ULA Atlas V successfully launches at the second attempt with AEHF-2

by William Graham

The United Launch Alliance Atlas V has successfully launched the second Advanced Extremely High Frequency (AEFH-2) communications satellite into orbit for the United States Air Force. Lift-off from Space Launch Complex 41 at the Cape Canaveral Air Force Station, Florida, occurred at 2:42pm EDT on Friday. The second attempt came after Thursday’s attempt was scrubbed due to an overtemp condition on the Centaur Interstage Adapter purge.


Thursday’s scrub came after the Atlas V anomaly team failed to find a solution to an overtemp condition within the allocated launch window.

A plan was being worked to send a team out to the third level of the pad to manually check a valve, but it was decided that with only too little time to resolve, along with a radio interference issue with the range, a 24 hour scrub would be the best option.

“The launch of an Atlas V carrying the United States Air Force’s Advanced Extremely High Frequency-2 (AEHF-2) payload was scrubbed today due to lack of helium flow from the ground support equipment to the Interstage Adapter compartment on the launch vehicle,” noted the ULA statement that followed the scrub. 

“The Atlas V vehicle and AEHF-2 are safe and secure at this time. The launch is rescheduled for Friday, May 4 from Space Launch Complex-41 at Cape Canaveral Air Force Station, Fla. The opening of the launch window is 2:42 p.m. EDT and extends until 4:42 p.m. The forecast for May 4 shows an 80 percent chance of favorable weather conditions for the launch tomorrow.

FRIDAY’S Atlas V Mission:

Advanced Extremely High Frequency, or AEHF, is a series of communications satellites being launched to supplement, and eventually replace, the earlier Milstar spacecraft, which were launched between 1994 and 2003. AEHF is designed to be secure, survivable, and resistant to attempted jamming, and will provide communications for the US military, as well as the armed forces of the United Kingdom, Canada, and the Netherlands.

Current plans will see two further launches increase the number of AEHF satellites in orbit to four; one satellite is already in orbit, one is awaiting launch, and a fourth is under construction. Negotiations are underway regarding the procurement of two further satellites, increasing the number of spacecraft to six; the number which was originally planned before the programme was scaled back in favour of the now-cancelled Transformational Satellite Communications System, or TSAT.

AEHF-2 is a 6,170-kilogram (13,600 lb) spacecraft, which was constructed by Lockheed Martin, and is based on the A2100M satellite bus. Its communications payload, which was built by Northrop Grumman, provides an uplink at a frequency of 44 gigahertz in the Extremely High Frequency band, and a downlink at 20 gigahertz in the Super High Frequency band, with a variable data rate from 75 bits per second to 8.192 megabits per second.

The spacecraft’s propulsion system consists of an IHI Aerospace BT-4 liquid-fuelled apogee motor, a liquid-fuelled reaction control system, and a system of Hall current thrusters. Including research and development, AEHF-2 is estimated to have cost around two billion dollars.

The launch of AEHF-2 comes 21 months after that of AEHF-1, which is now known as USA-214, in August 2010. The day after launch, USA-214 was expected to perform a manoeuvre to begin raising its orbit, however shortly after ignition its apogee motor failed. Following another failed burn two days later, forcing engineers to devise an alternative plan to raise the satellite into its final orbit. Using its manoeuvring engines and Hall thrusters, the satellite finally arrived in geosynchronous orbit in late October last year; fourteen months after launch, and almost a year behind schedule.

The problems with USA-214 resulted in the launch of AEHF-2, which at the time of the first AEHF launch was scheduled for February 2011, being delayed to ensure that it would not be affected by the same problem, and to allow testing of USA-214 in orbit. The next launch, that of AEHF-3, is expected to occur in September next year.

AEHF-2 will be launched by AV-031; an Atlas V rocket in the 531 configuration. This configuration consists of a Common Core Booster, or CCB, first stage, with a single-engine Centaur upper stage, and three Aerojet solid rocket motors. The satellite and Centaur are encapsulated in a 5.4-metre (17.7 foot) diameter payload fairing, with a length of 20.7 metres (68 feet).

A forward load reactor is connected to the fairing at the top of the Centaur, and is used to dampen vibrations, improving the fairing’s rigidity. This is the shortest of three lengths available; a medium length fairing is 23.4 metres (77 feet) long, whilst the long faring is 26.5 metres (87 feet) in length. Smaller, four-metre (13 foot) diameter fairings, which attach atop the Centaur, rather than enclosing it, are also available for smaller payloads.

The configuration and fairing used depend on mission requirements. Zero to five solid rocket motors can be attached to the first stage; although no more than three can be used in conjunction with a four-metre fairing. Single and two-engine variants of the Centaur are available, two engines giving increased performance to lower orbits, however all flights to date have used the single-engine configuration.

The configuration is denoted by a three digit number, the first digit of which indicates the fairing diameter; 4 for the four-metre fairing and 5 for the five-metre one. The second digit gives the number of boosters, and the third digit the number of engines on the Centaur.

Lower and higher capacity versions were also planned; an Atlas V Light, or MLV-D, with an Agena-2000 upper stage, and an Atlas V Heavy with two additional Common Core Boosters augmenting the first stage, however these have not been developed.

The launch of AEHF-2 marks the thirtieth flight of the Atlas V rocket, a vehicle which was developed by Lockheed Martin as part of the Evolved Expendable Launch Vehicle (EELV) programme, and is currently operated by United Launch Alliance.

The Atlas V first flew in August 2002, under the operation of International Launch Services, carrying a payload for Eutelsat’s Hot Bird 6 satellite (which has since been renamed Hot Bird 13A). Its second flight came in May 2003, carrying Hellas Sat 2; the first Greek satellite to be launched. Both of these launches used the 401 configuration, which consists of a CCB, a Centaur, no solid rocket motors, and a four metre fairing.

The third flight was the first to use the five metre fairing, flying in the 521 configuration. The payload was the Rainbow 1 satellite for Cablevision, which has since been sold to EchoStar, and renamed EchoStar XII. The fourth flight used the same configuration, carrying the AMC-16 satellite for SES Americom, whilst the fifth flight used the 431 configuration to carry Inmarsat-4 F1 for Inmarsat.

The sixth Atlas V launch occurred in August 2005, and was the first to carry a payload other than a commercial communications satellite. Flying in the 401 configuration, AV-007 deployed NASA’s Mars Reconnaissance Orbiter into a heliocentric orbit.

The next launch, in January 2006, used the 551 configuration, with an additional Star-48B solid rocket motor acting as a third stage, to propel the New Horizons spacecraft out of the Solar System. New Horizons will be the first spacecraft to visit the dwarf planet Pluto, which was still considered a planet at the time of its launch.

Astra 1KR was the payload of the eighth Atlas V, in April 2006, which was the first flight of the 411 configuration and the last Atlas V to be launched by ILS. In 2006, Lockheed Martin sold its shares in International Launch Services, and took over operations of the Atlas V. No launches were conducted between this, and the December 2006 formation of United Launch Alliance, to which Atlas operations were then transferred.

The first ULA Atlas V launch occurred in March 2007, when an Atlas V 401 deployed the ASTRO, NEXTSat-CSC, STPSat-1, CFESat, MidStar-1 and FalconSat-3 spacecraft as part of the STP-1 mission for the Space Test Program. This was also the first launch of an Atlas V with a payload for the US military.

The next launch, in June 2007, was the first Atlas V mission for the US National Reconnaissance Office. Designated NROL-30, the mission used an Atlas V 401 to deploy two ship-locating Naval Ocean Surveillance System, or NOSS, satellites. The Centaur performed two burns during the mission, with a coast phase in between. During this phase, a valve failed to close properly, resulting in liquid hydrogen leaking out.

At the end of the second burn, the Centaur shut down prematurely, resulting in the spacecraft being placed into a lower than planned orbit. Although the spacecraft were able to manoeuvre into a usable orbit, and ULA considers the launch a success, independent analysts categorise the launch as a partial failure. It is the only Atlas V launch to date which has not been successful.

The eleventh flight, in October 2007, was the first launch of the 421 configuration, carrying the first Wideband Global Satcom spacecraft for the US Air Force. Two months later, an Atlas V 401 was used for NRO Launch 24, deploying an SDS communications satellite. Then, in March 2008, the Atlas V made its first flight from Vandenberg Air Force Base, carrying the NROL-28 mission, which has been identified as an “Improved Trumpet” electronic signals intelligence satellite.

In April 2008, an Atlas V 421 launched the ICO-G1 (now DBSD-G1) communications satellite. Despite the launch being successful, a problem was noted with an actuator in the first stage engine assembly, which resulted in the Atlas being grounded for several months whilst it was investigated. Launches did not resume until April 2009, when the second WGS satellite was launched, also using the 421 configuration.

This was followed by the June 2009 deployment of NASA’s Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite (LCROSS), and the launch of the PAN communications satellite for an undisclosed government agency in September, both using Atlas V 401 rockets.

A second launch from Vandenberg occurred in October 2009, using the 401 configuration to deploy a Defense Meteorological Satellite Program (DMSP) weather satellite. A month later, an Atlas V 431 launch from Cape Canaveral deployed Intelsat 14, the most recent commercial payload to launch on an Atlas.

Four Atlas V launches occurred in 2010. These began with NASA’s Solar Dynamics Observatory on a 401 in February, followed by the first flight of the X-37B Orbital Test Vehicle, on the first Atlas V 501, in April. August saw the first flight of the 531 configuration, with the first AEHF satellite. The fourth launch of the year was from Vandenberg in September, using the 501 configuration to deploy the first in a new series of radar imaging satellites for the NRO, on the NROL-41 mission.

In 2011, five Atlas were launched; the first being a 501 with the second X-37B in March. After this, an Atlas V 411 launched from Vandenberg with a pair of NOSS satellites, the NROL-34 mission, in April, and in May an Atlas V 401 deployed the first geosynchronous Space Based Infrared System (SBIRS) missile detection satellite.

The last two launches of the year carried planetary probes for NASA; an Atlas V 551 launched the Juno mission to Jupiter in August, and in November an Atlas V 541 launched the Mars Science Laboratory mission to the red planet.

The most recent Atlas V launch occurred in February, with the MUOS-1 military communications satellite on an Atlas V 551. One of the heaviest spacecraft to be placed into geosynchronous transfer orbit, MUOS-1 is the first in a series of satellites which will replace the US Navy’s Ultra High Frequency and UHF Follow On (UHF and UFO) spacecraft.

Unusually for a large US military satellite, MUOS-1 does not appear to have been given a USA-series designation; the next available designation, USA-234, was instead assigned to the radar imaging satellite launched by a Delta IV last month. MUOS-1 is believed to be the heaviest payload ever launched by an Atlas rocket, and its launch marked the 200th flight of the Centaur upper stage.

The Common Core Booster which forms the first stage of AV-031 is powered by an RD-180 engine, developed by NPO Energomash of Russia. A derivative of the RD-170 engine used on the Energia, and the RD-171 used on Zenit, the RD-180 burns a mixture of RP-1 propellant and liquid oxygen oxidiser. Ignition of the first stage occurs 2.7 seconds before the countdown reaches zero, at which point the engine will have sufficient thrust for liftoff.

The solids are expected to ignite at T+0.8 seconds, with liftoff itself occurring at T+1.1 seconds. A second after liftoff, maximum thrust will be achieved, and 3.4 seconds later the Atlas will begin to manoeuvre to its ascent trajectory, with an azimuth of 90.13 degrees. Around 39.3 seconds after liftoff, AV-031 will reach Mach 1, and begin supersonic flight, passing through the area of maximum dynamic pressure, or max q, 8.5 seconds later. Following max-q, the pressure will briefly decrease, before peaking again about ten seconds later.

At about T+92.8 seconds, the solid rocket motors will complete their 92-second burns. Around 23.1 seconds after burnout, two of the boosters will separate, followed by the third 1.5 seconds later. Three minutes and 34.4 seconds into the mission, the payload fairing will be jettisoned, with the forward load reactor separating five seconds afterwards.

Four minutes and 18.1 seconds after launch, Booster Engine Cutoff, or BECO, will occur; having exhausted its propellant, the first stage RD-180 engine will shut down. Six seconds later, the spent stage will be jettisoned, with the Centaur’s RL10A-4-2 engine igniting ten seconds after separation. The Centaur is a cryogenically-fuelled stage, fuelled by liquid hydrogen, and oxidised by liquid oxygen. AV-031’s Centaur is the 201st to fly, and the 178th to do so as part of an Atlas-Centaur rocket.

The Centaur’s first burn will last 562.5 seconds, completing 13 minutes and 56.6 seconds into the launch. The flight will then enter a coast phase for 488.9 seconds, before the RL10 is restarted for the Centaur’s second and final burn. This burn will last 342.5 seconds, and at 27 minutes and 48 seconds after liftoff, AV-031’s powered flight will end.

Following the end of the second burn, another coast phase will occur, lasting 23 minutes and 23 seconds, with the Centaur rolling to provide temperature control. Fifty one minutes and 11 seconds after launch, AEHF-2 will separate from the Centaur. The orbit at separation is expected to be an approximately 225 by 50,000 kilometre (140 by 31,000 statute miles, or 120 by 27,000 nautical miles) supersynchronous transfer orbit, with 21.0 degrees inclination, and an argument of perigee of 180 degrees.

AEHF-2 will then use its apogee motor to raise its perigee, before manoeuvring into geosynchronous orbit over a period of several months using its Hall thrusters. It is not expected to have the same problems AEHF-1 had in this regard, indeed the payload processing team patch for AEHF-2 jokingly states that the satellite is “now 876% faster to GEO”.

All the above mission profile milestones were conducted successfully.

The launch of AEHF-2 was conducted by United Launch Alliance, a company formed in 2006 to provide EELV and Delta II launch services to the United States government. Including commercial launches conducted on behalf of Boeing and Lockheed Martin, AV-031 was the sixtieth rocket to be launched by ULA.

ULA has launched 22 Atlas V, 12 Delta IV, and 26 Delta II rockets. Its first launch was of a Delta II carrying the USA-193 satellite, on 14 December 2006. Despite a successful launch, the mission, which was also designated NRO Launch 21, was unsuccessful, with the satellite failing immediately after launch, and eventually being destroyed by an anti-satellite missile in February 2008 as part of Operation Burnt Frost.

The first Atlas V to be launched by ULA was AV-013, with STP-1, whilst the first Delta IV was Delta 329, the second flight of the Delta IV Heavy, carrying the USA-197, or DSP-23, missile detection satellite.

In total, ULA has conducted eleven launches for the National Reconnaissance Office, six launches of planetary probes and seven of other scientific missions for NASA; and has launched as primary payloads seven GPS satellites, five weather satellites, four missile defence spacecraft, nine commercial payloads, excluding two GOES weather satellites launched under commercial contracts, eight military communications satellites including AEHF-2, the STP-1 technology development mission, and two flights of the X-37B Orbital Test Vehicle.

AV-031 launched from Cape Canaveral’s Space Launch Complex 41. Built as a Titan IIIC launch pad in the 1960s, the first launch from the complex, then designated LC-41, occurred in December 1965, when a Titan launched the LES-3, LES-4, Oscar 4 and OV2-3 satellites.

The pad was used for ten Titan IIIC launches, serving as the main Titan III launch complex during the late 1960s whilst LC-40 was undergoing conversion work for the Manned Orbiting Laboratory programme. Following the cancellation of MOL and the resumption of launches from LC-40, LC-41 was converted to accommodate the Titan IIIE, which used a Centaur upper stage in place of the Titan IIIC’s Transtage.

Seven Titan IIIE rockets were launched from LC-41 between 1974 and 1977, carrying the Helios spacecraft which studied the sun, the Viking missions to Mars, and the Voyager missions to the outer planets. The complex was next used in 1989, for the maiden flight of the Titan IV, a rocket which made ten flights from the complex, ending in April 1999 with the failed launch of a Defense Support Program satellite. The complex had been renamed Space Launch Complex 41, or SLC-41, in 1997.

Six months later, the complex’s fixed and mobile service towers were demolished in controlled explosions, beginning work to convert the pad for use by the Atlas V. AV-031 is the twenty sixth Atlas to fly from SLC-41, with Space Launch Complex 3E at Vandenberg Air Force Base being the launch site for the other four launches.

The launch of AEHF-2 was the second flight of an Atlas V in 2012; the first being AV-030 with MUOS-1 in February. The next launch is scheduled for June, when an Atlas V 401 will conduct the NROL-38 mission for the US National Reconnaissance Office. This will also be the next launch for ULA; whilst the Delta II is still in service it currently has no launches scheduled, and the next Delta IV launch; the NROL-15 mission, also for the NRO, is expected to occur later in June than NROL-38.

(Images via ULA and Lockheed Martin).

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