Boeing X-37

Development

In 1999, NASA chose Boeing Integrated Defense Systems to create an orbital vehicle, with the California branch of Boeing Phantom Works handling construction. Over four years, the project spent $192 million, contributed by NASA ($109 million), the U.S. Air Force ($16 million), and Boeing ($67 million). A subsequent $301 million contract was awarded to Boeing in late 2002 under NASA's Space Launch Initiative. The X-37's aerodynamic shape drew from the larger Space Shuttle orbiter, giving it a similar lift-to-drag ratio and a lower cross range at high altitudes and Mach numbers than DARPA's Hypersonic Technology Vehicle.

An early requirement called for a total mission delta-v of 7000 mph for orbital maneuvers, and an initial goal was for the spacecraft to rendezvous with satellites for repairs. Originally designed to be carried in the Space Shuttle's cargo bay, the X-37 was redesigned for launch on a Delta IV or comparable rocket after a shuttle flight was deemed uneconomical. The program transferred from NASA to DARPA on 13 September 2004, becoming classified due to military applications.

DARPA promoted the X-37 as part of the independent space policy pursued by the U.S. Department of Defense since the 1986 Challenger disaster. The X-37A drop test glider lacked propulsion and had an enclosed, reinforced upper fuselage instead of payload bay doors. In September 2004, DARPA announced that the X-37A would be launched from the Scaled Composites White Knight aircraft for initial atmospheric drop tests. On 21 June 2005, the X-37A completed a captive-carry flight under the White Knight from Mojave Spaceport.

Structural upgrades, including reinforcement of nose wheel supports, occurred through the second half of 2005. The first free flight, scheduled for 10 March 2006, was canceled due to an Arctic storm, and a subsequent attempt on 15 March 2006 was canceled due to high winds.

Design

The X-37 Orbital Test Vehicle is a robotic spaceplane that can be reused. It is about 120 percent the size of the Boeing X-40, measures over 29 feet long, and has two angled tail fins. It rides into space on an Atlas V 501, a SpaceX Falcon 9, or a Falcon Heavy rocket, and can reach speeds up to Mach 25 when coming back through the atmosphere. The vehicle showcases a better thermal protection system, upgraded avionics, a self-piloting guidance system, and a more advanced frame.

Its heat shield uses silica ceramic tiles, building on older reentry designs. Boeing later used the avionics from the X-37 to develop its CST-100 crew capsule. A NASA fact sheet said the X-37 was built to help design the agency’s Orbital Space Plane, which was meant to carry crews to and from the International Space Station for rescue or transport. For NASA’s version, the spaceplane was supposed to use one Aerojet AR2-3 engine that burned storable propellants and produced 6600 pounds of thrust.

That engine had already flown on the NF-104A astronaut trainer and was recertified for the X-37 with hydrogen peroxide and JP-8 fuel. Reports later said this was swapped for a hypergolic system using nitrogen tetroxide and hydrazine. The X-37 lands on its own after returning from orbit, making it the third reusable spacecraft with that ability, after the Soviet Buran and the U.S. space shuttle (which had automatic landing by the mid-1990s but never used it).

It is the smallest and lightest orbital spaceplane ever flown, with a launch weight around 11,000 pounds and about one-quarter the size of the Space Shuttle orbiter. On April 13, 2015, the Space Foundation gave the X-37 team the 2015 Space Achievement Award for pushing forward reusable spacecraft and orbital operations over three missions totaling 1,367 days in space.

Operational history

Two operational X-37Bs have completed seven orbital missions, accumulating a combined 4,208.66 days (11.53 years) in space. The first X-37B launched on OTV-1/USA-212 aboard an Atlas V from Cape Canaveral SLC-41 on 22 April 2010 at 23:52 UTC, entering low Earth orbit. Amateur astronomers identified the spacecraft in an orbit with an inclination of 39.99°, circling Earth every 90 minutes at 401 by 422 km, passing over the same spot every four days at an altitude typical for military surveillance satellites and also common among civilian LEO satellites.

The U.S. Air Force announced a 3–6 December landing on 30 November 2010; the X-37B de-orbited and landed autonomously at Vandenberg SFB on 3 December 2010 at 09:16 UTC, the first US autonomous orbital landing onto a runway since the Soviet Buran shuttle in 1988. OTV-1 suffered a tire blowout during landing and minor underside damage. The second X-37B launched on OTV-2/USA-226 aboard an Atlas V from Cape Canaveral SLC-41 on 5 March 2011 at 22:46 UTC, a classified mission described as testing new space technologies.

On 29 November 2011, the Air Force extended the mission beyond the 270-day baseline; in April 2012, General William L. Shelton called it a "spectacular success." The spacecraft landed autonomously at Vandenberg AFB on 16 June 2012. OTV-3, the second flight of the first X-37B, was originally scheduled for 25 October 2012 but postponed due to an Atlas V engine issue, launching successfully on 11 December 2012 at 18:03 UTC as USA-240, and landing at Vandenberg AFB on 17 October 2014 at 16:24 UTC.

Variants

The X-37A Approach and Landing Test Vehicle, or ALTV, was an early NASA design that underwent drop glide tests in 2005 and 2006. The U.S. Air Force later used a modified version, the X-37B, building two units for multiple orbital flights. In 2011, Boeing revealed plans for a larger variant, the X-37C, which would be 165 to 180 percent the size of the X-37B.

This version was intended to carry up to six astronauts in a pressurized compartment within its cargo bay, launching on an Atlas V rocket. It could have competed with Boeing's own CST-100 Starliner. As of 2024, no further development of the X-37C has been announced.