A United Launch Alliance (ULA) Atlas V 501 rocket has launched with the X-37B OTV-1 spacecraft. Launch was on schedule at Cape Canaveral Air Force Station (CCAFS) at the start of a nine minute launch window that opened at 23:52 GMT (18:52 local) Thursday night.
The X-37B OTV-1 flight is a classified mission for the US Air Force. It is believed to be carrying technology demonstration and development experiments for the USAF’s Rapid Capabilities Office.
The duration of the mission has not been announced; however once it is complete the X-37B will reenter the atmosphere, and land at Vandenberg Air Force Base in California.
Edwards Air Force Base is available as a backup landing site if necessary. The X-37B was designed to be reusable, and can remain in orbit for up to 270 days at a time.
The X-37 was developed by Boeing, originally as part of a NASA programme. In 2004, the Defense Advanced Research Projects Agency took over the programme, and in 2006 the US Air Force began development of the X-37B derivative for military applications.
Originally scheduled for launch aboard a Space Shuttle, the X-37B was moved to a Delta II in the aftermath of the Columbia accident. In this configuration the Delta II would have flown without a payload fairing, which raised concerns over the aerodynamics of the vehicle and led to the decision to launch on the larger Atlas V.
The X-37B is 8.9 metres (39 feet and 3 inches) long, has a wing span of 4.5 metres (14 feet and 11 inches), and stands 2.9 metres (9 feet and 11 inches) high. It has a mass at launch of about 5,000 kilograms (11,000 pounds). The spacecraft is powered by lithium ion batteries, which will be recharged in orbit by gallium arsenide solar arrays.
The rocket which will launch the X-37B is Atlas V AV-012. It will be the first Atlas to fly in the 501 configuration, which features a five metre diameter payload fairing, no solid rocket motors, and a single-engine Centaur upper stage. United Launch Alliance is responsible for conducting the launch.
AV-012 is the fourth Atlas to use the five metre fairing, and the first in over four years. It was last used in January 2006, for the launch of New Horizons aboard AV-010. The five metre fairing is produced in Switzerland by RUAG, who also produce a similar fairing for the Ariane 5 rocket.
Its exact external diameter is 5.4 metres (17.7 feet), and three lengths of fairing are available; a short fairing is 20.7 metres (68 feet) long, a medium fairing is 23.4 metres (77 feet) long, and a long fairing is 26.5 metres (87 feet) long. AV-012 will use the short fairing.
The first stage of AV-012 is a Common Core Booster, propelled by a Russian-built RD-180 main engine, which will ignite 2.7 seconds before the countdown reaches zero. The RD-180 is derived from the RD-170 engine developed for the Energia and Zenit rockets, and burns RP-1 fuel with liquid oxygen being used as an oxidiser.
At T+1.1 seconds, AV-012 will be released from the launch platform, and begin its ascent towards orbit. Nineteen seconds into the mission, the rocket will perform a pitchover, and 33.3 seconds later it will establish a zero-angle-of-attack flight profile.
Three minutes and 39.4 seconds into the launch, the payload fairing will separate from the rocket, exposing the Centaur upper stage and X-37B to space for the first time. Five seconds later the forward load reactor, which is used to dampen the vibrations and provide support for the upper section of the payload fairing, will be jettisoned. About 265 seconds after launch, the first stage engine will shut down, and six seconds later it will separate from the Centaur.
Ten seconds after staging, the Centaur’s single RL10A-4-2 engine will ignite to perform a burn which will last for twelve minutes and thirty seven seconds. Once the burn is complete, the RL10 engine will shut down, leaving the rocket in an unpowered coast. Mission events after this have not been confirmed.
If the rocket is flying a direct ascent flight profile, then following the end of the burn the Centaur will reorient itself, and the X-37B will separate shortly afterwards. If the flight is not using a direct ascent profile, then the Centaur will make a short second burn, probably during its first orbit, before spacecraft separation occurs. In either case, after separation, the Centaur will perform a collision avoidance manoeuvre to put distance between it and the X-37B.
AV-012 will lift off from Space Launch Complex 41 at Cape Canaveral. SLC-41 was built in the 1960s, along with SLC-40, for use by the Titan family of rockets. It was first used in December 1965, for a Titan IIIC launch. It was later used by Titan IIIE, or Titan-Centaur, rockets, for the launches of the Helios, Viking and Voyager missions during the 1970s.
The Titan IV first used the complex in June 1989, when it made its maiden flight. The final Titan launch from SLC-41 occurred in April 1999, and failed to place a Defense Support Program satellite into geosynchronous orbit. Six months later both the fixed and mobile towers at the pad were demolished by controlled explosions. The first Atlas launch from the complex was made a little under three years later.
AV-012 was assembled atop a Mobile Launch Platform in the Vertical Integration Facility, located about 550 metres from the launch pad. The rocket and launch platform were transported to the launch pad on Wednesday. They departed the Vertical Integration Facility at 14:24 GMT (10:24 local), and arrived at the launch pad about thirty six minutes later.
AV-012 will be the twenty-first Atlas V to launch. The twenty previous launches were all successful, except for AV-009 which placed the USA-194 satellites into a lower than planned orbit after a valve allowed cryogenic propellant to leak from the Centaur during a coast phase.
This is the second Atlas V and third EELV launch of the year. The next Atlas V launch is scheduled to occur on 30 July, carrying the first Advanced Extremely High Frequency communications satellite for the US Air Force. The next EELV launch will be of a Delta IV Medium+(4,2), carrying the GPS IIF-1 satellite; this is currently scheduled to occur on 21 May.
The next X-37B launch, OTV-2, is expected to occur next year at the earliest. It is unclear whether the same spacecraft will be used for that mission.