, while the DoD is the
steward of GPS. From 1996 to 2004, the IGEB oversaw the GPS policy matters. In
2004, the U.S. President George W. Bush updated the national policy directive, and
then the IGEB was replaced by the national executive committee for space-based
Positioning, Navigation and Timing (PNT) to advise and coordinate federal departments and agencies on matters concerning the GPS and related navigation systems.
The PNT executive committee is chaired jointly by the deputy secretaries of defense
and transportation, and its membership includes equivalent-level officials from the
departments of state, commerce and homeland security, as well as the joint chief of
staff and the NASA. Furthermore, components of the executive office of the president participate as observers of the executive committee, and the chairman of Federal
Communication Commission (FCC) participates as a liaison.
Since the GPS deployment, the improvements of the system performance have
been implemented consistently, including the added new signals; updated ground
stations; improved navigation accuracy and increased continuity, integrity, availability, anti-jam and autonomous survivability. Meanwhile, all of the improvements
maintained compatibility with existing GPS equipment. Modernization of the GPS
satellites has been an ongoing by the DoD through a series of satellite acquisitions to
meet the growing needs of the military, civilian and commercial markets. Between
1997 and 2004, a total of 12 GPS replenishment satellites called Block IIR were
launched, of which the first launch was unsuccessful due to the rocket’s failure and
the other 11 satellites successfully entered into the orbits. There are two significant
advancements for the Block IIR satellites. One is with the autonomous navigation
capability by using the inter-satellite crosslink ranging, known as AutoNav, and the
other is to use the onboard reprogrammable processors to do their own fixes in flight.
Moreover, the Block IIR also demonstrated the concept of Distress Alerting Satellite System (DASS). Between 2005 and 2009, a total of eight GPS replenished and
modernized satellites were successfully sent into the orbits, known as Block IIR-M.
The Block IIR-M satellites emitted the added signals of two codes, the M-code as a
new military code and the L2C code as a new civilian code. Between 2010 and 2016,
a total of 12 GPS follow-on satellites called Block IIF were put into the constellation. Compared with the Block IIR-M, the improvements of the Block IIF include
the third civil signal L5 (1176.45 MHz), 12-year design lifetime, improved rubidium
frequency standards, direct orbit insertion and operational DASS repeaters. The third
civil signal and the L2C signal, with double carrier frequencies, are very helpful for
ionosphere modeling, to further improve the positioning accuracy for civilian users.
It was reported that the SPS horizontal accuracy was better than 3.5 m in 2015, using
the high-quality GPS receivers with Federal Aviation Administration (FAA) grade.
Of course, there would be many factors affecting this accuracy, such as receiver
noise, atmospheric issues and multi-path delay.
In December 2018, the new generation GPS satellite Block III-1 was launched
successfully, with the design lifetime of 15 years, and by 2023, a total of ten Block
III will be deployed to the constellation to meet higher demands of both military and