So, how much MORE is it at the space station? Or, even outside the van
Allen Belts?
I believe the details within and where within the Van Allen
belts (I think they discovered something new about them
recently, by the way) have no bright line definitions. It's
constantly changing and some places are better than others,
given that. The trailing dark-side edge pulses in bursts as
the lines develop and then cross each other and release
energy. I'm not sure there is any specific place to be
positioned with security in mind. The Van Allen belts
themselves pose their own radiation hazards.
I have very little real knowledge about current details. I
remember the Forbush effect (I think first noticed as a
reduction in cosmic ray events due to coronal mass ejections
from the sun and later, I think, applied to the effects of
the solar wind on arriving cosmic rays -- which cuts them in
about half, memory serving, but depending on where in the
solar cycle the sun is at.) I'm not sure how much effect the
Van Allen belts have on cosmic rays, though the atmosphere
certainly has a huge impact as they arrive. But probably the
radius of gyration deflects most of them.
I think galactic cosmic rays and solar proton events from the
sun are the biggest concerns.
But I generally hear it's horrible -- not something to do for
extended times. One of the guys I worked with for years had
spend years himself as part of a team designing satellite
systems. He talked about how they start out neutral, but are
impacted by energetic particles, which split charges with
some going to the satellite and the rest going to ions that
are dislodged for a distance then re-attracted back but
somewhere you don't want them to stick as "brown crud" that
accumulates in bad places. Charge and heat accumulation are
serious problems, I gathered. As far as astronauts go, the
ISS (I read) experiences 150mSv/yr for astronauts inside. But
the Skylab astronauts experienced over 500mSv/yr rates. The
new Mars rover is taking data there, not sure what the
results are (or if any are published yet.)
From:
http://www.nap.edu/openbook.php?record_id=1224&page=384
You can see that the global average background radiation is
on the order of 1mSv/yr. Elsewhere, I read figures of
1.5mSv/yr and slightly higher. And it depends on where you
are, of course. But that gives an idea for comparison
A Mars mission is estimated to result in a 1 Sv dose, which
seems consistent with the Skylab rate.
There are no known effective measures. Even lead is mostly
vaccuum. Liquid hydrogen isn't bad, nor water -- both are
needed anyway. But best would be a nice big asteroid with the
astronauts nicely in the center of it. Active shielding
(magnetics and electrostatics mixed) may help, but no one has
fielded any serious testing of the idea.
In interstellar space the problem is even more acute.
By the way, I just found this link:
http://www.ncbi.nlm.nih.gov/pubmed/2818404
Which is germane to my point about measuring radiation in an
airplane at 37,000' altitude.
"The dose equivalent to air carrier crewmembers from galactic
cosmic radiation was estimated for each of 32 nonstop flights
on a variety of routes to and from, or within, the contiguous
United States. Flying times were from 0.4 to 13 hours. The
annual dose equivalents received on the flights ranged from
0.2 to 9.1 mSv (20 to 910 mrem), or 0.4 to 18% of the
recommended annual limit for occupational exposure of an
adult."
This is entirely consistent with the measurements I took on
that flight I mentioned. I found that in a 2hr flight you
receive about 1 year's ground level dose. My estimate,
because I didn't calibrate things beforehand, is approximate.
I would say that you get about 0.5mSv to 1mSv per hour of
flight at altitude, given my readings.
In short, every two hours of altitude flying gives one year's
sea level dosage. Nice.
The really FUN thing to do is to take your geiger counter and
show it to a few passengers BEFORE boarding and then show it
to them AFTER reaching altitude. They will FREAK! The level
is about 4000 times higher. And if you teach them about the
switch that selects the range before they board, they will
see that you switch ranges a few times when at altitude and
it scares them. hehe. It's a "must do" when you get a chance.
Jon
