Researchers calculate radiation exposure associated with journey to Mars

May 30, 2013
The RAD instrument measures radiation dose using silicon detector and plastic scintillator technology. The latter has a composition somewhat similar to tissue and is more sensitive to neutrons than are the silicon detectors. This illustration of RAD shows the silicon detectors (A, B & C) that measure charged particles and the plastic detectors (D, E & F) that measure both charged and neutral particles. Credit: Hassler et al., 2012. Space Science Reviews, 170, 503.

On November 26, 2011, the Mars Science Laboratory began a 253-day, 560-million-kilometer journey to deliver the Curiosity rover to the Red Planet. En route, the Southwest Research Institute-led Radiation Assessment Detector (RAD) made detailed measurements of the energetic particle radiation environment inside the spacecraft, providing important insights for future human missions to Mars.

"In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Dr. Cary Zeitlin, a principal scientist in SwRI's Space Science and Engineering Division and lead author of Measurements of Energetic in Transit to Mars on the Mars Science Laboratory, scheduled for publication in the journal Science on May 31.

"Understanding the inside a spacecraft carrying humans to Mars or other deep space destinations is critical for planning future crewed missions," Zeitlin said. "Based on RAD measurements, unless propulsion systems advance rapidly, a large share of mission will be during outbound and return travel, when the spacecraft and its inhabitants will be exposed to the radiation environment in interplanetary space, shielded only by the spacecraft itself."

Two forms of radiation pose to astronauts in deep space: a chronic low dose of (GCRs) and the possibility of short-term exposures to the (SEPs) associated with and coronal mass ejections. is measured in units of Sievert (Sv) or milliSievert (1/1000 Sv). Long-term population studies have shown that exposure to radiation increases a person's lifetime cancer risk; exposure to a dose of 1 Sv is associated with a 5 percent increase in fatal .

GCRs tend to be highly energetic, highly penetrating particles that are not stopped by the modest shielding provided by a typical spacecraft. These high-energy particles include a small percentage of so-called heavy ions, which are atomic nuclei without their usual complement of electrons. Heavy ions are known to cause more biological damage than other types of particles.

Energetic protons constitute about 85 percent of the primary galactic cosmic ray flux and easily traverse even the most shielded paths (reds) inside the MSL spacecraft. Heavy ions tend to break up into lighter ions in thick shielding, but can survive traversal of thin shielding (blues) intact.

The solar particles of concern for astronaut safety are typically protons with kinetic energies up to a few hundred MeV (one MeV is a million electron volts). Solar events typically produce very large fluxes of these particles, as well as helium and heavier ions, but rarely produce higher-energy fluxes similar to GCRs. The comparatively low energy of typical SEPs means that spacecraft shielding is much more effective against SEPs than GCRs.

"A vehicle carrying humans into deep space would likely have a 'storm shelter' to protect against solar particles. But the GCRs are harder to stop and, even an aluminum hull a foot thick wouldn't change the dose very much," said Zeitlin.

"The RAD data show an average GCR dose equivalent rate of 1.8 milliSieverts per day in cruise. The total during just the transit phases of a Mars mission would be approximately .66 Sv for a round trip with current propulsion systems," said Zeitlin. Time spent on the surface of Mars might add considerably to the total dose equivalent, depending on shielding conditions and the duration of the stay. Exposure values that ensure crews will not exceed the various space agencies standards are less than 1 Sv.

"Scientists need to validate theories and models with actual measurements, which RAD is now providing. These measurements will be used to better understand how radiation travels through deep space and how it is affected and changed by the spacecraft structure itself," says Donald M. Hassler, a program director at Southwest Research Institute and principal investigator of the RAD investigation. "The spacecraft protects somewhat against lower , but others can propagate through the structure unchanged or break down into secondary particles."

Only about 5 percent of the dose was associated with solar particles, both because it was a relatively quiet period in the solar cycle and due to shielding provided by the spacecraft. Crew exposures during a human mission back and forth to Mars would depend on the habitat shielding and the unpredictable nature of large SEP events. Even so, the results are representative of a trip to Mars under conditions of low to moderate solar activity.

"This issue will have to be addressed, one way or another, before humans can go into deep space for months or years at a time," said Zeitlin.

SwRI, together with Christian Albrechts University in Kiel, Germany, built RAD with funding from the NASA Human Exploration and Operations Mission Directorate and Germany's national aerospace research center, Deutsches Zentrum für Luft- und Raumfahrt.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, Calif., manages the Laboratory Project. The NASA Science Mission Directorate, at NASA Headquarters in Washington, manages the Mars Exploration Program.

Explore further: Red moon at night; stargazer's delight

More information: "Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory," by C. Zeitlin et al. Science, 2013.

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User comments : 18

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1.4 / 5 (9) May 30, 2013
Bootstrap this module to the international space station. Add a nuclear reactor and ion engines and send the ISS to orbit mars.
1 / 5 (8) May 30, 2013
The solution to radiation isnt heavy is med8cine the mediates pand prevents dna damage due to radiation, possibly accelerating the correction process of damahed dna as well
5 / 5 (3) May 30, 2013
Buzz Aldrin described a permanent Earth-Mars orbiter that astronauts would catch when it neared Earth and jump off close to Mars. Constructing such a module in space with ice from comets melted to water and put into a shield around a round module as a shield could be feasible.

I believe 15 feet of ice are needed to stop most GCR's and SEP's. Ice already in space would be the cheapest to get perhaps. Bernoulli spheres by the thousands could be built in space and provided with modularized components built on Earth, the Moon or maybe asteroids. I would think the mass of solar system planets ought not be changed much.
1.8 / 5 (5) May 30, 2013
and prevents dna damage due to radiation

Medicine doesn't prevent damage. Medicine is chemicals. Radiation damage is a physics. (Basically high energy particles shooting through your DNA like blasts from a shotgun)

Bootstrap this module to the international space station. Add a nuclear reactor and ion engines and send the ISS to orbit mars.

You're not too much into math (or reality for that matter), are you?
1 / 5 (5) May 30, 2013
"Medicine doesn't prevent damage. Medicine is chemicals."

Well here's a chemical that protects against lethal doses of radiation. Search for:
"Caffeine protects mice against whole-body lethal dose of gamma-irradiation."
5 / 5 (1) May 30, 2013
antialias: In theory, DNA damage could be repaired chemically. In practice, nothing we possess today can do that effectively. If we could, it would be useful for more than healing radiation damage. Much more.

Solon: Caffeine is an addictive, psychoactive drug with many harmful side-effects. Taking it in high doses over an extended period is contraindicated, not to mention seriously dangerous.

Further, gamma rays are photons. Cosmic rays are particles with much higher mass, energy content and potential to wreak DNA damage than gamma rays.

Your 'radiation is radiation' argument reminds me of the old 'parts is parts' silliness that predated the internet. You can't replace a radiator with a spark plug; and a solution for gamma rays is not a solution for cosmic rays.

1.5 / 5 (8) May 30, 2013
Medicine can improve the body's ability to withstand radiation. The body already has mechanisms to repair damage and medicine can enhance these abilities. We are constantly exposed to background radiation, without repairing mechanisms...
How does it knows what to do? I don't know, but can only accommodate a certain level.
And the fact is that none of your cells use the whole formula in your DNA. They each only use a small subset. As long as those are not damaged you should be fine. An embryo might be in a more precarious position as could be your gametes.
Going to Mars that way, it may be better to just build the DNA there rather than taking it along and live underground. A few hundred mistakes are made during the natural process of making a complete human code. Starting with none might improve someone's odds of not getting cancer. Shortly we may be able to cure most of it. A third or more of cancers are caused by viruses. If we screen, they may have less cancer than we do.
2 / 5 (7) May 30, 2013
I find it irrational to cry over a 1Sv total dose which raises the lifetime risk of death from cancer by 5%, while the "lifetime risk" from techical malfunctions during the trip is more like 95%.
2 / 5 (8) May 30, 2013
and prevents dna damage due to radiation

Medicine doesn't prevent damage. Medicine is chemicals. Radiation damage is a physics. (Basically high energy particles shooting through your DNA like blasts from a shotgun)

Bootstrap this module to the international space station. Add a nuclear reactor and ion engines and send the ISS to orbit mars.

You're not too much into math (or reality for that matter), are you?

Be nice and explain how the torque would twist the IIS apart.
1.9 / 5 (7) May 31, 2013
The Earth's magnetic field protects us down here on the surface from most solar radiation; could we not design a mini-magnetic field around a spacecraft to do the same? I believe we could, and that this will be the ultimate solution to protecting astronauts and passengers from interplanetary radiation exposure. It is just a matter of engineering.
not rated yet May 31, 2013
Ironic. I thought the SEP (solar wind, CME) problem was the dominant with the GCR the minor.

Unfortunately it is very difficult to do something about CRs without adding prohibitive mass shells. Something equivalent to a dm of regolith is needed, which means hauling a lot of water (easiest to place around the crew compartment as flexible bags) that has to be recycled if used.

@JM: "Bootstrap this module to the international space station."

Gobbledygook. Showing that you don't understand language ("bootstrap"), the article ("this module") or ISS.
not rated yet May 31, 2013
@NN, qwrede: 5 % cancer death is not "fine" or "irrational", it is a known and accepted ethical problem.

And we still don't know if repair mechanisms can be overwhelmed (likely). DNA isn't "a formula", the genome is a (small, in humans) part of it. Human genome is ~ 5 % genes by mass (IIRC), but that is already included in the cancer risk; and humans aren't the only species projected to go with, edible food plants is also a concern.

@RTG: "The Earth's magnetic field protects us down here on the surface from most solar radiation".

No, no, no, not that piece of folk physics again! It is, to the best of my knowledge, the atmosphere that protects us from solar wind/CMEs, and the magnetic field that protects the atmosphere.

Also, the main problem here is GCR. Indeed here instead the atmosphere only blocks ~10 % of it, the rest has been blocked by the vast solar magnetic field. There is no way that we can replicate what the Sun does on a scale of ~ 100 au on a scale of meters.
2.3 / 5 (6) May 31, 2013
The Earth's magnetic field protects us down here on the surface from most solar radiation; could we not design a mini-magnetic field around a spacecraft to do the same?


No, no, no, not that piece of folk physics again! It is, to the best of my knowledge, the atmosphere that protects us from solar wind/CMEs

That's partly correct. As demonstrated by exposure experiments in low Earth orbit, the magnetic field does provide 'some' protection. The atmosphere gives a much higher level of protection.

The RAD instrument mentioned above is still operating on Curiosity on the surface now, and it has shown a pleasant surprise. Even though Mars doesn't have a magnetic field, even the thin Martian atmosphere provides about the same level of protection as the Earth's magnetic field in low Earth orbit. So it looks like explorers on Mars should be as safe as astronauts in the ISS.

Torbjorn: You are correct that solar radiation is actually the biggest worry.

1.8 / 5 (5) May 31, 2013
RAD didn't measure much solar ratiation, but that's just because it didn't get hit by a CME. In calm conditions, the cosmic rays are the biggest problem, but it would be insane to plan a mission not prepared for a CME hit.

A single CME blast can change the problem from lifetime cancer risk to short term death. One of the things that will be hard to mitigate will be potential damage to the spacecraft itself. We do the best we can to protect satellites from solar radiation, but CME's still take them down from time to time. You might be able to build an effective storm shelter for the astronauts, but enshielding every part of a spacecraft is a fools errand.

I believe SOHO is collecting good data on CME's but we probably need to test various scenarios to protect astronauts before we ask anyone to take the risk. It is only ethical to ask them to take the risk if we know what the risk will be.
2.3 / 5 (3) May 31, 2013

i upvoted you --

and a few other people -- looks like "open" has be down voting legit responses again.

-- Earths magnetic field indeed protects us humans on the ground -- but it is very very weak -- in fact a refrigerator magnet is like 100x stronger. Why not have a few huge magnets onboard -- or make the hull magnetic ??? is that feasible -- would it change the situation.

fyi -- the ISS operates inside the magnetosphere thereby reducing radiation exposure -- however i believe they do pass through a couple radiation belts.
2.3 / 5 (6) May 31, 2013
or make the hull magnetic ??? is that feasible -- would it change the situation

Not really. It's a complicated subject, and way too much to really answer your question here in detail. In summary, not really. There's a bunch of different types of radiation.


If you followed the link, you see that neutron radiation is one of the worst, since it easily penetrates thick layers of shielding, it's not magnetic so your magnet idea won't work, and it creates highly dangerous secondary particles when it hits something.

You could spend days just getting accquainted with this topic, and it is extremely rewarding in terms of how many different fields it touches on. I highly reccommend that you do a few web journeys on this topic and enjoy all there is to learn about it. Most people don't have an F'n clue about it, and it's alway fun to know stuff like that. :)
2.5 / 5 (13) Jun 04, 2013
Maybe the Bush II administration had the right idea, after all? Get us back to the Moon first, using that experience as a starting point for manned missions to Mars? With a base, even a small, crude shelter, on the Moon to operate out of, the Moon could be integrated into Mars missions. And maybe it would need to be, if there's anything to Gary Gibson's idea that materials available in space could be exploited for shielding purposes.

( http://ares.jsc.n...008.HTML )

More importantly, extended stays on the Moon would give us experience at dealing with the radiation hazards of space, as well as serving as a driver for developing the technologies required. Mars missions might be assembled and launched from lunar orbit.

Most pertinent of all: Continue development of NASA's Fusion Driven Rocket. Cutting the trip-time to 30 days would not only greatly reduce radiation exposure, it would improve the feasibility of the mission overall.
1 / 5 (6) Jun 04, 2013
With a base, even a small, crude shelter, on the Moon to operate out of, the Moon could be integrated into Mars missions
And why would you think that expending the energy and resources to enter and leave another gravity well, and having to deal with regolith, and spending additional time exposed to radiation, would provide any benefit whatsoever??
Mars missions might be assembled and launched from lunar orbit
And why would you think that there would be any advantage in assembling components necessarily fabricated on earth, in orbit around the moon as opposed to much closer to home where support and natural radiation shielding exist??

Are you just postulating to hear yourself postulate?

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