MeBeJedi

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The Inner V.A. Belt reaches its maximum intensity at 5000 km (3000 miles) but extends inward to about 1000 km (600 miles) The Outer Belt starts at 1500 km (9300 miles) and peaks at 22000 km (15500 miles). That belt is dominated by trapped electrons from the solar wind; the Inner Belt is marked by protons brought in mainly as cosmic rays. Two important conclusions from the discovery of the Van Allen Belts: 1) they have for eons provided protection from these potentially devastating particle bombardments - a fact critical to the successful development of life on Earth; and 2) both spacecraft and humans would need to be shielded effectively when passing through the Belts.LINK

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The Van Allen Belt's Impact on Space Travel

Solar cells, integrated circuits, and sensors can be damaged by radiation. In 1962, the Van Allen belts were temporarily amplified by a high-altitude nuclear explosion and several satellites ceased operation. Magnetic storms occasionally damage electronic components on spacecraft. Miniaturization and digitization of electronics and logic circuits have made satellites more vulnerable to radiation, as incoming ions may be as large as the circuit's charge. The Hubble Space Telescope, among other satellites, often has its sensors turned off when passing through regions of intense radiation.

A object satellite shielded by 3 mm of aluminum will receive about 2500 rem (3) (25 Sv) per year.

Conspiracy theorists have argued that space travel to the moon is impossible because the Van Allen radiation would kill or incapacitate an astronaut who made the trip. In practice, even at the peak of the belts, one could live for several months without receiving a lethal dose.

Apollo nevertheless deliberately timed their launches, and used lunar transfer orbits that only skirted the edge of the belt over the equator to minimise the radiation. Astronauts that have travelled to the moon probably have an increased lifetime risk of cancer, but would be expected not to (and did not) have noticeable illness.LINK

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"The Van Allen belts are full of deadly radiation, and anyone passing through them would be fried."

Needless to say this is a very simplistic statement. Yes, there is deadly radiation in the Van Allen belts, but the nature of that radiation was known to the Apollo engineers and they were able to make suitable preparations. The principle danger of the Van Allen belts is high-energy protons, which are not that difficult to shield against. And the Apollo navigators plotted a course through the thinnest parts of the belts and arranged for the spacecraft to pass through them quickly, limiting the exposure.

The Van Allen belts span only about forty degrees of earth's latitude -- twenty degrees above and below the magnetic equator. The diagrams of Apollo's translunar trajectory printed in various press releases are not entirely accurate. They tend to show only a two-dimensional version of the actual trajectory. The actual trajectory was three-dimensional. The highly technical reports of Apollo, accessible to but not generally understood by the public, give the three-dimensional details of the translunar trajectory.

Each mission flew a slightly different trajectory in order to access its landing site, but the orbital inclination of the translunar coast trajectory was always in the neighborhood of 30°. Stated another way, the geometric plane containing the translunar trajectory was inclined to the earth's equator by about 30°. A spacecraft following that trajectory would bypass all but the edges of the Van Allen belts.

This is not to dispute that passage through the Van Allen belts would be dangerous. But NASA conducted a series of experiments designed to investigate the nature of the Van Allen belts, culminating in the repeated traversal of the Southern Atlantic Magnetic Anomaly (an intense, low-hanging patch of Van Allen belt) by the Gemini 10 astronauts. This site is my favorite

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