On Saturday, June 16, 2012, at 5:48 AM Pacific Daylight Time (12:48 Zulu), the X-37B program’s unmanned Orbital Test Vehicle Two (OTV-2) set down onto the three-mile runway at Vandenberg Air Force Base, Calif. OTV-2’s mission (officially designated USA-226 – the second for the X-37B program) lasted a record-setting 468 days, 13 hours, and 2 minutes, orbiting the Earth more than 7,000 times since its launch aboard an Atlas V Model 501 booster from Cape Canaveral on March 5, 2011.

While the activities the two X-37Bs have engaged in on-orbit remain classified, those who do have insight into the capabilities of the two mini-shuttles are saying that the first flights of OTV-1 (USA-212 which flew for 224 days) and -2 are revolutionizing space access for the United States. However, according to Deputy Undersecretary of the Air Force for Space Programs Richard W. McKinney, the X-37Bs are mainly reusable “trucks” to carry experimental space technologies into orbit.

“We’re in a very serious and important business in providing national security space capabilities for our nation,” McKinney said. “As you well know, some of those technologies are state of the art, highly complex, very technical, and our ability to examine those technologies before they’re made operational is a long sought after capability. Now we can test those capabilities well in advance of putting them in operation. So rather than having it go up for the first time and do an operational mission, we could actually test those capabilities. We’re going to use this to put experiments on orbit. We’re going to check them out. We’re going to test them and we’re going to bring them back. That’s what this is.”

However, it is highly unlikely that the X-37Bs are only being used as platforms for testing experimental space technologies. In fact, these innovative products of Boeing’s famous “Phantom Works” in Palmdale, Calif., are likely already being used for a variety of operational military space missions while simultaneously carrying out experimental tasks in orbit. The keys to this wide range of capabilities are likely explained by several design features of the two OTVs, including:

• Cargo bay – Of all the features of the recently retired space shuttle fleet, none was cherished by mission planners more than the orbiter’s vast cargo bay. And while the X-37B’s cargo bay is modest by comparison (12 feet long, and 4 feet in diameter for about 600 cubic feet of usable volume) to the shuttle’s, that is a lot of room for talented engineers to pack payloads into. Assuming that the X-37B’s cargo bay has some sort of powered/networked modular/palletized cargo mounting system, this makes it possible to integrate a wide variety of payloads into the diminutive spacecraft.
• On-orbit dwell time – Likewise, of the major limitations of the space shuttles, none probably challenged mission planners more than their limited on-orbit dwell time. The need to feed fuel cells with a mix of liquid hydrogen and oxygen meant the shuttles were limited to missions of about two weeks duration. By using a deployable solar panel array feeding rechargeable batteries, the X-37Bs are able to fly missions limited only by maneuvering fuel and mission requirements, not power or consumables issues.
• Flight automation – One of the keys to the success of the first two X-37B missions has been the advanced flight automation software flying the mini-shuttle. Virtually every aspect of the OTV’s operations have been automated for ground controllers, up to and including re-entry and landing. This has clearly allowed controllers to minimize maneuvering fuel usage, allowing the requirement-mandated 270-day missions originally planned to be pushed to almost twice that duration on OTV-2’s maiden flight.

So just what were the OTVs doing on their flights? It may be that the X-37s are doing a bit of everything while on-orbit. One real possibility is that an optical sensor package like the ORS-1/USA-231 reconnaissance satellite might be aboard, able to image both ground and co-orbital targets. Electronic/communications intercept payloads are also a distinct possibility. Designed from the start to be capable of refueling friendly satellites in orbit, the X-37B might also be testing its capability to act as an on-orbit replacement carrier for small “NanoSatellite” constellations should U.S. satellites be knocked out by hostile forces. Finally, the OTVs may also be functioning as killer spacecraft in their own right, using something like the 1980s “Brilliant Pebbles” interceptors as the weapons. The X-37B’s cargo bay makes it possible to carry examples of all the systems mentioned above, along with the experimental payloads mentioned by McKinney.

It’s worth noting that OTV-2 on Mission USA-226 flew longer and farther that the shuttle Discovery did (365 days and 5,400 orbits) on 39 flights over three decades. That means that with just two X-37Bs in the fleet, the Air Force can keep one up at all times for the indefinite future.

Another potential long-term benefit of the basic X-37 design is that it is scalable into both larger and smaller versions at a strikingly low cost. Already Boeing has released notional imagery of an evolved version, the X-37C, which would be approximately 165 percent to 180 percent bigger than the X-37B, fully man-rated, capable of delivering a crew of six into orbit, and would be launched by a version of the Atlas V family.

How impressive is the X-37B program right now? Consider that both the Russians and Chinese have active programs to produce similar spacecraft. In addition, NASA has contracted with Sierra Nevada Systems to produce a manned mini-shuttle for crew/cargo deliveries to orbit. Plan on seeing more of these versatile little spacecraft as access to near-Earth space becomes more common in the years ahead.