What has the X-37 spaceplane been up to?

The X-37 is inspected following its landing in 2010 [Image source: [U.S. Air Force photo gallery]

Earth’s sole operational orbital spaceplane, the X-37, has been generating much speculation on when its epic 630+ day mission will end.

I once caught a glimpse of this beast sitting on the runway at Palmdale in 2006. The project had just moved into the black after suffering landing gear damage during a runway overrun at Mojave. Slightly larger than the Tarago-sized support vehicle parked alongside it, the X-37 sat there brooding in the desert sun. Nearby, technicians wearing the ubiquitous hazmat suits loitered ominously.

Since that time the project has spawned two operational X-37B vehicles. Each has now been to space twice, smashing endurance records on the way. The current mission, OTV-4, is approaching its sister ship’s record of 674 days for the longest duration spaceflight of a reusable orbital vehicle.

Publicly released information on the X-37’s activities remains scarce. However, Air and Space Smithsonian magazine recently offered some informed speculations on what it might have been up to during its sojourn:

Orbital testbed: The X-37’s payload bay is large enough to house compact experimental communications and navigation systems. NASA and the USAF have also publicly revealed that an Aerodyne XR-5A Hall Thruster was one of the advanced payloads that was tested on OTV-4. This testing could be part of a dedicated R&D effort to develop systems for smaller next-generation satellites. With such improvements, satellites could operate at lower altitudes and obtain superior imagery.

Advanced surveillance sensors: The X-37 could conceivably carry sophisticated space-based sensors such as space-based LIDAR or hyperspectral sensors. With its impressive maneuvering capability, it could rapidly re-position to look down over newly emerging global hotspots.

Spying on satellites: The X-37’s flight envelope is impressive. It can operate between 200 and 925 kilometers, and has sufficient delta-v to rendezvous with LEO satellites. This gives the vehicle a unique capability to inspect the world’s 1400+ LEO satellites from close range.

Anti-satellite or counter-anti-satellite operations: More speculatively, the X-37 could be utilized for clandestine missions to jam, spoof or sabotage an adversary’s satellites. With rapid turn-around capability, even newly launched satellites could be swiftly targeted.

Satellite maintenance and retrieval: The X-37 could perform in-orbit maintenance to extend a satellite’s lifespan. If fitted with a robotic arm, it could even retrieve previously deployed cubesats and bring them back to Earth for refurbishment.

Rescue vehicle for the ISS: Longer-term, and if fitted out with human-rated hardware, the X-37 could potentially be used as a rescue vehicle for astronauts should an emergency cripple the ISS.

What the USAF really intends for the X-37 program will likely remain classified for some time. But what is indisputable is that they now have the capability to operate a viable reusable orbital vehicle with significant, flexible, multi-mission capability. This is an X-Plane to watch.

The X-37B OTV in 2009 at Vandenburg AFB, Calif [Image source: U.S. Air Force photo gallery]