The International Space Station, the $100 billion outpost that has steadfastly orbited the Earth for more than a decade, may get a chance to explore new horizons when it retires in 2020. NASA is considering using part of it to build a spaceship that would be sent to an asteroid, while also mulling more exotic artificial-gravity designs reminiscent of Arthur C Clarke.

President Barack Obama jettisoned his predecessor's plan to return astronauts to the moon by 2020 and in April proposed to send them to an asteroid by 2025 instead.

NASA is now trying to work out the details of how to carry out such a mission and is hosting a conference on the topic in Washington, DC, on Tuesday and Wednesday.

On Tuesday, Brian Wilcox of NASA's Jet Propulsion Laboratory in Pasadena, California, presented (pdf) some of the ideas generated by the agency's engineers during brainstorming sessions in January and June.

Mother ship Tranquility
One idea is to take apart the International Space Station, which is currently set to be retired in 2020, and use one of its crew compartments to build an asteroid-bound spacecraft in orbit instead of launching a similar capsule from Earth.

"These [asteroid] missions are going to occur at about the time that the space station is near retirement, so one has to wonder, 'Is it possible to use assets from the station as part of your mission complement?'" he said.

A space station compartment called Node 3 or Tranquility, which launched to the station aboard a shuttle mission in February, is particularly attractive for recycling because it has docking ports that could be used to attach to a pair of smaller, more nimble spacecraft. After arriving at the asteroid, astronauts could enter the smaller spacecraft and detach from the main ship in order to inspect the asteroid up close (see an illustration of the docked craft).

Spinning space odyssey
A separate idea is to use a rotating design in order to generate artificial gravity, a concept made famous in the film 2001: A Space Odyssey, by Arthur C Clarke and Stanley Kubrick. Two spacecraft would be tied to opposite ends of a tether a few hundred metres long and set rotating around each other at speeds of tens of metres per second (see illustration).

The rotation would make astronauts in the spacecraft feel a constant acceleration similar to Earth's gravity, preventing some of the bone and muscle loss that would otherwise occur over the months-long missions. "You can introduce quite a substantial equivalent gravity field ... [eliminating] the deleterious effects of microgravity," Wilcox said.

Wilcox described the proposals as concepts rather than part of a final design for an asteroid mission. Further discussion of how to carry out such a mission is scheduled to take place at the conference on Wednesday.