US X-37B robot minishuttle: 'Secret space warplane'?
No, but it could do some naughty orbital stuff
Tomorrow, the US Air Force will finally launch the long-delayed X-37B unmanned mini space shuttle, dubbed by the Iranian government a "secret space warplane". But what is it actually for?
Probably nothing hostile, most of the time, is the answer. But it could do some quite naughty and interesting things if required - and what's more, it could probably do them without anyone knowing about it.
Secret, yes. Warplane? Probably not
The X-37 has had a long and chequered development history. It was built by Boeing's "Phantom Works" advanced-concepts shop, originally for NASA - though it had Air Force heritage from the beginning, drawing heavily on the USAF's X-40 experiments.
NASA saw the craft as a potential "lifeboat" for the International Space Station, but that requirement wouldn't really call for a winged re-entry vehicle: the ISS lifeboat is in fact a common-or-garden Soyuz capsule - perhaps now to be replaced at some point by an American Orion salvaged from the ruins of the Constellation moonbase programme. Neither has wings, or any real need for them.
NASA dropped the X-37 after some work involving release of test airframes in the atmosphere and so on. But the spaceplane lived on, supported at times by funds from maverick military tech bureau DARPA and some from the Phantom Works itself. Nowadays the project is run by the US Air Force Rapid Capabilities Office as the X-37B, which was originally set for an orbital test as soon as 2008.
That timeline has slipped well to the right, perhaps as a result of reported technical hiccups including one where a prototype atmosphere test craft, dropped off in the stratosphere by Scaled Composites' famous "White Knight" high-altitude jet mothership*, came in successfully for a landing at Edwards Air Force Base in California - but then ran off the end of the runway.
Be that as it may, the X-37B is now said to be fully ready to go, and is waiting atop an Atlas V rocket stack for launch tomorrow at Cape Canaveral Air Force Station, having been delayed the past few days by the late arrival of space shuttle Discovery. (Airspace has to be kept rigorously clear in the area when a shuttle might be coming down at Kennedy Space Centre, preventing rocket launches.)
Why would a re-usable vehicle need wings specifically?
The USAF has remained fairly tight-lipped about the X-37B, refusing even to reveal how much it costs as it is funded from the classified (or "black") budget. Programme managers won't reveal anything about tomorrow's payload or even how long the little spaceplane is to stay up before landing at either Edwards or Vandenberg in California. However the Rapid Capabilities Office does say:
Actual length for the first mission will depend on the meeting the mission objectives, which consists of checkout and performance characteristics of the spacecraft systems.
Objectives of the OTV [Orbital Test Vehicle] program include space experimentation, risk reduction and concept of operations development for reusable space vehicle technologies.
Spokesmen have also tended to play up the fact that the X-37B is intended to be an "economically viable experimental test platform", as it is supposed to be much more advanced in terms of turnaround time, heat shields and so on than the Shuttle.
This sort of innocuous talk, combined with the partly civilian history of the project, would tend to indicate a simple tech prototype, not really aimed at any specific military mission. Certainly the Iranian state-funded media channel Press TV's description of the craft  as a "secret space warplane" seems a trifle alarmist.
Even so, the fact that the X-37B has a strong heat shield and wings, relatively smaller but similarly shaped to those of the space shuttle, is interesting to military space buffs. Perhaps the main reason that the shuttle had such big wings and such a tough (though as it turned out somewhat unreliable) heat shield was that the US Air Force wanted it to. Consider this quote from the Columbia accident investigation report :
The Department of Defense wanted the Shuttle to carry a 40,000-pound payload in a 60-foot-long payload bay and, on some missions, launch and return to a West Coast launch site after a single polar orbit. Since the Earth's surface - including the runway on which the Shuttle was to land - would rotate during that orbit, the Shuttle would need to maneuver 1,100 miles to the east during re-entry. This "cross-range" requirement meant the Orbiter required large delta-shaped wings and a more robust thermal protection system to shield it from the heat of re-entry.
It's often forgotten nowadays that the Shuttle was originally intended not just for NASA operations from Cape Canaveral, but also for military operations from a dedicated complex at Vandenberg Airforce Base in California. This would have launched military shuttles into polar orbits rather than generally easterly, low-angle ones as from Florida.
Polar-type orbits tend to be favoured for spy satellites, as the Earth turns beneath the circling spacecraft. This allows an orbital spyeye to pass over any given spot regularly, observing events of interest below.
The fact that the Earth turns, however, would normally mean that a spacecraft lifting off from Vandenberg and orbiting once around would then be above the Pacific, with no hope of returning to its base until many more orbits had passed and the western United States came round again. By that point such a spacecraft would very likely have been seen by suitably alert watchers around the world and details of its track worked out - so, perhaps, giving useful clues as to the path of anything it might have dropped off or picked up.
Not so in the case of a craft with heatproof wings and "cross range" capability, however. A shuttle would have been able to lift off from Vandenberg, orbit at a high angle from the Equator once - during which time it could deploy something or pick something up - and then re-enter, using its wings to bend its re-entry track east and so put down again in California, never having overflown any nation of concern.
Air Force 'Mission 3B' back on the cards?
The "some missions" referred to by the Columbia report were probably the so-called 3A and 3B flight plans (described here ) which called for single-polar-orbit hops from Vandenberg, either deploying or recovering a spy satellite without any pass over the USSR by the shuttle. Later, even more difficult missions were specified by the Air Force, in which the shuttle would both deploy and then recover a spy satellite during a single mission.
A certain Shuttle-y look about the wings.
The military spy-sat requirements have been blamed by many space enthusiasts for crippling the shuttle's design. It's argued that without its large, heavy, heatshielded wings - necessary for the cross-range re-entry requirement, rather than for actually landing as such - it might have been a much more efficient machine for putting stuff into space.
In the event, by the time the Shuttle began to fly its performance was seen as deficient for polar-orbit spysat missions lifting increasingly hefty "KeyHole" payloads. High-angle launches forfeit the valuable speed boost gained by eastward takeoffs close to the Equator, as from Canaveral, and require more grunt from the launcher. Plans were developed in the 1980s for lightened solid boosters, and even extra strap-on liquid rockets, to be used on missions out of the multibillion-dollar shuttle base at Vandenberg's Space Launch Complex Six.
Then came the Challenger disaster of 1986, which imposed years more delay and still more expense. By the time the shuttle had weathered that storm, the military had mostly turned its back on the troubled spaceplane. No shuttles ever flew from Vandenberg on polar missions, and the ambitious military plans to recover and re-use colossally expensive spy sats - perhaps modifying and upgrading them, or repairing them after faults, as one might a normal aeroplane - came to nothing.
But there are more satellites up there than just US ones
It seems, to be fair, that the military was probably just as disappointed in the shuttle as civil space enthusiasts were. Unlike the civil space programme, however, the US Air Force is carrying on with the spaceplane idea.
The "concepts of operations" which the Rapid Capabilities Office hopes for out of the X-37B seem likely to focus on the same things the Air Force originally wanted from the Shuttle: mainly the ability to recover horrifyingly expensive surveillance hardware from space for repairs, replenishment of manoeuvring fuel and/or upgrading.
Possession of a larger X-37B, for instance, would have avoided the international furore which resulted two years ago when the US government decided to shoot a crippled spy sat out of orbit  with a missile-defence interceptor rather than allow it to fall into the atmosphere uncontrolled.
Retrieval capability alone might justify the Air Force continuing with X-37B and possible larger successors, depending what the secret running costs of the "black" space programme actually are. However the design of the robot spaceplane, coupled with the talk of improved heat shielding, suggests that sneaky, low profile cross-range re-entries may also be a card the US military yet aspires to have up its sleeve.
If you want to get out into the wilder speculative realms you could postulate a mission lifting off to retrieve, not a US satellite, but someone else's. The initial launch would be explained as delivery of a normal secret payload, but in fact the spaceplane would lift empty, scoop up its target on one pass and return to land on a "Mission 3B" style profile without ever flying above a hostile telescope or radar station. The owners of the sat-napped spacecraft, out of sight on the other side of the world, would never know what had happened to their kit.
Less aggressively, missions of this sort might instead make a close pass by opposition spacecraft without anyone knowing about it - maybe just to get a good visual or electronic look at them, or perhaps to interfere with them in some suitably deniable way. This sort of thing would perhaps be practical with the existing X-37B; there'd be no need for a larger follow-on craft.
The US itself is known to be quite paranoid about this sort of thing being done to its own satellites: it is spending a lot of money  on kit which would let a satellite's operators know what was happening to it in such an event (normally it would simply go mysteriously offline) and on dedicated guardian sats  intended to watch over other US spacecraft even when they're above other people's airspace.
In general one can be sure that if the US military is worried about being done to, it is also thinking of ways to do unto others as well. So perhaps the Iranians are right - maybe the X-37B is in fact intended as a space fighter or interceptor of sorts.
There's a US Air Force factsheet on the robot spaceplane here . Readers may also be interested to note that a second X-37B has already been ordered by the USAF. ®
*The White Knight is best known for carrying the Ansari X-Prize winning suborbital rocketplane SpaceShipOne up to ignition height. It has also carried out a lot of other, less visible work for various US government customers.