Americans got their first glimpse of the vehicle -- which resembles a miniature, 29-foot-long, silicon-coated version of the Space Shuttle -- when it returned from a seven-month maiden flight through Earth orbit to land at California's Vandenberg Air Force Base in 2012.
Military tech website War on the Rocks calls X-37B "the first true military spaceplane," and predicts that over time, experimental flights with the X-37B will give rise to "massive fleets of very large, maneuverable, and reusable spacefaring vehicles" working for the U.S. Space Force.
Starfighters for the Space Force
X-37B is a wonder of technology. Once put in orbit, a spy satellite generally stays in that orbit, circling the Earth on a defined path at a steady rate of speed, such that its intended targets can predict ahead of time when it will be overhead -- and hide. X-37B, in contrast, can use its refuelable Rocketdyne AR2-3 engine to maneuver in an unpredictable manner.
By changing speed and direction, X-37B can alter its course so as to appear in unexpected places at unexpected times. It's this ability to maneuver sharply and repeatedly in orbit that sets X-37B apart from ordinary spy satellites. (Plus, you know, its ability to land back on Earth, and be launched back into orbit again.)
As former Air Force Secretary Heather Wilson told Military.com in 2019, X-37B can alter its orbit "on the far side of the Earth from our adversaries," such that "our adversaries don't know ... where it's going to come up next." It's an invaluable tool, and one that contributes to Boeing's $26.2 billion-a-year Defense, Space, and Security business (according to data from S&P Global Market Intelligence).
Of course, tiny X-37B's ability to maneuver in orbit -- its "delta-v" -- is constrained its fuel capacity. This is one reason why the U.S. military has recently been funding experiments in refueling satellites and spaceships in orbit.
Which brings us to SpaceX.
SpaceX -- Space road tanker
Perhaps the most important development in this regard is SpaceX, and its plan to use Starship rockets to carry fuel from Earth to space, where they can refuel other Starships, spaceships, and satellites in orbit.
With its 100-ton payload capacity and $2 million-per-launch operating cost, Starship promises to drop the cost of putting payloads in orbit -- any payload, be it satellites, astronauts, or rocket fuel -- from $2,500 per pound currently to as low as $10 per pound. Once Starship becomes operational, refueling Boeing's X-37B in orbit should become a real option.
But why stop there?
A star cruiser for Space Force
As War on the Rocks explains, X-37B may be more maneuverable than a satellite, but "its spacefaring capabilities remain rudimentary at best" when compared to what a larger spaceship, with more engines and more fuel on-board, might achieve -- a spaceship like Starship itself.
Viewed as a "starcruiser" in its own right (as WotR puts it) rather than simply a fuel tanker, Starship's huge fuel tanks give Starship a "delta-V on an unprecedented scale." Starship's vast size may seem ungainly in atmosphere, but in the weightless vacuum of space, its six vacuum-optimized Raptor engines provide a delta-V of 6,900 meters per second -- about 69x more maneuverable than the most agile satellite.
Approximately 6.9km/s-- Elon Musk (@elonmusk) July 17, 2019
In that environment, Starship could become the platform for "a true space-going U.S. Space Force," enabling it to conduct both intelligence, surveillance, and reconnaissance and combat missions anywhere from LEO, to Geostationary or Geosynchronous Orbit, to cis-lunar (between Earth and moon) orbit and beyond.
And acquiring these vessels wouldn't even be that expensive -- a crucial point given Space Force's constrained budget of $15.2 billion, or less than one-tenth of what the Air Force gets. A best-guess at the construction cost of a single Starship comes in at $216 million. At that price point, the Space Force should be able to buy a Starship for less than the cost of a single KC-46 refueling tanker, far less than the Pentagon is believed to have spent developing the secretive X-37B, and maybe even cheaper than that, if buying multiple Starships in bulk.
And at that price point, SpaceX could very well displace Boeing as the Pentagon's go-to defense contractor in space.