Fire cannons into orbit
One ring, one magnetic field - not much more is needed to transport spacecraft from ground to earth orbit. And cheap too. At least that's what scientists calculated who took a closer look at the matter on behalf of the US Air Force.
The basis of an idea that sounds unrealistic at first glance is a huge ring made of superconducting magnets: Small spaceships are to be accelerated to enormous speeds through it and thereby hurled skyward into earth orbit. So far at least the business games of US scientists. Who actually finances the creation of such visions?
In this case it was the US Air Force. They commissioned and paid for quite serious scientific testing of the satellite gun concept and reaped realistic results. According to the engineers' idea, a space catapult would be similar to a particle accelerator. It would consist of a six kilometer tunnel running in a circle surrounded by superconducting magnets.
The fields generated by the magnets could levitate satellites within the tunnel without contact and at the same time accelerate them - similar to a magnetic levitation train. If the satellites were kept circling and constantly accelerating, they could reach a speed of ten kilometers per second. At this speed, the idea was that the spaceships would be guided onto a kind of ski jump. Because of their enormous momentum, they flew into space from there all by themselves. A small rocket at its rear end could eventually launch it into the desired Earth orbit.
This basic idea is now worth another hundred thousand dollars to the US Air Force for a follow-up study to deepen the concept. It is scheduled to run for two years and is being carried out by the US company LaunchPoint Technologies. "The space catapult could be used to launch payloads for manned space flight, for example," says Jim Fiske, who headed the study, optimistically.
Space experts, however, have numerous objections against the concept. About classic-physical: A significant disadvantage of the catapult would be that the accelerated satellites would have to withstand enormous forces. "When an object flies around in a circle at 10 kilometers per second, as designed, it has a centrifugal acceleration that is 10,000 times the acceleration of gravity," explains Michael Khan, mission analyst at the European Space Operations Center (ESOC).
So the satellites would have to be extremely robust. The US military is already using artillery shells with built-in electronics that can withstand 20,000 times the acceleration of gravity - but these are shells, not sensitive space technology.
Another point of criticism is the high speed with which the satellites would leave the catapult. In order to get into space, they would have to penetrate the lower, dense layers of the atmosphere at about twenty times the speed of sound. Considerable frictional forces are at work here, together with the associated heating. "The satellite would need a shell made of heat-resistant armor plates to prevent it from burning up after launch," says Khan. This is a disadvantage, especially for small spacecraft, for which the system is officially intended. Because a significant part of the total mass of the aircraft would be used for the armor and not much would be left for the payload.
"I suspect this concept is not about launching satellites at all," says Khan. He addresses a fear that American experts like Alan Epstein from the Massachusetts Institute of Technology also have: that the military could be interested in the catapult to test its suitability for weapons. It would be conceivable, for example, to shoot many small shotgun shells into orbit around the earth in order to pollute them with debris. The debris could destroy satellites and impede communications in space. It doesn't have to be, according to Khan, for the military to consider using this weapon themselves. But they might want to see what an opponent can do with it.
The idea of a space catapult or space cannon is not new. It has been haunting drawers in different versions for decades. "All of these concepts always have the same problem," says Khan, "the highest speed is reached in the lower layers of the atmosphere, the thermal load is very high."Should the technology nevertheless work, the launch costs per satellite could be reduced dramatically, argue the researchers at LaunchPoint Technologies. Current rocket launches cost several thousand dollars per kilogram of payload. According to the Air Force study, it could be a hundredth of that with the space catapult "Of course, one should be careful with such estimates. With the help of the American space shuttles, it was once intended to transport space goods into space for a few hundred dollars per kilogram. In fact, today the transport costs more than ten thousand dollars per kilogram.
