LOS ANGELES - Space travel can be hazardous to an astronaut's health. Cancers can be triggered by space radiation. Long periods in zero gravity can cause bone loss. Then there's the health effects of solar storms. These are some of the risks NASA is struggling with as it plans to send astronauts on long space voyages, maybe even to Mars.

The space agency asked the Institute of Medicine (IOM) to help develop a set of guidelines for venturing into this unknown territory. The results were released Wednesday in a 187-page report.

Long spaceflights and exploration missions "will likely expose crews to levels of known risks beyond those allowed by current health standards," according to the report. The report was authored by Jeffrey Kahn and his team at the Johns Hopkins Berman Institute of Bioethics. Missions may include both extended stays on the International Space Station and long missions to an asteroid or Mars.

Besides radiation-induced cancers and bone loss, solar storms can cause nausea and exhaustion. Blurred vision is another danger. Radiation in deep space is considered one of the biggest barriers to long-term space travel. It comes from high energy particles and can cause cancer and other health problems. On Earth, there are limits to how much radiation a person can safely be exposed to.

Keep Risks To A Minimum

And that's just a short list of the health dangers that researchers considered. There is also the long-term psychological effect of people being cooped up together for long periods of time on board a spacecraft. Astronauts will also be exposed to risks that at this point can not be predicted and are unknown.

Among the report's recommendations: Avoid harm by keeping risks to astronauts to a minimum. Make sure the benefits outweigh the risks. Operate in an open and accountable way, and keep astronauts informed of the risks they face. The experts' basic message to NASA was to act responsibly and not to hide anything.

Any sort of long-term space travel could very well take astronauts past the current radiation safety limits. And this creates a problem for NASA. In 2011, NASA sent a exploration rover, Curiosity, to Mars to send back information about the red planet. A study that tracked the Curiosity rover's radiation exposure on its way to Mars, which took more than eight months, found that the round-trip journey could potentially exceed the currently acceptable limits for astronauts.

Scientists may have to figure out how to make the trip shorter or better protect the astronauts. Another option, according to a scientist, would be to change the radiation limits for long-distance space travel.

Exceptions Should Be Limited

So what does NASA do? Lower the current standards? Change the radiation exposure standards for long-distance space travel? No go, the report said.

The committee decided that lowering the health standards would not be good.

The only way would be to allow exceptions is on a case-by-case basis, they said.

"Exceptions to health standards should be considered on a mission-by-mission basis," they‏ said. The exceptions should be very limited and follow the recommended guidelines.

The agency should offer lifetime health care for its astronauts, the experts said. Also, different astronauts may have different levels of risk. NASA should constantly monitor the astronauts and collect health information on them, but their privacy must be respected.

In spaceflight, there always has been and will continue to be great risk, the authors pointed out.

From the beginning, "human spaceflight has pushed the boundaries of acceptable health and safety risks," they wrote.