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
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
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
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
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.
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.
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
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.
Second, Mr. Wozney misrepresents the legal limits. Whole-body
exposure limits are summarized here in the primer.
Average Radiation Exposure
For Apollo Flight Crews
(Bailey, J. Vernon, "Radiation Protection and
in Biomedical Results of Apollo, Johnson Space
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
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
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.