The spacecraft Nasa is developing to replace the shuttle has passed a critical milestone¹.

美国航空航天局正在计划的用于取代旧航天飞机的新飞船已经通过审评。

Nasa hopes its Orion ship will take it back to the Moon

The Orion capsule, which is intended to carry at least four astronauts into Earth orbit and beyond, has completed its preliminary design review, or PDR.

The review is an essential engineering assessment² that certifies³（证明，保证） the concept is fit for purpose.

The completion of the PDR paves the way for the US space agency to start to build the capsule for flight.

"This is the successful culmination⁴（顶点，最高潮） of all of the design trade studies and activities to date," said Mark Geyer, manager of the Orion Project Office at Nasa's Johnson Space Center in Houston.

"As a project, a programme and an agency, we are reviewing the design maturity⁵, strategy and plans for Nasa's next human spacecraft and agreeing that this is the architecture we are going to build."

The US space agency is scheduled to retire its space shuttles next year, and has begun the development of a new human space launch "architecture" called Constellation⁶.

The architecture calls for two new rockets: the Ares 1 to launch crew, and a new heavy-lift rocket known as Ares 5 that could put into orbit the equipment needed by an Orion capsule to travel to the Moon and beyond.

However, all the systems are under review by a top-level panel led by former Lockheed Martin chairman and chief executive Norm Augustine. President Barack Obama has asked the panel to assess different options for getting US astronauts into space.

Some commentators⁷ expect the Ares development plans to be modified or even cancelled.

Orion is scheduled to enter service no earlier than March 2015.

Under current plans, this would see the vehicle ferrying crews to the International Space Station (ISS) the following year. It was tasked by former President George W Bush of taking the US back to the Moon by 2020.

Whether Nasa could maintain this schedule even if President Obama endorses⁸（支持，赞同） the Constellation programme is open to question, however.

The Augustine panel has established that the shuttle replacement⁹ project is underfunded presently by about $3bn (£1.8bn) a year.