Too much radiation?
Published on Mar 31, 2008 at 11:57 am.
24 Comments.
Filed under cosmic rays, space exploration.
On Space.com’s web site, I read an article today suggesting that radiation exposure for astronauts might be too much for long duration space missions. Though radiation exposure to astronauts is a real concern, it isn’t really news. Radiation exposure is something that has been a concern since the very first days of spaceflight. In fact, one reason for sending animals into space before humans was to study the effect that radiation has on the body. Even America’s first satellite, Explorer 1, has a Geiger counter aboard to measure the radiation above the Earth’s atmosphere.
Physicists have known for many years that radiation is coming to Earth form space. The discovery of these cosmic rays is generally attributed to Victor Hess, who in 1912 took an electroscope aloft in a balloon. An electroscope is a device (now practically obsolete) used to measure electric charge. Electric charge would charge the electroscope, causing gold foil leaves to separate due to electrostatic repulsion. But, the electroscopes would always gradually discharge themselves. In the presence of the newly discovered radioactive materials, electroscopes would discharge more quickly. In fact, that is one way to define ionizing radiation: it is something that can ionize air. But, it can also ionize other things, including the atoms in your body. Ionizing atoms in your body changes their behavior, and that can be a bad thing if the atoms are part of DNA. The standard warning symbol for ionizing radiation is the trefoil, seen above. But, even when there was no known radioactive source nearby, electroscopes would discharge. This was taken to be due, in part, to background radiation resulting from the presence of radioactive atoms in the surroundings. Of course, some of the discharge was due to leakage of charge from the atmosphere itself. To differentiate between the atmospheric effects and the background radiation effects, Hess decided to take an electroscope high aloft in a balloon to get it away from background radiation from the ground. To his surprise, he found that there was more radiation at higher altitudes! Later measurements of radiation from mountaintops confirmed his findings. Not only do we have to contend with background radiation from the Earth, but we also have radiation bombarding us from above. This radiation from above is called cosmic rays.
People living at high altitudes, therefore, receive more radiation exposure than people living at lower altitudes. A couple of years ago, I wrote a rather long post about cosmic rays and radiation exposure for airlines. I was surprised in my research to find that airline crew members can receive more annual radiation exposure than many people working with radioactive materials. And, almost nobody wants to talk about that!
Astronauts already receive a lot of radiation exposure. However, that radiation exposure is going to be even greater for missions to the Moon or to Mars. Some cosmic rays are charged particles from the Sun. Others, the higher energy ones, are typically from deep space, originating far beyond our solar system. Many of these galactic cosmic rays are also charged particles. Charged particles are influenced by magnetic fields. The Earth’s magnetic field protects us from the direct effects of the solar cosmic rays, and some of the galactic cosmic rays, too.
The earliest space flights were all within the Earth’s magnetosphere (the region of space where Earth’s magnetic field dominates). Even the International Space Station and the Space Shuttle are within Earth’s magnetosphere. But, the Apollo missions to the Moon took astronauts beyond the shielding of the Earth’s magnetic field. Cosmic rays are pretty much a constant threat in space. But, worse are solar storms, in which the Sun can eject massive amounts of material into space. Astronauts, and even aircraft flying at high altitudes, can experience very large doses of radiation during such storms, and that is within the Earth’s magnetosphere. Astronauts exposed to such storms outside of Earth’s magnetosphere would receive very dangerous levels of radiation. Radiation exposure at such levels would most certainly be injurious to astronauts. And that, of course, is what this recent news story is about.
It isn’t really news, though. As I said, we’ve known about this for a long time. But we don’t really know just how much radiation exposure astronauts might get outside of Earth’s magnetosphere. A National Research Council report (again, not new) suggests that this radiation exposure is too high to safely conduct missions to Mars or extended missions to the Moon without serious radiation mitigation. New Scientist has a similar report several years ago, but as important an issue as this is, in needs to be continually in the minds of mission planners. The problem is that shielding against high energy radiation is tough, and the shielding is heavy. Estimates of the cost of sending a round trip spacecraft to the Moon or Mars are perhaps as high as $200,000 per pound (most of that is the cost of the rocket and fuel). So, heavy shielding could prove cost prohibitive. There are suggestions for lighter weight shielding, such as plastics, but more study is needed. It has also been suggested in numerous plans to use the on board water supply needed by the astronauts as shielding. Water makes a good shield for many forms of radiation. For lunar missions, it has long been suggested that burying a lunar colony might shield it from radiation. Another idea is to use electromagnetic shielding. After all, that is how Earth does it, right? So, perhaps it might be possible to build an electromagnetic shield that could deflect most of the harmful radiation. If so, then that would be the lightest and most cost effective way of shielding astronauts from hazardous cosmic radiation.
Radiation exposure is something that needs to be addressed before we can truly be serious about a mission to Mars or an extended stay on the Moon. But, at least there are people thinking about it.
-Astroprof
Magnetosphere drawing courtesy NASA
Triple D on March 31, 2008 at 9:08 pm: 1
The big issue is that NASA is spending billions trying to get back to the moon but not doing the basic research work needed to protect the astronauts who would be going. And nobody knows where the agency will find money to do the work.
Observer on March 31, 2008 at 11:06 pm: 2
I ran into a guy two weeks ago who insisted the Apollo missions were faked because the astronauts couldn’t have survived the radiation in the Van Allen belts. I asked him if he knew the exposure rate in rem (or any other unit for that matter) for a human in the Apollo capsule, and he said that was typical of a scientist to be in denial.
I’m sure he did great, though, on his standardized test that allowed him to graduate with a high school diploma!
Elias on April 2, 2008 at 7:58 pm: 3
I agree with your general comments. Although its good to get articles about space exploration published, I really wish that “journalists” would spend time understanding the subject of their articles.
The engineering issues surrounding cosmic ray shielding is fairly well understood (otherwise the panel’s report would have looked a lot different). What we need are people convincing congress to fund space exploration, not poorly written articles telling us that it is too hard.
http://www.newcomensengine.com/2008/04/end-of-professional-journalism.html
Astroprof on April 2, 2008 at 8:45 pm: 4
For sure, the problem of radiation exposure is not insurmountable. However, there needs to be some more work on the subject. Unfortunately, NASA needs to be properly funded to do the work. I agree, we don’t need to be saying that it is too hard. Instead, we need to be thinking about how to overcome the difficulties. And, that will require Congress to begin to take funding space exploration seriously.
Elias on April 2, 2008 at 9:21 pm: 5
At least we both agree that they need to spend more money. I agree with you that GCR exposure is not as well understood as it should be. I’m not sure what forces are behind all the recent cuts, its almost as if congress is trying to punish NASA for something. Odd.
CCPhysicist on April 5, 2008 at 9:27 pm: 6
Just about every paragraph in your excellent article triggered an observation that deserved additional comment, so I put them in my blog
http://doctorpion.blogspot.com/2008/04/space-radiation-madness.html
rather than hijacking your comment section.
Keep up the good work!
CosmicKevin on April 14, 2008 at 4:22 pm: 7
Great post. One additional option that until recently seemed to be just science fiction is the “anti-radiation pill.” The new issue of Science magazine (April 11, 2008) has a peer-reviewed study examining radiation resistance in monkeys and mice after taking an anti-radiation pill currently in development:
http://www.sciencemag.org/cgi/content/short/320/5873/226
I’ve also posted some of the possibilities and questions related to the application of such anti-radiation meds in space travel:
http://www.kevinabarnes.com/KaBlog/2008/04/14/a-cure-for-the-radiation-space-travel-blues/
Thanks for calling attention to the often overlooked issue of radiation exposure for astronauts.
Jeff on November 12, 2008 at 4:21 pm: 8
This definitely is something we need to look in to. I’m sure there will be a lot of push back for more funds (especially given the economy right now) but when it comes to radiation and personal safety you really cant mess around over a few extra dollars.
Alwin on October 1, 2009 at 10:44 am: 9
I’m having problem how to piece the scenario. we do have showstopper so what kind of radiation shielding used in 1969? it says “Astronauts en route to the Moon and Mars are going to be exposed to this radiation, increasing their risk of getting cancer and other maladies. Finding a good shield is important” source
http://science.nasa.gov/headlines/y2005/24jun_electrostatics.htm
considering apollo 17 stayed on moon for 3days plus travel time to from moon n earth
Alwin on October 1, 2009 at 10:46 am: 10
same question how astronauts shielded themselves from moon radiation?
source
http://science.nasa.gov/headlines/y2005/08sep_radioactivemoon.htm
Astroprof on October 2, 2009 at 8:45 am: 11
There was minimal shielding for the Apollo astronauts. Basically, NASA hoped that there would not be a major solar storm while they were on their missions. The only protection that the astronauts has was that they were exposed to the radiation for only a few days. However, a mission to Mars would take about 8 months to get there, and 8 months to get back (not to mention waiting on Mars until the planets were positioned correctly again to come back). The long duration of the mission gives far higher radiation exposure, and it also increases the risk of a major solar storm occurring during the mission.
Alwin on October 2, 2009 at 3:13 pm: 12
But the NASA site said good shielding is needed en route to the moon which means simple journey requires good shielding right? because they are at risk for developing maladies like cancer etc..
how about the shieldings needed by astronauts on lunar surface. Apollo 17 stayed on moon for 3 days right? how was the problem resolved? pls see NASA sites I posted
Astroprof on October 3, 2009 at 7:08 am: 13
There was minimal shielding on the Apollo missions. Radiation dosage is computed from multiplying the radiation intensity by the time of exposure. Two ways of protecting yourself from radiation are to either limit the time of exposure or to attenuate the radiation. Shielding does the latter. The Apollo missions were only a few days long. The lunar outposts that you reference in the NASA links would be manned for months. Extending the exposure time by a factor of 10 or so exposes radiation dosage by a factor of 10. Worse, it increases the likelihood of a solar storm while the astronauts are on the mission. Had such a solar storm occurred during the Apollo missions, then the radiation exposure could have been fatal. So, the radiation dosage problem was solved on Apollo by keeping the missions short. Something else has to be done for long term stays on the Moon or for long term missions to Mars. Oh, and it is my understanding that the Apollo era astronauts do have a higher incidence of cancer than the general population of people in similar physical condition, so that might be related to radiation exposure.
Alwin on October 4, 2009 at 2:02 pm: 14
But my question based on site I posted again is what kind of radiation shielding used by apollo astros on moon? we all know astronauts were considered nuclear workers but beyond earth’s safety belt is a different story.I quote
“The surface of the Moon is baldly exposed to cosmic rays and solar flares, and some of that radiation is very hard to stop with shielding. Furthermore, when cosmic rays hit the ground, they produce a dangerous spray of secondary particles right at your feet. All this radiation penetrating human flesh can damage DNA, boosting the risk of cancer and other maladies.”
source: http://science.nasa.gov/headlines/y2005/08sep_radioactivemoon.htm
cosmic rays are constant radiation in space right? were there secondary radiation protection used by astronauts on moon?
Astroprof on October 4, 2009 at 4:43 pm: 15
Alwin, go back and read that source more carefully. They are talking about extended missions and cumulative radiation exposure, not short term exposure of only a few days. The Apollo capsules had very little shielding, and none against cosmic rays. The astronauts carried medication to take in the event of a massive solar storm, but thankfully they never needed it. The primary way that they mitigated radiation exposure was to limit missions to only a few days. The longer the mission, the greater the accumulated dosage. That is the problem with long duration missions, and that is what prompted the person to write the story that you read about long duration missions.
Alwin on October 4, 2009 at 11:39 pm: 16
On the first site I posted is that they mentioned Astronauts “en route” (means along the way)to the Moon and Mars are going to be exposed to this radiation, increasing their risk of getting cancer and other maladies. Finding a good shield is important.
I read it many times reason I told you I’m having problem understanding the whole thing. you overlooked the word “en route” not just long term. I researched both of these two sites. I understood the aim of NASA for future moonlanding and special prep.so definitely they don’t have special shielding to protect themselves while on lunar surfacefor short period.
Astroprof on October 5, 2009 at 8:33 am: 17
Alwin, the en route part is what prompted my posting in the first place, but that was for the Mars trip, not the Moon trip. Recently, I went to a space radiation conference. NASA’s own estimates of the radiation exposure on a trip suggest that outside of Earth’s magnetosphere, which protects us from radiation, the exposure would reach tolerance levels in about 150 days (under one model). That is only six months. It takes 8 months to get to Mars. And, a six month tour of duty on the Moon would put them right to the limit (excluding the secondary cosmic rays, which might put them over). Yes, the trip to the Moon exposes the astronauts to radiation, but not all that much due to the short time of the trip. It is the long trip to Mars or the long stay on the Moon being forecast that is the issue.
The same journalist wrote both of the articles that you looked at. He has also written many others, and he may have been assuming that readers were following him along.
Astroprof’s Page » Space Radiation (Part I) on October 6, 2009 at 10:36 am: 18
[…] weekend, I attended a symposium on space radiation. This is an interesting topic, and I’ve written about it before. But, space radiation is not confined to space. Cosmic rays raining down on Earth also create […]
Alwin on October 22, 2009 at 1:26 pm: 19
Why did the writer mention en route to the moon and mars if he’s only
referring to mars. why did he still need to mention moon? Isn’t it
easy to say “astronauts need additional protection for long term
exposure on moon” if that’s what he’s trying to imply.I assume you knew
NASA Ames Research Center and Space Radiation Analysis Group what their
radiation test results are similar to what NASA posted 2nd site how
about the radiation astros will receive right at their feet from lunar
surface if not properly protected which they added hard to stop, is
their tolerance level is still 150 days so again my initial question is
what type of radiation shielding used by apollo astros esp. apollo 17
stayed for 3 days. even satellites and other spacecraft (far superior
than apollo) that orbit the Earth at several hundred kilometers
altitude through the south atlantic anomaly periodically, exposing them
to several minutes of strong radiation requires extra shielding to deal
with this problem. you said tolerance level is 150 days?knowing space
is continuously being bombarded with different tytpes of deadly
radiation what a significant change they made on symposium anyway don’t
you find it odd NASA is having some inconsistencies? I can hardly
comprehend the logic astroprof how did they come up with the new findings on symposium I wanna see their URL
Astroprof on October 22, 2009 at 4:08 pm: 20
Alwin,
The writer of those web sites may have been a bit sloppy when he mentioned the part about en route to both the Moon and Mars. Or, he may not have understood the difference. If you look at his resume, he is a science reporter, not a scientist, having taken several science courses in college, but not getting a degree in science. The part about both the Moon and Mars may have escaped an editor who read it fast.
As for the feet issue, the astronauts had very minimal radiation protection in their spacesuits in the Apollo missions. Being on the surface of the Moon for a few days was not an issue.
And, as for inconsistencies among NASA web sites, this is an area of current research. Different researchers are using different data and making different assumptions, so they come to different figures. That is the nature of science. Eventually, all of these numbers will agree. In the mean time, you have different web sites posting data developed at different times during the process. Look for the most recent one written by the person with the best credentials for the most up-to-date information.
The 150 day figure is average for exposure outside of Earth’s magnetosphere, excluding solar storms. It is a figure based on quite solar activity and normal galactic cosmic ray exposure. The figure is far shorter in the event of a solar storm or extended period of time in the van Allen belts.
The symposium I went to had speakers presenting their research. It wasn’t online, so I can’t give you a URL for it.
Branden - the gift basket specialist on November 13, 2009 at 4:27 pm: 21
That is why we need very large space ships with large fusion reactors and all the shielding we can get electromagnetic shielding, plastics, store water in between walls, and “safe” houses for the bad storms. As stated the largest cost is getting the ship into space. That is why we need the space elevator. Just think how these projects would help our country.
Alwin on December 25, 2009 at 10:26 am: 22
the writer was sloppy? so far I haven’t seen any feasibility studies done we have the tech.shielding our astros beyond LEO and NASA site confirms John mauldin’s book Interstellar travel p225 said “By comparison solar flares can dliver GEV protons in the same range as cosmic
particles but at such higher intensities increase of energy accounts of energy accounts for
most of the increased radiation danger because Gev protons or their products will prenetrate
several meters of materials
cosmic particles are dangerous come from all sides and require at least 2 meteres of solid shielding
all around living organisms”..and Mr von Braun statements…but according to Harold Loden Apollo mission controller of Apollo 11 Untold Story atlantic productions 2006
“the skin of the crew cabin was very thin and that was all done because of weight savings and
weight was a very critical that it was always has to be considered in anything that you did
if you really took your finger and poke harder you can poke right thru it the outer skin of
the spacecraft it was about the thickness of a two layers of alunimum foil but it’s a kind of
thing that you reasonably cautious that you didn’t jab any pointed object thru ” I don ‘t think NASA was sloppy at all it is a fact based on words of these scientists undergone careful research
Joe on June 11, 2011 at 10:21 pm: 23
Alwin,
The article’s author has said there was no significant shielding. Others you cite have said there was no significant shielding. I (and others) have gotten very close to the Apollo CM, and Smithsonian full-scale LEM mockups. There was no significant shielding. Aluminium, other metals, and some plastic. No purpose-constructed shielding. The radiation encountered was not sufficient to either kill the astronauts outright or give many of them cancer later on. So what is your point, exactly?
D on February 5, 2012 at 11:59 am: 24
I think he is trying to say that the radiation should have killed them. Ifind it troublesome that NASA would have sent the people to the moon without any significant shielding considering that a random solar flare could have apparently caused a fatality. It is almost too good to be true , or miraculous that no one was harmed in any Apollo flights.