asteroid or Mars.]]> voyages, maybe even to Mars.]]> extended stays on the International Space Station and long missions to an asteroid or Mars.]]> exhaustion.]]> committee decided that lowering the health standards would not be good.]]> exploration missions "will likely expose crews to levels of known risks beyond those allowed by current health standards," according to the report.]]> Avoid harm by keeping risks to astronauts to a minimum.]]> psychological effect of people being cooped up together for long periods of time on board a spacecraft.]]> barriers to long-term space travel.]]> nausea and exhaustion.]]> acceptable limits for astronauts.]]> exceed the currently acceptable limits for astronauts.]]> exceptions is on a case-by-case basis, they said.]]> venturing into this unknown territory.]]>