From: vince@offshore.ai (Vincent Cate)
Newsgroups: sci.space.tech
Subject: Radiation shielding for hotel at GEO?
NNTP-Posting-Host: 209.88.68.230
Message-ID: <9186edb5.0308081641.5036919e@posting.google.com>

How much water (or pick some other) shielding would it take for a hotel 
at GEO to get the total radiation down to numbers like 25 rem/year or 5 rem/year?

It seems that the radiation in GEO is higher than in deep space 
(say same distance from the Sun but not near earth).  GEO is
outside the Van Allen Belts, so this was a surprise.  But it
seems that it is inside the magnetosphere and that the radiation
is sort of compressed as it squeezes past the Earth.  Since
GEO is in this squeezed area radiation levels are higher.   
Is this correct?

It would only be the Sun's radiation that was concentrated,
not the galactic cosmic radiation (GCR), right?

It also seems that almost all radiation from the Sun can be stopped by
like 25 grams/cm^2 of water (including solar particle events).  
It is only the GCR that would bother you if you had this much 
shielding.  It also seems that even with this much shielding 
the GCR would be such that you might not want to be there for 
more than a year.  

In the Lunar Base Handbook section 16.3.3 they indicate that 
75 gram/cm^2 would reduce the GCR to around 25 cSv, which 
I think is 25 rem as well.  Going from 45 to 75 grams did not 
improve things much on the graph, so it seems it would take a lot.  
I have heard numbers like 3 meters or 5 meters of regolith.  
The moon at least shields you one one side.  So it seems 
like GCR in open space is going to be like twice this.
Is there a conversion ratio to go from regolith to water shielding?


If a guy wanted to understand radiation at GEO and shielding humans
from this radiation, is there a book anyone can recommend?

It seems like tossing to a hotel/space-station in GEO is the best
way to use a space tether picking up a suborbital payload.  With
this we could toss something every 90 minutes.  Shielding the 
hotel is an issue, but the space tether can launch stuff so much
cheaper that this seems manageable.  I think I am only worried 
about the GCR for long term staff at the hotel, not for tourists 
visiting for a week.  But I want to understand this better.

Passing through the Van Allen Belts on a GTO seems like it may 
add something like 0.2 rem each way, depending on shielding.
Does this seem about right?

Can anyone recommend some software for simulating space radiation
and shielding?

The SPENVIS - SPace ENVironment Information System program looks
really nice.  You can give it a trajectory, shielding description,
and it can calculate a radiation dose.  However, I have not been
able to get a user name and password yet.  It may be that they do
not permit access from outside the USA.

   http://www.spenvis.oma.be/spenvis/


NASA has these AE-8 and AP-8 models for electron and proton
radiation around Earth.  Has anyone used this?  This is only
part of what I want to know, still need the shielding info.

   http://nssdc.gsfc.nasa.gov/space/model/magnetos/radbelt.html

Any other recommendations?

  -- Vince