Space Travel and the Van Allen Radiation Belt

The Van Allen Radiation Belts are often mentioned in space-travel related discussions on the internet. Two donut shaped rings of pure death surround the earth and make space travel impractical or impossible. The inner belt is situated from 400 to 6.000 miles above the earth, the outer one extends from 8.000 to 36.000 miles. The belts contain charged particles that loop around the Earth at high speeds. On the top end, the particles have enough energy to penetrate 14mm of lead. It was actually Greek physicist Nicholas Constantine Christofilos who was one of the first to explore the possibility of trapping charged particles. He later was one of the driving forces behind Operation Argus (1958).

Operation ARGUS was the designation given to the three high-altitude nuclear test shots conducted by the United States in the South Atlantic Ocean from August 27 to September 10, 1958. The ARGUS shots were conducted to test the Christofilos theory, which argued that high-altitude nuclear detonations would create a radiation belt in the upper regions of the Earth’s atmosphere. It was theorized that the radiation belt would have military implications, including degradation of radio and radar transmissions, damage or destruction of the arming and fuzing mechanisms of ICBM warheads, and endangering the crews of orbiting space vehicles that might enter the belt. 

So back then shooting nukes in the sky and trying to create a radiation or electron belt in the upper parts of the atmosphere was thought to be a pretty good idea, of tactical value in case of war, for example to disable enemy satellites. Of special interest is the location chosen for Argus, about a 1.000 miles southwest of Cape Town.

This is an area in range of the so called South Atlantic Anomaly, where the inner Van Allen belt is closest to Earth, as low as 125 miles from the surface. The borders and shape of this Bermuda Triangle of Space are not static, the anomaly is actually moving and expanding slowly. It is speculated that the weakening of the Earths geomagnetic field may be a contributing factor. Interesting to note: the ISS required extra shielding to be able to safely pass through the anomaly. About 200 satellites (2010) face the problem of passing through the Anomaly, some programmed to shut down sensitive equipment for the duration of the passage.

Our understanding of the belts and their function is still developping. Recently it was discovered that the belts, interacting with the Earths plasmasphere, function as a barrier to high speed electrons. So all things considered, it is probably something we do not want to mess with too much.

Van Allen himself (apparently) responded to questions about the belt and the consequences for space-travel, and more specifically a FOX TV show that posed the NASA Moon Missions were a hoax:

"The radiation belts of the Earth do, indeed, pose important constraints on the safety of human space flight. The very energetic (tens to hundreds of MeV) protons in the inner radiation belt are the most dangerous and most difficult to shield against. Specifically, prolonged flights (i.e., ones of many months' duration) of humans or other animals in orbits about the Earth must be conducted at altitudes less than about 250 miles in order to avoid significant radiation exposure.

A person in the cabin of a space shuttle in a circular equatorial orbit in the most intense region of the inner radiation belt, at an altitude of about 1000 miles, would be subjected to a fatal dosage of radiation in about one week.  However, the outbound and inbound trajectories of the Apollo spacecraft cut through the outer portions of the inner belt and because of their high speed spent only about 15 minutes in traversing the region and less than 2 hours in traversing the much less penetrating radiation in the outer radiation belt.

The resulting radiation exposure for the round trip was less than 1% of a fatal dosage - a very minor risk among the far greater other risks of such flights. I made such estimates in the early 1960s and so informed NASA engineers who were planning the Apollo flights. These estimates are still reliable. The recent Fox TV show, which I saw, is an ingenious and entertaining assemblage of nonsense. The claim that radiation exposure during the Apollo missions would have been fatal to the astronauts is only one example of such nonsense."

So not fully understood and dangerous but also possibly instrumental in keeping Earth safe from deadly cosmic influences. Not recommended in case of a prolonged visit but also not an unpassable barrier. Otherwise we could not have gone to the Moon, right? And with 60s technology to boot! But that is another topic, which I will leave for a later post.