Now fly me to the asteroids as well

• New Scientist, 22 March 2007 by David Shiga

They are still a long way from returning to the moon, but NASA is already thinking about sending astronauts to an asteroid. Such a mission could be accomplished using the same spacecraft and launch vehicle being designed to take Americans back to the moon.

"This would be the first time that humans go outside of the Earth-moon system," says Paul Abell of NASA's Johnson Space Center in Houston, Texas.

About two years ago, NASA started work on a new crew capsule and rocket to send astronauts to the moon by 2020 (New Scientist, 11 August 2005, p 6). Now, Abell and his team say that the Orion capsule and Ares rocket could also take humans to one of the many asteroids with orbits that bring them near Earth.

The team's analysis shows that the mission would require less fuel than going to the moon, because the vastly weaker gravity of an asteroid means hardly any effort is needed to escape its tug on the way back. Also, because of the weaker gravity, Orion would be able to simply hover close to the asteroid, and thus dispense with a lander, making for a lighter mission overall.

A round trip to a 30-metre asteroid called 1998 KY26, for example, which will pass by Earth in 2013 and 2024, could be completed in three months. However, 1998 KY26's relatively rapid spin may make it an undesirable candidate. The team expects that ongoing asteroid searches will identify more suitable targets.

Besides studying the structural properties of the asteroid using radar sounding - important if we ever needed to deflect such an asteroid - the mission would serve as a testing ground for a mission to Mars. It would be a "baby step towards Mars", says team member Robert Landis, adding that going to an asteroid is not meant to replace going back to the moon.

Any asteroid mission faces two major challenges. One is ensuring there is enough water, oxygen and food to sustain the crew on such a long mission. The lunar version of Orion is designed to carry enough supplies to support a crew of four for two weeks. Abell's team believes that the spacecraft can be reconfigured to carry just two or three, increasing the weight that can be used for supplies.

The second issue is the radiation hazard from cosmic rays and solar flares, which can put astronauts at increased risk of developing cancer. "I see no easy way to mitigate the problem on this mission except to make the duration as short as possible," says David Smith of the Lunar and Planetary Institute in Houston, Texas, who is not part of the team. The astronauts might just have to accept the increased risk, he says.

Landis says the crew's water supply could be used as a shield against the radiation, and that their waste could be saved for the same purpose, but the team admits that radiation remains a challenge. "It's one of the issues we'll have to address," Abell says.

Abell presented the idea at last week's Lunar and Planetary Science Conference in Houston, Texas.

Cohesion: Using Repetition and Reference Words to Emphasize Key Ideas in Your Writing

Cohesion is the glue that holds a piece of writing together. In other words, if a paper is cohesive, it sticks together from sentence to sentence and from paragraph to paragraph. Cohesive devices certainly include transitional words and phrases, such as therefore, furthermore, or for instance, that clarify for readers the relationships among ideas in a piece of writing. However, transitions aren't enough to make writing cohesive. Repetition of key words and use of reference words are also needed for cohesion.