Space Forum / Space Flight / December 2003

Most flare radiation and cosmic radiation is blocked by Earth's
magnetosphere, not by the atmosphere.  LEO is inside the magnetosphere.

No, 10-20cm of water around a small "storm shelter" area will suffice --
the only flares of concern are the giant ones, which are rare and brief --
and that can almost certainly be arranged using things like food supplies
(even dehydrated food has a high water content) which have to be there
anyway.

Because the trip to Mars is outside Earth's magnetic field, just like
most sources of radiation in space. Space craft and space stations in
low Earth orbit receive an enormous amount of radiation protection
from Earth's magnetic field.

No, it doesn't have to be lead. Any mass will do. Lead just puts a lot
of mass in a small volume, so lead shielding is not thick. [1] Ten to
eleven centimeters of water shielding is just as good as 1cm of lead
plate, and you can use the water for a lot of things (drink it, wash
in it, make oxygen out of it, use it for reaction mass, etc.) Lead
isn't useful for much on a ship.

[1] However, lead isn't much denser than steel. If price is not a
problem and you can waste mass on dedicated metallic shielding, use
tungsten or depleted uranium for shielding. That's density.

Mike Miller, Materials Engineer

As to the shielding, I suspect it will be a plastic or part plastic.
If it contains lead or other heavier metal, they will be on the outside.
And the low density materials will be on the inside.
Read up on "graded shielding" for radiation.

When high energy particles and high energy photons strike
a thin dense shield,  they liberate a "spray"
of other particles and photons.While the spray will have
somewhat lower energy, the beta particles will
have higher linear energy
transfer. In short, a thin shield of a relatively dense
material even as humble as aluminum may result in a
higher radiation dose to the space traveler.
The inner plastic layer would absorb the betas and
soft gammas and x-rays.

My ideal for sheilding would be to have such a large
space ship that a outer wall could like that on a battleship
and still have a low overall density of structure not including
the fuel. I know, I am dreamer.

sleeeppy...............................William A. Noyes

I always figured that shielding on a interplaneraty spacecraft should
use materials usable at other moments and for other purpose in the
mission. A dense outer shell should try not to stop the particules but
refract or reflect them. One might conceive a outer skin made of
hundreds of small panels (maybe a few centimeters accross) of light
materials on which incoming high-energy particules would skim accros
and mostly go back toward space, like a stealh fighter mostly reflects
radar (F-117), or an X-ray telescope focuses incoming photons.

For the particles which could not be be reflected due to their
incident angle, a second layer would absorb some of the energy. 15
centimeters of water could be used for that purpose. Only the water
would be kept as ice, providing some protection from hard impacts from
debris. When needed the water could be thawed back to liquid form.

Photodetectors could be installed in the ice shell, monitoring the
incoming radiation. But I think it would be best to try to provide a
space in which radiation would not be stopped, but directed away from.

I'll try this again - my posts seem to be routinely ignored.  Ah well.

The Earth's magnetic field traps a lot of the charged particle
radiation that emanates from the Sun.  Flights into space that fly
below this field are protected from the brunt of radiation found in
interplanetary and cislunar space.

Information about your query can be found at the following site;

http://radhome.gsfc.nasa.gov/radhome/papers/seeca3.htm
http://books.nap.edu/books/0309056985/html/5.html#pagetop
http://content.aip.org/APCPCS/v246/i1/130_1.html

Basically, the Van-Allen radiation belt sheilds astronauts in Low
Earth Orbit from deadly solar and charged cosmic radiation.  Since
rocket boosters are limited in terms of speed and size, their payloads
must be miminum and travel along slow minimum energy orbits.  So
called hohmann transfer orbits

http://www.ucar.edu/eo/staff/dward/sao/ceres/appendix.htm

These orbits take years to complete, and if you're sending people, you
need to execute them twice!  Once out another back.

So, folks will be exposed to a minimum of 2.5 to 3 years to very high
levels of radiation - or more.  This pushes their exposure up past 130
Rems - if they're well sheilded, and far higher, if they're not!

http://srhp.jsc.nasa.gov/project/BNL.htm

NASA and Brookhaven together was able to show that even for a trip to
Mars, which is our neighbor in interplanetary space, there is a real
risk that some if not all of the astronauts would suffer ill effects
from radiation, and if sheilding were not available, may not survive
the trip!

Lead sheilding is heavy even lighter  sheilding adds up.  Even so, one
can imagine that with robotic systems pre-placed on Mars before their
arrival, it may be possible to send astronauts encased in sufficient
sheilding, who operate throughout their ship and beyond via
telepresence.

http://ranier.hq.nasa.gov/telerobotics_page/FY95Plan/Chap2g.html
http://www.foresight.org/Updates/Update08/Update08.2.html

Radiation hazards are very much the outcome of small payloads and low
final rocket velocities.  Larger and more capable rockets will change
this.

Large, fast moving, heavily sheilded vehicles wouldn't require special
sheilding.  Its only small, slow moving, lightly constructed vehicles
that have this problem.

http://www.astronautix.com/lvfam/orion.htm
http://www.astronautix.com/articles/probirth.htm
http://science.nasa.gov/newhome/headlines/prop12apr99_1.htm

The nuclear pulse rockets described in the source material above are
capable of flying large heavily constructed, adequately sheilded
throughout, spacecraft on high-speed orbits throughout the solar
system.

This is the way to go in space.

 (1) set up launch centers at radiation waste sites and old bomb
     test sites throughout the world;

 (2) convert all nuclear weapons centers into nuclear pulse
manufacturing
     sites;

 (3) use current inventory of nuclear materials as fuel source for a
small
     fleet of very large spacecrft;

 (4) fly off the nuclear material and deposit remotely operated labs
t
     throughout the solar system - involving a fleet of dozens of
ships
     and tens of thousands of astronauts;

 (5) return to the moon, where a long term base is established and
reusable
     chemical rockets maintain contact with Earth;

 (6) establish an international nuclear research center on the moon,
and
     continue the advance of nuclear pulse rockets, as well as space
based
     defense research to enforce an enhanced nuclear nonproliferation
regime
     on Earth and in space;

This will not only address radiation hazards on a Mars trip, but also
significant radiation hazards on Earth!