Making its third launch of the month, United Launch Alliance’s Atlas V rocket has successfully deployed the penultimate Block IIF Global Positioning System satellite. Liftoff from Cape Canaveral – rescheduled for Saturday – occurred at the start of a nineteen-minute window that opened at 12:13 EDT (16:13 UTC).
Atlas V Launch:
The launch will deployed the eleventh of twelve Block IIF spacecraft, the final block of satellites in the second-generation Global Positioning System constellation.
Having originally been intended as a 33-satellite block to modernise the GPS constellation, replacing the Block II Replenishment, or Block IIR, spacecraft that had been launched since 1997, the Block IIF was reduced in 2001 to the status of an interim, replacing older satellites to keep the constellation in service until the next generation of spacecraft were ready to enter service.
The order for Block IIF spacecraft was reduced, first to twelve and later to nine, before increasing again to twelve satellites in 2006.
The US Air Force’s Global Positioning System, or GPS, which has become synonymous with satellite navigation, is a program which was initiated in the 1970s to provide greater locational awareness for US military assets.
While the program was still under development, the destruction of a South Korean airliner which strayed into Soviet airspace led to the opening up of the GPS network to civilian users, with the constellation made available for free use upon completion.
Launches of the Block IIF spacecraft began in May 2010, four years behind schedule and nine months after the final spacecraft of the preceding block, Block IIR(M), lifted off atop a Delta II rocket.
Unlike previous Block II spacecraft, which used Star-37 solid rocket motors to reach their operational orbits after deployment into lower transfer orbits by a Delta II rocket, Block IIF satellites are deployed directly into their operational semi-synchronous medium Earth orbits by United Launch Alliance’s more powerful Evolved Expendable Launch Vehicles; the Atlas V and Delta IV.
The spacecraft launched, GPS IIF-11, was the fifth to fly atop an Atlas, with the Delta IV deploying the other six satellites. The final launch, currently scheduled for next February, will also use the Atlas V.
Built by Boeing, GPS IIF-11 is a 1,630-kilogram (3,590 lb) satellite designed for twelve years of service. The spacecraft is equipped with L-band transponders to transmit signals for navigation, operating in three signal bands; L1, L2 and L5.
The L5 signal, which was introduced with the Block IIF series having been tested using a late IIRM spacecraft, is billed as a “Safety of Life” signal, primarily intended for civil aviation.
GPS IIF-11, which has Space Vehicle Number (SVN) 73, will serve in slot 2 of the GPS constellation’s ‘E’ plane from where it will broadcast pseudo-random noise (PRN) signal 10. The former occupant of this slot, GPS IIR-10 or USA-175, will become an on-orbit spare.
An old reserve satellite in plane D, GPS IIA-14 or USA-96, is to be decommissioned in order to free up space in the constellation – with its PRN-04 signal to be reused by the next Block IIF satellite when it launches.
The Atlas rocket carrying GPS IIF-11 into orbit had the tail number AV-060. The fifty-ninth Atlas V to be launched, AV-060 flew in the 401 configuration, sporting a four-metre payload fairing, no solid rocket boosters to augment the first stage, and a single-engine Centaur second stage.
The launch took place from Space Launch Complex 41 (SLC-41) at Cape Canaveral, a former Titan launch pad which has been used by the Atlas V since the rocket’s maiden flight in 2002.
Built in the 1960s, Complex 41 was first used for the Titan IIIC’s third flight in June 1960. Between 1967 and 1969 the complex served as the Titan IIIC’s primary launch site while Complex 40 was undergoing conversion work for the later-cancelled Manned Orbiting Laboratory (MOL) space station program.
Following Launch Complex 40’s return to service, Complex 41 was taken out of service to adapt it of the proposed Titan IIIE rocket, which added the cryogenic Centaur upper stage to boost the vehicle’s ability to launch missions beyond Earth orbit.
Titan IIIE rockets flying from LC-41 lofted the Voyager probes to the outer planets, the Viking missions to Mars and the Helios solar research probes.
Following the end of Titan IIIE operations, Launch Complex 41 fell dormant and was not used again until the Titan IV entered service in 1989.
The final Titan launch from the pad occurred in April 1999, with an attempt to place a Defense Support Program missile detection satellite into orbit. The launch ended in failure after the rocket’s Inertial Upper Stage malfunctioned, the second of three consecutive failures suffered by the Titan IV.
The end of Titan launches from Space Launch Complex 41 made way for the pad to be reused for the Atlas V. A few months after the DSP launch, the pad’s fixed and mobile service towers were demolished and work to convert the complex to the Atlas V’s clean pad approach began.
A new Vertical Integration Facility (VIF) was constructed southwest of the pad, replacing the former Vertical Integration Building shared between Complexes 40 and 41 during the Titan era. Atlas rockets are assembled in the VIF and rolled to the pad atop a mobile platform.
Although the Atlas was designed to fly from a clean pad, with no permanent service towers, construction of a crew access tower at the pad began recently to support proposed commercial crew missions to the International Space Station using Boeing’s CST-1000 Starliner spacecraft.
In preparation for the launch, AV-060 was transported to the launch pad on Thursday afternoon. The launch was set to take place on Friday, before being delayed 24 hours due to an issue with the sound suppression system at the pad.
AV-060’s launch began with first stage engine ignition, 2.7 seconds ahead of the planned T-0. The first stage of the Atlas V, the Common Core Booster (CCB) is powered by a single RD-180 engine developed by Russia’s NPO Energomash.
Derived from the RD-170 engine developed for the Zenit rocket, the RD-180 is a twin-chamber engine which burns RP-1 propellant, oxidised by liquid oxygen, to power the Atlas for the first four minutes of her mission.
Approximately 1.1 seconds after the zero mark in the countdown, the thrust generated by the RD-180 exceeded the weight of the vehicle and the ascent towards orbit began.
Climbing away from her launch pad, AV-060 executed a series of pitch and yaw manoeuvers beginning at 17.3 seconds into the flight, to attain a flight azimuth of 45.8 degrees and the necessary attitude to attain orbit.
The trajectory took the rocket out over the Atlantic heading in a north-easterly direction.
The rocket achieved a speed of Mach 1, equal to the speed of sound, 78.5 seconds into its flight; passing through the area of maximum dynamic pressure, or max-Q, 11.7 seconds later.
First stage flight ended with Booster Engine Cutoff, or BECO, at four minutes and 3.8 seconds mission elapsed time. The spent first stage separated six seconds later, with the second stage beginning its prestart sequences in preparation for Main Engine Start 1 (MES-1), ten seconds after staging.
The second stage of the Atlas V is a Centaur. Fuelled by liquid hydrogen and liquid oxygen, the Centaur is equipped with an RL10C-1 engine to propel itself and its payload into orbit.
The Centaur’s first burn lasted twelve minutes and 42.7 seconds. Approximately eight seconds into the burn, the payload fairing separated from around GPS IIF-11, with the rocket high enough above the denser regions of Earth’s atmosphere that its protection is no longer required. The burn ended at seventeen minutes and 2.5 seconds elapsed time.
The coast phase between the end of the first burn and the start of the second burn, during which time the Centaur will coast to the apogee of its orbit, lasted 1.7 seconds short of three hours.
The second and final Centaur burn lasted just one minute and 27 seconds, raising the perigee of the rocket’s trajectory in order to circularise the orbit. At cutoff the rocket was in its planned target orbit, which is circular at an altitude of 20,459 kilometres (12713 miles, 11047 nautical miles) and an inclination of 55 degrees.
Satellites in this orbit make two revolutions per day, each lasting twelve hours. Spacecraft separation occurred four minutes and 46 seconds after powered flight ends; at three hours, twenty three minutes and 13.8 seconds mission elapsed time.
The third Atlas V launch of October 2015, this mission is one of eight conducted so far this year by the Atlas, which has supplanted the venerable Delta II as the workhorse rocket of America’s space industry.
One further Atlas launch is planned for the year, carrying a Cygnus spacecraft en route to the International Space Station for Orbital Sciences Corporation. This will also be United Launch Alliance’s final mission of the year, with the company expected to open its 2016 campaign with the final Block IIF GPS launch in early February.
(Images via ULA, Boeing, and L2).