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I work with a lot of Boy Scouts who want to complete the Space Exploration merit badge. It's a great program, and one of the coolest requirements is building, launching, and recovering a model rocket. Unfortunately, my Scouts are in the city and finding a location to launch rockets is ... well ... tricky.

In the past, we'd drive out to the countryside and use either a park or a friendly farm to launch the rockets off. It never used to be a big deal ... but someone got it into their head recently that these rockets pose a significant fire hazard (despite over a decade of fun without a single problem).

The biggest argument I've heard against the rockets is the nature of the engine. Basically, model rocket engines are black powder-based. A small electric igniter lights the engine and it produces a lot of heat and smoke to propel the rocket.

The parks and farms that have since banned us from launching rockets finally conceded that, if I could find a way to launch rockets without burning anything, they'd let me bring the Scouts back.

Every reference I can find to "cold rocket engines" seems to refer to older 1970s freon-based engines. I don't want to go that route, but I'm looking for some ideas for cold or low-temperature rocket engines. Even if it's something I'd have to build myself ...

Any ideas or suggestions?

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compressed air? You can certainly launch a potato quite a ways using a compressed air device, even without ignition. I don't see why you wouldn't be able to get pretty decent thrust on a rocket. – Jerry Schirmer May 6 '11 at 21:33
Pressurised gas or gas and water rockets work, and there are "toy" vinegar and baking soda rocket on sale here and there that will exceed a hundred feet pretty easily. That's a low temperature reaction. And I suppose one could make the menthos and Coca-cola reaction do the job. – dmckee♦ May 6 '11 at 22:01
I used to work for my university's outreach program. This involved making paper rockets with the black powder engines. We always set them off in the school's playing fields. Maybe ask a local science teacher for permission to use their grounds? – Nic May 7 '11 at 8:09
@Jerry Schirmer ""You can certainly launch a potato quite a ways using a compressed air device"" Not only potatoes! Look here: punkinchunkin.com/images/galleries/2009/alex/index.htm – Georg May 7 '11 at 14:24
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EAMann: your objection to the water rocket doesn't make any physics sense to me. The energy is stored in compressed air contained by the rocket itself (at least it was in the water rockets I played with as a kid). Sure, that energy came from somewhere else, but that's no different than saying the gasoline in my car came from an external source). If you don't like water rockets because they're not as cool as the black powder rockets, then I'm with you, but the "self-contained" objection is malarky. Maybe a mini-C02 cylinder could be a viable middle ground? – Anonymous Coward May 10 '11 at 18:49
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3 Answers

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EAMann,

I know this is a physics site, and you are looking for a physics answer; but I noticed that you are in Portland, Oregon. It seems amazing to me that you can not find a site reasonably close.

If nothing is closer, it seems to me that one of your beautiful beaches would make a nice launch site. That is (IIRC) more than an hour away, but you could combine it with a camping trip.

My high school biology professor used to take us out to the Gingko petrified forest in eastern WA. Along the way we would stop and jump down the sand dunes on the WA side of the Columbia River, not too far (a few hours) from where you are.

There is a lot of desert in eastern WA and eastern OR. Can't imagine not being able to find a launch site out there. The other thing I would do is network through your own organization, BSA, to find out where other nearby scout troops are going.

I hope this helps.

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The trick is trying to bundle activities for the Scouts. Taking a separate trip just to launch rockets is overkill when only a handful will be participating. I've also exhausted all the free resources nearby for launching rockets as property owners seem to classify anything with an igniter as a "firework" and don't want to shoulder any added liability. The nearby troops do 3rd-party sponsored programs that cost $30-50/Scout. Infeasible for my unit. – EAMann May 10 '11 at 20:14
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I found this water rocket video, which appears to attain sufficient altitude. The group that makes them has a nice website and tutorial.

Perhaps launching black powder based rockets from a boat might be an alternative solution.

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Launching from a boat makes the rockets very difficult to recover. The requirements (linked in my question) require the Scouts to launch one rocket twice - as in launch, recover, reload, re-launch. – EAMann May 8 '11 at 14:31
Another unlikely possibility is to seek permission to launch just after a good rain = zero possibility of a fire. – JoeHobbit May 8 '11 at 20:02
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This doesn't answer the question, but it does solve the problem. Do it on the 4th of July along side your neighbors who (I assume) will also be launching bottle rockets etc. Here in South Carolina it sounds like a war zone on the 4th from about 8-12pm. It that doesn't work, maybe ask to do it before/after a fireworks display?

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