DEFENCE experts this week reacted with scepticism to the latest brainwave from the Pentagon. The Bush administration wants to revive a defunct NASA spaceplane and use it to drop bunker-busting bombs from space.

Defence secretary Donald Rumsfeld is studying the idea of a "sub-orbital space vehicle" that can fly halfway around the world in 30 minutes—and bomb targets from an untouchable altitude of 60 miles. The aim would be to strike hard and fast at the first hint of conflict. Currently, the US Air Force's B2 stealth bomber takes many hours to reach its global targets.

NASA's aborted X-33 spaceplane could be adopted as the "space bomber", because the project came so close to completion. In March, bloated costs led to NASA quitting development of a half-sized version of the X-33, despite spending $900 million getting it 85 per cent complete. But research on the craft's advanced and highly controllable ...