A few weeks shy of the tenth anniversary of its maiden voyage, United Launch Alliance’s venerable Delta IV booster has triumphantly launched a new Global Positioning System (GPS) satellite into orbit, 11,000 miles above Earth. Liftoff of the Delta – which flew in its Medium+ ‘4-2’ configuration, with a 4-metre-wide (13-foot) payload fairing and two strap-on solid rocket motors – occurred on time at 8:10 am EDT on Thursday from Space Launch Complex (SLC)-37 at Cape Canaveral Air Force Station. Preliminary data indicates that the GPS satellite separated from its payload attach fitting about three and a half hours later and is presently moving into its correct operational orbit.
First flown on 20 November 2002, the Delta IV boasts an impressive safety record, having completed 20 missions between then and 29 June of this year. Of those missions, 19 have been classified as full successes and only a single launch – the first flight of the Delta IV Heavy configuration in December 2004 – experienced a premature shutdown of its Common Booster Cores (CBCs), which caused one of its satellite payloads to enter an incorrect orbit and the other to fail to reach orbit entirely.
Unlike the Delta IV Heavy, which is equipped with three CBCs, the variant used in Thursday’s launch has just one, propelled by a single Rocketdyne RS-68 engine. When this powerplant was first introduced, ten years ago, it became the first large liquid-fuelled engine to be developed in the United States since the Space Shuttle Main Engine. Loading of liquid oxygen and hydrogen propellants into the first stage required a complex, four-and-a-half-hour procedure, terminating a little over two hours before launch. Ignition of the RS-68 occurred at T-5 seconds, followed by the twin solid rocket motors at T-0.01 seconds and release of the 206-foot-tall Delta at T-zero.
Pounding the SLC-37 pad surface with 663,000 pounds of thrust, the behemoth booster thundered aloft, initiating its computer-controlled pitch, yaw and roll program manoeuvre around eight seconds into the climb to establish itself onto the proper 105-degree flight azimuth for delivery of its primary payload into orbit. The Delta broke through the sound barrier shortly after T+46 seconds and pressed on towards orbit, under the combined impulse of the RS-68 and solid motors. Eventually, a minute and a half after launch, the strap-ons were exhausted and cut loose, followed, three minutes later, by the shutdown and jettison of the CBC. At this point, the Delta’s second stage – equipped with a Pratt & Whitney RL-10B2 engine, capable of 24,750 pounds of thrust – took over.
This restartable engine was responsible for the remainder of the boost into orbit. Twelve minutes after leaving the Cape, under computer command, it achieved its initial ‘parking’ orbit and was shut down, before coasting for nine minutes to reorient itself for a second burn. This three-minute burn established the Delta and its precious payload onto a three-hour coast, after which a third burn, lasting two minutes, was executed. Finally, three hours and 33 minutes into the flight, the GPS satellite – the third in the Block IIF series – was released from its payload attach fitting at an altitude of a little more than 11,000 miles, inclined 55 degrees to the equator. At that time – 11:43 am EDT – controllers successfully established contact with the satellite. Activation of the GPS signals will commence in the next few days.
“Congratulations to the entire team on today’s successful launch of the GPS IIF-3 satellite,” said Jim Sponnick, ULA vice president, Mission Operations. “ULA and our mission partners have a rich heritage with the GPS program and we are proud to have served alongside the government and contractor teams over the last two decades to provide important Global Positioning System capabilities for our national defense and for millions of civilian and commercial users around the world.”
Weighing 3,600 pounds, GPS IIF-3 is the latest in an ‘interim’ class of Global Positioning System satellites to keep a critical worldwide positioning, velocity and timing asset operational until the next-generation GPS Block IIIA comes online sometime in 2014. The spacecraft launched today boasts, among other features, improved-accuracy positioning systems, a reprogrammable processor, capable of future upgrades, an interference-free civilian signal for commercial aviation search-and-rescue and better resistance to electronic jamming through the new ‘M-code’ military GPS signal. To date, five satellites for a planned 12-strong constellation of Block IIFs have been completed, with the first two launched in May 2010 and July 2011.
The third spacecraft, launched today, arrived at Cape Canaveral Air Force Station earlier this summer aboard a C-17 Globemaster III airlifter for final processing. “As each IIF satellite becomes operational, we continue the seamless transformation of the GPS constellation into an even more accurate, reliable and durable navigation resource for the US military and the global civilian user community,” said Craig Cooning, vice-president and general manager of prime contractor Boeing Space & Intelligence Systems. “Our efficient pulse-line manufacturing process, adapted from Boeing’s commercial airplane production lines, also ensures that we deliver each spacecraft on time and on cost.”
In the meantime, the US Air Force awarded Lockheed Martin a $1.4 billion contract in May 2008 to develop the Block IIIA network, which may eventually consist of as many as 32 satellites. At present, the Air Force has formally contracted for four Block IIIAs. With 500 times the transmitter power of current systems, Block IIIA will also benefit from new navigational warfare capabilities, enabling them to shut off GPS service to limited geographical locations whilst maintaining service to U.S. and allied forces.
UPDATE: Despite the successful injection of the GPS IIF-3 satellite into its correct operational orbit, it became apparent shortly after launch that something had gone awry with the performance of the booster. This suspicion was confirmed by ULA’s Jessica Rye in a 5 October announcement and indicated an “unexpected data signature” when the Pratt & Whitney-built RL-10B2 upper stage engine experienced a period of reduced thrust. Fortunately, the Delta’s robust system design, flight software, vehicle margins and propellant reserves compensated for this engine shortfall and enabled a successful completion of the mission.
Both ULA and Pratt & Whitney have begun an investigation to identify the direct and root causes of the incident. “Though the GPS IIF-3 mission was a complete success,” said Jim Sponnick, ULA’s vice president of Mission Operations, “ULA fully understands the challenges of launch and will thoroughly investigate and implement appropriate actions to reliably deliver our customer’s critical capabilities to the orbital positions required.” The next ULA mission is an Atlas V for the US Air Force, which utilises a different model of RL-10, but a full analysis of the Delta’s problems will be completed before this next flight is cleared for launch.Missions » GPS »