During the middle of 1989, procurement began for 21 additional satellites ("replenishment SVs") from Lockheed Martin, formerly General Electric. The Block IIR SVs will present an identical SIS interface to the User Segment. Under a survivability scenario, the Block IIR SVs will have the capabilities to autonomously navigate (AUTONAV) themselves and generate their own 50 Hz navigation message data. These AUTONAV capabilities will enable the Block IIR SVs to maintain full SIS accuracy for at least 180 days without Control Segment support. AUTONAV will also significantly improve both the reliability and integrity of the broadcast SIS. Accuracy improvements are expected to be approximately 7 meters spherical error probable (SEP) in a full Block IIR constellation.The Delta II expendable launch vehicle is used to launch GPS satellites from Cape Canaveral Air Force Station, FL, into nearly 11,000-mile circular orbits. While orbiting the earth, the systems transmit signals on two different L-band frequencies. Their design life is six years. The Block II GPS satellites weigh 1,860 pounds (in orbit) and are five feet wide, 17.5 feet long (Length includes wingspan), with solar panels generating 700 watts. The new block of satellites boasts dramatic improvements over the previous Block IIA satellites at approximately a 33-percent reduction in cost per unit. This includes the ability to determine its own position by performing inter-satellite ranging with other IIR space vehicles. It also features reprogrammable processors that enable problem fixes, upgrades in flight, and increased satellite autonomy and radiation hardness. Additionally, the Air Force can launch the Block IIR into any required GPS orbit (with a 60-day advanced notice and dependent upon launch vehicle availability), and requires fewer ground contacts to maintain the constellation. All of these improvements increase accuracy for GPS users. The Air Force has already awarded a contract for the post-Block IIR satellite, the Block IIF, with the expected first launch in 2002.
The primary contractor is Martin Marietta (formerly General Electric) Astro Space.
The first launch of a Block II R satellite came on Jan. 17, 1997 at 11:28 a.m. EST, when the U.S. Air Force launched a McDonnell Douglas-built Delta II rocket from Launch Complex 17-A at Cape Canaveral Air Station, Fla. An anomaly occurred approximately 12 seconds into powered flight. The vehicle self-destructed, then the flight control officer sent precautionary destruct functions at 21 seconds into flight, when it ceased powered flight. Vehicle components fell into a cleared safety area in the Atlantic Ocean and onto the Air Station. No personnel were injured. No estimate on the damage was initially available, pending an investigation is underway to determine the cause of the mishap. There was no immediate impact to the Global Positioning System satellite constellation as a result of the unsuccessful launch. The space segment team recommended launching a IIR next, followed by the last IIA
July 22, 1997 a Delta II launch vehicle lifted an improved next-generation satellite into space from Cape Canaveral Air Station, FL. The launch was the first Air Force flight of the McDonnell Douglas Corp.-built Delta II since the attempt to launch the first GPS IIR satellite exploded shortly after liftoff Jan. 17.
|Weight:||1,860 pounds (in orbit)|
|Orbit altitude:||10,900 miles|
Solar panels generating 700 watts
2 NiH batteries
|Dimension:||5 feet wide, 17.5 feet long (length includes wingspan)|
|Launch vehicle:||Delta II|
|Primary contractor:||Lockheed-Martin - Block IIR|
additional radiation hardening
cross link ranging
two atomic clocks on at all times (hot backup)