NASA is considering putting fuel depots in orbit.
Under the plan outlined in the document, the propellant depot would be launched first, and then other rockets would carry fuel to the depot before a spacecraft arrived to fill up. That would increase the complexity for an asteroid mission — 11 to 17 launchings instead of four — but could get NASA astronauts to an asteroid by 2024, the study said. The total budget needed for the project from 2012 through 2030 would be $60 billion to $86 billion, the study said.
By contrast, a study last year that designed an asteroid mission around a heavy-lift rocket estimated that it would cost $143 billion and that the trip could not happen until 2029. The earlier study briefly considered propellant depots but quickly dismissed them.
This idea of putting fuel depots in space merely mirrors the 1960s proposal of using the Gemini capsule and the Titan rocket to assemble a spaceship in orbit for getting to the moon. According to the earlier proposal it would have been faster and cheaper to use existing smaller rockets and many additional launches than to build a giant Saturn 5 rocket that could put everything into orbit in only one launch. I have always thought this idea had merit.
The fuel depot concept is further confirmation that a heavy-lift rocket is not necessarily the only way one can get humans beyond Earth orbit.