GPS Block IIIF

GPS Block IIIF, also called GPS III Follow On, is the second group of advanced GPS satellites. These satellites are part of the Global Positioning System, which helps people find their way anywhere in the world. The United States Air Force started working on these satellites in 2016.

In 2018, they gave a big contract to a company named Lockheed Martin to build them. There will be up to 22 of these satellites. The first one is planned to launch in 2027, and more will keep launching until at least 2037. These new satellites will help make GPS even more accurate and reliable for everyone who uses it.

System enhancements

Work on the Block IIIF satellites began in 2016, 16 years after the government started updating GPS III in 2000. This brought many new features and improvements compared to older GPS satellites.

Improvements

Nuclear detonation detection system

Block IIIF satellites have a new system to detect nuclear explosions. It is smaller and lighter than older systems. It uses sensors in space and equipment on the ground to find, identify, and report nuclear explosions in Earth's atmosphere and space.

Fully-digital navigation

Block IIIF satellites are the first to have a completely digital navigation system. This digital system gives better accuracy, reliability, and stronger signals than older systems.

Improved satellite bus

Starting with GPS IIIF-03, these satellites use a new design. This helps protect against cyber attacks and gives better power, propulsion, and electronics.

Novel capabilities

Energetic charged particle sensor

Block IIIF satellites will be the first to carry a special sensor to detect energetic charged particles. This helps us learn more about space weather and tell apart natural events from possible dangers.

Search and rescue distress beacon detection

All Block IIIF satellites will help with search and rescue. They can detect special distress signals from beacons on Earth and send them to ground stations to start emergency help quickly.

Laser retro-reflector array

Block IIIF satellites will have special reflectors. These let ground stations measure their positions very accurately. This makes the GPS system better at giving exact location and time information.

Unified S-band capability compliance

Block IIIF satellites will use a unified system for communication. This makes it easier to manage their signals from the ground.

Regional military protection capability

These satellites have technology to protect military GPS signals in certain areas from being blocked by enemies.

On-orbit servicing

Starting with GPS IIIF-03, these satellites can be upgraded or serviced while they are in space, thanks to a special interface.

Main article: Nuclear Detonation Detection System

Main article: U.S. Secretary of the Air Force

Main article: space domain awareness

Main article: space weather

Main article: Cospas-Sarsat

Main article: retro-reflector

Main article: spot beam

Launch history

The first GPS Block IIIF satellite is planned to launch in 2027. The satellite numbers will continue from the previous GPS satellites.

Navigational signals

Main article: GPS signals

The GPS Block IIIF satellites use the same navigation signals as older GPS satellites. These older satellites include Block I, Block II, and Block III. The signals they send are not new; they were all used by satellites before them.

Design

GPS IIIF is an updated version of GPS III, using the A2100 bus as its base. The new models use the modern LM2100 bus and a fully digital navigation system from L3Harris. This is a big improvement over the older system used in GPS III.

Starting with the third satellite, an upgraded LM2100 Combat Bus will be used. This makes it easier to add new features while the satellite is in space.

The Canadian government and the Canadian Armed Forces are adding special tools to help find people in trouble much faster—reducing the time from an hour to just five minutes, with better accuracy.

The United States Naval Research Lab will build Laser Retroreflector Arrays (LRAs), which help make the satellite’s position more exact. The National Geospatial-Intelligence Agency will help pay for these LRAs.

Other improvements include a new unified S-Band (USB) connection, tools to watch for dangerous space weather, and the ability to send strong military signals to certain areas.

The U.S. Air Force has planned four times during the life of the GPS Block IIIF satellites when they can add new features. These are the only times new things can be added to these satellites.

Technology Insertion Point 1 (estimated FY2026)

• First Space Vehicle: GPS IIIF-01
• Proposed/possible new functionality:
  • On Orbit Reprogrammable Digital Payload
  • High Power Amplifiers (SSPA's)
  • Regional Military Protection (RMP)

Technology Insertion Point 2 (estimated FY2028)

• First Space Vehicle: GPS IIIF-07
• Proposed/possible new functionality:
  • M-Code Space Service Volume

Technology Insertion Point 3 (estimated FY2030)

• First Space Vehicle: GPS IIIF-13
• Proposed/possible new functionality:
  • Near Real-Time Commanding
  • Advanced Clocks

Technology Insertion Point 4 (estimated FY2033)

• First Space Vehicle: GPS IIIF-19
• Proposed/possible new functionality:
  • TBD

Development

The U.S. Air Force had a two-step process to choose a company to build GPS Block IIIF satellites.

In May 2016, they gave three companies—Boeing Network and Space Systems, Lockheed Martin Space Systems Company, and Northrop Grumman Aerospace Systems—small contracts to test if they could make the satellites. Boeing and Northrop Grumman showed they could build working parts.

In April 2017, the Air Force started the second step, asking companies to bid for the job of making the satellites. In November 2017, they named these satellites "GPS Block IIIF" and said they would pick one company to build all 22 satellites. The request for proposals was sent out in February 2018. Boeing and Northrop Grumman did not bid, but Lockheed Martin did.

On September 14, 2018, the Air Force chose Lockheed Martin and gave them a contract to build the satellites.

The ground control system for GPS Block IIIF will be the same as for GPS Block III and the Next Generation GPS Operational Control System. In April 2021, the U.S. Space Force gave Raytheon Intelligence and Space a contract to update this system. The updated system was planned for delivery in July 2025, but as of September 2024, the delivery is now expected in February 2026.