The scheduled Oct. 29 launch of the Air Force’s eighth Global Positioning System IIF series (GPS IIF-8) satellite will be its first using GPS metric tracking (GPS MT) as opposed to radar to track the Atlas V launch vehicle, the Air Force said last week.

Artist’s illustration of the GPS IIF satellite. Photo: Boeing.
Artist’s illustration of the GPS IIF satellite. Photo: Boeing.

Utilizing GPS MT allows the Air Force to reduce ground radar infrastructure because it eliminates the requirement for radars with C-band tracking capability. The GPS method is designed to complement telemetered initial guidance (TMIG) as a range safety tracking source. The two independent tracking sources render radar unnecessary to support launches of these vehicles, according to the Air Force.

The Air Force is planning to keep a small amount of radars to support the launches of vehicles that do not have GPS MT yet, the Air Force Space & Missile Systems Center (AFSPC) said in a statement.

Savings of using GPS MT instead of radar are estimated to be upward of $1 million per year, depending on how many radars are kept to support vehicles without the GPS MT capability, the statement said. The Air Force elaborated that it will also be able to avoid the cost of modernizing the radar suite, an estimated one-time savings of $30 million.

Four previous Delta IV and Atlas V launches successfully used the GPS MT capability as part of the certification process: MUOS-1 Feb. 24, 2012; GPS IIF3, Oct. 4, 2012; NROL-36 Sept. 13, 2012; and NROL-65, Aug. 28, 2012. They used both GPS MT and C-band transponders. All Delta IV flights have used GPS exclusively since the NROL-65 launch. Future launches of both the Atlas V and Delta IV launch vehicles will use GPS tracking exclusively instead of C-band beacon tracking, the Air Force added in the statement.

The GPS IIF-7 launch vehicle was the last launch vehicle to be equipped with a C-band beacon (Defense Daily, July 28).

The GPS IIF-8 launch is scheduled for 1:21 pm EDT from Cape Canaveral Air Force Station at the Kennedy Space Center, Fla. The launch window will remain open for 18 minutes, the Air Force noted in a statement on Monday. Liftoff will use a ULA Atlas V launch vehicle. If the launch and all systems proceed as planned, GPS IIF-8 will join a worldwide position, timing and navigation (PNT) system of 38 satellites in orbit approximately 11,000 miles above the Earth’s surface.

Director of Space and Missile Systems Center’s Global Positioning System Col. Bill Cooley said Friday during a teleconference that while there are 39 healthy satellites in the constellation, 31 of them are currently used at any one time. The remainder are held as a residual capability and used as needed.

GPS IIF-8 will become coded SVN-69 and will replace SVN-61, an older and less accurate model launched in May 2000, Cooley said. The older model will enter residual status, as a backup unit.

Cooley noted that GPS IIF-8 is the last of four GPS IIF launches in 2014. This is the highest GPS launch tempo in over 20 years. Ron Furston, ULA’s Deputy Director of Mission Management, noted  that Atlas V is currently running a streak of 50 consecutive successful launches.

Boeing [BA] develops the GPS IIF series satellites. ULA is a joint venture of Lockheed Martin [LMT] and Boeing.