ULA Atlas V succesfully deploys new GPS satellite

by William Graham

United Launch Alliance (ULA) launched an Atlas V Wednesday evening, successfully delivering the fourth satellite in the US Air Force’s new series of Global Positioning System satellites. Liftoff from Space Launch Complex 41 at the Cape Canaveral Air Force Station occurred at 21:38 UTC (17:38 local time).

Atlas V Launch:

The fourth Block IIF GPS satellite, GPS IIF-4 is the sixty-fourth GPS satellite overall, and the first to launch on an Atlas since Navstar 11, also known as USA-10, in October 1985. That satellite, a the last Block I prototype satellite, was boosted into orbit by an Atlas E/F with an SGS-2 upper stage, flying from Space Launch Complex 3W at Vandenberg Air Force Base.

Since then, launching GPS spacecraft has been left solely to Delta rockets, with the Delta II 6925 used for Block II launches, the Delta II 7925 for Block IIA, IIR and IIRM, and the Delta IV Medium+(4,2) for the three Block IIF launches to date.

GPS 11F-4GPS IIF-4 has Space Vehicle Number (SVN) 66. It will use PRN-27; a signal modulation previously used by USA-84, or GPS IIA-6 (SVN-27), a twenty-year-old satellite which was retired from service last October. IIF-4 will serve as a replacement for USA-117 in slot 2 of plane C of the GPS constellation.

Launched in March 1996 as GPS IIA-16, USA-117 is a Block IIA spacecraft which carries SVN-33, and uses PRN-03. Once IIF-4 replaces it, USA-117 will remain in service as a backup satellite, presumably moving to Slot 5 of its plane.

The GPS constellation consists of six planes, designated A to F, with six slots in each, numbered 1 to 6. Slots 1 to 4 contain operational satellites, with 5 and 6 housing reserve spacecraft. Plane C currently contains satellites in slots 1-4 and 6; two Block IIA spacecraft, one Block IIR, and two Block IIRMs. The most recent launch to plane C was GPS IIR-18(M) in December 2007.

Constructed by Boeing, Block IIF GPS satellites are expected to operate for twelve years, broadcasting signals at three different frequencies, including the L5 “Safety of Life” signal for civil aviation. The three Block IIF satellites launched to date, SVNs 62, 63 and 65, are operating in slots B2, D2 and A1 of the constellation respectively.

Atlas VThe Atlas V that launched GPS IIF-4 flew in the 401 configuration, with tail number AV-039. The launch was the thirty-eighth flight of the Atlas V, and the eighteenth flight of the 401 configuration.

The Atlas V consists of two stages; a Common Core Booster (CCB) and a Centaur. The CCB is powered by a single RD-180 engine, produced by NPO Energomash of Russia. It burns RP-1 propellant, oxidized by liquid oxygen.

The Centaur is powered by RL10A-4-2 engines burning liquid hydrogen and liquid oxygen; one or two engines are present depending on mission requirements – for this launch the single-engine configuration will be used, as denoted by the one in the 401 designation. The zero indicates that no solid rocket motors will be used; up to five Aerojet SRMs can be attached to the first stage to augment thrust at liftoff, however for this flight none are necessary.

The four gives the diameter of the payload fairing, in meters. Four and five-meter fairings can be used, with three different lengths of each. The Long Payload Fairing (LPF), which despite its name is the shortest of the four-meter fairings, will be used on AV-039. The other two four-meter fairings, the Extended and Extra-Extended (EPF and XEPF) Payload Fairing, are 90 and 180 centimeters longer respectively.

Rollout of Atlas V GPS IIF-4, Cape Canaveral AFSAV-039 was assembled in the Vertical Integration Facility, which is located approximately half a kilometer to the southwest of the launch pad.

Rollout to the launch complex occurred on Wednesday, with the rocket departing the VIF atop a mobile platform shortly after 15:00 UTC, and arrived at the launch pad around 50 minutes later. It was the fifty-ninth rocket to launch from SLC-41, and the thirty-second Atlas V to do so.

Before the Atlas V was introduced in 2002, SLC-41 was a Titan launch complex. Twenty seven Titan rockets, including Titan IIIC, IIIE and IV configurations, flew from the pad between December 1965 and April 1999.

The last launch, a failed attempt to place a Defense Support Program (DSP) satellite into geosynchronous orbit, was conducted by a Titan IV(402)B with an Inertial Upper Stage. Six months later the fixed and mobile service towers were demolished, and the complex was rebuilt to accommodate the Atlas. The majority of Atlas V launches use the pad.

The launch was conducted by United Launch Alliance (ULA). Formed in December 2006, ULA have taken over Atlas V construction from Lockheed Martin, and launch operations from International Launch Services. They are also responsible for constructing and launching Delta II and Delta IV rockets.

T-0 for Wednesday’s launch occurred at 21:38 UTC; which was the opening of an 18-minute window. At T-2.7 seconds, the RD-180 engine ignited and begin throttling up, reaching full thrust 4.2 seconds later. At T-0, the engine was ready for flight, and liftoff occurred 1.1 seconds later when the thrust generated by the first stage engine exceeded the weight of the rocket.

Flight ProfileFollowing liftoff, AV-039 maneuvered to a 45.8 degree launch azimuth, and pitched over for its ascent into orbit. One minute and 18.4 seconds after launch, the rocket’s speed reached Mach 1, passing through the sound barrier and beginning supersonic flight.

A minute and a half into the mission, the RD-180 throttled down in preparation for passing through the area of maximum dynamic pressure, Max-Q, which occurred 90.5 seconds after launch.

The first stage burned for four minutes and 4.4 seconds before it was extinguished, an event known as Booster Engine Cutoff (BECO). Six seconds later, the spent Common Core Booster was jettisoned, and following a further ten seconds of unpowered flight, the Centaur ignited for the first of two burns – a flight milestone which was designated Main Engine Start 1 (MES-1).

Fairing separation occurred eight seconds after the Centaur ignites. The Centaur’s first burn lasted twelve minutes and 46.6 seconds, ending with Main Engine Cutoff 1 (MECO-1), as the flight entering an extended coast phase.

The coast phase lasted three hours, 30.7 seconds, before Main Engine Start 2 (MES-2) began another burn of the Centaur’s RL10 engine. This second burn, intended to circularize the vehicle’s orbit, lasted 89.3 seconds, with its end, MECO-2, marking the end of powered flight. Spacecraft separation occurred four minutes, 45.7 seconds later; at T+ three hours, 23 minutes and 52.8 seconds.

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Mission PatchThe satellite separated into a circular orbit, at an altitude of 20,459 kilometers (12,713 statute miles, 11,047 nautical miles), and an inclination of 55 degrees to the equator.

Unlike earlier spacecraft, Block IIF GPS satellites are launched directly into their operational orbits, eliminating the need for each satellite to carry an apogee motor and the necessary fuel to raise itself out of a transfer orbit.

Wednesday’s launch was the fourth Atlas V mission of 2013, and the fourth launch of the year to be conducted by ULA. ULA’s next EELV launch is scheduled for 23 May, when a Delta IV will place the fifth Wideband Global Satcom spacecraft into orbit.

The next Atlas will fly on 19 July, when an Atlas V 551 will orbit the second MUOS communications satellite. The next GPS launch is expected to be in October, with a Delta IV lifting GPS IIF-5.

(Images via ULA).

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