Loaded up with liquid hydrogen and oxygen and ready for lift-off – the space shuttle Discovery is poised for launch tonight, with Nasa engineers keen to see whether safety upgrades will stand the test. The seven-strong crew are upbeat despite the tension.
In 2003 seven astronauts died when the shuttle Columbia broke up on re-entry because a piece of foam had hit the fuselage at launch. Nasa is confident it has fixed the problem.
But if the shuttle is damaged it is likely that the fleet will be permanently grounded, meaning the International Space Station is likely to be left unfinished.
The shuttle is the only craft capable of carrying the pieces needed to complete the research centre project.