radiation and the van allen belts
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"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." -- Dr. James Van Allen

If you have not yet read the radiation primer, you are invited to do so.

There is too much radiation in outer space for manned space travel.

This general charge is usually made by people who don't understand very much at all about radiation. After witnessing the horrors of Hiroshima and Nagasaki and the tragedy of Chernobyl it is not surprising that the idea of radiation should elicit an intuitively fearful reaction. But when you understand the different types of radiation and what can be done about them, it becomes a manageable problem to avoid radiation exposure.

It doesn't matter how difficult or expensive it might have been to falsify the lunar landings. Since it was absolutely impossible to solve the radiation problem, the landings had to have been faked.

This is a common method of argument that attempts to prove something that can't be proven, by disproving something else. In this case the reader is compelled to accept the conspiracy theory and all its attendant problems and improbabilities, simply on the basis that no matter how difficult, absurd, or far-fetched a particular proposition may be, if it's the only alternative to something clearly impossible then it must -- somehow -- have come to pass. This false dilemma is aimed at pushing the reader past healthy skepticism and into a frame of mind where the absurd seems plausible.

The false dilemma is only convincing if the supposedly impossible alternative is made to seem truly impossible. And so conspiracists argue very strenuously that the radiation from various sources spelled absolute doom for the Apollo missions. They quote frightening statistics and cite various highly technical sources to try to establish to the reader that the radiation poses a deadly threat.

But in fact most conspiracists know only slightly more about radiation than the average reader. This means only a very few people in the world can dispute their allegations, and the conspiracists can simply dismiss them as part of the conspiracy.

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.

NASA defenders make a big deal about the Southern Atlantic Magnetic Anomaly, but the Apollo spacecraft ventured into the more intense parts of the belts.

True, but the point was to validate the scientific models using hard data, and to ascertain that a spacecraft hull would indeed attenuate the radiation as predicted.

We know the space shuttle passes through the Southern Atlantic Magnetic Anomaly (SAMA), but since the shuttle astronauts have time in each orbit to recover, the effects are not felt as strongly. The Apollo astronauts spent around four hours at a single stretch in the Van Allen belts. [Mary Bennett]

This is exactly the opposite of the recovery principle. If the shuttle astronauts spend 30 minutes of each 90-minute orbit passing through the SAMA, that sums to an exposure of 8 hours per day. The human body does not recover from radiation in a matter of minutes but rather hours and days. The damaged tissue must be regenerated. If radiation exposure is more or less continuous over several days, such as in the shuttle scenario, the tissue never has time to regenerate before being damaged by continuing radiation.

A short, intense exposure is safer than continuous or periodic exposure at lower intensity.
Even though the outlying parts of the Van Allen belts contain more intense radiation than the SAMA, a four-hour passage followed by days of relatively little exposure offers a better recovery scenario than days of accumulated low-level exposure.

The four-hour figure is reasonable, but somewhat arbitrary. Since the Van Allen belts vary in flux and energy, it's not as if there's a clearly demarcated boundary. It's a bit like walking over a hill. If the slope gently increases from flat and level to 30° or so, where do you say the hill starts?

It would require six feet (two meters) of lead in order to shield from the Van Allen belts. The Apollo spacecraft had nowhere near this amount of shielding and so could not have provided the astronauts adequate protection.

The "six feet of lead" statistic appears in many conspiracist charges, but no one has yet owned up to being the definitive source of that figure. In fact, six feet (2 m) of lead would probably shield against a very large atomic explosion, far in excess of the normal radiation encountered in space or in the Van Allen belts.

While such drastic measures are needed to shield against intense, high-frequency electromagnetic radiation, that is not the nature of the radiation in the Van Allen belts. In fact, because the Van Allen belts are composed of high-energy protons and high-energy electrons, metal shielding is actually counterproductive because of the Bremsstrahlung that would be induced.

Metals can be used to shield against particle radiation, but they are not the ideal substance. Polyethylene is the choice of particle shielding today, and various substances were available to the Apollo engineers to absorb Van Allen radiation. The fibrous insulation between the inner and outer hulls of the command module was likely the most effective form of radiation shielding. When metals must be used in spacecraft (e.g., for structural strength) then a lighter metal such as aluminum is better than heavier metals such as steel or lead. The lower the atomic number, the less Bremsstrahlung.

The notion that only vast amounts of a very heavy metal could shield against Van Allen belt radiation is a good indicator of how poorly though out the conspiracist radiation case is. What the conspiracists say is the only way of shielding against the Van Allen belt radiation turns out to be the worst way to attempt to do it!

Official NASA documents describing the pre-Apollo studies of the Van Allen belts clearly state that shielding was recommended for the Apollo spacecraft, yet no shielding was provided. [Mary Bennett and David Percy]

"Shielding" does not always mean thick slabs of dense material.
Commensurate with the common perception of radiation as an inescapably deadly force is the notion of radiation shielding as universally heavy and dense. Percy and others seem to rely on the notion that radiation shielding, if present, would have been very conspicuous -- or prohibitively bulky.

As discussed in the previous question, shielding against particles is not the same as shielding against rays. To say that the Apollo spacecraft did not provide adequate shielding is to ignore both the construction of the Apollo command module and the principles of radiation shielding.

And it must be kept in mind that shielding was only one element of a multi-pronged solution for safely traversing the Van Allen belts. It was never intended that the shielding in the command module would provide the only protection for the astronauts. The shielding was adequate to protect the astronauts against the circumstances of the trajectory and exposure duration worked out by the mission planners.

NASA apologists come up with different numbers for estimates of the exposure in the Van Allen belts. This suggests they really don't know what they're talking about. [Mary Bennett and David Percy]

All the estimates we've seen lie within the same order of magnitude and generally outline a plausible method of computation. This stands in contrast to the conspiracist estimates which generally have no quantitative support.

Computing the precise exposure for Apollo astronauts is very difficult. That's why the astronauts wore dosimeters to measure the actual exposure. The factors involved in computing expected exposure analytically include:

Exact trajectory. The Van Allen belts are not uniformly shaped. They have thick and thin spots. And the level of radiation is not constant at all points. Toward the center of the belt cross sections there is more radiation than at the edges. Most Apollo enthusiasts do not know the exact trajectory or how it relates to the location of the Van Allen belts. But they know that they don't know this, and so they frequently do their computations assuming the astronauts passed through the densest parts, and therefore err on the side of overestimating the exposure.

Exact velocity. Exposure time is very important to a correct computation of radiation dosage. Because the velocity of the spacecraft is constantly changing, the same ambiguity which governs the geometry of the trajectory also governs the rate at which it is followed. And most enthusiasts (and all conspiracists) lack the information and skill to precisely determine the velocity of the spacecraft during the Van Allen belt traversal, and therefore the exposure time.

Exact energy and flux. In any given cubic meter of the Van Allen belts there will be a soup of particles at various energy levels and fluences. Energy describes the velocity of the particle, how far it will penetrate, and how much damage it will do if it hits something. Flux is the density of particles, how many of them pass through a given area in a second. Generally, the higher the energy the lower the flux. Low-energy particles (i.e., protons 30 MeV and below) can be ignored because they do not penetrate the spacecraft outer hull. But at each point along the trajectory through the Van Allen belts there is a different continuum of flux and energy. It requires a lot of mathematics to fully solve this system. And since some of the variables are hard to determine, they're typically approximated.

Probabilistic factors. Even should a high-energy particle penetrate the spacecraft hull to the interior, it will only cause problems in the human organism if it is absorbed in tissue. It is possible for the particles to pass through the body without colliding, in which case they are harmless. The human body varies in density. Particles are more likely to collide with dense tissue like bone. The amount of absorbed radiation is a statistical probability based on how much radiation is detected by dosimeters.

To summarize then, a fully accurate analytical solution must first determine the exact trajectory of the spacecraft through the Van Allen belts. This will give a continuous function describing particle flux and energy at each point along the trajectory.

At each point in the trajectory we will have a function giving flux per given energy level. So a 100 MeV proton will have, say, a flux of 20,000 particles per square centimeter per second at that point in space. But for other energy levels the flux will be different at the same point. The total irradiation inside a spacecraft will be the sum of all the fluences at energies capable of penetrating the hull and shielding.

And at each point along the trajectory the velocity of the spacecraft must be determined so it can be known how much time the spacecraft spends at that point. This is multiplied by the conglomeration of fluences to arrive at a dose.

This dose is simply the amount of radiation present. It must be converted to a meaningful value that describes its likely effect on human tissue. Again, energy and fluence come into play, because low-energy particles (but still high enough to penetrate the shield) are likely to accumulated in the outer layers of the skin and cause damage which is sloughed off harmlessly. High-energy particles are absorbed in the bones and internal organs, causing much greater injury.

The procedure for analytically computing a radiation dose is simple enough in principle as outlined above, but of course is very difficult to actually carry out. This is why engineers generally don't try to compute the dosage to any great degree of accuracy ahead of time. They are happy simply to arrive at an order of magnitude which provides adequate design criteria. The actual radiation exposure is always measured, not computed.

So then was it measured on Apollo?

Yes. Each astronaut wore a personal dosimeter. The accumulated dose for each astronaut was regularly reported to Mission Control over the radio.

New evidence has shown that the Van Allen belts are indeed stronger and more dangerous than NASA says. [Bart Sibrel]

Sibrel misinterprets the source article published by CNN. It was reported only that the Van Allen belts were slightly larger in places and slightly denser than previously understood. This is not a new reality, merely a refinement of existing figures. We are still studying the Van Allen belts and must occasionally revise our numerical models. The new findings have implications for the astronauts in the Alpha space station. Since these astronauts will be exposed to the fringes of the Van Allen belts for an extended period, it is prudent now to provide a bit of extra polyethylene shielding to the sleeping quarters. For transitory exposure such as in Apollo missions, the new findings add only a negligible hazard.

Sibrel and others argue that NASA has under-reported the intensity of the Van Allen belts for many years as part of a cover-up. They argue that the real magnitude of the radiation is now being made known, and that it's strong enough to have precluded a successful Apollo mission.

Unfortunately that's a very naive argument. The United States has never been the only spacefaring nation, nor the only nation ever to study the Van Allen belts. Canada provide valuable data to the Apollo project, and the USSR duplicated all the U.S. research, and may even have conducted more. For thirty years the same body of engineering data used to produce the Apollo spacecraft has been used by all nations in designing communication satellites, probes, and other devices intended to operate in and beyond the Van Allen belts. If this data had seriously under-reported the actual radiation present, the spacecraft engineered to those standards would all have failed prematurely due to radiation damage.

This is a very important point since it involves the financial interests (to the tune of billions of dollars!) of countries with no special desire to protect the reputation of the United States. Had this data been seriously wrong, someone surely would have complained by now. Satellites are insured against premature loss, and the insurers want to make sure the spacecraft are engineered to the best possible standards. There is immense worldwide economic incentive to having the best available data on the Van Allen belts, so it's highly improbable the the U.S. has been intentionally providing erroneous data to the entire world for thirty years.

An orbital nuclear detonation in 1962 code-named Starfish Prime created a third Van Allen belt composed of high-energy electrons. This belt was a hundred times more intense than the existing Van Allen belts and was computed to have a half-life of 20 years. [Bennett and Percy, Dark Moon, p. 309]

Fig. 1 - The aurora produced by the Starfish Prime high-altitude nuclear detonation.
The authors give no reference for the claim that this artificial radiation belt was "a hundred times" more "intense" than the naturally-occurring belts. Nor do they define what is meant by "intense". The Starfish Prime test did in fact produce a temporary artificial radiation belt, and it's true that this belt persisted longer than anticipated. But it was not an impediment to the Apollo missions because it had dissipated to a safe level by then, and was very small (and easily avoided) to start with.

Radioactive half-life applies to radioisotopes only. It does not apply to clouds of magnetically-retained charged particles. The authors imply that their theory is confirmed by expert authors, but in fact the author they cite discusses only the general concept of radioactive half-life. Bennett and Percy are responsible for having misapplied it to this problem. Radioactive half-life and particle belts have nothing at all to do with each other. The dispersal of this belt doesn't have anything to do with radioactive decay, and a great deal to do with solar weather and shifting magnetic fields.

The authors argue that such a radiation belt would still be highly intense to this day. However they have shown no evidence that any of the radiation from Starfish Prime is still there. Instead they refer to irrelevant scientific principles and claim it "must" still be there.

A secret study done by the Soviet Union and obtained by the CIA determined that a meter of lead would be required to shield against deep space radiation.

Many conspiracists allude to this alleged report, but none of them can attest to actually having seen it. Since they can argue the alleged report is closely held by the CIA and therefore still top secret, the conspiracists are protected from refutation. No one can prove the non-existence of any document, much less one that is allegedly classified by an intelligence agency. Unfortunately it's more straightforward to note that the conspiracists cannot expect the world to accept an argument based on evidence which they cannot produce. If it's so top secret, how do they know about it?

It's fairly easy to show that such a document likely does not exist. We know that great thicknesses of lead are not required to shield against particle radiation. We know that Soviet science and engineering were excellent. We note with no small amusement and no small suspicion that the conclusion of the alleged report contradicts the commonly accepted principles of physics, and that it instead bears a striking resemblance to the naive assertions of inexpert conspiracy theorists who claim that only thick sheets of lead are suitable for radiation shielding. The alleged report is plausible to the lay reader but utterly unconvincing to the scientist.

The Soviet lunar spacecraft design demonstrates they did not believe a meter or two of lead was required to shield against radiation.
History provides the final proof. Had the Soviets actually believed that great thicknesses of material were required to shield against radiation, they would have questioned the design of the Apollo spacecraft. The spacecraft clearly did not provide a meter of lead shielding, yet NASA claims it successfully traversed the Van Allen belts. Yet the Soviets acknowledged then and continue to acknowledge today that the Apollo program was a clear success.

In recent years the Western world has been able to examine the Soviet spacecraft design which was to have carried cosmonauts to the moon. They did not provide a meter of lead for their spacecraft either.

Soviet cosmonauts have been quoted as saying radiation was a very grave concern.

And NASA officials have been quoted as saying essentially the same thing. Radiation is a very great concern, but there's a vast difference between a "concern" and an insurmountable obstacle. The conspiracist argument relies on the radiation problem being insurmountable, and nothing said by either NASA or cosmonauts conveys the notion that these problems couldn't have been solved.

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