# Re: starship-design: high-velocity interstellar medium collisions

```Hi SSD,

----- Original Message -----
From: Gene Marlin <rmarlin@network-one.com>
To: <starship-design@lists.uoregon.edu>
Sent: Monday, February 22, 1999 8:24 AM
Subject: starship-design: high-velocity interstellar medium collisions

>
>Could somebody point to an archive or website that discusses energy loss
and
>craft damages that is incurred by collisions with particles in the
>interstellar medium?

That's not too hard to figure out yourself if you can find a reference on
the amount of dust and matter that exist out in the Galaxy. The rough
calculation for the amount of energy received/second..

assume inelastic collisions [highly likely at near-light since the particles
are crashing into you] so all energy of incoming particles is dissapated.

P [Energy per second] = 0.5*p*A*v^3 i.e.half the mass density of
interstellar matter [p] times the cross-sectional area of the star-ship [A]
times the cube of the velocity [v]

Why the velocity cubed? Because in each unit time your ship sweeps up the
volume of your area times the distance travelled in that time.

As for direct damage it's roughly severe radiation damage, which varies for
the material you're using as a shield. Basically it's a hail of cosmic rays,
which is best blocked by metres of ice, which has the added advantage of
dissipating impact energies from dust efficiently. The ultimate shield would
be either a plasma shield or a gravity shield, or both. But ice does quite
well, especially if it can used for fuel/mass along the way.

I am also interested in the the 'star bridge' concept.
>The only resource I have on this is _The Millennial Project_ by Savage.
Does
>anyone have any suggestions?
>
Savage stuffs his figures up. He imagines that a "1000 AU" accelerator can
boost you to near-light, so that trips last subjective days. You can do it
if you can stand multi-thousand gee accelerations!!! The Relativistic time
distortion factor goes up by 1 every light year you accelerate at a gee. A
light-year is 63,000 AU, so a 1000 AU at a gee is a miniscule increase in
time-distortion factor. At 1000 g it gives you a TDF of about 15, so the
higher acceleration the better. Just how you stop becoming strawberry jam is
another matter...