The Palestinian must stop throwing stones, and the Israelis must stop firing rockets. And in the view of the Sharm el-Sheikh summit, rockets are equal to stones.
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.
The key virtue of orbital assembly is that it eliminates the tight connection between the size of the expedition and the size of the rockets used to launch it.
Past experience, on the shuttle and the Titan rockets, suggests that large multi-segment solid rockets have a probability of failure of 0.5 to 1 per cent.
Sometimes people wonder why aeroplanes are so cheap and rockets are so expensive. Even the most superficial comparison shows one obvious difference: aeroplane engines use outside air to burn their fuel, while rockets have to carry their own oxidisers along.
Since SpaceX's very beginnings, they have talked about recovering and reusing at least the first stages of their rockets.
Solid-fuel rockets can't easily be shut down on command.
Whether solid rockets are more or less likely to fail than liquid-fuel rockets is debatable. More serious, though, is that when they do fail, it's usually violent and spectacular.
Claiming that solid rockets are necessary for a heavy-lift launcher is obvious nonsense.
Large solid rockets have never been a very good way to build launchers that might have crews on top, especially because of the problems in getting the crew away from a failing launcher.
