A U.S. scientist says human missions to Mars face technical challenges well beyond those faced during the exploration of the moon.

In two new papers, Donald Rapp, formerly with NASA’s Jet Propulsion Laboratory, reviews the current state of our understanding of life support and radiation safety and concludes that significant additional research will be required before safe and affordable human missions to Mars can become a reality.

Rapp reviews the current state of the understanding of life support for human missions to Mars and concludes current plans for life support contain optimistic assumptions regarding the degree of recycling and reliability that can be achieved and the amount of mass that life support systems may require.

In his second paper, he compares and contrasts the levels of radiation shielding required for human missions to the moon and Mars and finds currently planned missions to both bodies are not without potentially serious radiation risks.

Both papers are published in the current issue of The Mars Journal, a peer reviewed, open-access journal focused on Mars science, exploration and policy.

We’ve reported on NASA’s problem with funding cuts a few times already this year, and there’s no sign of things getting better any time soon. Costly foreign wars and soaring budget deficits mean that every federal department has to tighten their belts, and budget overruns surrounding space technology mean that projects are coming under scrutiny by Congress and the Government Accountability Office (GAO).

First in the firing line is a planned weather monitoring satellite network, called Geostationary Operational Environmental Satellite-R, or GOES-R. GOES-R was originally planned to cost around $6 billion, but recent estimates have put that figure at almost double, even though it is still in the planning stages. GOES-R is not planned to enter operation until 2014. Despite dropping certain sensors from the design, the GAO still wants an accurate estimate from NOAA on just how much it will cost. A prior NOAA project, the National Polar-orbiting Operational Environmental Satellite System (NPOESS), has already been affected by cost overruns.

NOAA aren’t the only people in trouble. NASA’s proposed shuttle replacement, the Orion Crew Exploration Vehicle (CEV) is also under increased scrutiny from the House Science Committee, as NASA is having trouble accurately forcasting the exact cost of a return to the Moon when the project is so early in the planning stages. Although current estimates are around $230 billion, NASA’s proposals still have shortfalls from 2014-2020.

“I don’t think it’s a foregone conclusion that we’re going to do this [CEV development] no matter what,” Bart Gordon, the ranking Democrat on the committee, said. “There is a point at which we might very well say, ‘This is too expensive. This is not working. Let’s stop, cut our losses.'”

Whether or not a return to the Moon will survive a change of leadership in Washington, DC remains to be seen. If only the CEV could be carried aloft by the soaring budget problems, we could get there next week.