GPS satellite blocks

GPS satellite blocks are the different versions of the Global Positioning System (GPS) that we use for satellite navigation. The very first GPS satellite, called Navstar 1, was launched by the United States Air Force on February 22, 1978. Today, these satellites are looked after by the 2nd Navigation Warfare Squadron (2 NWS) at Mission Delta 31, part of the United States Space Force.

These special satellites travel around Earth at a height of about 20,000 kilometers, or 12,427 miles. They orbit the planet so quickly that they make two full trips around Earth every single day. This helps us find our way anywhere in the world, using tools like maps on our phones or in cars.

Satellites by block

Block I satellites

Rockwell International was chosen in 1974 to build the first eight Block I satellites. Later, they were asked to build three more. Starting with Navstar 1 in 1978, ten Block I GPS satellites were launched successfully. One satellite, Navstar 7, was lost when its launch failed on December 18, 1981.

These satellites were launched from Vandenberg Air Force Base using special Atlas rockets. Rockwell International built them in Seal Beach, California. The Block I satellites helped test and improve the system. What was learned from these ten satellites helped create the later, fully working Block II series.

The satellites used energy from the Sun with solar arrays and stored extra power in nickel–cadmium batteries. They communicated using S-band and UHF signals and had a hydrazine system to move in orbit. They sent out navigation signals at two special frequencies: 1575.42 MHz (L1) and 1227.60 MHz (L2).

The last Block I satellite was launched on October 9, 1985, and stayed in use until November 18, 1995 — longer than its planned five-year life.

Block II satellites

The Block II satellites were the first full-size working GPS satellites. They could run for 14 days without needing to talk to controllers on Earth. Rockwell International made these satellites. They were launched between February 1989 and October 1990. The last one stopped working in March 2007, much longer than its planned life of 7.5 years.

The Block IIA satellites were improved versions that could work for 180 days without contact. There were 19 of these, launched between November 1990 and November 1997. Two had special mirrors to help track them from the ground.

The Block IIR satellites were made to replace older ones. The first try to launch one failed, but the next one worked. Twelve were launched successfully. At least ten had extra equipment to help with search and rescue.

The Block IIR-M satellites had new signals for better military and public use. Eight of these were launched between September 2005 and August 2009.

Block IIF series

Main article: GPS Block IIF

The Block IIF satellites were made by Boeing. They were designed to use a new signal called L5 and could last 12 years. The first one launched in May 2010, and the last one in February 2016.

Block III satellites

Main article: GPS Block III

Main article: GPS Block IIIF

The Block III satellites are the first group of advanced GPS satellites. They use new signals and have a longer life span of 15 years, which is three times longer than the earliest satellites. The first one was launched on December 23, 2018, using a SpaceX Falcon 9 Full Thrust rocket. The last of these satellites, called SV10, will launch in April 2026.

The Block IIIF series will be the next group of these advanced satellites. There could be up to 22 of them. These launches are planned to start in 2027 and continue until 2037.