Designs for shuttle replacement may need rethinking

 作者:韩般久     |      日期:2019-02-27 03:15:03
By Maggie McKee NASA’s new chief Michael Griffin has hinted he may drastically change plans for the space shuttle’s replacement. And this might rely on the current shuttle’s launch design. The spaceship, dubbed the crew exploration vehicle (CEV), is meant to exceed the shuttle’s capabilities, blasting beyond low Earth orbit to the Moon and eventually on to Mars. In January 2004, US president George W Bush announced the CEV would begin flying astronauts into space in 2014. NASA gave about $3 million to each of eight competing companies to sketch out ideas for the vehicle in September 2004, and later outlined some guidelines for their requirements. The first limited the CEV or its component parts to a lift-off weight of 20 tonnes, excluding cargo and external boosters, although the agency wrote it would consider lighter and heavier versions so as not to “curtail innovation”. The first conceptual designs were due on Monday, and at least two consortiums of companies – one led by Lockheed Martin and the other by Northrop Grumman and Boeing – submitted proposals. Now, Griffin has implied the teams may have to go back to the drawing board. “The CEV, with all that I want it to do in terms of its ability to service the space station and, later, go to the Moon, cannot be easily assumed to weigh less than 30 tonnes – the weight of the Apollo Command and Service Module stack,” he said at a breakfast meeting in Washington, DC, US, according to That 50% increase in weight “is a big change in the requirement”, says Robert Melton, a professor of aerospace engineering at Pennsylvania State University, US. It is possible in the timescale, he says, “but it’s going to cost more”. And Griffin hinted that the overall design of the existing shuttle setup – involving two solid rocket boosters and a large fuel tank to form a “stack” that carries the shuttle into space – could be used to carry the CEV and associated hardware for a Moon base. These payloads could weigh up to 100 tonnes. “As NASA administrator, I already own a heavy lifter [in] the space shuttle stack,” said Griffin. “I will not give that up lightly and in fact can’t responsibly do so because…any other solution for getting 100 tonnes into orbit is going to be more expensive than efficiently utilising what we already own.” That change could also prove a “nontrivial engineering challenge” for the proposal teams if they have already designed their vehicles to launch on top of a heavy-lift rocket, says physicist Andrew Case, acting director of the SubOrbital Institute, a US trade association promoting crewed rocket flights to the edge of space. Indeed, the Northrop Grumman team declined to discuss its proposal with New Scientist because it might have to radically redesign its CEV concept. But a web page on its partner Boeing’s site shows the team had at one time planned to launch atop the company’s Delta 4 Heavy rocket, designed to lift 23 tonnes to low Earth orbit. And Case says Griffin’s comments may point to an even broader philosophy of assembling the CEV and related pieces of hardware on Earth rather than launching separate modules and assembling the pieces in space – an approach both teams appear to have taken in their proposals. “I’m a little disappointed by that,