GPS Block III

GPS Block III consists of the first ten GPS III satellites, which are used to keep the Navstar Global Positioning System operational. Lockheed Martin designed, developed and manufactured the GPS III Non-Flight Satellite Testbed and all ten Block III satellites. The first satellite in the series was launched in December 2018.

History

The United States' Global Positioning System reached Full Operational Capability on 17 July 1995, completing its original design goals. Advances in technology and new demands on the existing system led to the effort to modernize the GPS system. In 2000, the U.S. Congress authorized the effort, referred to as GPS III.
The project involves new ground stations and new satellites, with additional navigation signals for both civilian and military users, and aims to improve the accuracy and availability for all users.
Raytheon was awarded the Next Generation GPS Operational Control System contract on 25 February 2010.
The first satellite in the series was projected to launch in 2014, but significant delays pushed the launch to December 2018. The tenth and final GPS Block III launch is projected in FY2026.
While continuing the conventional satellite naming scheme in official usage, the United States Space Force's Space and Missile Systems Center also began unofficially naming each Block III satellite after a famous explorer.

Development

Block III satellites use Lockheed Martin's A2100M satellite bus structure. The propellant and pressurant tanks are manufactured by Orbital ATK from lightweight, high-strength composite materials. Each satellite will carry eight deployable JIB antennas designed and manufactured by Northrop Grumman Astro Aerospace
Already delayed significantly beyond the first satellite's planned 2014 launch, on 27 April 2016, SpaceX, in Hawthorne, California, was awarded a US$82.7 million firm-fixed-price contract for launch services to deliver a GPS III satellite to its intended orbit. The contract included launch vehicle production, mission integration, and launch operations for a GPS III mission, to be performed in Hawthorne, California; Cape Canaveral Air Force Station, Florida; and McGregor, Texas. In December 2016, the Director of the U.S. Air Force's Global Positioning Systems Directorate announced the first satellite would launch in the spring of 2018. In March 2017, the U.S. General Accounting Office stated "Technical issues with both the GPS III satellite and the OCX Block 0 launch control and checkout system have combined to place the planned March 2018 launch date for the first GPS III satellite at risk". The delays were caused by a number of factors, primarily due to issues found in the navigation payload. Further launch date slippages were caused by the need for additional testing and validation of a SpaceX Falcon 9 rocket which ultimately launched the satellite on 23 December 2018. On 22 August 2019, the second GPS III satellite was launched aboard a Delta IV rocket.
On 21 September 2016, the U.S. Air Force exercised a US$395 million contract option with Lockheed Martin for the ninth and tenth Block III space vehicles, expected to be available for launch by 2022.

Launch history

9 of 10 GPS Block III satellites have been launched. 8 are currently operational, with 1 undergoing post launch commissioning.

Satellite	SVN	Launch date	Rocket	Launch site	Status	Ref.
USA-289 GPS III-01 Vespucci	74	23 December 2018 13:51	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-293 GPS III-02 Magellan	75	22 August 2019 13:06	Delta IV M+	Cape Canaveral, SLC37B
USA-304 GPS III-03 Matthew Henson	76	30 June 2020 20:10	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-309 GPS III-04 Sacagawea	77	5 November 2020 23:24	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-319 GPS III-05 Neil Armstrong	78	17 June 2021 16:09	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-343 GPS III-06 Amelia Earhart	79	18 January 2023 12:24	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-440 GPS III-07 Sally Ride	80	17 December 2024	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-545 GPS III-08 Katherine Johnson	81	30 May 2025 17:37	Falcon 9 Block 5	Cape Canaveral, SLC40
USA-581 GPS III-09 Ellison Onizuka	82	28 Jan 2026 4:53	Falcon 9 Block 5	Cape Canaveral, SLC40
GPS III-10 Hedy Lamarr	83	March 2026	Vulcan Centaur VC2S	Cape Canaveral, SLC41

New navigation signals

Civilian L2 (L2C)

One of the first announcements was the addition of a new civilian-use signal to be transmitted on a frequency other than the L1 frequency used for the existing GPS Coarse Acquisition signal. Ultimately, this became known as the L2C signal because it is broadcast on the L2 frequency. It can be transmitted by all block IIR-M and later design satellites. The original plan stated that until the new OCX system is in place, the signal would consist of a default message that contains no navigational data. OCX Block 1 with the L2C navigation data was scheduled to enter service in February 2016, but was delayed until 2022 or later.
As a result of OCX delays, the L2C signal was decoupled from the OCX deployment schedule. All satellites capable of transmitting the L2C signal began broadcasting pre-operational civil navigation messages in April 2014, and in December 2014 the U.S. Air Force started transmitting CNAV uploads on a daily basis. As of October 2017, L2C was being broadcast from 19 satellites; by June 2022 there were 24 satellites broadcasting this signal. The L2C signal remains in pre-operational status with 25 broadcasting space vehicles in December 2025. The L2C signal is tasked with providing improved accuracy of navigation, providing an easy-to-track signal, and acting as a redundant signal in case of localized interference.
The immediate effect of having two civilian frequencies being transmitted from one satellite is the ability to directly measure, and therefore remove, the ionospheric delay error for that satellite. Without such a measurement, a GPS receiver must use a generic model or receive ionospheric corrections from another source. Advances in technology for the GPS satellites and the GPS receivers have made ionospheric delay the largest source of error in the C/A signal. A receiver capable of performing this measurement is referred to as a dual frequency receiver. Its technical characteristics are:

L2C contains two distinct PRN sequences:
* CM is 10,230 bits in length, repeating every 20 milliseconds.
* CL is 767,250 bits, repeating every 1,500 milliseconds.
* Each signal is transmitted at 511,500 bits per second ; however, they are multiplexed to form a 1,023,000 bit/s signal.
CM is modulated with a 25 bit/s navigation message with forward error correction, whereas CL contains no additional modulated data.
The long, non-data CL sequence provides for approximately 24 dB greater correlation protection than L1 C/A.
L2C signal characteristics provide 2.7 dB greater data recovery and 0.7 dB greater carrier tracking than L1 C/A.
The L2C signals' transmission power is 2.3 dB weaker than the L1 C/A signal.
In a single frequency application, L2C has 65% more ionospheric error than L1.

It is defined in IS-GPS-200.

Military (M-code)

A major component of the modernization process, a new military signal called M-code was designed to further improve the anti-jamming and secure access of the military GPS signals. The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P code. The new signal is shaped to place most of its energy at the edges. Unlike the P code, the M-code is designed to be autonomous, meaning that users can calculate their positions using only the M-code signal. P code receivers must typically first lock onto the C/A code and then transfer to lock onto the P code.
In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna, in addition to a wide angle antenna. The directional antenna's signal, termed a spot beam, is intended to be aimed at a specific region and increase the local signal strength by 20 dB. A side effect of having two antennas is that, for receivers inside the spot beam, the GPS satellite will appear as two GPS signals occupying the same position.
While the full-Earth M-code signal is available on the Block IIR-M satellites, the spot beam antennas will not be available until the Block III satellites are deployed. Like the other new GPS signals, M-code is dependent on OCX—specifically Block 2—which was scheduled to enter service in October 2016, but which was delayed until 2022, and that initial date did not reflect the two year first satellite launch delays expected by the GAO.
Other M-code characteristics are:

Satellites will transmit two distinct signals from two antennas: one for whole Earth coverage, one in a spot beam.
Binary offset carrier modulation.
Occupies 24 MHz of bandwidth.
It uses a new MNAV navigational message, which is packetized instead of framed, allowing for flexible data payloads.
There are four effective data channels; different data can be sent on each frequency and on each antenna.
It can include FEC and error detection.
The spot beam is ~20 dB more powerful than the whole Earth coverage beam.
M-code signal at Earth's surface: –158 dBW for whole Earth antenna, –138 dBW for spot beam antennas.