"Think creative";  You could use a smaller multi-ringed mirror, with
Piezo power (resonant setup) or a pager motor used to counter-rotate the
mirror ring segments?  (differentially move them to balance out
precession effects.)  These mirrors can be rather light (vacuformed
plastic should do; Hmmm!  How about doing this on a fresnel-like, flat
media basis?  Use any AOL CD-Rom and mill it, then silver it <G>)

The motors would be a 'power hog', but for not very long of a run -
NiCad's would work well, I'd think.  Top off the charge and spin up the
mirrors before launch;  then use a 3V/60R to maintain spin?  (Hmmm,
could we use an escapement mechanism to spin the mirror without a
battery?  The mirror segments would be the counterweights on that
escapement.)

Yeah, the segments wouldn't give as good of a signal if things were
resonant, but it might be lighter than electrical...

My earlier idea I'd mentioned to Sean, was to use a multi-focal mirror
with 2 photodiodes (IIRC), per quadrant (or ?tridrant? to reduce weight
<G>) - One for wide scan, the other for close in.  Photodiodes are cheap
and low-weight, could definitely mix and match these ideas so you have
one tiny ring mirror which both sets of diodes "watch".

Nothing's wrong with using a PIC-based tracking launcher with lots more
IR tracking capability, either, though you might want to seal that just
before launch to prevent damage from the exhaust.  Wind vane on the
launcher (even just a round vertical rod with X,Y strain gauges) could
tell you the wind stats at ground level, too.

  Mark, mad rocketeer at heart <G>

Sean Breheny wrote:
> Hi Dave,
>
> Unfortunately, something like this is a bit heavy and complex to put in
> 400 gram rocket which has to cost less than $1k (preferably much less)!! <G>
>
> It is an ingenious design, though!
>
> Sean
>
> On Wed, 13 Sep 2000, David VanHorn wrote:
>
> > The sidewinder seeker head is a pretty interesting design.
> >
> > The tip is a four quadrant photodiode, looking aft, at a rotating mirror.
> > The mirror is segmented. So, an IR source is modulated by the mirror
> > rotation. This also makes it easy to implement digital filtering, since the
> > rate of the chop is always absolutely known.
> >
> > There are several (three or four) sections to the mirror, outward from the
> > center, so that a target off to one side of the view produces a high tone,
> > and as it gets closer to the center, the tone steps lower.
> >
> > --
> > Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

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