The commercial company SpaceX has now completed six successful re-supply missions to the International Space Station (ISS). Along the way it has created a lot of headaches for its competitors, who don't appear to be able to compete on a cost basis.
The latest SpaceX launch took place earlier this month. As well as delivering much needed supplies to the ISS, the company made another daring attempt to land the first stage booster of its Falcon 9 rocket on a pad in the middle of the Atlantic ocean.
While this and a previous attempt were unsuccessful, it represents the first small steps towards making a reusable space launch system.
Getting into space remains a very expensive activity. Exact numbers are hard to come by because of business sensitivity, but the cost of lifting "stuff" to low earth orbit is somewhere between US$5, 000 and US$15, 000 per kilogram.
In large part this is because all current space launch systems are expendable.
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Think of purchasing a high performance sports car, using it for the first time to drive to the beach, and then throwing away the keys. This is essentially what those who operate space launch systems do.
In this situation the obvious thing to do is buy the cheapest sports car that does the job, and maybe not purchase all the optional extras. But "cheap" can sometimes mean unreliable. So there is a minimum cost below which satellite launch systems do not go in order to be reliable.
Retrieve and re-use
The real answer to the cost problem is to be able to drive the sports car more than once. In the case of SpaceX, it is trying to at least use part of it's space launch system again. To do this it must retrieve it in a way that it can be used again.
All space launch systems operating today have multiple stages. The first stage booster is the largest, as it lifts all the upper stages and the payload above the thick part of the atmosphere.
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