[ExI] Fish in space

[John Clark]

On Sat, Mar 18, 2017 at 10:30 AM, BillK <pharos at gmail.com> wrote:

>
>> ​>​
>> I'm more curious about what would happen to vertebrates and other macrobes
>> ​
>>  under lunar or Martian gravity, simulated or actual.
>
>
> ​> ​
> I thought NASA already knew that?
>

​How could NASA know that? They know that long term exposure at zero-g is
harmful to humans because there is a way to test for that and they have
done so, but the only way to know if living for a long time at lunar 1/6 g
or at martian 1/3 g ​is harmful is to send astronauts to the Moon or Mars
and have them life there for a long time. Maybe there is a threshold and if
the g force is greater than that you're OK, or maybe there is a linear
relationship between harm and g force all the way from zero g to 1 g. I
rather doubt that last one is true because most things in the universe are
not linear,


> ​> ​
> There is also cosmic ray damage to worry about as Mars and the Moon
> has no protection.
>

We know more about that. As far as radiation exposure is concerned it's
pretty clear there is a
​
threshold
​
and it's somewhere around
​
100
​
millisieverts
​
(mSv)
​.​
If you're below that figure the radiation has not harmed you, and as likely
as not has probably improved your health more than zero milliseverts
​
would have, but if you're well above that figure then you're in trouble,
and unfortunately if you're in space you soon get above that figure.

On the surface of the Earth you get
​
about 2.4
​
mSv
​
per *year*
​
from normal
​​
background radiation, but
​
on the surface of
​
the Moon
​
you'd get
​
1.2
​
mSv
​
 per *day*,
​ and
on surface of Mars you'd get
​
0.7
​
mSv
​
per *day*
*​*
. And going as fast as possible with chemical rockets a astronaut would
receive 330
​
mSv
​
on the journey before he even set foot on Mars
​,​
​ assuming the ship had as much shielding as the ​Apollo command module.


​ ​
John K Clark
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