Cosmic rays a threat to Mars travel

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The uncertainty of science: New research using rats has found that cosmic rays might damage human brains during a long mission to and from Mars.

Radiation oncologist Charles Limoli and his colleagues at the University of California Irvine bombarded mice and rats with low-doses of ionized oxygen or titanium. These charged particles have similar energies to those of cosmic rays that can pass right through the shielding on spacecraft. The dosage levels that the researchers used were similar to what astronauts would be exposed to during a three-year round-trip mission to Mars, Limoli says.

The researchers looked at the prefrontal cortex, the brain region linked to decision-making, executive function, and long-term memory. They saw significant damage and inflammation in the brains of exposed animals as long as six months after the exposure. The radiation damaged the tiny branches on neurons that help transmit electric signals to the nerve cell body. This led to a loss in learning and memory. The exposed animals performed poorly on behavioral tests that measure intelligence, and they showed higher, constant anxiety levels.

Though the uncertainties here are enormous, the research here has essentially discovered the obvious. The radiation experienced during a long interplanetary voyage is unhealthy, and any interplanetary vessel for carrying humans on such a voyage must be designed with sufficient shielding to protect its passengers. That this research has proven that cosmic rays are a threat also means that providing a ship with a safe room where passengers can take refuge during solar storms is not sufficient. Cosmic rays are random and come at all times in an unpredictable manner. The research suggests that the shielding will have to protect the ship’s entire living quarters.

The payload weight requirements for any rocket that will launch the first interplanetary ships just went up significantly. This means that space stations we have been building (Mir, ISS, and Tiangong) are not even close to sufficient for interplanetary travel, and need significant redesign to make them work. This also means that human interplanetary travel will require cost-efficient heavy lift rockets such as the Falcon Heavy.


  • wayne

    Full paper is at–

    ..and what we’ve known for quite some time:
    “Behavioral and Neurophysiological Changes with Exposure to Ionizing Radiation”

  • wayne

    This is a fascinating topic, all around.

  • Tom Billings

    What I find fascinating is the idea that this paper was published *after* SpaceX announced its intention of an average 115-day flights to and from Mars. Combine that with the use of lava tube caves detected on Mars as shelters for settlements, and the radiation dosage durations drop from 36 months to less than 4 months for settlers and less than 8 months duration for 2-way travelers. Granted, as long as you get propellant from Earth, lifting more propellant for more speed costs money and complication. Getting the propellant from In Situ Resources, like 2016 HO3 would be far cheaper, however. Speed is only one way to cut dosages.

    Another is to cut dosages using an extension of the safer squadrons that Musk spoke of for going to Mars, instead of singleton missions NASA speaks about. Basically, using mixed squadrons of cargo and passenger vessels, the squadron formation can be arranged so that the cargo ships are on the outside of the formation and the passenger ships are on the inside of the formation. Then, you can use plasma magnets transmitting 10s of kilometers from one cargo ship to another around the exterior of the formation to generate magnetic fields hundreds of kilometers in diameter, and make those strong enough to bend these heavy charged particles away from the hulls of the passenger ships.

    While there *are* more massive ways to do the job, why do it the hard and expensive way?

  • Edward

    The advantage of a Mars Cycler ( ) is that it remains constantly in transit and needs little propellant for its own trajectory. The majority of the propellant would be used by the smaller, lighter, less shielded “dinghy” ships that transfer people to and from the cycler.

    A cycler can be large, heavy, and have all the shielding/magnetic field that it needs, because it is not accelerated or decelerated at each end, only the dinghy is accelerated. It could also have a spinning section to provide artificial gravity.

    Repairs and maintenance would have to be done (literally) on the fly, but by the time we are that space savvy, that should not be a big problem.

  • wayne

    Tom Billings/Brendan–
    -Interesting stuff! I was wondering about the feasibility of using magnetic fields of some sort.

    There is also a body of research regarding chemical agents & drugs that provide some measure of protection, to some types/doses of radiation, in some situations. But that’s in no way ready-for-primetime.

    (It is sorta “interesting” the number of “Space Is Dangerous” articles of late. I’m old enough to remember that Space-Was-Always-Dangerous.)

    I still maintain we should take control of the Moon, first.

  • m d mill

    SpaceX projects an 80 day one way trip time, which reduces the exposure significantly…or
    are the cosmic rays at the surface of mars just as bad, as on the trip?

  • wayne

    m d mill–
    That came up in a different thread if I recall correctly, but don’t have it handy.

  • wayne

    Ref– Radiation exposure on Mars.
    JPL has recent research on that & there is a “cosmic ray exposure map” that has been generated, but I don’t have a good link handy.

  • wodun

    The payload weight requirements for any rocket that will launch the first interplanetary ships just went up significantly.

    Maybe, and it wouldn’t hurt, but even with them, there will be in orbit assembly.

  • steve mackelprang

    why is the exposure level significantly higher than for those in orbit?,,, and do you think this could be a shill for NASA making an excuse why we won’t try to go there sooner rather than later?…..

  • Tom Billings

    Steve asked:

    “why is the exposure level significantly higher than for those in orbit?,,, and do you think this could be a shill for NASA making an excuse why we won’t try to go there sooner rather than later?…..”

    The heavy ions have been a growing concern of the Health Physics community for at least 2 decades. They are a decided minority of GCR activity, and detectors that would sort them out are somewhat specialized because their higher mass means greater momentum and larger curved tracks in detectors, and thus more expensive detectors. Also, more expense for the greater mass sent into orbit. Still, they have enormous mass compared to the singleton protons making up most GCR, and their break up into secondary radiation is extremely unhealthy on a per ion basis.

    Getting some data, finally, is a good thing for our team’s concepts of using the lava tube caves on the Moon and Mars as shelter for settlers. 50 meters of basalt deals with any radiation this side of neutrinos just fine. As I said above though, a hundred kilometer diameter magnetic field should bend them away from passenger ships with good drops in REM numbers without consuming too much power for the plasma magnets.

  • Timothy Weaver

    The study is inherently flawed. The dosage rates were orders of magnitude higher than what a manned crew will ever face.

    Yes, I know it’s Zubrin who is biased on the subject, but there is one source I believe address some of the issues that Zubrin has.

    The study assumes the LNT model (linear no threshold) which assumes that radiation poisoning is cumulative and assumes 30 cG of radiation over a course of minutes is no different from 30 cG over the duration of 2 1/2 years. Studies call this into doubt.

  • pzatchok

    The guy who came up with this drug idea was wondering why stomach acid didn’t cause stomach cancers far more than it does.
    This chemical seems to correct DNA damage.

    It does not reduce or remove existing tumors but does stop them from forming due to hard radiation.

    It was originally named EX-RAD as an homage to the game Wastelands drug RAD X.

  • Localfluff

    @Tom Billings Great idea about using a fleet of ships for shielding! I don’t think that the potential advantages of having a formation of crewed space ships has been seriously considered since Wernher von Braun in the 1940s (and maybe Elon Musk today). Opportunity for original ideas there. SpaceX should offer a couple of scholarship for researching it. Today they don’t want anything floating near the space station, but there’s nothing to make a spaceship turn and crash. They could separate before doing course corrections.

    @Edwards I love the space cycle idea (thank you Dr. Aldrin!) But that’s probably not how it will begin, it requires a big upfront investment which is (financially) risky to make before having gone to Mars to figure out how it should be done in detail. The cycler could be reused for 100 years and be steadily upgraded. With Solar electric propulsion, new kinds of cycler orbits are possible. Quite some course correction is possible even for a heavy spaceship when SEP tugs for 26 months. The transfer vehicle to and from the cycler could be as small as Orion.

    For safety, a fuel tank with an engine (and maybe some life support resources like air and water) could follow the habitable large cycler a few days behind. If a crewed (Orion type with a couple of weeks of life support) launch fails to reach the cycler, the tanker could pick them up and bring them either to the cycler or back to Earth. It would only be used and replaced once it is needed. It could maybe be refueled at Mars or Earth and be reused, although it shouldn’t happen often enough to make that economical.

    The cycler concept does not require launchers (much) heavier than Saturn V. A high delta-v launch is required, but something substantially less than an ITS rocket is sufficient. The problem is to launch something like that from Mars. Maybe the crew would have to launch buckled up in a small crowded Soyuz like spacecraft and less than a day later dock with an “upper stage” in Mars orbit before going for the cycler.

  • wayne

    Mars: First Radiation Measurements from Planet’s Surface

    references this paper-
    “Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover”
    (which unfortunately, is behind a pay-wall.)

  • Localfluff

    A three(?) year mission to Mars? What kind of trajectory plan did they use? There are 26 months between conjunctions. The first human trip to Mars should be done in 2033, returning in 2035, both those conjunctions offer 6 months Hohmann transfers, which is the delta-v optimal way to go (in the ellipse that is tangent to both Earth’ and Mars’ orbits in an elegant conic math way). This happens about every 7th conjunction. Other times it takes up to 9 months. Total mission time is always 26 months anyway, it is only the stay on Mars that varies between 8 and 15 months.

    What’s good with this experiment is that they use heavy ions. I assume that it does mimics cosmic rays in interplanetary space well. Oxygen ions representing O and similarly massive C which are the by far mot common astronomical metals. And titanium to represent heavy ions. Sounds quite right. It is unknown whether one can extrapolate from electron, proton and alpha particle rays up to very high speed heavy ions. But this topic is so very complicated that it is impossible to draw theoretical conclusion by extrapolation. One learns about this by doing and measuring what happens.

    A realistic experiment would look like this:

    First of all, use animals with large heads, maybe pigs, The thick cranium gives protection, and the inner part of the brain is more protected than the outer parts. On the other hand, hard rays might cause more damages in a large brain because of the secondary radiation spraying through a larger volume. And the experiment should be performed during 26 months literally.

    During 6 months (transfer time in open space)
    Every day:

    8 hours behind half a meter of liquid water shield, since the astronauts will sleep in side the radiation bunker which anyway is necessary to handle Solar eruptions. A cylinder that keeps the mission’s water storage and other shielding supplies.

    4 randomly scheduled sessions each 1 hour long inside that same bunker, because some waken work and relax will be done there.

    10 hours a day next to the bunker, giving one meter water shield from one side. The bunker should be located in the center of the spaceship and most of the time will be spent next to it where the control rooms, the gym, the dining room are located.

    2 hours a day inside shielding similar to that of Bigalow’s modules.

    During 14 months (on Mars)
    Every day:

    All of the time with only half the radiation beam turned on to simulate the coverage of Mars itself.

    8+4 hours behind a five meter bunker of liquid water while sleeping and working/relaxing in a bunker.

    12 hours behind half a meter of water shield which is the roof of the Mars surface base.

    Some of the days, maybe every third, 8 hours with shielding simulating only Mars’ atmosphere and the space suit, to represent excursions.

    During 6 months (transfer to Earth)
    Repeat the first 6 months.

    The space hypochondriacs claim that the crew goes mad from radiation, go on strike and mutiny because “they can’t see Earth”, become cripples because of weightlessness, poisoned by Martian dust and infected by alien life. I’d like to see some evidence for those sci fi doomsday stories which the anti civilization crowd mongers. The true risk is that the blow up on the launch pad or in the atmosphere or are killed by a vacuum leak. Those are the only ways 14 astronauts have died to date. No higher cancer rate has been detected among the 500+ astronauts.

  • Localfluff

    The time intervals are important because the immune system might work differently when almost entirely free from new radiation damages popping up and alarming it. Maybe it is relaxed and less efficient, or maybe it focuses more efficiently on the existent damages. We can’t sit here on Earth and figure it out theoretically. Realistic experiments must be performed, and the trip has to be made in order to find out. Learning by doing. Maybe every robotic mission to Mars should carry equipment to characterize the radiation exposure in detail from different aspects. Maybe even carrying a lab rat.

  • Localfluff

    When outside of the bunker in the spaceship, and even during EVAs out in open space (if those were common enough to motivate it, maybe rather when working at a milligravity environment like an asteroid or Phobos/Deimos), a crew member could put a half a meter thick 2×2 meter water filled radiation shield floating between herself and the outer part of the spaceship, being protected by the bunker (or Phobos) on the other side. Eliminating almost all radiation exposure. Micro- and milligravity makes it manageable to handle such shields.

    Radiation can be taken care of by simple clever design measures, without much extra mass needed. They should have tons of water anyway, for life support redundancy. Even used water which is not cleaned, is as useful for shielding purposes.

    No need to cover the entire spaceship with a radiation shield, beyond what Bigelow does.

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