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Re: (TFT) Mars - Vasimr & Radiation.
Hey Rick,
Sorry for the late reply!
Here's the data I was looking at:
Radiation doses en route:
http://cdsweb.cern.ch/record/957495/files/12433-usa-mewaldt-RA-abs1-sh35-oral.pdf
http://www.nature.com/embor/journal/v4/n11/full/embor7400016.html
The former estimates the Sv (not mSv) on a trip to Mars of less than 2 years
is .5 - 1.14. This is based on normal solar and galactic rays/proton events
during solar minimum. A large SPE could be lethal, and would be more likely
at solar maximum, although GCRs would lessened compared to solar minimum
levels.
I was not able to find any data on the percentage of particles deflected by
the magnetosphere, but the consensus is that the magnetosphere does deflect
many of these particles, with a large proportion of the remainder being
"absorbed" by the atmostphere. These, combined with the actual mass of the
Earth that blocks out most of the sky, are the reasons we live in a fairly
GCR-free environment. Of course, all of this ignores the much higher levels
that most likely exist outside of the Sun's own magnetosphere and extended
atmosphere.
I say all of this to show where I'm coming from. I don't pretend to be an
expert, just an enthusiast. I'm unable to give a true scientific opinion of
the merits or demerits of my sources because my understanding of physics is
patchy at best. If you have better data or studies and can point me in the
right direction, I'll happily read these!
Best,
Denis
On Fri, Aug 26, 2011 at 12:53 PM, Rick Smith <rsmith@lightspeed.ca> wrote:
> Hi Denis,
> What percentage of cosmic rays does the Earth's
> magnetic field stop? Do you have a reference?
>
> A 6 month trip to Mars would hardly be a death
> sentence due to radiation. A complete there and
> back trip would have 50 REM's of exposure over
> more than 2 years. This will have no immediate
> effect and a 1% increased chance of cancer in
> the next 30 years. Thousands of people have had
> greater exposures to radiation with out dying.
>
> Warm regards, Rick
>
> On Thu, 2011-25-08 at 09:34 -0400, Denis DesHarnais wrote:
> > Hey Rick,
> >
> > I wasn't really dissing Zurbin. I found a lot of what he proposed to be
> > interesting, even visionary. I think some of his more hard core fans can
> > get a little dismissive of anything short of immediate colonization of
> the
> > red planet though.
> >
> > While you're correct that the Earth's magnetic field does not stop cosmic
> > rays, it does deflect many of them. That, coupled with the effect of the
> > atmostphere on the particles and the simple fact that being on Earth or
> in
> > LEO allows the planet to shield us from a substantial proportion of the
> rays
> > makes life on Earth possible, and the 1st and 3rd effects make ISS and
> Mir
> > life tenable for shorter periods. Being totally unprotected on a trip to
> > Mars for a trip of six months ... it may be possible, or it may be a
> death
> > sentance. I don't think we really know for certain yet.
> >
> > All of that aside, once we get there, the simple fact that we can find
> > carbon in situ does make it a far better candidate for permanent bases
> than
> > the moon, or really any other planet besides our own, so in that respect,
> I
> > think we're in total agreement.
> >
> > I hope that better explains what I was trying to say in my previous
> e-mail.
> >
> > Denis
> >
> > On Wed, Aug 24, 2011 at 9:30 PM, Rick Smith <rsmith@lightspeed.ca>
> wrote:
> >
> > > Hi Dennis,
> > > The point was made by Zubrin, that he would have
> > > LOVED to have been invited to various talks where
> > > they trashed his ideas and be given a chance to
> > > defend them. In scientific circles, you must expect
> > > criticism of your ideas and be prepared to defend
> > > them if someone says their are off.
> > >
> > > The Earth's magnetic field does not stop cosmic
> > > rays. We are bathed with them all the time. In
> > > fact, if scientists want to avoid them they have
> > > to do experiments deep underground, and even then
> > > they get an occasional bit of secondary debris
> > > from super high energy ones.
> > >
> > > Yes, at solar maximum, a few of the lower energy
> > > Cosmic Rays (CR) are deflected by the sun's magnetic
> > > field. But you pay for it with much higher chances
> > > of a big solar flare. Perhaps a couple such flares.
> > > Overall, you are better going during a solar minimum.
> > >
> > > As for the radiation on the typical Mars plans,
> > > there are more than a dozen humans (mostly Russian
> > > cosmonauts) who have taken more cosmic ray radiation
> > > than expected from long duration missions on Mir or
> > > the ISS. Not only have none of them experienced
> > > any radiological effects (which is to be expected)
> > > but none have shown any cancers (which is also to
> > > be expected given the probabilities). Radiation is
> > > very, very well studied. Far better than any
> > > chemical carcinogen. We know what to expect.
> > >
> > > As for adventuring on Mars, I wrote us some
> > > incomplete rules for Barsoom for TFT long ago. And
> > > GURPS Mars has taken real Mars geography, and (like
> > > Space 1899) added a Burroughs like (we don't have to
> > > pay copyright) society and races to it. I thought
> > > it was quite well done actually.
> > >
> > > Warm regards, Rick
> > >
> > > On Wed, 2011-24-08 at 10:24 -0400, Denis DesHarnais wrote:
> > > > Alas, poor VASIMR, I knew it well ... okay, maybe not *well, *but
> > > > well-ish.
> > > > Still can't really blame the dude for not showing up when the invite
> > > > included a promise for a nice public evisceration.
> > > > The article was very interesting; however, I think the author is
> rather
> > > > unwarrantedly dismissive of the effect of the Earth's magnetic field
> on
> > > > cosmic rays.
> > > > I am a big fan of terraforming, but the hardcore "Case for Mars" fans
> get
> > > a
> > > > little non-chalant about radiation en-route. Maybe if we plan a trip
> for
> > > > the following
> > > > solar maximum we might get there with existing technology (i.e. 13
> years
> > > > from now). I'd love for it to be sooner, but I think we'd need to
> send
> > > up
> > > > people
> > > > who were okay with the strong possibility of dying on the way, which
> > > means
> > > > non-American astronauts, I guess. We're all far too pragmatic in
> this
> > > > country
> > > > to really embrace the "give me Mars or give me death" ethos.
> > > >
> > > > As far as KREEP goes, all of I've got is the wiki article (and those
> > > > referenced in it):
> > > >
> > > > http://en.wikipedia.org/wiki/KREEP
>
>
> > >
> > >
> > > >
> > > >
> > > >
> > > > Denis
> > > >
> > > > On Wed, Aug 24, 2011 at 7:39 AM, Rick Smith <rsmith@lightspeed.ca>
> > > wrote:
> > > >
> > > > > If you go to the Mars Society site, there is an
> > > > > essay that is called, "The VASIMR Hoax"
> > > > >
> > > > >
> http://www.marssociety.org/home/press/tms-in-the-news/thevasimrhoax
>
>
> > >
> > >
> > > > >
> > > > >
> > > > >
> > > > > Which pretty much puts paid to the technology.
> > > > > Dr. Chang Diaz was invited to drive across town
> > > > > and defend his claims, but he failed to show
> > > > > up and only those who were critical of his work
> > > > > were at the conference.
> > > > >
> > > > > Your point about having a base on the poles and
> > > > > periodically directing light into the greenhouses
> > > > > with mirrors or light pipes is a good one.
> > > > >
> > > > > Luna has not had much volcanism, and no hydrology
> > > > > which are the major ways of concentrating ores.
> > > > > Thus, the moon is likely made up of Junk Rock,
> > > > > where the various elements are mixed together
> > > > > but useful ores are rare or non-existent. I
> > > > > know a fair bit about Lunar geology (tho admittedly
> > > > > some years old), and had not heard anything about
> > > > > ores of Rare Earth Elements (REE). If there is a
> > > > > link that discusses this I would be very interested
> > > > > in hearing about it.
> > > > >
> > > > > Sorry for the long time before I replied to this.
> > > > > I've been quite busy.
> > > > >
> > > > > Warm regards, Rick.
> > > > >
> > > > >
> > > > > On Wed, 2011-10-08 at 09:00 -0400, Denis DesHarnais wrote:
> > > > > > Hey Rick,
> > > > > >
> > > > > > That's a very interesting prospect. If we end up going with a
> > > > > > nuclear/plasma rocket ala Franklin Chang Diaz (or something else
> that
> > > can
> > > > > > attain those speeds), such that we can get our astronauts there
> > > alive, we
> > > > > > could have a real shot at colonizing the near solar system within
> a
> > > few
> > > > > > decades ... maybe less.
> > > > > >
> > > > > > I wonder if the roast/freeze equation on the moon could be
> altered if
> > > a
> > > > > > colony could be built in the permanent "twilight zone" along the
> > > > > day/night
> > > > > > hemisphere boundary - maybe in the KREEP-rich Oceanus
> Procellarum, or
> > > > > maybe
> > > > > > along the side of a convenient crater that gave similar shelter?
> > > Also, I
> > > > > > would think that PV cells would be much more efficient on the
> moon,
> > > given
> > > > > > the minimal attenuation of solar radiation from the moon's
> > > atmosphere.
> > > > > > Solar thermal would also be pretty efficient, so maybe the energy
> to
> > > run
> > > > > > artificial light during the darker periods would be easier to
> come
> > > by.
> > > > > What
> > > > > > do you think?
> > > > > >
> > > > > > Also, it would be kind off awesome to beat China in the rare
> earth
> > > > > elements
> > > > > > market by mining them off the moon. Probably not practical, but
> > > awesome
> > > > > > nonetheless.
> > > > > >
> > > > > > Denis
> > > > > >
> > > > > > On Tue, Aug 9, 2011 at 10:38 PM, Rick Smith <
> rsmith@lightspeed.ca>
> > > > > wrote:
> > > > > >
> > > > > > > Hi Dan,
> > > > > > > The main problem with artificial light is it is so
> > > > > > > expensive. One square km of plants needs the power
> > > > > > > to run a large city. The plants on the farms of
> > > > > > > Rhode Island (that agricultural giant) would require
> > > > > > > more power than the civilization of the whole Earth.
> > > > > > >
> > > > > > > That is the main problem of growing crops on Luna.
> > > > > > > Its 28 day long day means that the plants roast and
> > > > > > > freeze. (Apart from the fact that all the volatiles
> > > > > > > that plants need except oxygen are missing from the
> > > > > > > moon.) Mars is the one place in the solar system
> > > > > > > apart from Earth where plants can grow using natural
> > > > > > > sunlight.
> > > > > > >
> > > > > > > Plants can take 1/3 as much light as Earth gets and
> > > > > > > still do OK. This means that plants that don't need
> > > > > > > strong sunlight can do well on Mars. Beyond Mars it
> > > > > > > gets very hard to grow plants with only natural sun
> > > > > > > light. (But on the asteroids you could use natural
> > > > > > > sunlight and a quite modest amount of artificial
> > > > > > > light to help. Rotate your asteroid so it has about
> > > > > > > a 24 hour day tho.)
> > > > > > >
> > > > > > > Artificial light (which has the correct wave lengths)
> > > > > > > can grow plants. However, getting a broad spectrum
> > > > > > > light is a more expensive than the cheaper lights.
> > > > > > >
> > > > > > > Mars' atmosphere is enough to screen out all
> > > > > > > normal solar radiation and most of the solar radiation
> > > > > > > from a solar storm. (People should go into storm
> > > > > > > shelters for a few hours during the coronal mass
> > > > > > > ejection.) The cosmic ray dose is less than half of
> > > > > > > deep space. (The ground stops half, and the thin
> > > > > > > atmosphere actually helps a bit. Remember that the
> > > > > > > scale height is 3 times Earth so even tho the pressure
> > > > > > > is 1/100 Earth's, it protects as if the pressure was
> > > > > > > 3/100th's Earth's.) This is fine for explorers. If
> > > > > > > you were going to live all your life on Mars, you
> > > > > > > would want a habitat that had a meter of dirt over
> > > > > > > you. But being completely underground is not needed.
> > > > > > > You can have windows.
> > > > > > >
> > > > > > > If you were going to have mines on the Asteroid belt,
> > > > > > > you would likely end up with a triangle trade:
> > > > > > >
> > > > > > > -- High tech, low mass materials from Earth to Mars.
> > > > > > > -- Low tech food and crafts (clothes, plastics, wire,
> > > > > > > metals, ceramics, etc.) from Mars to the Asteroids.
> > > > > > > -- High value metals, gold, platinum, rhodium, palladium,
> > > > > > > etc. go from the Asteroids to Earth.
> > > > > > >
> > > > > > > It is at least 50 times cheaper to go from Mars surface
> > > > > > > to Ceres as it is to go from Earth's surface to Ceres,
> > > > > > > so anything that can be built on Mars would be. Only
> > > > > > > the highest, most complex items would be shipped from
> > > > > > > Earth.
> > > > > > >
> > > > > > > Warm regards, Rick.
> > > > > > >
> > > > > > >
> > > > > > > On Tue, 2011-09-08 at 18:54 -0400, dwtulloh61@cox.net wrote:
> > > > > > > > Hey Rick,
> > > > > > > >
> > > > > > > > Assuming subsurface water exists in sufficient quantity to
> > > support
> > > > > life,
> > > > > > > do
> > > > > > > > you think it would ever be possible for humans to live
> > > underground in
> > > > > > > some
> > > > > > > > sort of self-sufficient capacity there?
> > > > > > > >
> > > > > > > > Everything I've read suggests that plants do not grow well in
> > > > > artificial
> > > > > > > light
> > > > > > > > which, if true, presents a serious problem to developing a
> > > > > > > self-sustaining
> > > > > > > > in space.
> > > > > > > >
> > > > > > > > Dan
> > > > > > > > =====
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