The third GPS launch of 2014 took place on Friday evening, with the United Launch Alliance (ULA) Atlas V lofting the GPS IIF-7 satellite into space. Liftoff from Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC-41) was on schedule at 23:23 local time (03:23 UTC Saturday), following a smooth countdown.
Atlas V Mission:
GPS IIF-7 forms part of the US Air Force’s Global Positioning System (GPS); a program aimed at providing worldwide navigational data which began in the 1970s.
Although originally developed for military use, some GPS signals are also made freely available for civilian navigation and the network is used by most commercial navigation devices.
The decision to make the GPS available to civilian users was taken by Ronald Reagan in 1983, after 269 people were killed when a Korean airliner became lost and strayed into Soviet airspace, where it was shot down.
The first GPS satellites, retrospectively known as Block I, were prototypes.
Deployed by Atlas E/F rockets, they demonstrated that it was practical to use a constellation of satellites in Medium Earth orbit for navigation – previous attempts at establishing navigation constellations, such as the Transit program, had relied upon large numbers of satellites in lower orbits making global coverage impractical.
The GPS system, originally known as the Navigation System using Timing and Ranging (NAVSTAR), needs just twenty-four spacecraft across six orbital planes to achieve accurate worldwide coverage.
Eleven prototype spacecraft were launched between 1978 and 1985, ten of which achieved orbit successfully. They were followed by the first series of operational satellites, the Block II and later IIA, which were orbited by Delta II rockets between 1989 and 1997.
The 1994 launch of USA-100 (GPS II-24 or GPS IIA-15) brought the constellation up to full operational capability for the first time.
Following an initial launch failure in 1997, Block II Replenishment (GPS IIR), satellites began launching to augment and replace the earlier Block II and IIA spacecraft. Thirteen were deployed, with an additional eight being converted to the Block IIRM specification. The final IIRM satellite was USA-206, launched in August 2009.
The Block IIF series is intended to serve as an interim, replacing the IIA and IIR series while providing enhanced capabilities ahead of the introduction of the next generation GPS satellites. The first of these next-generation spacecraft, GPS IIIA-1, is scheduled to be launched in 2016.
The payload for Friday’s launch is the seventh of twelve Block IIF satellites to fly, of which ten have currently been manifested.
With a mass of 1,630 kilograms (3,590 lb) the Block IIF spacecraft are lighter than their predecessors, a mass reduction achieved by the use of more powerful rockets which can place them directly into their operational orbits rather than having to equip the satellites with apogee motors.
GPS IIF launches use the Atlas V 401 and Delta IV-M+(4,2) rockets, rather than the smaller Delta II which launched the Block II and IIR satellites.
The GPS IIF-7 satellite has an expected service life of twelve years. It will replace USA-132 (GPS IIR-2), which was the first Block IIR satellite to enter service. Launched in July 1997, USA-132 currently resides in slot 3 of the constellation’s F plane.
Once its replacement has entered service successfully, USA-132 will relieve the second-oldest satellite in the GPS fleet, USA-83 (GPS IIA-5 or II-16). This twenty-two year old satellite is currently serving as an operational reserve in plane F.
The Atlas V, along with its stablemates the Delta II and Delta IV, is operated by United Launch Alliance. Formed in 2006, this partnership of Lockheed Martin and Boeing provides Evolved Expendable Launch Vehicle (EELV) launch services to the US Government, as well as being subcontracted to perform commercial missions.
Friday’s launch was the eighty-sixth for the company since its first, which carried the NROL-21 (USA-193) mission for the National Reconnaissance Office in December 2006.
For the launch of GPS IIF-7, ULA made use of an Atlas V rocket flying in the 401 configuration. Consisting of two stages, a Common Core Booster and a Centaur, the rocket has tail number AV-048.
The 401 configuration was the smallest Atlas V configuration to be developed, and is also the most flown.
Friday’s launch was the forty-seventh flight of an Atlas V since the rocket was introduced in 2002, and the twenty-third launch of the 401 configuration. AV-048 was the second Atlas V to fly in support of the GPS constellation; in May 2013 AV-039 was used to deploy the GPS IIF-4, or USA-242, satellite.
The launch site for Atlas V missions from Cape Canaveral is the former Titan pad at Space Launch Complex 41. Constructed in the 1960s, the facility was first used by the Titan IIIC rocket in December 1965.
In the 1970s it hosted the Titan IIIE, which deployed the Viking missions to Mars, the Voyager probes to the Outer Planets and the Helios spacecraft which studied the Sun. After the Titan IIIE was retired in 1977, however, the complex fell out of use and would not see another launch for twelve years.
Launches resumed with the Titan IV in 1989, with the final Titan launch from the pad being a failed attempt to place a Defense Support Program satellite into geosynchronous orbit in 1999.
Demolished and rebuilt for the Atlas V, the next launch from Space Launch Complex 41 was the Atlas’ maiden flight in 2002, which carried Eutelsat’s Hot Bird 6 (now Eutelsat 8 West C) communications satellite.
Prior to Friday’s attempt, twenty eight Atlas V launches have made use of SLC-41, with the remainder flying from Space Launch Complex 3E at the Vandenberg Air Force Base in California.
Friday’s launch began with ignition of the first stage at T-2.7 seconds. Powered by an RD-180 engine, the Common Core Booster first stage burned for four minutes and 6.3 seconds, propelling the rocket out of the atmosphere.
After ignition the engine took a few seconds to build up thrust, with liftoff occurring at around T+1.1 seconds when the thrust exceeded the weight of the vehicle.
A series of manoeuvres, beginning 17.2 seconds into the mission, placed the Atlas onto its prescribed trajectory for the journey into orbit.
Flying downrange on a heading of 45.8 degrees, AV-048’s speed reached Mach 1 a minute and 18.2 seconds after liftoff with the rocket passing through the area of maximum dynamic pressure, max-q, 12.1 seconds later.
The first stage burn ended with Booster Engine Cutoff (BECO), four minutes and 3.6 seconds into the flight. Six seconds after cutoff the spent stage will be jettisoned.
The second stage of AV-048 is a Single-Engine Centaur, powered by an RL10A-4-2 engine. After completing its prestart sequence the RL10 fired ten seconds after staging. Sixteen seconds into the second stage burn the payload fairing separated from the nose of the rocket.
Lasting 12 minutes and 49.2 seconds, the Centaur’s first burn established a parking orbit with an apogee close to the satellite’s target orbit. At the end of this burn the mission entered an extended coast phase as the Centaur ascended to this altitude.
The coast between the first and second burns took a few tenths of a second short of three hours. Once completed the stage restarted for a circularization burn with a planned duration of two minutes and 8.4 seconds.
This completed the powered portion of Friday’s mission. Spacecraft separation occurred four minutes and 45.7 seconds after cutoff.
AV-048 was targeting a circular orbit at an altitude of 20,460 kilometres (12,700 miles or 11,050 nautical miles) and an inclination of 55 degrees. This semisynchronous orbit will see the satellite orbit the Earth once every twelve hours.
The fifth Atlas V launch of 2014, Friday’s mission marked the fourteenth launch of the year for the United States and the ninth for United Launch Alliance.
The next Atlas launch is scheduled for 13 August, when the 401 configuration will be used to deploy the WorldView-3 imaging satellite in what will be the first commercial Atlas launch from Vandenberg.
The next GPS launch is expected to occur in mid-October, with another Atlas orbiting GPS IIF-8.
(Images via ULA and USAF).