X-37B: America’s Spaceplane


    As dawn broke on Saturday, the 12th of November 2022, Americans across central Florida woke to sonic booms [source]. This disruption of an otherwise quiet morning marked the conclusion of a two-year-long mission by the X-37B. Specifics of the vehicle remain highly classified. Publicly available information paints an incredible picture of innovation and scientific achievement. So, what is the X-37B? What is the history of the program? What are the missions it has undertaken? And what can it do?

    An X-37B undergoing a post-flight checkup following OTV-5 on the 27th of October 2019. OTV-5 saw the spaceplane deploy the FalconSat-8.
    An X-37B undergoing a post-flight checkup following OTV-5 on the 27th of October 2019.

    1. What is the X-37B?

    The X-37B, or Orbital Test Vehicle (OTV), is a reusable robotic spaceplane. It is roughly the same size as a medium-sized school bus [source]. Internal storage space allows for the carrying of cargo [source]. This feature can deploy satellites into orbit, as well as be used to conduct experiments [source][source][source]. Taken all together, the X-37B is a significantly cheaper alternative to competing space flight programs. Capable of long-term missions and reuse, the X-37B represents the future of space flight.

    1.1 Dimensions

    • Wingspan: 4.5m (14’ 11”) [source]
    • Length: 8.9m (29’ 3”) [source]
    • Height: 2.9m (9’ 6”) [source]
    • Weight: 4,990kg (11,000 lbs) [source]

    1.2 Power Supply and Engine

     The X-37B relies on gallium arsenide solar cells for power generation, which are notable for their high efficiency, performance, and well-documented electrical and heat resistance [source][source]. Lithium-Ion batteries within the airframe store collected solar energy for future use [source]. It additionally comes equipped with an Aerojet Rocketdyne engine for orbital maneuvers [source]. This engine uses storable propellants for reliability, safety, longevity, and reducing long-term costs [source].

    1.3 Endurance Capabilities

    These features allow the X-37B to stay in low Earth orbit (150 – 500 miles above the surface) for extended periods [source][source]. In fact, at the time of this writing, the X-37 has spent 3,774 days in low Earth orbit [source]. These include two marathon runs of 780 and 908 days in 2017-2019 and 2020-2022, respectively [source][source]. 

    1.4 Getting to Space

    Like a satellite or the Space Shuttle (to which it bears a striking resemblance), the X-37B requires a launch vehicle to put it on an orbital trajectory. These can be the United Launch Alliance Atlas V, manufactured by Lockheed Martin, or the Falcon 9, manufactured by SpaceX [source][source]. The Falcon 9 is also reusable [source]. Combined with the reusable nature of the X-37B, a consistent pairing of the two will significantly reduce program costs.

    1.5 Atmospheric Reentry

    While in low Earth orbit, the X-37 can withstand Mach 25 (8,575 m/s) [source]. For re-entry, the X-37B comes equipped with various insulating systems. These include conformal reusable insulation blankets and heat-resistant ceramic and silica tiles, much like the Space Shuttle [source]. The X-37B will land the same way as a plane. 

    OTV-5 (5th X-37B taking off from the Kennedy Space Center aboard a SpaceX Falcon 9. This is the first time the rocket and plane were used in conjunction.
    OTV-5 taking off from the Kennedy Space Center aboard a SpaceX Falcon 9. This is the first time the rocket and plane were used in conjunction.

    2. History of the X-37 Program

    2.1 From NASA… (1998-2004)

    The concept of the X-37 began in August 1998 when NASA announced the “Future-X” program [source]. “Future-X” called for a vehicle to test next-generation space technology, significantly reducing spaceflight costs [source]. In December of that same year, NASA entered negotiations with The Boeing Company [source].

    Work began in July 1999 as part of a four-year contract, which included the delivery of an Approach and Landing Test Vehicle (ALTV) and an Orbital Vehicle [source][source]. NASA extended the contract in 2002 [source]. The design of the X-37 would be a derivative of the earlier Air Force X-40A, also designed by Boeing [source]. The USAF tested the X-40A extensively before the X-37 began production [source]. NASA initially designed the X-37 to be taken into orbit from within the Space Shuttle’s cargo bay [source]. However, studies showed that such a launch vehicle would be economically inefficient [source]. Boeing redesigned the X-37 afterward to allow for launch from a rocket [source]. 

    2.2 To DARPA… (2004-2006)

    In 2004, NASA transferred the program to the Defense Advanced Research Projects Agency (DARPA) [source]. Under DARPA stewardship, the program became classified [source]. In 2006, the ALTV was completed and successfully tested [source]. This would become known as the X-37A [source].

    2.3 To the USAF… (2006-2019)

     Following the success of the ALTV, the USAF announced plans to develop its own X-37 variant, the X-37B [source]. While the Orbital Vehicle initially envisioned by NASA never came to pass, the X-37B is its successor [source]. There are Two X-37B’s in Air Force inventories [source]. With the addition of the single X-37A, the X-37 family has three existing airframes.

    2.4 And beyond… (2019-Present)

    Upon its establishment in 2019, the X-37B passed onto the US Space Force (USSF) [source]. 

    3. X-37B Operational History

    The X-37B has completed six orbital missions, codenamed OTV-n [source]. The first four three missions remain classified [source]. What follows is a list of the various OTV missions, with the launch and return dates, time in orbit, notable achievements, and stated mission (where applicable).

    3.1 OTV-1

    • Launched on the 22nd of April 2010 and landed on the 3rd of December 2010 [source]. The X-37B spent 224 days and 9 hours in orbit [source]. This mission is notable for being the first X-37B flight [source].

    3.2 OTV-2

    •  Launched on the 5th of March 2011 and landed on the 16th of June 2012, spending 468 days and 14 hours in orbit. OTV-2 was the first flight of the second X-37B manufactured.

    3.3 OTV-3

    • Launched on the 11th of December 2012, returned on the 17th of October 2014 [source]. Orbital flight time clocked at 674 days and 22 hours [source]. It was the second flight of the first produced X-37B, confirming that the vehicles were reusable [source].

    3.4 OTV-4

    • Launched on the 20th of May 2015 and landed on the 7th of May 2017 [source]. Total time in orbit, 717 days and 20 hours [source]. OTV-4 saw the X-37B deploy several CubeSats (miniature satellites) and carry around 100 samples to test their integrity in the vacuum of space [source][source]. These satellites were launched without UN notice and thus may violate UN Resolution 3235, which requires their prior registration [source]. As of the time of writing, the UN have brought no charges forward.

    3.5 OTV-5

    • Launched on the 7th of September 2017 and returned on the 27th of October 2019 [source]. The total time in orbit was 780 days [source]. The X-37B was launched by the SpaceX Falcon 9, marking the first mission in which both vehicles were reusable [source]. OTV-5 saw the X-37B deploy the FalconSat-8, which the USAF developed to conduct orbital experiments [source].

    3.6 OTV-6

    • Launched on the 17th of May 2020 and landed on the 12th of November 2022, the X-37B spent 908 days in orbit [source][source]. OTV-6 introduced an additional service module, increasing the number of experiments capable of being conducted during a mission [source]. Experiments included material and seed reactions to exposure to space [source]. Additionally, a Photovoltaic Radiofrequency Antenna Module was attached to the X-37B. This experiment “aimed to transmit [solar] power [collected by the X-37B] to the ground as radio frequency microwave energy” [source].
    An X-37B returning to its hangar at the Kennedy Space Shuttle Landing Facility following the successful completion of OTV-4.

    4. Speculation regarding Capabilities

    Given the classified nature of early OTV missions, speculation is abundant about the X-37B’s purpose and capabilities. Keep in mind that almost all of these are unconfirmed or theoretical. These include;

    • Deployment of unregistered spy satellites [source].
    • Delivery of nuclear or conventional weapons to targets on Earth [source].
    • Delivery of anti-satellite weapons [source].
    • Spying on rival space stations [source].
    • Covert orbital reconnaissance [source].
    • A testbed for future spy satellite technology [source].
    • Capturing satellites [source].

    Speculation certainly is exciting. However, the US insists that the X-37B remains a testbed for emerging technologies and experiments [source]. Technology such as an ion thruster, which uses significantly less fuel than chemical thrusters, may revolutionize space travel [source][source]. Studying the effects of material and organic exposure to space supplements similar experiments conducted on the ISS [source]. Given the ISS’s planned decommissioning in the 2030s, X-37B experiments may be a valuable stopgap [source]. Fundamentally, the X-37B remains the same vehicle that NASA requested in 1998.

    5. Conclusion

    The X-37B is an incredible machine. It promises to reduce the costs of future space travel. Additionally, it produces valuable scientific data and tests technology that may further drive human expansion into space. Spaceplane development is still in its infancy; if the X-37B is anything to go by, advancement in this field will be revolutionary.

    Maxwell Goldstein
    Maxwell Goldstein
    Maxwell is a Junior Intelligence Analyst and student pursuing an international master's degree through the Erasmus Mundus IMSISS programme. His areas of focus are aerospace, technology, and the Indo-Pacific.

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