On Thu, Oct 09, 2014 at 12:45:44PM +1100, Ian Whitchurch wrote:
> The same lasers that hit ships at the same multi light second range
> should be able to deal with any dangerous fragments.

The characteristics required for Traveller missile defense are *very*
different from the characteristics required for attacking starships.

You can't hit missiles at multi-light second ranges with any
significant accuracy, for the simple reason that all the sensor
information is many seconds out of date and the objects you're trying
to hit can maneuver across their own diameter in about a hundred
milliseconds.

So you need to hit them comparatively close.  An enemy fleet (or even
a single large capital ship) could arrange thousands of missiles to
all cross that range within seconds on different approach vectors.  To
defend against that would require immense rates of fire, and even one
failure to completely vaporize the missile means an enormously
energetic impact that could destroy the ship.

It is much better to intercept further out.  At greater range it
suffices to merely disable and deflect the missile, as opposed to
requiring that it be completely vaporized.

If the fighters miss some, the final line of defense at the ship has a
very much easier time picking off the remainder.

> In any case, almost by definition fighters will be unable to mount
> the same array of point-defense weaponary

They are the array of point-defense weaponry!  Just mobile and further
from the single basket full of valuable eggs.

If you like, think of taking each few dtons of the point-defense
systems on a capital ship hull, then putting thrusters and a small
power plant on it.  The analogy isn't exact, but it's there.  The
point-defense systems won't be huge spinal mounts or bay weapons,
those will be almost certainly geared toward sustaining an ongoing
barrage of super-powerful blasts.  Point defense requires more along
the lines of high slew rates and rapid bursts of much lower energy
required only for short periods, and infrequently.

The main thing that point-defense weaponry is likely to require is
surface area.  It's probably quite "shallow" in terms of the volume of
support systems required within the ship per unit hull area occupied.
So it seems to me that it makes sense to increase the available
surface area by making it mobile with its own hull.

> making them even more vulnerable to a bucket-of-sand attack than
> ships that can carry the power plant you need to support multiple
> sets of rapid-fire lasers.

They don't need a huge power plant.  They need an energy bank that
holds enough for probably a few seconds of rapid fire at a time, with
a small power plant to recharge it between missile salvos.  If a
missile gets close enough to use a bucket of sand, the point defense
is already being overwhelmed.

- Tim