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One option which I haven't seen mentioned is the use of retroreflective paint and a powerful spotlight. By lining up your eye with the beam, any exposed surface will light up like a Christmas tree. Using this principal I can easily spot tiny spiders from across my back yard, using a powerful LED torch to light up their eyes.
If nothing else, it might be a useful backup method of locating it... Can't hurt to try multiple systems of recovery.
Also, I hate to be the one to say it, but if you can't find a place to shoot it with absolute safety... Then don't fire it at all. As much as we all want results, it's not worth it to risk killing someone. Send it to another member if you can't pull it off.
I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.
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The problem with that is the exposed surface part. It will be in a little hole in the ground where it lands. Also, the retroreflective spheres may well come off during flight.
As for sending it to another member, I believe that is what is happening.
Now, for the interesting bit, the smoke cartridges. First of all, any individual capable of making this sophisticated a projectile and a launcher capable of making its construction worthwhile should be able to, if so inclined, design a percussive fuse for it. This is probably the easiest part to construct. I suggest repacking a handgun cartridge with smoke composition, placing it appropriately in a tube with a pin, and packing the any empty space with powder. Even easier: have a manually ignited magic string designed to burn for an arbitrarily long time- say 3 minutes. Light it, load, fire, get down range/out of cover, watch.
All that said, do you think you could find room in there for a CO2 cartridge, nail, and some visible powder for a dust cloud effect?
EDIT: wow. I should read all the topics about this before I post.
I feel the need to reiterate what I mentioned in another thread for projectile recovery. " a small radio transmitter would be placed in the projectile and set to a known frequency. Then you would get a handheld radio and attach a pipe wrapped in aluminum foil to the end of the antenna with the open end pointing away from you and set the radio to that frequency and just follow the direction of the noise."
This method would last longer than pyrotechnics and give non-line of sight detection that the reflective paint would not.
I agree this seem to be the best option, providing it's in a band that can transmit below ground (a bit).
Now... my electronic is way too rusty, so... who want to build, test and share this transmitter for this project and the next MiniBoy?
A very, very small transmitter. A long with a very, very small power source. Then there is the balance, load shift and possible damage on impact and to mention (drum roll here) the cost. You get what you pay for if your buying it outright.
When life gives you lemons...throw them back they suck!
We did discuss this in depth in the "spudgun range..." thread and I moved away from the idea because a UHF transmitter would need to be use so the aerial wouldn't be bigger than a few inches. The problem with that is everything starts getting a little more expensive than just an FM transmitter circuit. While it could be built for $75 or so, I don't really want to pay that
Unless anyone here thinks it can be done for cheap?
The real difficulty is in the receiver for finding the transmitter. Look up Radio Direction Finding for more info. Contacting your local Amateur Radio club for help would be a good idea.
The photos from the edge of space guys use GPS in the balloon payload, but that projectile is too small for that.
Would it be possible to use the projectile itself as the antenna? if so, you might be in the 16" area for a 1/4 wave antenna... about 740mhz. The transmitter might be do-able with a RF oscillator. Perhaps an RC resonator that dumps through a sidac. The receiver could be harder, though. According to wolfram alpha, that's in the broadcasting range. So... portable mini TV with directional antenna? or an emergency radio that can read audio in the UHF range.
300MHz would be the top of VHF. can we get away with a 1/16 wave antenna?
Now that I'm thinking about the sabot, I wonder if some reducer like that exist in those specific sizes:
large external diameter should be a little smaller than 48.5 mm, and small internal diameter bigger than 20mm.
Does that beast exist in the (non-metric!) plumber world? I never bought PVC (or ABS) fitting, but I guess I must be the only one here
My idea is to slice it in 2 parts as the 2 separating parts of the sabot, using the reduction surface at an angle to open it quickly with the air drag to it when it exist the barrel.
Of course, a plug would push both parts from the small end to make the sabot functional.
 some precision: I intend to machine some UHMW ring to fit the barrel, so the diameter of the reducer is of no importance. just need to be smaller than the barrel and capable of fitting inside the 19mm diameter missile.
yepp.. they exist as DW fittings here in america.
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A sabot could be as simple as a small cylinder the projectile sits on and a bit of foam to orient and center the projectile. This arrangement worked well for me launching a AA battery out a 2.5 inch barrel.
On launch the projectile would separate from the sabot as the sabot slows down upon exit.
Battery sabot is a water bottle with a foam cylinder to orient and center the battery
I would be afraid that the fins get in the way, get in the foam somehow and unbalance the missile direction.
Besides, I would like a perfect fit as the goal is to launch as far as possible, so with as less pressure lost as possible.
And it is an hybrid, maybe the foam and plastic would melt and make a mess?
All those points make me think it would need to be better than that for ultimate precision/power. What do you think?
The foam cylinder does not have to be a single piece. Slice it into 4 apple slices and the air in the nose will peel the four segments of the foam apple off the projectile.
Do I need to make and photograph an example? It really isn't difficult.
I think we'd be better using something a little stronger. While using a plastic bottle to reinforce the back of the foam and stop it from collapsing is a good idea, I doubt it would work so well in the hybrid. I've used similar plastic for sabots and they either crack or get severely deformed.
I also think it could be difficult stabilising the projectile inside the barrel using only foam and thin plastic, considering the imperfect fit and weak materials I too would be worried about pressure loss and possibility of the projectile not launching correctly.
Lately I've been thinking about firing a drill bit or such to see what damage it could cause and I would probably use something similar to you, Tech, though I wouldn't want to take the risk for this particular test considering the projectile we'll be using.
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