A new look at the space radiation environment concludes that the dangers of long-term astronaut exposure to space radiation “would not allow a human crew to undertake a Mars mission and might also seriously limit long-term Moon activity.” The report also recommends that in the short term NASA not waive its current radiation exposure limits and that it provide adequate funding for continued studies of the radiation hazards astronauts will be exposed to during missions to future Moon bases and subsequent missions to Mars.


Since the beginning of human spaceflight, numerous studies have been done exploring the potential dangers humans face from prolonged exposure to cosmic radiation. The possible side effects include immune system problems, neurological disorders, degenerative tissue diseases and cell damage or destruction that might result in cancer or other serious health problems, according to
“Managing Space Radiation in the New Era of Space Exploration.”


The study was conducted by the Committee on the Evaluation of Radiation Shielding for Space Exploration, which was created by the National Research Council’s Aeronautics and Space Engineering Board at the request of NASA’s Exploration Systems Mission Directorate. NASA asked the National Research Council to evaluate the radiation shielding requirements for lunar missions and to develop a strategic plan for developing the radiation mitigation capabilities needed to enable the planned lunar mission architecture known as Project Constellation, which was developed in response to the Vision for Space Exploration approved by U.S. President George W. Bush.


The National Research Council is part of the National Academy of Sciences. A “prepublication copy” of the report was released March 31 by the National Academy of Sciences.


Uncertainties remain


Much remains uncertain regarding the actual risks that space radiation poses for the body, said
committee member Walter Schimmerling, a scientist now retired from NASA’s space radiation program. All these uncertainties mean that safety margins have to remain high, limiting how long astronauts can stay in space. This in turn could rule out a mission to Mars, as well as long-term or multiple missions to the
Moon because of the length of time astronauts would be exposed to radiation.


“The way to deal with that problem is to reduce the margins of uncertainty,” Schimmerling said.

To enable at the very least lunar missions with astronauts, the committee stressed that radiation biology research deserved the highest priority. However, the experts noted that NASA’s space radiation biology research has been significantly compromised by recent cuts in funding, leading to major gaps in
knowledge about
the health risks of radiation, such as cancer, neurological damage and degenerative tissue disease.


NASA’s entire space radiation biology research program is critically dependent on the NASA Space Radiation Laboratory, which in turn relies on the U.S. Department of Energy’s heavy ion physics program. The committee strongly recommended that NASA do as much research at this lab as it could, in case the Department of Energy’s priorities shift and dramatically reduce the availability of the lab.


“The committee strongly recommends that NASA’s Space Radiation Biology Research Program be adequately funded. NASA should perform research at the NASA Space Radiation Laboratory aggressively to take advantage of the existing window of opportunity while this facility is still available,” the study concluded. “The results of the biological research will thus be able to impact the Project Constellation missions in the short term, as well as provide knowledge essential for management of space radiation risk in the long term.”


“No one knows how long the window of opportunity is for how long this laboratory is available – 10 or 15 years seems a reasonable guess,” Schimmerling said.


The laboratory is located at the Department of Energy’s Brookhaven National Laboratory, and the report notes that the
Department of Energy could at some point choose to shut the lab down as it has done with other facilities in the past.


Possible solutions


When it comes to shielding astronauts from radiation, spacecraft designers and mission planners have to consider trading off a safe amount of protective material – say, high-density plastic – with cutting weight in order to enter space practically. Spacecraft that are too heavy simply cannot
carry enough fuel to make flight practical.


Further research could not only look into better shielding materials, but also spacecraft designs that put electronics and machinery in the periphery between astronauts and harm’s way.


“Lava tubes on the
Moon might also be useful as habitats from a shielding point of view,” Schimmerling said. “I don’t know how realistic the idea is, but they would have the advantage of reduced exposure to radiation.”


The sun is a major source of dangerous radiation astronauts might encounter especially during solar storms that can erupt with little notice. The committee also recommended further research into forecasting these outbursts.