Exposure to High Levels of Radiation May Pose Threat to Astronauts Constructing International Space Station

WASHINGTON -- As U.S. astronauts and Russian cosmonauts build the International Space Station, NASA should consider taking further measures to limit their exposure to radiation that sporadically occurs around the station, says a new report from a committee of the National Academies' National Research Council. Construction plans call for approximately 43 shuttle flights and more than 1,500 hours of activity outside the orbiting station, most of which will occur during the peak phase of the sun's 11-year activity cycle when intense solar storms can cause increased levels of radiation.

"An unofficial NASA flight rule specifies that changes in flight plans must be based on current data that reflect the weather immediately around the space station," said committee chair George Siscoe, research professor of astronomy and space physics, Center for Space Physics, Boston University, Mass. "Information about the size and shape of a solar storm and data on its occurrence, intensity, and duration can be retrieved from other sources, but under current guidelines, this information could not be used by flight directors to take immediate action. These rules unnecessarily restrain ground-based flight directors because other valid data could be used to assist in avoiding radiation exposure."

NASA should use existing equipment and models that produce real-time data on the intensity and geographical size and shape of solar storms, the report says. This is one of the most important projects that the agency can implement early in order to have an impact on reducing an astronaut's risk of radiation exposure during construction of the space station.

Construction began in 1998 and is expected to be completed by 2004. This time frame coincides with the peak in the 11-year activity cycle of the sun, which can include severe solar storms that emit streams of high-energy, electrically charged particles in the space station's path. This peak cycle also is combining with the station's orbit around the Earth, adding a new element of risk. Because of a change in plans, the orbit now cuts through high-latitude radiation environments that are sometimes quite harsh though not life-threatening even in worst-case estimates.

NASA originally planned a different orbiting pattern for the space station, but an agreement in 1993 to partner with the Russian Space Agency in constructing and maintaining the station altered those plans. A new pattern, closer to where Russia's abandoned Mir space station is orbiting, was chosen to accommodate Russian launch capabilities.

Data Collectors

An electron dosimeter, which can help determine the intensity of radiation exposure by measuring the number of electrons around the space station, should be installed on the spacecraft as soon as possible, the report says. This piece of equipment can warn astronauts working outside the spacecraft of increases in radiation levels and prompt them sooner to return to safety inside. Key NASA and National Oceanographic and Atmospheric Administration (NOAA) managers also should meet to consider ways to provide real-time radiation data and to formulate a plan for transmitting such data to radiation risk managers at NASA's Johnson Space Center in Houston.

NOAA's Space Environment Center collects space-weather data generated from government satellites. These data are provided to NASA's Space Radiation Analysis Group at the Johnson Space Center and made available to radiation risk managers. The safety of astronauts would be improved if these weather observations were to be used in models that accurately predict the weather immediately around the space station, the report says. Some capability to model and predict the space environment already exists, but NOAA is still in the process of implementing these models. Of more significance is the current policy of not providing "tailored" support to any other government units. The report recommends that the policy be changed to allow NASA to receive specific data that are not available from other sources.

The report also proposes revitalizing NASA's existing Radiation Coordination Team by elevating the group to a higher level within the agency. This task force would be responsible for managing the agency's radiation plan and would answer directly to high-ranking officials at NASA headquarters.

Exposure Levels

While these radiation events are not immediately life threatening, astronauts may be exposed to single doses of radiation that are the equivalent of several hundred chest X-rays. These levels would put them in danger of exceeding short-term limits for overall exposure and increase their chances of developing cancer later in life. In addition to health consequences, exposure to dangerous levels of radiation could interrupt a shuttle mission, impact future flight schedules, and alter crew rotations.

The study was funded by the National Aeronautics and Space Administration. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

Read the full text of Radiation and the International Space Station: Recommendations to Reduce Risk for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).

NATIONAL RESEARCH COUNCILCommission on Physical Sciences, Mathematics, and ApplicationsSpace Studies Board

Committee on Solar and Space Physics

George L. Siscoe (chair)Senior Research ProfessorCenter for Space PhysicsBoston UniversityBoston