From runway to orbit and back
Every decade or so, enthusiasts around the world dream up plans for yet another spaceplane, a craft that can take off from a runway like a conventional aeroplane, fly into orbit, deliver a payload, and then glide back to Earth for a runway landing. Then be ready to do the same again within a day or two. Nothing has ever come of them. Even so, the dream persists.
What is not to like about a workhorse launch vehicle that jettisons none of its parts while climbing up to orbit and returns to Earth intact, ready to be refueled for yet another flight? Unfortunately, the complexity and weight inherent in such designs has always rendered them impractical. Simple, multi-stage rockets with expendable boosters and fuel tanks remain the cheapest way of putting satellites into orbit, or ferrying crew and cargo to a space station.
Complexity extracts a particularly heavy toll. Towards the end of their life, NASA’s fleet of partially reusable Space Shuttles, which took off vertically while strapped to a pair of expendable solid-fuel booster rockets and an enormous fuel tank that was jettisoned before going into orbit, could carry a kilogram of payload into low-Earth orbit for $10,400. Meanwhile, the Falcon 9 two-stage rocket, designed by SpaceX, a private company, to do some of the heavy lifting since the Shuttles retired, can do the job for $4,100. SpaceX’s next-generation launcher, the Falcon Heavy, is expected to do it for $2,200. When conceived back in the late 1960s, the Shuttle promised a turnaround time of around 30 days. In the event, the entire fleet of six vehicles (two disintegrated in flight, claiming the lives of all crew members) managed little more than half a dozen flights a year between them, even fewer after the tragic accidents.
The Shuttle’s biggest problem was maintenance. The delicate silica tiles that protected the airframe from melting during re-entry had to be laboriously inspected, tested and replaced where necessary. The engines had to be pulled from the airframe and examined for hairline cracks and microscopic wear. The turbo-pumps had likewise to be removed and rebuilt in many instances. The fastest Shuttle turnaround ever was 53 days. Most went 180 days or more between launches. So much for reusability.
That has not deterred the space cadets one bit. The Pentagon recently announced plans for another reusable spaceplane known as the XS-1. This is being designed specifically to put satellites weighing up to two tonnes into orbit at short notice for around $5m a launch (ie, $2,500 per kilogram). According to Pamela Melroy, a former astronaut and now a deputy director at the Defence Advanced Research Projects Agency (DARPA), the XS-1 is to be a true “10X” vehicle, ie, able to fly ten times in ten days, at ten times the speed of sound (Mach 10) as well as being ten times cheaper at putting surveillance satellites in orbit than the US Air Force’s admittedly expensive Minotaur IV, a four-stage rocket based on a decommissioned MX intercontinental ballistic missile.
Yet, even if the XS-1 can be made to work as planned, it will still be no cheaper than SpaceX’s forthcoming Falcon Heavy launcher. Why this fascination with complicated, unproven spaceplanes rather than simple, well-tried rockets? One answer is the unshakable belief by many in high office that, provided enough taxpayer dollars are thrown at a problem, clever engineers will find ingenious solutions. Turf wars also play a part. The Air Force has never forgotten what happened in the 1970s when it was forced to abandon its own manned space programme in favour of the Shuttle. When Shuttle flights were halted for over two-and-a-half years following the Challenger accident in 1986, the Air Force suffered badly.