Question

When the astronauts go into space, what protects them from solar radiation (microwaves, etc.) which the ozone and atmosphere protect the Earth from?

Most forms of solar radiation are easily blocked by the walls of the spacecraft or the spacesuits worn by the astronauts. These simple opaque materials block ultraviolet, visible, and infrared radiation, for example. The Sun is a relatively weak source of longer-wavelength radiation such as the microwaves you mention, and these are not harmful in any case. (Note that microwaves also pass easily through the Earth's atmosphere). The only electromagnetic radiation that can be a problem are high energy gamma rays, which require a heavier protective material for shielding. The biggest problem is not electromagnetic radiation at all but the charged atomic particles emitted by the Sun (often called solar cosmic rays). During solar flares, these fast-moving particles are the most dangerous and the most challenging to block. The Earth's magnetosphere fortunately provides some shielding, but this did not protect the Apollo astronauts who went to the Moon. Future human flights beyond low Earth orbit will require special shielding against the high energy solar cosmic rays occasionally emitted by large solar flares.

David Morrison
NAI Senior Scientist
August 5, 2003