starship-design: Re: Starship Engineering

[Johnny Thunderbird <jthunderbird@nternet.com>]

Hi y'all...

Kyle R. Mcallister wrote:

> L. Clayton Parker wrote:
>
> > It seems that this is one of the things we need in order to build a
> > starship. It would increase structural strength while decreasing vehicle
> > mass and that has to be a good thing. I assume the ones that have been made
> > already were aluminum or aluminum alloy.
>
> Yes, something like this would be very good. But we couldn't replace
> everything with it. SInce it is less dense, it will be a much less
> efficient radiation shield than denser metal. Perhaps this material
> could be used for internal parts of the ship?
>
> Kyle R. Mcallister

LCP sez a foamed metal has better structural weight per mass unit so
implementation can be lighter. KRM sez less density means worse
shielding. I say nonmetallic superstrength materials live up to their name,
so are structurally preferable to metals in low-mass engineering.

Sheilding's a complex issue. Creeping up on C we start dealing with
_real hot_ stuff. To expect a linear relation of shielding efficacy with
structural material density is oversimplifying. For example, impingent
particles are hungry for nuclear interactions, so to portray this as a
subset of ionizing radiation is putting too pretty a face on it. Nuclear
cross section in barns is a property of the element. This has to do
with its presence, not with its physical nor even chemical state.

The material's density is very indirectly related to shielding effect
for impingent relativistic particles, but I would think foaming a
material might actually improve its shielding ability, on the general
principle that you'd like high energy breakups tend to happen
farther away from the protected wetware, rather than closer.

Lead and beryllium have particularly useful shielding properties,
which are not related to structural properties. I feel that ice would
be a useful material to push in front of your starship. Its shielding
properties are not all that great, but you could keep the nose of
it painted with heavy metals, to fulfill the objective of having the
energetic stuff happen way out there. For the sneaky rays,
which get through lots of matter, there's nothing so comforting
as having lots of matter between you and their source.

You'd like that lots of matter to have lead, and beryllium, and
heavy metals, even  transuranics if you can find any lying around,
and mainly iron because it's cheap, and lots of ice because it's
real real cheap. I'm afraid our criteria for minimizing mass in
starship design have led to underestimating the crucial significance
of mass for shielding, so many of our estimates will need to be
rebalanced in the light of realistic shielding concerns.

Ice is a structural material, with the added benefit it's full of
rocket fuel ( in this case meaning reaction mass that's easy
to handle ), and helps shield the nose of your vehicle because
it's there. It's available for the cost of the delta-v it takes to
collect it, no cost multiplier for being sunk in a gravity well.
You can count on it being available in the next system, at
the same cost, so if most of the mass of your ship is
composed of ice you can rebuild your ship by replacing
this expendable.

It's just this feeling of comfort you get from flying behind
a glacier which makes me favor it, over naked shivering
can styles. Shielding is needed fore and aft of a starship,
but I like a fusion drive in the jet, and favor primary
reactions which produce no neutrons; these factors
make the friendly fire less worrisome, so reduce the
shielding requirements aft.

Anybody else like starships made of ice?

Johnny Thunderbird
http://www.dejanews.com/~liteage