David Mackay

It's very sad that there's going to be a hiatus in manned space flight from the U.S. The Shuttle was a fantastic, hugely complex vehicle. It was inevitable it would come to an end, but this is the opportunity for the commercial world to get involved. As the Shuttle era ends, another window of opportunity opens.

Supplying fuel for a Mars expedition from the lunar surface is often suggested, but it's hard to make it pay off - Moon bases are expensive, and just buying more rockets to launch fuel from Earth is relatively cheap.