
Cosmic radiation exposure and persistent cognitive dysfunction - pwg
https://www.nature.com/articles/srep34774?error=cookies_not_supported&code=01085646-d8e1-4d84-b74f-893382c8aeb5
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wolf550e
Robert Zubrin, founder of the Mars Society and author of "The Case for Mars"
and "Mars Direct", has a Ph.D. in Nuclear Engineering. In his review of a
different article on the same topic, he writes [1]:

"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...](http://www.marssociety.org/r-zubrin-radiation-hucksters-strike-
again/)

~~~
Analemma_
> 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.

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.

~~~
njarboe
Like most things where one cannot do repeated, controlled experiments, no one
really knows where the truth lies apart from some vague notions. What is used
as the "truth" will be a political decision.

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.

------
WhatIsDukkha
It's a persistent and PERNICIOUS myth that mass is an effective shield for
cosmic radiation.

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...](https://engineering.dartmouth.edu/~d76205x/research/Shielding/)

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...](https://home.cern/about/updates/2015/08/superconducting-shield-
astronauts)

It's unfortunate that propulsion is where everyone seems to focus their
attention when the shielding is so much more important to human settlement.

~~~
mikeytown2
Getting there faster is one of the best ways to reduce the amount of radiation
absorbed. Nuclear power is needed for faster rockets and powerful magnets;
safe and reliable access to LEO is the first step to getting reactors in
space.

~~~
WhatIsDukkha
"There" isn't safe either.

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.

------
narrator
The future is already here. It's just not evenly distributed:

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](https://www.ncbi.nlm.nih.gov/pubmed/19914272)

~~~
fsloth
What the... where did this idea of injecting hydrolyzed fullerenes come from?
Fantastic that it works, but coming up with the idea in the first place sounds
completely bonkers (in a good way).

~~~
narrator
They did a study a while back to see if fullerenes were toxic in mice and they
doubled the mice life span. Lots of research outside of the U.S after that.
[http://www.sciencedirect.com/science/article/pii/S0142961212...](http://www.sciencedirect.com/science/article/pii/S0142961212003237)

Nobody cares about this kind of research in the U.S because it's a synthetic
substance that's not patentable.

~~~
fsloth
That's amazing! I had no idea of this result.

------
njarboe
Hopefully this problem with radiation exposure when traveling to Mars can
change the way people evaluate nuclear propulsion. One could offset a lot of
radiation exposure from a nuclear power plant by getting to Mars in weeks
instead of months. People traveling to Mars are not going to have a "safety
first" philosophy that is dominant in the current US culture and would be able
to understand and accept the trade-off.

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.

~~~
nradov
The trouble with nuclear propulsion is not the safety of the astronauts
travelling to Mars, but rather the safety of people on Earth. If you launch a
large reactor from Earth then a catastrophic launch vehicle failure could
cause a radiological incident. Space agencies have launched RTGs before, but
those are much smaller and more durable than the real reactors that would be
needed to drive a useful propulsion system.

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.

~~~
njarboe
If one gives this problem a bit of thought I think it is really political
problem, not a safety issue. First, nuclear fuel is just pieces of metal or
ceramic. If it blows up on launch these won't explode in a nuclear chain
reaction like what happens in a nuclear weapon. They will just scatter and
fall into the sea. They have not been activated yet so they have very low
radioactivity at that point. Brand new nuclear fuel is basically harmless. The
worry with nueclear fuel is after it is used it becomes very radioactive.

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.

------
QAPereo
Radiation shielding is either heavy, or difficult. Heavy is too expensive, and
the quietly cold calculus of many seems to have been, “well these early
explorers won’t live as long as us.” This however injects the possibility of
mission failure, not just a bad end for early Mars colonists on slow boats
from Earth.

------
WalterBright
One possibility is to find an asteroid that moves between earth and mars
orbits, and hitch a ride on it for the bulk of the journey. The asteroid's
mass can serve as shielding, and also as a source of raw materials.

~~~
pocketstar
Electromagnetic shielding with superconductors is probably better than a mass
solution.

~~~
jayd16
Hmm. How hard is it to get superconduction in space? Its not like it has to be
room temperature.

~~~
heeen2
Objects in space heater up significantly on the sun facing side though.

------
nnfy
I wonder how many of those with the qualifications to be selected for a trip
to mars would make such a sacrifice.

If you knew you weren't coming back, would you still be willing to be the
first person on mars?

~~~
T-A
Immediate response: no way, why would I want to do that? Second thought: maybe
if I were terminally ill and had nothing special left to do on Earth. Third
thought: ... but given my usual luck, in that case a cure for my condition
would be announced as soon as I had passed the point of no return. :P

~~~
jayd16
Theoretically they could send the cure but they announce cancer cures every
other week.

