Construction workers on Earth learn to live with sunburn while on the job in summer months, but for those building NASA's space station the threat of solar radiation is more acute.

A National Research Council (NRC) report released Thursday warns that there is a high probability that solar storms will take place during some station construction flights in the next few years, posing significant hazards to a spacewalking crew.

To minimize the threat, the NRC panel is urging NASA to create an ambitious early warning system that would give mission controllers time to order astronauts back inside before dangerously charged particles reach the station.

Though the NRC panel says the worst-case scenarios are not life threatening, it adds that crews could be exposed to unacceptable levels of radiation during station construction that could cause "symptoms of acute radiation sickness" such as nausea and vomiting.

A single dose could be the equivalent of several hundred chest X-rays. Solar activity is the greatest concern, though astronauts on the space station must worry about three kinds of radiation--particles in the Van Allen belts that surround the planet like a donut, galactic radiation that permeates space as well as the kind that comes from solar activity.

While the first two are as easy to predict as the tides, the sun is more tempestuous. Giant flares and enormous coronal mass injections can occur quickly -- and could pose major health risks for astronauts protected from the charged particles by only thin spacesuits. Predicting such mercurial events is difficult.

"We're worse off than the terrestrial weather people," says George Withbroe, who heads the NASA office responsible for understanding solar activity. He likens the problem to that of predicting the rate of meteor showers like the Leonids.

That is why Withbroe asked the NRC last year to come up with a practical scientific strategy to understand solar flares and coronal events. The 10-member NRC panel chaired by George Siscoe, a Boston University physicist, went a step further. The NASA-funded panel, as expected, calls for the agency "as soon as possible" to install dosimeters on the outside of the nascent station, use existing weather satellites to forecast the electron radiation environment and convene a meeting of space scientists to determine ways to gather more and better data.

But it also urges NASA to work with the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Air Force on the issue and to establish an agency-wide and high-level task force that can develop a radiation plan.

A single dose of solar radiation could be the equivalent of several hundred chest X-rays.

The report even lays out a scenario in which a solar event occurs on an afternoon shortly before completion of the station: Space weather forecasters in Boulder, Colorado, upon noticing signs of solar activity, predict when it will erupt. Activity monitored by other spacecraft is also taken into account. The information is fed to Johnson Space Center controllers, who decide to postpone a planned spacewalk.

When it is clear doses will remain well within safety levels, controllers proceed with the EVA a few hours later, which they likely would have had to have canceled if there were less warning time and less clear data on the extent and duration of the event.

"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," says Siscoe. A coordinated data system could provide greater flexibility to station managers already concerned about the complexity of building the orbiting base.

Withbroe is confident that NASA will have a better grip on predicting solar events in the near future. A small spacecraft slated for launch in summer 2000 will study solar flares during the sun's peak of activity, while the Solar and Heliospheric Observatory (SOHO) -- a joint NASA and European Space Agency effort -- is already providing important data on solar activity. In the long term, a NASA mission to look at coronal mass ejections is planned for 2004. And a Japanese mission is in the works -- also with a 2004 launch date -- to examine the sun's magnetic fields.

NASA Johnson Space Center officials say they have not had time to read the report, and they declined comment. But the matter is obviously of enormous concern to astronauts worried about both the short- and long-term health effects of exposure to space radiation. The great solar storm of 1972 could have injured and even killed Apollo astronauts had they been on a lunar mission.

The NRC researchers also warn that there is a "non-negligible likelihood" that astronauts conducting spacewalks "could receive a radiation dose that is significant in terms of increased cancer risk and of reaching allowable dose limits." And it is also a matter of career: the report notes that "no astronaut wants to reach the short-term radiation limits, much less the career limit," which could put them on the sidelines permanently.

The 2004 missions likely will come too late for station construction workers -- who are due to wrap up their effort in early 2005. However, the NRC report emphasizes that close coordination among researchers and flight controllers at NASA, senior managerial attention, along with cooperation from NOAA and the Air Force, will go a long way to managing the problem in the near term.

They note that space weather experts scattered in academia, government and industry are capable of developing the tools to forecast space radiation, and should participate directly in the station effort. "The point is to keep the doses low -- like diagnostic X-rays," says Withbroe. "So the challenge for us is to understand and predict this environment." That gives his basic research a new edge, he adds. "The knowledge will have a pretty utilitarian benefit."