新托福阅读材料：“发现号”再次推迟发射

“发现号”的发射时间再次推迟

The final mission of the space shuttle Discovery has been postponed again because of a fuel leak.

After 26 years of service, the vehicle is due to make one last flight to the International Space Station (ISS) before being retired to a museum.

NASA has struggled all week to get Discovery off the ground, frustrated by poor weather and technical problems.

Escaping hydrogen detected midway through fuelling left NASA no choice but to stand Discovery down once more.

The agency is now planning a launch date on 30 November, to give plenty of time to fix the leak.

NASA has simply run out of time in the current launch window, which ends on Monday.

There then follows a three-and-a-half-week period of unfavourable sun angles at the orbiting platform that produce strong heating on a docked shuttle.

Fleet leader

US politicians have confirmed that the reusable orbiters should give way to a new era of spaceflight, and one by one these remarkable vehicles are taking a final bow.

Discovery is the oldest of the surviving ships. First launched in 1984, it has since completed 38 missions, travelling some 230 million kilometres in the process. Its commander on the final mission, Steve Lindsey, says Discovery is probably the most important of three remaining shuttles.

"It is obviously a very historical vehicle, having flown the 'return to flight' test missions after both the Challenger and Columbia accidents," he said.

"It deployed Hubble (and) it's the fleet leader in terms of number of flights - it'll have flown about a year on orbit by the time we're done with it, which is pretty remarkable for a space shuttle."

After Discovery returns, only the Endeavour shuttle has a firm date to launch, in February next year.