Cosmic radiation exposure and persistent cognitive dysfunction
nature.com
nature.com
"On a Mars mission, astronauts would receive a dose of 1 rad per month during the 6 month outbound and return transfers, and about 0.5 rad per month during 18 months on Mars, for a total of 21 Rads. (1 Gray = 100 rads)".
In the paper, the animals were irradiated "at dose rates between 0.05 and 0.25 Gy/min".
Zubrin writes that the huge difference in dose rates (0.01 Gy per 60 * 24 * 30 = 43200 minutes vs. 0.05 Gy per minute) makes such studies completely useless because at the lower dose rate the body can self repair and at the higher dose rate it can't.
Quoting him again:
"For example, if an individual were to drink one shot of vodka per second for 100 seconds, he would die. But if the same person drank one shot of vodka a month for 100 months, he would experience no ill effects at all. This is about the same ratio of dose rates as... ".
1 - http://www.marssociety.org/r-zubrin-radiation-hucksters-stri...
I think it's worth pointing out his views, but I also think people should know Zubrin is going against the grain here. Most researchers, as well as nuclear regulatory agencies, use the Linear No-Threshold model for connecting radiation exposure and risk. This is exactly what it sounds like: the model assumes that risk accumulates as a linear function of dose. Whether the LNT is true at small doses is a matter of considerable debate (it's hard to study in humans because the purported effect size is small and it's hard to do such a study ethically), but Zubrin should not talk as though the matter is settled.
I think in the case of going to Mars, building a ship that can get there, land, and come back is the hard part. Finding out how bad or not the radiation will be on people will be found out by the people who end up going. Inform them the best we can, so they can make their own decision, monitor their radiation doses, so we can learn more about long-length, high-level radiation exposure in humans, and let people decide if they want to risk it. As long as the radiation dose is not so high to make them sick in the first few years and ruin the mission, let people take the risk if they want to. I don't see why going to another planet should have to be less risky than taking a wagon on the Oregon Trail, to allow people to try it. A safety first philosophy will not get humans living off of Earth.
To quote this page -
"""Manned missions to planets such as Mars require extended missions that will expose astronauts to harmful radiation in the form of energetic particles from solar and galatic sources. Traditional methods for protecting spacecraft and occupants from these forms of radiation involve some configuration of a massive material shield to absorb the energy of incoming particles. For the high energy galactic cosmic rays (GCRs) that astronauts will be exposed to, these so-called passive shields are too massive to be practical and will likely produce showers of secondary radiation that could be more harmful than the GCRs themselves."""
https://engineering.dartmouth.edu/~d76205x/research/Shieldin...
It's concerning that so many people that are interested in space exploration are unaware of this.
The primary enabler for actual space exploration is most likely superconducting magnetic fields but this is an unsolved problem, though the European Space Agency did complete some work in 2016 towards it by reusing technology from CERN
https://home.cern/about/updates/2015/08/superconducting-shie...
It's unfortunate that propulsion is where everyone seems to focus their attention when the shielding is so much more important to human settlement.
Mars has no magnetosphere.
Estimates are that people exploring Mars will have to spend 20 hours a day under 10+ meters of rock to protect from solar radiation alone. I don't believe this protects from the GCR.
Much of that time in the cave will be spent on the conical treadmill to make up for the .3g low gravity. The impact on human biology over longer term is unknown.
I think for actual work, living and use space is almost uninhabitable without the active shielding problem being solved. Risking cancer for a select few isn't the issue, its making space a place humans can live.
However with active shielding, approaches like L5 colonies and in deep space become viable. They could be made far more human habitable then any of the planets or moons.
The polyhydroxylated fullerene derivative C60(OH)24 protects mice from ionizing-radiation-induced immune and mitochondrial dysfunction. : https://www.ncbi.nlm.nih.gov/pubmed/19914272
Nobody cares about this kind of research in the U.S because it's a synthetic substance that's not patentable.
Maybe someone will start working on nuclear rockets again. I think a large number quality people would come out of the woodwork to be able to be part of such a project.
Maybe someday we'll be able to mine fissionable materials from asteroids and construct nuclear rockets in deep space with no risk to Earth. But that technology is firmly in the realm of science fiction today.
And, even if the fuel was a problem, reactors are going to be designed to be refueled. One could send up the reactor and fuel on different launches with the fuel sent in packaging the would survive any explosion (although the fuel itself already would)
RTGs are actually more of a radiological hazard, as the fuel for those are necessarily very radioactive.
In the end I do agree with your position that the safety of the people on Earth are likely to be a problem because safety is a feeling, not some well defined risk factor. Without some large generational educational project (or maybe change the name?), most people will think that nuclear power can never be safe, even when driving their gasoline powered car on a two lane road to work.
Mars's moon Deimos might be the best candidate -- delta-v between Deimos and Earth-Moon L4/L5 is about 3800m/s [1], and there's no need to move the bulk of your shielding lower into the gravity well on either end.
In this scenario, you'd want to use something like an Aldrin Cycler [2] to provide radiation shielded transport between Earth and Mars. This isn't exactly the same thing as hitching a ride on an asteroid, but it's the same basic principle.
You'd definitely need nuclear electric or maybe solar electric propulsion to make such a scheme work, though.
[1] https://en.wikipedia.org/wiki/Delta-v#Delta-vs_around_the_So...
In fact, a large, heavy one can be created or moved into such an orbit, then Mars/Earth journeys only need small, light ships to dock with it at each end.
If you knew you weren't coming back, would you still be willing to be the first person on mars?
I could keep myself occupied and entertained the same way I do now, with some personal computing devices and game consoles, and I should be able to steer my craft and make direct observations while maintaining communications with Earth as long as the distance allows.
It would be a privilege rather than a sacrifice, and it will help humans back here in understanding the cosmos better than unmanned probes would.