phil hunt wrote:
George William Herbert wrote:
I've done several iterations of this problem,
though not with systems that went to full scale
development or production.

I believe that for suitably moderated operational
requirements, the problem can be much simpler than I
believe Derek thinks it is.

I belive that Phil is grossly underestimating the
real requirements, even for those suitably moderated
operational requirements.

Which requirements am I underestimating? (Bear in mind I'm
considering missiles for several different roles).

Let me give you an example... assume that you need a certain
pixel width of an object to successfully identify it
(say, 10 pixels across) with a certain contrast ratio.

You also have certain limitations on the maneuverability
of the airframe this is all one. It can't pull more than
a certain number of G's etc.

To successfully design the homing mechanism, you need to
assess the distance and light or background noise conditions
of the frequencies you're looking at (visual, IIR, whatever)
and the magnification of the imaging system and its optical
resolution. You need to have a wide enough field of view that
you can see the targets as you fly along searching, but not
so wide that you won't be able to discriminate a target
until it's so close that maneuvering to hit it becomes
a serious problem. You need to assess the impact on
the sensor and field of view of the background coloration
across the target areas, etc.

With a much simpler system, laser spot homing, I spent
some months working out that nested set of problems.
Taking one shortcut made the weapon not lock on if
the ballistic miss trajectory was too far off.
Taking another meant that it typically locked
on early in a portion of its flight that led to
it flying out of control as it lost energy trying
to track the laser spot as it flew out. It would
scrub too much forwards velocity off early and then
start to come down too short of the target and stall
out trying to correct for that. Bigger lifting
surfaces would solve that but cause other problems
for weapon packaging. The final solution was to
modify the trajectory limitations, with the more
aggressive sensor system. Which scrubbed a bit off
the maximum range (could still reach the old range,
but if your aim was off too much in the initial
firing it would just out and out miss short).

You actually have to sit down, design a notional design,
put a notional sensor on it, figure out what the
parameters are, and simulate it for a while to see
what the gotchas are. That requires models of the
sensor, guidance, optics or transmitter, target
behaviour, aerodynamics, and trajectory / movement
dynamics of the weapon.

Even getting a rough first pass of that to tell you
what the roughly right answers are is nontrivial,
can easily be months of work, and requires experience
across a very wide range of diciplines (or a keen
ability to figure out what you don't know and find
it via research).

But few of those have progressed to production.
The new Marines/Navy Spike missile is one
exception,

This is the Israeli ATGM, isn't it?

No, there are two missiles named Spike,
and I'm referring to the US Navy / China Lake one.
http://www.nawcwpns.navy.mil/~pao/pg...es/SpikeND.htm


-george william herbert