[ExI] Why space tech isn't cutting edge

[Charlie Stross]

On 19 Nov 2012, at 17:55, Adrian Tymes <atymes at gmail.com> wrote:

> On Mon, Nov 19, 2012 at 9:22 AM, spike <spike66 at att.net> wrote:
>> Any shielding that is light
>> enough to be carried into space creates a shower of secondary particles when
>> hit with a sufficiently energetic cosmic ray
> 
> Composite armor, just like tanks use.  Outer layer converts massive
> attacks into a spray of smaller attacks.  Inner layer optimized to
> stop a bunch of smaller attacks.

Ultra-high energy cosmic rays have energies up to 5 x 10^19 eV. (There's a high cut-off due to interactions with the cosmic microwave background.) 

That's about 8 joules. In a single particle! (The highest ever observed energy was 3 x 10^20 eV, or about the same kE as a baseball traveling at 100km/h.)

To put it in perspective, these particles can drill through multiple kilometres of air, and multiple (possibly double-digit) metres of water. And lead shielding isn't going to make things better: it's got a higher capture cross-section, but if you whack the energy of a baseball into a single lead nucleus it is going to explode violently, producing a whole mess of muons and other decay products. If anything, the secondary radiation produced by blocking it may be worse than the particle itself.



-- Charlie