Because the surface of Mars today is bone-dry and frozen all year round, it's difficult to find any place on Earth that is truly Mars-like. But two locations, Antarctica's Upper Dry Valleys and the hyper-arid core of Chile's Atacama Desert, come close. They have become magnets for scientists who want to understand the limits of life on Earth and the prospects for life on Mars.
The Challenger and Columbia space shuttle disasters were perhaps two of the most prominent reminders of how crucial it is that everything work just right for a spacecraft to travel to space and successfully return back to Earth. Whether it was the failure of the seal used to stop hot gases from seeping through, or a piece of foam insulation that damaged the thermal protection system, scientists and engineers must make thousands of predictions of all the things that could go wrong during flight.
As Nasa prepares to retire its fleet of space shuttles, it is encouraging private companies to build new rockets to get its astronauts into orbit.
Among the firms landing huge contracts to build the next generation of spacecraft is SpaceX.
Science correspondent David Shukman visited the company's rocket factory in California for a look inside the prototype capsule.