The Pentagon has repeatedly said that the space plane is simply a “test bed” for other technologies.

五角大楼曾多次表示，空天飞机仅是一个技术“试验床”。

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Commander Hadfield believes that the ISS provides the perfect test bed for developing deep space travel capabilities.

BBC: Chris Hadfield says Nasa's job is not to 'titillate'

The US space agency has been running the programme since 2001, using the 20m-deep Aquarius habitat as its test-bed facility.

BBC: UK astronaut Tim Peake makes 'asteroid splashdown'