It was once considered the most dangerous object in the universe, heading for Earth with the explosive power of 84 Hiroshimas. Now an asteroid called 2000SG344, a lump of rock barely the size of a large yacht, is in the spotlight again, this time as a contender for the next giant leap for mankind.

Nasa engineers have identified the 1.1m tonne asteroid, which in 2000 was given a significant chance of slamming into Earth, as a potential landing site for astronauts, ahead of the Bush administration's plans to venture deeper into the solar system with a crewed voyage to Mars.

The mission - the first to what officials call a Near Earth Object (NEO) - is being floated within the US space agency as a crucial stepping stone to future space exploration.

A report seen by the Guardian notes that by sending astronauts on a three-month journey to the hurtling asteroid, scientists believe they would learn more about the psychological effects of long-term missions and the risks of working in deep space, and it would allow astronauts to test kits to convert subsurface ice into drinking water, breathable oxygen and even hydrogen to top up rocket fuel. All of which would be invaluable before embarking on a two-year expedition to Mars.

Under the Bush administration, Nasa has been charged with sending astronauts back to the moon, beginning in 2020 and culminating in a permanent lunar outpost, itself a jumping off point for more distant Mars missions. With the agency's ageing fleet of space shuttles due to be retired soon after 2010, the agency has begun work on a replacement called Orion and a series of Ares rockets that will blast them into orbit.

In a study due to be published next month, engineers at Nasa's Johnson Space Centre in Houston and Ames Research Centre in California flesh out plans to use Orion for a three to six month round-trip to the asteroid, with astronauts spending a week or two on the rock's surface.

As well as giving space officials a taste of more complex missions, samples taken from the rock could help scientists understand more about the birth of the solar system and how best to defend against asteroids that veer into Earth's path.

"An asteroid will one day be on a collision course with Earth. Doesn't it make sense, after going to the moon, to start learning more about them? Our study shows it makes perfect sense to do this soon after going back to the moon," said Rob Landis, an engineer at Johnson Space Centre and co-author of the report, which is due to be published in the journal Acta Astronautica.

More precise measurements of the orbit of 2000SG344 have allayed fears that it could hit Earth sometime around the end of September 2030, but the asteroid is still expected to come close in astronomical terms.

The report lays out plans for a crew of two to rendezvous with a speeding asteroid that is due to pass close by Earth. After a seven-week outward journey, the Orion capsule would swing around and close in on the rock.

Because gravity is close to zero on asteroids, the capsule would need to attach itself, possibly by firing anchors into the surface. For the same reason, astronauts would not be able to walk around on the surface as they did on the moon. "On some of these asteroids, you could jump up and go into orbit, or maybe even leave for good," said Landis.

A round trip to an asteroid could be done with less fuel than a moon mission, but is technically very challenging. The asteroid is only 40 metres across and spins as it hurtles through space at 28,000mph.

Landis thinks that a trip to an asteroid could capture imaginations even more than a return to our nearest celestial neighbour. "When we head back to the moon, I think we'll see many of the same scenes we saw in the 60s and 70s Apollo programme. We've been to the moon, we got that T-shirt back in 1969. But whenever we've sent robotic probes to look at asteroids, we've always been surprised at what we've seen," he said.

Because asteroids were forged in the earliest days of the solar system, analysing samples from them could shed light on the conditions that prevailed when the Earth was formed.

"Near Earth objects are a potential collision hazard to Earth and it may one day be necessary to deflect an asteroid from a collision course with Earth," said Ian Crawford, a planetary scientist at Birkbeck College, London. "Having the capability in your back pocket to deflect an asteroid might be a good insurance policy for the future, and for that, you want to know what they are made of, how to rendezvous with them, and whether you risk getting hit by debris if you fire something at it."