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If you have not yet read the radiation primer, you are invited to do so. We have discussed the Van Allen belts in a separate page. This page discusses only solar events. It should be noted that most conspiracist arguments confound the two, although they are very different phenomena posing very different hazards.

There are lots of published sources which say that solar particle radiation is a hazard to astronauts.

And it is, but a hazard is not necessarily an insurmountable obstacle. Wet roads are a hazard to drivers, but people drive on them anyway. There are many hazards in a voyage to the moon. Care is taken to minimize them, but in the end it's still a dangerous thing to do. Just as there are people willing to brave the hazards of mountainclimbing, there are those willing to brave the hazards of outer space.

By repeating ad nauseam the statement that radiation is hazardous, the conspiracists attempt to instill the notion that it's unavoidably fatal or always there. It's not. Remember, this is the same area of space where dozens of countries operate sensitive communications satellites.

Experts say, "During a solar maximum, about 15 flares per day emit detectable X-ray energies." [David Wozney]

The source cited by Wozney for this claim is no longer at the web URL he gives. But we must distinguish carefully between a major event and a detectable event. Just because our instruments can detect the radiation of a solar event doesn't mean it presents a health hazard to a lunar astronaut. We could draw the parallel between a detectable earthquake and a catastrophic earthquake. Seismometers can measure earthquakes so gentle that people don't even notice them. This would be a detectable seismic event, and they occur all the time.

According to records, more than 1,400 solar flares occurred during the Apollo missions.

This number represents the total number of detectable solar events, not major flares that would have posed a danger to the astronauts. The records also show that no major solar flares occurred during the Apollo missions, but the conspiracists don't care to look that closely. The impressively large number is all they're interested in. The closest call came when the Apollo 12 spacecraft's external radiation sensors detected a minor flare, but the interior sensors did not indicate that any appreciable amount of this radiation penetrated the spacecraft hull.

Major solar events last for hours, or sometimes even days. [David Wozney]

Strangely enough, Mr. Wozney provides no reconciliation for his two claims. On the one hand we're told these major events occur 15 times a day. Now we're told they can last for days. Fortunately we at Clavius can offer a reconciliation. Major events can in fact last for hours or days. The events that occur 15 times a day during peak activity are the low-level events which pose no particular hazard to astronauts. They're strong enough to trigger our detection instruments, but not strong enough to warrant concern.

Solar flares produce huge amounts of radiation. One source says 3,000,000 REM for a one-year continuous exposure. Another source puts it at 100 REM per hour. NASA web sites say the radiation approaches 10 million electron volts! [David Wozney]

Is ten million electron volts a high energy level? The reader isn't told. It sounds like a big number. Put a nine-volt battery on your tongue and you'll get an unpleasant but harmless jolt. You see sparks from a 12-volt battery when you jump-start a car. We take great pains to shield ourselves from the 110-volt current in our houses because we know it can kill us. So ten million electron volts must be an enormous amount of unquestionably fatal energy. Right?

Well, no. The "electron volt" (eV) is not equivalent to the common "volt" that measures household electricity. Instead it's the amount of energy picked up by a single electron as it passes through an electrical potential of one volt. We realize that's not a very helpful definition to the layman, but it takes the equivalent energy of about 620,000,000,000,000 million electron volts (MeV) per second to light up a 100-watt light bulb. The figure is obviously cited because it's a big scary number, but it's like saying an automobile weighs 2.3 billion milligrams. A large number, but a small unit. The very large figure given for the light bulb is explained by knowing that each individual electron that participates in the operation of a light bulb has a fairly small energy level, but there are billions and billions of electrons involved. In radiation terms this is called a high "flux". In space the individual electrons can have very high energy levels, but there aren't as many of them. The flux is much smaller.

But solar events do in fact produce dangerous radiation. They have been known to knock out communications satellites and even disrupt terrestrial communications. But in order to correlate the conspiracists' numbers with the likely threat, we have to know what kind of particle the number refers to. A 10 MeV electron is relatively harmless, while a 10 MeV proton might be a cause for concern. But again, the energy level is only half the story. You also have to know the particle flux.

The dosage figures, which take into account both energy and flux, are likely to be fairly accurate. But the conspiracists make the fundamental error of multiplying these worst-case exposure characteristics by the 15-per-day figure, or 1,400 total figure, representing the number of merely detectable events, thereby arriving at what they believe to be the exposure level of a typical mission to the moon. If we stick with the earthquake analogy, it would be like counting the dozens of microquakes that occur on a daily basis and multiplying that number by the 7.0 or 8.0 Richter magnitudes for a single major earthquake, and then presuming that massive devastation must have taken place during those microquakes.

Various regulatory bodies have established the maximum safe dosage for the general public as 1 millisievert (mSv) per year, and 5 mSv in special circumstances. The Apollo astronauts would have been exposed to several orders of magnitude more radiation than these figures allow. [David Wozney]

First it must be understood that this claim is based on the improperly computed dosages described above. And if you read the radiation primer you'll learn that it's very difficult in practice to compute dosages. Radiation dosages are measured rather than computed. The Apollo astronauts wore dosimeters to measure how much radiation they were exposed to. And sensors both inside and outside the spacecraft measured radiation.

Average Radiation Exposure
For Apollo Flight Crews
Skin dosage
7 0.16
8 0.16
9 0.20
10 0.48
11 0.18
12 0.58
13 0.24
14 1.14
15 0.30
16 0.51
17 0.55
(Bailey, J. Vernon, "Radiation Protection and Instrumentation",
in Biomedical Results of Apollo, Johnson Space Center.)
Second, Mr. Wozney misrepresents the legal limits. Whole-body exposure limits are summarized here in the primer.

The table at right gives the average skin dosages for the Apollo astronauts as measured by their dosimeters during the trip. Skin exposure is not as drastic as exposure in blood-producing organs, and since those organs like deep within the body, they receive as much as 40% less exposure than the skin.

In 1971 the U.S. Atomic Energy Commission's limits on exposure were as they are today. (Standards for Protection Against Radiation. 10 CFR § 20, rev. July 15, 1971.) Without detailed flux data we cannot provide precise dose equivalents for the figures in the table. But we know the spacecraft hulls provided excellent shielding against protons, except for the most high-energy protons and cosmic rays.

The highest exposure is for Apollo 14, and the dose equivalent is about 2.85 rem (28.5 mSv), or about ten times the amount of normal background radiation per year, half the allowed yearly dosage for occupational radiation exposure, or 1/140 the lethal dosage.

In some places on earth, natural radiation supplies up to 28 rems (280 mSv) per year. No adverse effects from this dramatically increased background dose have been observed. We understand from this data that the limits imposed by the law are quite stringent, and may even derive from a sort of radiophobia among the general public. One can receive several times the legal limit of radiation dosage and still have no observable effects. Thus the legal limit is not an accurate measure of what a harmful radiation dosage might be.

Experts say 'High energy protons travel at the speed of light so there is no time to get under cover.' [David Wozney]

The source, Humans in Space, is a health and biology site, so we can forgive them for not understanding that only massless particles (e.g., photons) can travel at the speed of light. Particles such as protons which have mass cannot.

The hulls of the Apollo spacecraft were ultra-thin.

The hulls were "ultra-thin" compared to the tons of concrete the layman believes is necessary to shield against radiation. The protection was adequate for the Van Allen belts and normal particle flux from the sun, but probably not enough to protect against a major solar event. It would have indeed been prohibitive to supply the Apollo spacecraft with the shielding necessary to ward off solar event radiation entirely. But with the shielding provided, the astronauts would have been able to withstand a major solar particle event for as long as two hours without receiving a lethal dose.

But protection against radiation isn't always a matter of piling up enough material to weather the storm. Sometimes it's a matter of planning and evasion.

A major solar event doesn't just cut loose without warning. It is possible to observe the "weather" on the sun and predict when a major event will occur. And this is what was done on the Apollo missions. To be sure, the missions were planned months in advance and the forecasting was not that farsighted. But they would have had enough warning to call off the mission should a solar event have started boiling up from the depths of the sun.

Statistical probability was the main protection for the Apollo crews. The forecasters would have been able to rule out major events during the first few days of the mission. And so out of a nine-day mission that might only leave five or six days of vulnerability. The chances of a major solar event occurring within a given five-day period is quite remote, even during periods of exceptional activity.

Solar events are directional. They don't fan out from the sun in concentric rings; they're more like cosmic shotgun blasts. And so if an event should occur, it's more likely to throw particles in some other direction rather than toward the earth and its moon.

NASA says that solar event is the single biggest danger astronauts would have to face on a mission to Mars. Why wouldn't it also have been a grave danger to lunar missions?

A mission to the moon lasting at most two weeks has good odds of avoiding solar events. A mission to Mars lasting two years or more has very little chance of avoiding a major solar event.

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