A further response to Buck’s “VLF” post below.

Atmospheric pressure at the earth’s surface is 15 lbs/in^2.

This means every square inch of earth’s surface supports the weight of a column of air above it weighing 15 lbs. This is the equivalent of a 1 inch square column of water 33 feet high.

Air may be pretty flimsy stuff, but we have a lot of it above us. This can provide plenty of shielding, even against high energy gamma or x rays.

A 10″x10″ square of earth’s surface has a weight of air above it equivalent to 1500 lbs.

How thick would a 10″x10″ piece of lead plate have to be to weigh 1500 lbs? This is why our atmosphere is so effective against radiation. We just have so damn much of it. The atmosphere is transparent to some frequencies of photons, but some (such as UV) are stopped by the ozone layer, which is created by radiation ionizing the upper levels of our atmosphere.

Charged particles or atomic nuclei (cosmic rays or solar wind) may be deflected by upper levels of charged particles high in the Van Allen belts, and these could conceivably be affected by changes in the magnetosphere such as you describe might be caused by VLF. This stuff would never get to the earth’s surface because of the shielding I discuss above, but they would erode the atmosphere, making it thinner, eventually causing it to be lost to space. We suspect this is what happened a long time ago on Mars because it didn’t have the volcanism we have to replace the atmosphere, and because its lighter gravity allowed it to escape. Water vapor, for example, would be disassociated by radiation into hydrogen and oxygen. The latter would combine chemically with iron in the rocks, giving Mars its rusty color, the former would escape into space.

Although some forms of radiation are charged particles, such as naked atomic nuclei, protons, electrons and so on, some are electrically neutral like gamma and xrays. The former may conceivably be deflected by electrical or magnetic fields, or plasmas, the latter are just like little bullets, nothing can stop them except lots of matter. Any matter will do, even air, if you’ve got enough of it, but when we think of “shielding” we tend to think in terms of stuff like lead or concrete because its high density allows us to concentrate so much of it in a small volume.

This is what makes radiation shielding in spacecraft such a huge problem. Shielding has to be massive and mass has to be accelerated by consuming propellant. Its essentially dead weight. Although some forms of radiation could conceivably be deflected using electrical or magnetic fields, in general, you need mass, either some kind of heavy armor, or by using the ship’s own structure and cargo as shielding to protect the crew. On long missions, I would imagine spacecraft crew spaces would be deep inside the ship, surrounded by hull, machinery, supplies and fuel tanks. Radiation exposure is cumulative, and in space radiation is variable but continuous. At the very core of all this engineered protection, there might be a small, heavily shielded compartment, a radiation shelter, where the crew would sleep, or hang out off duty, or huddle in during solar storms.