While normally low, the fluxes of energetic particles can increase hundreds of times following an intense solar flare or during a large geomagnetic storm and can threaten the health of astronauts . Timely warnings are essential so that astronauts have sufficient time to return to the shuttle prior to the arrival of these particles. The average orbit altitude of the space shuttle is 185 miles, below where the Van Allen shields begin. Earth's atmosphere and magnetosphere allow adequate protection for us on the ground, but astronauts in space are subject to potentially lethal dosages of radiation. The penetration of high-energy particles into living cells, measured as radiation dose, leads to chromosome damage and, potentially, cancer.
Large doses can be fatal immediately.
In October 1989, the Sun produced enough energetic particles that an astronaut on the Moon , wearing only a space suit and caught out in the brunt of the storm, would probably have died . Once you are past the Van Allen shields, for example between the earth and the moon, or on the moon, you would be subject to the full brunt of solar flares. The Van Allen shields protect us here on Earth from this deadly radiation. A comparison of risk assessment in terms of total absorbed dose for each event is made for the skin, ocular lens, and bone marrow. Overall, the doses associated with the August 1972 event were higher than those with the October 1989 event and appear to be more limiting when compared with current guidelines for dose limits for missions in low Earth orbit and more hazardous with regard to potential acute effects on these organs.