DOD’s X-37B Spaceplane Flies Again

DOD’s X-37B Spaceplane Flies Again

A SpaceX Falcon Heavy rocket launched DOD’s X-37B spaceplane into orbit this evening. Two reusable Boeing-built X-37B Orbital Test Vehicles exist and this is the seventh flight for the program. Little is known about what these super-secret missions do while they are in space other than demonstrating very long flight durations. Each flight has broken the previous record, which currently stands at 908 days. X-37B looks like a small Space Shuttle, but does not carry people like NASA’s Space Shuttle did in the past.

After a number of delays for technical issues or inclement weather, the launch tonight went off without a hitch at 8:07 pm ET. This is the first time X-37B has launched on a Falcon Heavy, although one flew on a Falcon 9. The other five were on United Launch Alliance Atlas V rockets.

SpaceX’s Falcon Heavy lifts off into the night sky from Launch Complex 39A at Kennedy Space Center carrying DOD’s X-37B spaceplane, December 28, 2023. Screengrab from SpaceX webcast.


Liftoff of SpaceX’s Falcon Heavy with DOD’s X-37B spaceplane, December 28, 2023. Photo credit: SpaceX

Falcon Heavy is essentially three Falcon 9 boosters strapped together. Most Falcon 9 first stages return to land either on drone ships at sea or back on terra firma so they can be reused. The two side boosters on this flight are discolored — “sooty” — because they’ve flown four times already.

SpaceX’s Falcon Heavy with DOD’s X-37B spaceplane on the launch pad at Kennedy Space Center, FL. The two side boosters are “sooty” because they have flown before. This is the fifth flight for each of them. December 28, 2023. Photo credit: SpaceX

The X-37B lifted off from Launch Complex 39A at NASA’s Kennedy Space Center, which SpaceX leases from the government. The two side boosters came back to land at Cape Canaveral Space Force Station adjacent to KSC. The central core was not recovered this time.

Resembling a small Space Shuttle, X-37B actually began as a NASA effort to build a crew taxi for the International Space Station. The agency terminated the program in 2004 after President George W. Bush announced a strategy shift for the human spaceflight program that included cancelling the Space Shuttle once construction of the ISS was completed. NASA transferred X-37B to the Defense Advanced Research Projects Agency (DARPA) and it was later taken over by the Air Force’s Rapid Capabilities Office. Today’s flight is a partnership between the RCO and the U.S. Space Force (USSF) and designated USSF-52. It’s also called OTV-7 since it is the seventh Orbital Test Vehicle flight.

The spaceplane can touch down either at KSC or Vandenberg Space Force Base, CA. The last X-37B flight, OTV-6, landed at KSC a little over a year ago on November 12, 2022.

A technician walks to the U.S. Space Force’s X-37B uncrewed spaceplane after landing at Kennedy Space Center’s shuttle landing strip, November 12, 2022. Photo credit: U.S. Space Force

Where and when the spaceplane will return this time is unknown. Each flight has remained in space for longer and longer durations. OTV-6 reached two-and-a-half years.

First flight: 2010, 224 days
Second flight: 2011-2012, 469 days
Third flight: 2012-2014 674 days
Fourth flight: 2015-2017, 718 days
Fifth flight: 2017-2019, 780 days
Sixth flight: 2020-2022, 908 days

OTV-6 was the first to incorporate a service module that enabled the mission to host additional experiments. OTV-6 also deployed a small satellite, FalconSat-8, developed by the U.S. Air Force Academy.

The Space Force has said little about what OTV-7 will do, but noted it has a “flight proven” service module. That wording implied this was the same one used for OTV-6, but that service module was separated from the X-37B before reentry and “disposed of in accordance with best practices.” The Space Force also said this mission has “a wide range of test and experimentation objectives. These tests include operating the reusable spaceplane in new orbital regimes, experimenting with future space domain awareness technologies, and investigating the radiation effects on materials provided by NASA.”  The NASA experiment, Seeds-2, will expose plant seeds to space radiation during the duration of the mission.

The secrecy surrounding the program generates considerable speculation about what the X-37B does during those long durations on orbit. Some suggest it spies on other satellites or perhaps even carries weapons. The Secure World Foundation concludes that’s unlikely and is probably a testbed for new technologies just as DOD claims.

The extra orbital energy imparted by the Falcon Heavy is generating a lot of curiosity about what OTV-7 can do compared to previous flights. COMSPOC, a Space Situational Awareness company, posted speculative videos of two types of orbits the X-37B might fly: a Low Earth Orbit (LEO) trajectory like those of the previous missions that is essentially circular and takes about 90 minutes per orbit, or a Highly Elliptical Orbit (HEO) where the orbit comes close to Earth (perigee) over one hemisphere, but then swings high (apogee) over the other hemisphere allowing the satellite to linger over that part of the world for hours instead of minutes on each orbit.

HEO orbits are not uncommon, but would be a first for X-37B if that’s where it’s headed. Professional and amateur satellite trackers surely will be trying to find it.


This article has been updated and clarified to indicate the OTV-7 service module may be “flight proven” but is not the same one used for OTV-6.

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