On 21 Dec 2003 17:57:58 -0800, George William Herbert wrote:
phil hunt wrote:
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.

I can imaigne a small, light wooden airframe, designed for low
detectability, pulling much lower Gs than a faster airframe, which
might be made of metal.

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.

I think that examining how nature has solved similar problems is
useful. The human eye has lots of closely-placed pixels at the
center, and in the periphery pixels are much more widely spread.
Perhaps the system could use one (or more) wide angle lenses, and a
(possibly movable) telephoto lens for giving more detailed attention
to an object.

You need to assess the impact on
the sensor and field of view of the background coloration
across the target areas, etc.

Human eyes have 3 colours. There no reason in principle why an
artificial eye would have that number. (Though if we are using cheap
hardware, it probably would).

If a vehicle is stationary, and camoflaged, it's going to be a *lot*
harder to spot than a moving one. I think going for the ability to
spot moving vehicles well, and stationary vehicles a lot less well,
is adequate performance.

With a much simpler system, laser spot homing,

But who shines the laser on the right spot? Or are you assuming
there's a human with a laser designator in the loop?

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.

I'm not with you there... could you explain?

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.

Because it was manouvring too much at the start?

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 makes sense -- I'm sure lots of things wouldn't work right
first time.

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).

How much are simulated environments used in designing missile
homing systems? By a simulated environment, I mean the missile
software is working as it would be on the real missile, but output
instead of going to control surfaces, goes to a flight simulation
program, and input, instead of coming from a visula sensor (or
whatever) comes from a program which simulates what the output of
that sensor would be under those conditions?

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 two named Javelin, incidently.

and I'm referring to the US Navy / China Lake one.
http://www.nawcwpns.navy.mil/~pao/pg...es/SpikeND.htm

I can't load that URL.

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