Sidewinder engineering stoy/divide by zero

I was told by one of my college math teachers that there was an engineering
calculation in the early sidewinder days that involved a division by ZERO.
No one could figure it out so they ignored it. The missile when launched
destroyed itself in flight and the fix was to place a cross member in the
body of the missile which then made the equation work properly

Can anyone confirm or or deny this srory?

Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor
was often freelancing as an emgineering consultant

"leadfoot" wrote in message
news:50une.14524$7p.11605@fed1read06...
I was told by one of my college math teachers that there was an engineering
calculation in the early sidewinder days that involved a division by ZERO.
No one could figure it out so they ignored it. The missile when launched
destroyed itself in flight and the fix was to place a cross member in the
body of the missile which then made the equation work properly

Can anyone confirm or or deny this srory?

Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor
was often freelancing as an emgineering consultant

Sounds something like the installation of the mask dead ahead
in the seeker so that it essentially aims for a point where it
does *not* detect the heat source. That solved a lot of problems.

JK

"Jim Knoyle" wrote in message
...

"leadfoot" wrote in message
news:50une.14524$7p.11605@fed1read06...
I was told by one of my college math teachers that there was an
engineering calculation in the early sidewinder days that involved a
division by ZERO. No one could figure it out so they ignored it. The
missile when launched destroyed itself in flight and the fix was to place
a cross member in the body of the missile which then made the equation
work properly

Can anyone confirm or or deny this srory?

Could have been sparrow but I'm pretty sure he said sidewinder.
Instrucor was often freelancing as an emgineering consultant

Sounds something like the installation of the mask dead ahead
in the seeker so that it essentially aims for a point where it
does *not* detect the heat source. That solved a lot of problems.

Would it's abscene cause the missile to destroy itsekf in flight?


JK

leadfoot wrote:
I was told by one of my college math teachers that there was an engineering
calculation in the early sidewinder days that involved a division by ZERO.
No one could figure it out so they ignored it. The missile when launched
destroyed itself in flight and the fix was to place a cross member in the
body of the missile which then made the equation work properly

Can anyone confirm or or deny this srory?

Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor
was often freelancing as an emgineering consultant

Perhaps a corruption of this:
http://tinyurl.com/cu3rg

It is difficult to see where a division opperation of two variables is
needed in an early sidewinder.

An analog multiplier in such a situation is likely to saturate at full
output. As I understand it the early sidewinders simply followed the
target and didn't solve an system of differential equations that might
lead to a singularity.

Do you have more data on the nature of the divide by zero?

Most of the analog dividers I have seen actually produce the output Xo
= (X1 x X2)/Y. In other words they are intrinsically dividers and
multipliers. There are 'feedback multipliers', (that also do
division), Dynameter multiplier/dividers that use two moving coils in
coonected by shaft in oppostion that are blanced with a feedback
circuit and photocells, electron beam multipliers (use a cathode tube
with two pair of deflection plates and balance a phosphor dot on a
screen by photocell, 'servo mulitpliers'(slow but accurate), 'heat
trasfer multiliers' (good for 10 hertz), Simulataneous Pusle Width and
Pulse Amplitude multipliers, electronic time division multipliers.
(Dozens more in my copy of 'electronic analog computers by Korn and
Korn of 1956).

http://www.sci.fi/~fta/aim9.html
Reticle Seekers - A Brief Tutorial

The reticle seeker is the most common optical system design employed in
conventional heat seeking missiles. Invented by the Germans during the
latter phase of WW2, the reticle seeker provides a means of using a
single detector element to produce an error signal in rectangular
coordinates, with respect to a point target somewhere within the cone
which represents the field of view of the seeker.

The technique is based on the idea of mechanically chopping the light
flux which impinges on a detector, in such a fashion that the
characteristics of the chopped light pulses vary with the position of
the light source in the field of view. Because the detector produces an
electrical signal directly proportional to the impinging light flux,
electronic hardware can be built to extract a positional error signal
in x/y coordinates, suitable for driving a missile autopilot (or other
tracking device).

The simplest strategy for designing a rotating reticle seeker is the
Amplitude Modulation technique, such seekers being commonly referred to
as AM seekers. In an AM seeker of conventional design, the light
collected by a mirror system is focussed to a spot on the detector. In
between the detector and optics lies a whirling disc of optically
suitable (transparent) material, which has translucent and opaque
patterns etched on its surface, to interrupt the flux of infrared
light.

In an AM seeker, one half of the disc is translucent, and the other
half covered by a spoke pattern, radiating from the centre of the disc.
The result of this is pattern is an optical/electrical signal which is
a series of pulses, repeating with every revolution of the reticle. The
timing of these pulses with respect to the rotation of the reticle
produces a phase signal which is proportional to the position in one
axis, while the amplitude (size or strength) of the pulses provides an
error signal proportional to the position in the other axis.

The limitation of the AM seeker lies in the performance of the AM
detection (here x-axis) circuits, as the average signal from the
detector becomes quite weak in one direction thus producing poor
tracking performance in this axis. A scheme to resolve this is what is
termed frequency modulation (FM), whereby the number of spokes varies
with the radial distance from the centre of the reticle. In this
fashion a target closer to the centre of the reticle produces a smaller
number of pulses per revolution than a target closer to the outer edge
of the reticle. As a result the error signal in the radial axis of the
reticle can be resolved by a frequency discrimination circuit which is
locked to a reference frequency signal produced by the reticle motor.

Practical seekers use a range of variations on these two themes, with
various schemes using fixed cassegrainian mirrors and moving reticles,
or rotating secondary mirrors and fixed reticles, the latter
arrangement used in the Sidewinder family.

Other design issues in reticle seekers revolve about the detector
element, its supporting optics and cooling system employed. The
detector is a small piece of semiconductor material with suitable
photo-electric properties, ie it changes its electrical resistance or
produces an electrical current or voltage when illuminated. The key
design parameters in choosing a detector are sensitivity, a measure of
how faint a light signal will generate a useful electrical response,
and colour sensitivity, a measure of which visible or infrared
wavelengths will or will not produce a response. Most semiconductors
used for the purpose have some characteristic longest wavelength to
which they respond, while producing output for all shorter (hotter)
wavelengths. Therefore some detector materials can see only hot objects
like tailpipes, whereas others can see the whole aircraft.

Because all hot objects, such as the sun or flares, emit infrared
blackbody radiation, a missile seeker must have means of reducing or
removing such sources of infrared light to prevent seeker seduction.
Therefore optical filters are used. These filters are typically made of
a rare earth doped glass, with a multiple layer interference filter
deposited on the surface. Such filters are essentially transparent over
a narrow range of colours and opaque to all others, therefore passing
only the desired infrared colour through to the detector.

Cooling the detector is a means of improving its sensitivity. Even the
meagre amount of heat in a detector at room temperature will produce a
response in a good material, resulting in thermal noise which would
mask the target, therefore the detector must be cooled to prevent this.
Two strategies are typically used for this purpose, thermoelectric
cooling with a Peltier device or gas cooling. A Peltier is a
thermocouple which acts as a heat pump, albeit very inefficient, when
electrical current is passed through it. Gas cooling relies on the
expansion of compressed gas, and while lighter than Peltier schemes,
usually imposes a limit on total seeker cooling time when the gas
bottle is exhausted.

The evolution of heatseeking missiles over the last four decades has
seen almost every one of these schemes, or combinations thereof
employed. The Sidewinder is a good instance.

On Thu, 2 Jun 2005 07:40:35 -0700, Eunometic wrote
(in article .com):

Dozens more in my copy of 'electronic analog computers by Korn and
Korn of 1956

I think I have Volume II but it is in storage. Is that the complete name?
(Love analog). I have an initial condition/gain block in storage as well. 100
ten turn Beckman pots with a bunch of shafts and clutches to set them up for
a specific solution.

-- Charlie Springer

On Thu, 2 Jun 2005 07:40:35 -0700, Eunometic wrote
(in article .com):

The limitation of the AM seeker lies in the performance of the AM
detection (here x-axis) circuits, as the average signal from the
detector becomes quite weak in one direction thus producing poor
tracking performance in this axis. A scheme to resolve this is what is
termed frequency modulation (FM), whereby the number of spokes varies
with the radial distance from the centre of the reticle.

What do you call the no spokes version where you need to know the angular
position of the reticle? Say, from a synchronous motor's phase. I tried to
make one for tracking stars once long ago with a PMT. I still want to make
one work.

-- Charlie Springer

Charlie Springer wrote:
On Thu, 2 Jun 2005 07:40:35 -0700, Eunometic wrote
(in article .com):

The limitation of the AM seeker lies in the performance of the AM
detection (here x-axis) circuits, as the average signal from the
detector becomes quite weak in one direction thus producing poor
tracking performance in this axis. A scheme to resolve this is what is
termed frequency modulation (FM), whereby the number of spokes varies
with the radial distance from the centre of the reticle.

What do you call the no spokes version where you need to know the angular
position of the reticle? Say, from a synchronous motor's phase. I tried to
make one for tracking stars once long ago with a PMT. I still want to make
one work.

-- Charlie Springer

I'm not sure I understand what you mean. There were 'rossete scans'
that ended up in latter versions of sidewinder thse use a sort of
rotating and oscialting mirror. These also ended up in early German
infrared seekers intended for terminal homing on the Wasserfall missile
but actually derived from infrared imaging systems such as "Spanner".

The Basic AM seekers consists of a rotating transparent disk the half
segment of which is 'greyed' out with a fine speckled pattern of dots
to let in half the infrared light, the other half might consist of a
few dozen spokes. As it rotatres the infrared image produces either a
steady flat signal from the greyed portion or a series of high
frequency pulses from the spokes. The average instensity is the same.
A low pass and high pass filter distinquises the two and the phase
relative to the position of the disk determin the angle though not the
distance from the center. In one of the German versions intended for
the X-4 missile the disk did not rotate but the whole missile did
instead. A single gyroscope spun up at launch by a gramm of gunpowder
acting through a commutator kept track of "up"

Sidewinder I believe never had gyroscopes but used little wind driven
turbines in the tail acting as gyroscopes that mechanically acted on
little tail elevators to roll stabalise the missile. It rotated so
slowly it didn't matter to the seeker. Brilliant.

FM seekers are like AM ones only have another ring (or two or three)
with a different spoke pattern around the disk to widen the acquisition
angle but make the tracking more precise.

I think rossete scans took over a long time ago due to their higher
resistence to jamming and now imaging array systems.

The British Redtop missile (used on the lighting inteceptor) used a
different more sophisticated pattern. Its rotating disk 12 scimitar
spokes each of which had a different curve and width to the scimitar as
it widened toward the periphery. Thus the phase determined the angle
and the 'length' of the pulse the distance from the central axis. I
guess you'd call it 'phase modulation'.

I guess you could used 4 infrard photodetector arranged in a pie shape,
you even buy these from electronics suppliers such as RS components,
but the usual problem with these is that each must have exactly the
same gain and chracteristics.

On Thu, 2 Jun 2005 22:39:21 -0700, Eunometic wrote
(in article . com):

I'm not sure I understand what you mean. There were 'rossete scans'
that ended up in latter versions of sidewinder thse use a sort of
rotating and oscialting mirror. These also ended up in early German
infrared seekers intended for terminal homing on the Wasserfall missile
but actually derived from infrared imaging systems such as "Spanner".

There is a tracker form with a reticule that is half transparent and half
opaque and spun by a synchronous motor, so there is a reference for the
position of the reticle over time. The amount of time and the angle over
which the target is obscured generates the error signal. When perfectly
centered the signal is constant (half is always blocked).

If I could center it well enough, I could half mask the secondary of a
Cassigrain and spin it. I just find the analog solution more satisfying than
a digital image tracker.

I thought the turbine wheels in the fins of the Sidewinder were stabilizers
and generators, so it didn't need any batteries. I may be thinking of
something else.

-- Charlie Springer

Charlie Springer wrote:

On Thu, 2 Jun 2005 22:39:21 -0700, Eunometic wrote
(in article . com):

I'm not sure I understand what you mean. There were 'rossete scans'
that ended up in latter versions of sidewinder thse use a sort of
rotating and oscialting mirror. These also ended up in early German
infrared seekers intended for terminal homing on the Wasserfall missile
but actually derived from infrared imaging systems such as "Spanner".

There is a tracker form with a reticule that is half transparent and half
opaque and spun by a synchronous motor, so there is a reference for the
position of the reticle over time. The amount of time and the angle over
which the target is obscured generates the error signal. When perfectly
centered the signal is constant (half is always blocked).

If I could center it well enough, I could half mask the secondary of a
Cassigrain and spin it. I just find the analog solution more satisfying than
a digital image tracker.

I thought the turbine wheels in the fins of the Sidewinder were stabilizers
and generators, so it didn't need any batteries. I may be thinking of
something else.

Not generators. The AIM-9B-J used a gas-grain generator for power.

Guy