GPS IIF-9 set to launch atop ULA Delta IV Medium
CAPE CANAVERAL, Fla — Colorado-based United Launch Alliance (ULA ) is prepping a Delta IV Medium+ (4,2) launch vehicle to ferry the ninth GPS Block IIF satellite to orbit. Liftoff is currently scheduled to take place on Mar. 25 and will have a launch window which will last a total of 18-minute window, which opens at 2:36 p.m. EDT (18:36 GMT). Currently, weather conditions for launch are listed as 80 percent chance of favorable for flight.
The GPS Block IIF, or “GPS IIF”, satellites are described as an interim class of satellites that provide navigational services. This series of spacecraft will be utilized to keep the Navstar Global Positioning System up and running until the GPS Block IIIA fleet can be brought online.
Built by Boeing, the GPS IIF fleet is operated by the United States Air Force. Each of these spacecraft weighs in at about 3,590 lbs (1,628 kg) and each have a design life of about 12 years. The satellites orbit at an altitude of some 12,710 miles (20,460 km).
The GPS IIF constellation works similar to earlier models, orbiting in a semi-synchronous medium-Earth-orbit. Essentially, GPS IIF-9 will orbit the Earth at a period of about 12 hours – or twice a day.
These satellites are being fielded so as to replace 11 GPS Block IIA spacecraft which were launched between 1990 and 1997. These were designed to have an operational life of some 7 and a half years.
Unlike earlier Block II GPS satellites, the GPS IIF fleet do not have apogee motors. Whereas the IIA fleet was launched atop the less-powerful Delta II booster, these satellites are being sent to orbit atop the Atlas V and more-powerful Delta IV family of rockets. The Delta IV in particular is capable of ferrying the satellite – directly to is operational orbit.
The contract for the Block IIF satellites was signed in 1996 – and was for a total of 33 spacecraft. Delays and technical issues reduced that number to 12 spacecraft with the first launch slipping from 2006 to 2010.
These satellites broadcast L5 navigational signal which was demonstrated on the GPS IIR-20(M) satellite. They broadcast on the new M-code signal and are described being able to double their predicted accuracy. They are also promoted as being better able to resist jamming. Each satellite is equipped with reprogrammable processors which allow the spacecraft to receive software uploads.
The Rocket responsible for carrying this payload into orbit is the Delta IV and is capable of five different flying configurations for different missions. The smallest, Delta IV Medium, has only been used in three missions, has no solid rocket boosters and only a 4-meter upper stage. Next is the Delta IV Medium+ (4,2), used for tonight’s mission and has two solid rocket motors attached to the CBC. In this configuration, the stage has undergone modifications to provide the room needed for the GEM-60 solid rocket motors.
An Aerojet Rocketdyne RS-68 engine powers the Delta IV first stage, known as the Common Booster Core (CBC). The RS-68 was designed specifically for the Delta IV. Producing 2.95 meganewtons (301,000 kgf) of thrust at sea-level, the RS-68 burns cryogenic propellant (Hydrogen oxidized by liquid oxygen). The Delta Cryogenic Second Stage (DCSS) sits on top of the CBC and is powered by an RL10B-2 engine. During liftoff, the two solid rocket motors augment thrust of the first stage.
These new iterations of the GPS spacecraft will provide navigational services to civilians and the U.S. military. Like its predecessors, GPS-IIF9 will utilize improvements which should provide increased signal strength and enhanced performance.
The remaining GPS IIF satellites will launch atop Atlas 5 rockets, with targeted launch dates of June 16, Sept. 16, and Jan. 26, 2016.
Stay tuned to SpaceFlight Insider for continuing coverage of this mission.
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