Boeing X-37

The Boeing X-37 (also known as the X-37 Orbital Test Vehicle) is an American reusable unmanned spacecraft which is boosted into space by a rocket, then re-enters Earth’s atmosphere and lands as a spaceplane. The X-37 is operated by the United States Air Force for orbital spaceflight missions intended to demonstrate reusable space technologies. It is a 120%-scaled derived of the earlier Boeing X-40.

The X-37 began as a NASA project in 1999, before being reassigned to the U.S. Department of Defense in 2004. It conducted its first flight as a drop test on 7 April 2006, at Edwards Air Force Base, California. The spaceplane’s first orbital mission, USA-212, was launched on 22 April 2010 using an Atlas V rocket. Its successful return to Earth on 3 December 2010 was the first test of the vehicle’s heat shield and hypersonic aerodynamic handling. A second X-37 was launched on 5 March 2011, with the mission designation USA-226; it returned to Earth on 16 June 2012. A third X-37 mission, USA-240, was launched successfully on 11 December 2012.

In 1999, NASA preferred Boeing Integrated Defense Systems to design and develop an orbital vehicle, built by the California branch of Boeing’s Phantom Works. Over a four-year period, a total of $192 million was contributed to the project, with NASA contributing $109 million, the U.S. Air Force $16 million, and Boeing $67 million. In late 2002, a new $301-million contract was awarded to Boeing as part of NASA’s Space Launch Initiative framework.

The X-37 was at first designed to be carried into orbit in the Space Shuttle’s cargo bay, but underwent redesign for launch on a Delta IV or comparable rocket after it was determined that a shuttle flight would be uneconomical. The X-37′s aerodynamic design was derived from the Space Shuttle, therefore the X-37 has a parallel lift-to-drag ratio, and a lower cross range at higher altitudes and Mach numbers compared to DARPA’s Hypersonic Technology Vehicle.

As part of its mission goals, the X-37 was designed to meet with friendly satellites to refill them, or to replace failed solar arrays using a robotic arm. Its payload could also support Space Control (Defensive Counter-Space, Offensive Counter-Space), Force Enhancement and Force Application systems. An early requirement for the spacecraft called for a delta-v of 7,000 mph (3.1 km/s) to change its orbit.

Among the technologies demonstrated in the X-37 include an improved thermal protection system, enhanced avionics, an autonomous guidance system and an advanced airframe. The spaceplane’s thermal protection system is built upon previous generations of atmospheric reentry spacecraft, incorporating silica ceramic tiles. The X-37′s avionics suite was used by Boeing to develop itsCST-100 manned spacecraft. According to NASA, the development of the X-37 will “aid in the design and development of NASA’s Orbital Space Plane, designed to provide a crew rescue and crew transport capability to and from the International Space Station”.

The X-37 is independently powered by one Aerojet AR2-3 engine using storable propellants, providing thrust of 6,600 pounds-force (29.341 kN). The human-rated AR2-3 engine had been used on the dual-power NF-104A astronaut training vehicle, and was given a new flight certification for use on the X-37 with hydrogen peroxide/JP-8 propellants.

The X-37 lands automatically upon returning from orbit, and is the second reusable spacecraft to have such a capability, after the Soviet Buran shuttle. The X-37 is the smallest and lightest orbital spaceplane flown to date; it is approximately a quarter the size of the Space Shuttle orbiter.

The X-37A was the initial NASA version of the spacecraft; the X-37A Approach and Landing Test Vehicle (ALTV) was used in drop glide tests in 2005 and 2006. The X-37B is a modified version of the NASA X-37A, intended for the U.S. Air Force. It conducted orbital test missions in 2010, 2011 and 2012. In 2011, Boeing announced plans for a scaled-up variant of the X-37B, referring to the spacecraft as the X-37C. The X-37C would be between 165% and 180% larger than the X-37B, allowing it to transport up to six astronauts inside a pressurized compartment housed in the cargo bay. Its proposed launch vehicle is the Atlas V Evolved Expendable Launch Vehicle. The X-37C may compete with Boeing’s CST-100 commercial space capsule.

Specifications

Crew: None
Length: 29 ft 3 in (8.9 m)
Wingspan: 14 ft 11 in (4.5 m)
Height: 9 ft 6 in (2.9 m)
Loaded weight: 11,000 lb (4,990 kg)
Powerplant: 1 × Aerojet AR2-3 rocket engine (hydrazine), 6,600 lbf (29.3 kN)
Power: Gallium arsenide solar cells with lithium-ion batteries
Payload bay: 7 ft × 4 ft (2.1 m × 1.2 m)
Orbital speed: 28,044 km/h (17,426 mph)
Orbit: Low Earth orbit
Orbital time: 270 days (design)