Re: Orion Drive space battle

Random Thoughts:

The only plausible justification I can think of for gigantic
battleships is the need to scale up the pusher plates for improved
effective exhaust velocity. (Sorry, Thunderchild has a fatal design
error now.) Any smaller vehicles will automatically have lower
effective exhaust velocities. This suggests keeping the missiles on
the launch platform until the last possible moment. The missiles must
then sprint over a relatively short distance to have any chance of
hitting the target. If the target has sufficient time, its superior
exhaust velocity will trump the missile's superior thrust. If the
missile doesn't have superior thrust in the first place, it has
almost no chance.

Consider this case: The target is a uniform sphere 50m in diameter.
The target is capable of 10 m/s^2 acceleration in any direction. A
projectile is approaching at 20 km/s. The launcher already knows the
target's position and velocity and has aligned the projectile for a
direct center hit. If the starting distance is 1000 km, the target has
50 seconds to accelerate. In that time it can move its center point
12,500 m normal to the projectile's trajectory. It will easily dodge
an unguided projectile. If the starting distance is 44.7 km the
projectile will cut a half-diameter hole in the edge if the target.
Anything closer than this and the projectile always hits. The freshman
physics relationship is:
Position = 1/2 * Acceleration * Time^2.
Adjust the numbers to suit the specific case. This gives some feel for
how effective unguided projectiles will be. The example can also be
generalized to guided projectiles if the starting point is taken as the
last course correction.

It is also possible to describe an area the target may be in given a
certain amount of time. Using the same numbers as above, a canister
uniformly distributes a cloud of projectiles 100 km from the target.
The target can be anywhere within an area of 70,686 square meters at
the time of impact. The target itself is 1,963 square meters in cross
section. Therefore 36 projectiles are needed to guarantee one of them
will hit. (97% of the projectile mass is wasted!) This example can be
extrapolated to ballpark estimate the effectiveness of shrapnel against
battleships or missiles at any range. After having run this
calculation a few times with different parameters I am convinced that
shrapnel is ineffective unless it is being launched in enormous
quantities from a surface installation or orbital stockpile or unless
it is used at extremely close range. There is however another reason
to dislike shrapnel at close range. A cloud of shrapnel just won't
penetrate like a well designed solid of equal mass.

.

Relevant Pages