Surviving Radiation in Space

Apollo 10 image of Earth taken from 100,000 miles away.
[Credit: NASA]

For those who are interested in the reality of radiation exposure on Earth, in space, on the Moon, and what this exposure means for our prospects of manned exploration of the Solar System, read on!

The Myths and Truths of Death by Space Radiation

There are persistent groves of misinformation taking root about the lethality of radiation doses for astronauts, particularly for those who are bound for the Moon and/or Near-Earth-Objects, (such as asteroids for research or mining).

Unfortunately, these claims have been given the capacity for widespread proliferation in the fertile cyber-soil of the Internet, and worse, they usually sprout symbiotically with claims that the Moon landings were hoaxed, e.g.:

“We could never have landed on the Moon because the astronauts could never have survived the radiation from cosmic sources/the Van Allen Belts/solar wind.  Therefore, at a sound stage in the Nevada desert…”

Well, since most of these authors capitalize on the preexisting, prevalent fear of radiation to sugar-coat their misinformation pill, most people are unprepared to distinguish technically-compelling pseudoscientific fluff from interpretations of actual data.   So, the below is an effort to arm you, fellow readers, with a guide to help navigate these murky radiation/Moon hoax waters.

NOTE: NASA has produced a factsheet on space radiation as well, which covers the basics of radiation and its effects and measurement.

By reviewing some of this information, you’ll ideally emerge with an enhanced ability to see for yourselves if these radiation-lethality claims hold water.

(SPOILER ALERT: They don’t.)

So, to begin, let’s review what we know about radiation exposure right here on planet Earth.

Current Regulation Levels and Common Radiation Doses

After nearly a half-century of dedicated research, it has been found that there is no detectable increase in the incidence of cancer (the primary threat of penetrating gamma-ray radiation exposure) for people who receive an annual radiation dose of 5,000 millirem (5 rem) or less.

Consequently, the U.S. Nuclear Regulatory Commission’s (NRC) federal regulations currently limit nuclear workers to an annual dose of that amount.  Further, the U.S. Department of Energy’s (DOE) federal regulations, to be on the safe side, currently limit radiological workers’ annual doses to one tenth of the NRC’s limit (500 millirem) unless there is some sort of extreme circumstance or emergency.

But what do these numbers mean?  To help visualize this data, please see the below graph, which places these numbers in simple context with radiation doses we receive naturally from things we all can more easily comprehend, like a chest x-ray:

Current radiation exposure limits and common doses. [Chart credit: Ben W. McGee]

As you can see, there is a certain amount of radiation exposure that we all receive just from standing on planet Earth (see the far right-hand side of the graph).  This natural radiation is unavoidable – cosmic rays can penetrate just about any shield that is not located deep within the Earth, which is itself radioactive and contributing gamma rays from below.  In fact, you will note that the DOE administrative limit mentioned above is actually less than the amount of radiation we all already receive from Earth, plants*, rocks, air, and even ourselves* in a given year.  (*Roughly 1-2% of all potassium on earth is the radioactive isotope, K-40.)

The take-home here is that none of the numbers in the above graph indicate any sort of imminent danger.  In fact, all doses depicted above are evidenced to be “safe” levels, in that they are either natural or below any exposure that the data indicates increases the incidence of cancer in a population (see: ICRP, NCRP).

NOTE:  There are actually two separate dangers that get confused during conversations about the health effects of radiation.  The first kind of danger is for lower-level exposures, which is the danger of increasing your risk of developing cancer later in life.  -This is exactly like the common knowledge that more time spent sunning or tanning during youth equates to an increased risk of skin cancer later on in life.  (It won’t harm you now, but it could harm you later.  It’s a roll of the dice based on your own health, habits, luck, and genetics.) 

The second kind of danger is immediate – the damage and destruction of cells due to a brief, intense exposure to radiation.  Following the sun-tanning analogy, this is akin to a sunburn but spread throughout your body – damage directly caused by the radiation due to its intensity.  While this may also increase your risk of cancer, the threat here is direct injury and your body’s ability to cope.

How do these natural and regulated levels of radiation exposure compare to the radiation dose levels we really know to be definitely unsafe?  For that, see the following expanded graph, which has been color-coded to relate it to the previous one:

Dangerous radiation levels in context. [Chart credit: Ben W. McGee]

So, as you can see, this graph allows you to immediately identify relationships between ordinary and dangerous radiation exposures to help you understand the concept of radiation exposure and recognize how intense radiation has to be in order to be considered truly dangerous.

• For instance, you have to be exposed to an intensity of radiation ten million times that of Earth’s normal background levels before worrying about developing radiation sickness.  That’s ten thousand times more powerful than a chest x-ray.

• You would also need to receive 1,000 chest x-ray scans before worrying about definitely having increased your risk of developing cancer later in life by a single percentage point.

Now, with a little context, we can start to evaluate how bad the space radiation environment really is.

Explorer-1, launched in 1958. [Credit: NASA/MSFC]

Debunking Lethal Radiation from the Van Allen Belts

The United States’ first spacecraft, Explorer-1, detected the presence of so-called “belts” of radiation around the Earth.  These were named after the scientist who designed the instrument that discovered them, Dr. James Van Allen of the University of Iowa.  However, we have learned much since then, including measurements from the radiation instrument RADOM aboard the much more recent Chandrayaan-1 spacecraft (launched in 2008).

Results from RADOM showed that the inner Van Allen belt, which extends from roughly 1,000 miles above the Earth to a little more than 6,000 miles up, appears to be composed of highly energetic particles, such as solar protons, (meaning they pack a higher radiation “kick”).  The outer belt, on the other hand, extends from a little more than 9,000 miles up to a full 33,000 miles up, and it appears to be a little gentler – it is composed primarily of electrons (beta particles).

So, just how bad was the radiation measured there?  Well, it wasn’t something to dismiss (and was academically quite interesting), but it also wasn’t something that would strike fear into the hearts of mission planners:

Peak radiation exposure while traveling through the inner, more powerful belt reached 13,000 millirem per hour, (or 13 rem per hour).  So, if an astronaut were to park in worst part of the inner Van Allen belt for an hour with no shielding, he or she would receive a radiation dose nearly three times the annual “safe” dose for DOE workers and may have bumped up their lifetime risk of a fatal cancer by a percentage point.

Fortunately, however, the time the Apollo astronauts spent traveling through the highest radiation zone of the inner Van Allen belt (at a screaming 11,000+ miles per hr) was fractional – their doses averaged 120 millirem per day.

Go ahead and compare this to the above graphs.

So, it is clear that the Apollo astronauts’ radiation doses in this case were much less than a common CT scan and far less than what a modern astronaut on the International Space Station receives during a 6-month tour (~7,000 millirem).

Hence, simply passing through the Van Allen Belts is anything but lethal.

Astronaut exposed to the raw space radiation environment on Apollo 8. [Credit: NASA]

Debunking Lethal Radiation Doses from the Earth to the Moon

Like our own sun, all of the other stars in the night sky are nuclear reactors.  Consequently, a constant “rain” of high-energy particles and gamma rays comes at us from the rest of the galaxy, which we call Galactic Cosmic Radiation, or GCR.

Many claim that in “deep space,” e.g., the space between the Earth and the Moon or between Earth and Mars, GCR would prove lethal for a human being.  Yet, the data indicates otherwise.  (Actually, GCR is the primary source of radiation an astronaut normally experiences in all cases, whether in Earth orbit or beyond.)

Let’s have a look.

The data we have about radiation doses during travel from the Earth to the Moon, like with the Van Allen Belts, are not limited to the old Apollo mission data.  For example, the same Chandrayaan-1 spacecraft mentioned above also traveled from the Earth to the Moon and showed a dose during the five day trip (a.k.a. during “translunar injection“) of 1.2 millirem per hour.

Granted, while this is a level nearly a hundred times the average gamma-ray background radiation intensity on Earth, it is still low enough to not present an immediate concern.  Why?  See the above graphs for a comparison – An astronaut would have to spent more than 170 days in this radiation field before even reaching the NRC’s limit for nuclear workers, which equates to no statistical increase in developing cancer.

This sort of radiation exposure becomes an issue when planning long-term missions to the Moon or Mars, which involve several months to years of exposure time, but it certainly bore no immediate threat to Apollo astronauts traveling to-and-from the Moon in a matter of days.

View of the Taurus-Littrow Apollo 17 landing site. [Credit: NASA]

Debunking Lethal Radiation on the Moon

Like with the trip from the Earth to the moon, radiation doses on the lunar surface did not even approach immediate danger levels, and while they fluctuated strongly with changes in the Sun’s output, the Moon itself was observed to act as a shield from galactic cosmic radiation.

Consequently, doses received by astronauts on the lunar surface were actually less than that received in lunar orbit, and again, averaged 120 millirem per day.

This value is completely consistent with measurements from the RADOM instrument in 2008 that showed radiation dose rates in lunar orbit of approximately 1-2 millirem per hour.

And again, these are far from doses that would pose an imminent threat to an astronaut’s ability to function.  An astronaut would, quite simply, need to stand in a radiation field of an intensity one hundred thousand times greater for a full hour before suffering the effects of radiation sickness.

The final space radiation threat data in context, plotted in green, can be seen in the following chart:

Space radiation doses in context. [Chart credit: Ben W. McGee]

Looking Ahead to Planetary Exploration

What does this all mean for the future of manned space exploration?  While all of this does show that claims of radiation lethality in space are plainly false, it also indicates that radiation mitigation will have to be a central planning issue in order for future astronauts to remain within the current bounds of acceptable risk.

Prevailing wisdom accepts that spaceflight and planetary exploration is inherently dangerous and limits what is considered to be acceptable risk to a 3% increase in fatal consequences as a result of radiation exposure – regulations for radiation exposure that are more lenient for astronauts than for other radiation workers.  (Surprisingly, however, this level of risk acceptance is actually more conservative than what is currently accepted for workers in other, much more prosaic terrestrial jobs in many industrial and natural resource fields… but that’s another story.)

There is some research to suggest that chronic, lower-intensity radiation exposure to some of the soft tissues of the eye may lead to secondary negative health effects, such as cataracts, but we’ve only just begun to learn what effects the many alien factors of the space environment have on human physiology, including gravity-induced modifications of bone, muscle, and organ function.  -And again, these effects are not imminently prohibitive and are certainly not immediately lethal.

The Take-Home

Radiation exposure is one of space’s primary threats – but it is not the primary threat.

A lack of atmospheric pressure, the presence of boiling and/or freezing temperature extremes, an intrinsic lack of breathable air and water, and the necessity of shielding against (or avoidance of) micrometeoroids are all arguably more pressing threats.

Radiation at any exposure rate measured in cislunar space certainly wouldn’t prevent an astronaut from visiting the moon, and only if trapped in the most unlikely and unfortunate of orbits would an astronaut ever need be concerned about the possibility of developing a radiation-induced depression of the immune system and – at the extreme – acute radiation sickness.

Take alarmists with a grain of salt and look to the data for the truth.  In fact, it can be seriously argued that conquering our fear of the atom may actually be the means by which the rest of the solar system is opened to humanity.

In my view, that’s where the real conversation is.

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For more information on space radiation doses to astronauts, link (PDF) to the following landmark document, “Space Radiation Organ Doses for Astronauts on Past and Future Missions” by F.A. Cucinotta.