Nasa looks at setting up space base gateway to Mars
The US space agency wants to build a small outpost 60,000km from the moon as a base for manned landings on the red planet
Top Nasa officials have picked a leading candidate for the agency's next major mission: construction of an outpost that would send astronauts further from Earth than they have yet been.
The "gateway spacecraft" would hover in orbit on the far side of the moon, supporting a small crew and functioning as a staging area for future missions to the moon and Mars.
At 446,000 kilometres from Earth, the outpost would be far more remote than the current space station, which orbits a little more than 400km above Earth. The distance raises complex questions of how to protect astronauts from the radiation of deep space, and how to rescue them if something goes wrong.
Nasa administrator Charles Bolden briefed the White House earlier this month on details of the proposal, but it was unclear whether the scheme had the administration's support. Of critical importance is the cost, which would probably be billions, if not tens of billions of dollars.
Documents obtained by the Orlando Sentinel newspaper show that Nasa wants to build a small outpost, probably with parts left over from the US$100 billion International Space Station, at the Earth-Moon Lagrange Point 2, a spot about 60,000km from the moon.
At that location, the combined gravities of the Earth and moon reach equilibrium, making it possible to "stick" an outpost there with minimal power required to keep it in place.
To get there, Nasa would use the massive rocket and space capsule that it is developing as a successor to the retired space shuttle. A first flight of that rocket is planned for 2017, and construction of the outpost would begin two years later, according to Nasa planning documents.
Potential missions include the study of nearby asteroids and robotic trips to the moon that would gather rocks and bring them back to the outpost. The outpost would also lay the groundwork for more ambitious trips to Mars' moons and even the red planet, about 225 million km away on average.
From Nasa's perspective, the outpost would solve several problems.
It would give purpose to the Orion space capsule and the space launch system rocket, which are being developed at a cost of about US$3 billion annually. It would involve Nasa's international partners, as blueprints for the outpost suggest using a Russian-built module and components from Italy. And the outpost would represent a baby step toward Nasa's ultimate goal: human footprints on Mars.
But how the idea, and the cost, would play with President Barack Obama, Congress and the public remains a major question. The price tag is never mentioned in the Nasa report.
Spending is being slashed across the government in the name of deficit reduction; it is unlikely that in coming years Nasa can get more than its current budget of US$17.7 billion, if that.
Nasa spokesman David Weaver said: "There are many options, and many routes, being discussed on our way to the red planet. In addition to the moon and an asteroid, other options may be considered as we look for ways to buy down risk and make it easier to get to Mars."
A second major concern is astronaut safety. It would take days to get to the outpost, the furthest Nasa has flown humans since the moon missions of 40 years ago. Another concern is how Nasa would address the dangers of deep space, especially radiation.
The outpost would be more vulnerable to space radiation because it would be largely beyond the protective shield of Earth's magnetic field, said scientists with the US National Space Biomedical Research Institute. These worries are not lost on Nasa officials. The planning documents note that an outpost mission would require a "culture change" that included the "acceptance of risk significantly different" from the shuttle programme, which lost crews in 1986 and 2003.
However, the idea has the potential benefit of focusing Nasa's human spaceflight programme, which has languished in recent years.
The troubled Constellation programme, started under president George W. Bush to return astronauts to the moon by 2020, has been cancelled under Obama for being behind schedule and over budget. Then Obama and Congress launched the SLS heavy rocket programme with no clear destination, though the idea of a manned mission to an asteroid was a frequently mentioned goal.