ULA successfully delivers ninth GPS IIF satellite to orbit
CAPE CANAVERAL, Fla — A United Launch Alliance (ULA ) Delta IV Medium+ (4,2) rocket launched today, Wednesday, March 25, from Cape Canaveral’s Space Launch Complex 37 (SLC-37). It carried with it the ninth GPS IIF satellite for the U.S. Air Force. Liftoff occurred right on time and at the beginning of an 18-minute window at 2:36 p.m. EDT (18:36 GMT).
The rocket responsible for carrying this payload into orbit is a variant of the Delta IV Medium – which is capable of flying in five different configurations to suit different missions and payloads. The smallest, Delta IV Medium, has only been used in three missions, has no solid rocket boosters, has a modified Delta III second stage with 4-meter liquid hydrogen and liquid oxygen tanks, and also a 4-meter payload fairing. Next is the Delta IV Medium+ (4,2) – used in this mission – and is similar to the Medium, but with two solid rocket motors attached to the CBC. In this configuration, the first 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.
Approximately 5 seconds before liftoff, the RS-68 engine fired up, with the two solid rocket motors igniting as the countdown clock reached zero. Around 8 seconds into the flight, the rocket began a series of pitch and yaw maneuvers necessary to attain the trajectory needed for orbital ascension. The Delta IV broke the sound barrier after 47.5 seconds after liftoff; 13.2 seconds later, it passed through the area of maximum pressure, known as “max Q”.
Two Orbital ATK GEM-60s solid rocket motors burned for 1 minute, 34.6 seconds; separation occurred 5.4 seconds post burnout. The RS-68 engine continued powering the first stage flight until 4 minutes, 7.2 seconds after liftoff. Following a 7.3 second coast, the CBC was jettisoned and 15 seconds later, the RL10 engine fired up.
At 10.5 seconds after the second stage engine ignites, separation of the payload fairing occurred. The second stage burn will last 11 minutes, 2.5 seconds – with the second stage and payload now in a transfer orbit. Approximately 3 hours, 3 minutes, and 25 seconds after liftoff, the second stage will fire back up for 103.2 seconds and attain the desired separation orbit.
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 ½ 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 its 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 IIF satellites are viewed as being vital for the GPS constellation and the continuation of GPS services over the next 15 years as outdated satellites are replaced with newer, more capable versions.
Each satellite provides navigation data via Earth and Sun sensors and use reaction wheels for attitude control. They have a 16 Hydrazine thruster propulsion system perfect for any orbit adjustments. Thermal control is regulated with blankets, thermal coatings, radiators, and electric heaters. The vehicle launches with 145 kilograms of propellant and twelve 4.5-Newton and four 22.2-Newton Rocket Engine Assemblies.
Accurate navigation signals are provided by two high-stability Rubidium clocks and a single Caesium atomic clock. The IIF satellite signals are twice as accurate as previous models. Each satellite has the ability to supply M-Code Signals, which are secure, jam-resistant signals needed for military operations. The Block IIF satellites contain the L5 ‘Safety of Life’ Signal and RH32 reprogrammable central processors, capable of receiving in-orbit software updates.
SpaceFlight Insider is a space journal working to break the pattern of bias prevalent among other media outlets. Working off a budget acquired through sponsors and advertisers, SpaceFlight Insider has rapidly become one of the premier space news outlets currently in operation. SFI works almost exclusively with the assistance of volunteers.