[2] An X-37 first flew during a drop test in 2006; its first orbital mission was launched in April 2010 on an Atlas V rocket, and returned to Earth in December 2010.

The sixth mission launched on an Atlas V on 17 May 2020 and concluded on 12 November 2022, reaching a total of 908 days in orbit.

In late 2002, a new $301 million contract was awarded to Boeing as part of NASA's Space Launch Initiative framework.

[6] The aerodynamic design of the X-37 was derived from the larger Space Shuttle orbiter, hence the X-37 has a similar lift-to-drag ratio, and a lower cross range at higher altitudes and Mach numbers compared to DARPA's Hypersonic Technology Vehicle.

[7] An early requirement for the spacecraft called for a total mission delta-v of 7,000 miles per hour (3.1 km/s) for orbital maneuvers.

DARPA promoted the X-37 as part of the independent space policy that the United States Department of Defense has pursued since the 1986 Challenger disaster.

Instead of an operational vehicle's payload bay doors, it had an enclosed and reinforced upper fuselage structure to allow it to be mated with a mothership.

In September 2004, DARPA announced that for its initial atmospheric drop tests the X-37A would be launched from the Scaled Composites White Knight, a high-altitude research aircraft.

[15] On 24 March 2006, the X-37A flew again but a datalink failure prevented a free flight and the vehicle returned to the ground still attached to its White Knight carrier aircraft.

The X-37B was subsequently transferred to a shrouded configuration on the Atlas V rocket, due to concerns over the unshrouded spacecraft's aerodynamic properties during launch.

[25] NASA furthermore stated that renovations of the two hangars would be completed by the end of 2014; the main doors of OPF-1 were marked with the message "Home of the X-37B" by this point.

[26] The primary objectives of the X-37B are twofold: reusable spacecraft technology and operating experiments which can be returned to Earth.

The Pentagon subsequently denied claims that the X-37B's test missions supported the development of space-based weapons.

[30] In October 2014, The Guardian reported the claims of security experts that the X-37B was being used "to test reconnaissance and spy sensors, particularly how they hold up against radiation and other hazards of orbit".

[31] In November 2016, the International Business Times speculated that the U.S. government was testing a version of the EmDrive electromagnetic microwave thruster on the fourth flight of the X-37B.

[10] The spaceplane's thermal protection system is built upon previous generations of atmospheric reentry spacecraft,[46] incorporating silica ceramic tiles.

[50] 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.

[59][60] OTV-1 reputedly passed over the same given spot on Earth every four days, and operated at an altitude that is typical for military surveillance satellites.

[61] Such an orbit is also common among civilian LEO satellites, and the spaceplane's altitude was the same as that of the ISS and most other crewed spacecraft.

[23] The second X-37B launched on its inaugural mission, designated OTV-2/USA-226,[67] aboard an Atlas V rocket from Cape Canaveral SLC-41 on 5 March 2011 at 22:46 UTC.

[69] In April 2012, General William L. Shelton of the Air Force Space Command declared the ongoing mission a "spectacular success".

[79][80] Landing occurred at Vandenberg AFB on 17 October 2014 at 16:24 UTC, after a total time in orbit of 674 days and 22 hours.

[84] Objectives included a test of Aerojet Rocketdyne's XR-5A Hall-effect thruster in support of the Advanced Extremely High Frequency communications satellite program,[36][85] and a NASA investigation on the performance of various materials in space[21][56][86] for at least 200 days.

[92] While the complete payload for OTV-5 is classified, the Air Force announced that one experiment flying is the Advanced Structurally Embedded Thermal Spreader II (ASETS-II), which measures the performance of an oscillating heat pipe.

[40][94] The sixth X-37B mission (OTV-6), U.S. Space Force 7 (formerly known as AFSPC 7), launched on an Atlas V 501 rocket from Cape Canaveral SLC-41 on 17 May 2020 at 13:14:00 UTC.

[95] This mission is the first time the spaceplane has carried a service module, a ring attached to the rear of the vehicle for hosting multiple experiments.

The spacecraft will test a novel electromagnetic propulsion system, low-weight antenna technology and a commercial reaction wheel to provide attitude control in orbit.

This spacecraft was planned to be between 165% and 180% of the size of the X-37B, allowing it to transport up to six astronauts inside a pressurized compartment housed in the cargo bay.