I've forgotten most of it. It's been twelve years since I even had an interest in the "rocketry and loud noises" branch of physics geekdom--I used to be into model and high-power rocketry, to a neary insane extent. I bought a box of rockets (forty!) from a store which was trying to get rid of old inventory.
...those 40 rockets ended up garnering me quite a pretty penny when I decided to have my friend Victor sell 'em on Ebay. I told him that if the aggregate went over $200 (I think it was $200) I'd split the take 50/50 with him. For me, half of that would represent over 100% profit for me, since I'd bought the rockets for $40 plus tax. As I recall the end total of my cut was well over $400. I wish I could always get that rate of return on my investments.
Anyway, I enjoyed the building as well as the flying, and it was something I didn't need a huge group of friends around to enjoy. I have videotape of some of the launches and I've still got most of the rockets.
But when I joined Tripoli Rocketry Association (http://www.tripoli.org/) I learned some things.
I have two reasons for not discussing the particulars. First, as I said above, I forgot it all. Second, I don't want some numbskull to read this, decide to try it, blow up his dog and/or blast his gonads into the stratosphere, and then sue me. (Not that suing me would really do this hypothetical numbskull any good, considering that my income has been well below the poverty line since I lost my cushy avionics technical writing job in the wake of 9/11. You can't get blood out of a turnip.)
Anyway, in Tripoli, I learned some neat things about the chemistry of things that fly and/or go bang. You see, anything that makes a really good propellant typically is one tiny step removed from being high explosive; some of them are high explosives.
There is a propellant which was popular in the early days. It uses a mixture of zinc and sulfur powders. If you do everything exactly right, when you set the rocket off, it will leap into the sky with a BOOM and come down somewhere in the next time zone, depending on the prevailing winds. If you fail to do everything right, you could:
a) get blown up;
b) get serious flash burns;
c) receive numerous shrapnel wounds;
d) or all of the above.
So DO NOT TRY IT.
Do not try it, because chances are you know nothing about handling finely powdered, highly reactive chemicals; and you probably do not have a concrete bunker from which to fire the thing. And if you tried to do this anywhere but in the middle of a freaking desert you would probably get a surprise visit from the FAA, FBI, and BATF. And your local police. Particularly if the rocket fell on someone.
Actually, you would still get a visit from the FAA even if you did try this in the middle of a desert. You have to get a waiver from the FAA in order to launch really powerful rockets, and a zinc-sulfur rocket qualifies, particularly since they typically have no recovery systems.
They could never build a Zn-S rocket bigger than 4". Anything larger just exploded, rather than going anywhere.
Estes rockets--the ones you can buy all over the place--largely use black powder propellant. The propellant is basically the same as gunpowder, only the oxidizer-to-fuel ratio is a bit different. Gunpowder is a deflagrating explosive, which means it must be contained in order to cause an explosion. Since a rocket motor, by definition, has an orofice through which gasses can escape, it's reasonably safe.
(In quantities above around a pound or two, gunpowder becomes self-containing. It will cause an explosion even if there is a loose pile laying on the ground. But a couple pounds of gunpowder is a lot.)
The next step up is ammonium perchlorate propellant. The stuff is basically identical to what is used in the solid rocket boosters for the Space Shuttle--HTPB (a kind of plastic), ammonium perchlorate, some aluminum (or other metal) powder to modify the burn rate--and it's found in the really big motors. Estes has always sold rocket motors in sizes A through D, with each successive letter representing a doubling in specific impulse. If you have the correct certifications you can now buy motors into the "P" range. A P motor is 216 times more powerful than an A motor. (216=65536.)
Actually, they may have gotten even bigger by now. It's been a few years.
Anyway, back in 1994, there were guys in the local Tripoli prefecture who were into making their own rocket motors. You can do all kinds of neat things if you spend some money on equipment, and the materials are/were dirt cheap. It's dangerous and you MUST know what you're doing.
The beginner will start by making "caramel candy" motors. The fuel is plain old sugar, and the oxidizer is either ammonium or sodium nitrate. Either one will work just fine. The devil is in the ratio of fuel to oxidizer, of course. And they must be intermixed; you cannot just mix the powders together and expect it to work. So you get a hot plate, and a saucepan and candy thermometer that you don't mind ruining, and you mix oxidizer and fuel in the pan and heat until molten. If you get them too hot, the whole thing will go up in your face--and go up fast, like a rocket (pun intended)--so do it outdoors and use a long stick to stir it. Once the stuff is thoroughly molten, you pour it into the stout carboard tubes you prepared with graphite nozzles and such before you even switched on the hot plate. You pack delay smoke powder on top of the "caramel" and then--once it's cold--add some black powder for an ejection charge. Then all you need do is put something atop that to keep it all inside the motor casing under thrust; you're on your own for that.
If you've done everything exactly right, you have made yourself a rocket motor. But I can guarantee that you will not have done everything exactly right the first time, and if you try to fly anything with that rocket motor, you will be building another rocket in short order. Just one problem which you will have to solve is the issue of voids--air bubbles--forming in the propellant slug.
The thrust of a solid rocket motor is dependent on the specific impulse of the propellant and the surface area of the burn. By changing the core design you can change the thrust characteristics of the motor without changing anything else. Cored one way, the motor produces one sharp, short spike of high thrust, then rapidly fades out. Cored another way, it produces a steady thrust for a LONG time (this is known as a "moon burn" core, because it will virtually put a model rocket on the moon).
But if there are voids in the propellant, you get sudden, and unplanned, increases in the burn area. If it's bad enough, the increased burn area overpressurizes the motor casing, and you have what is called a "CATO". I'm not sure what it means exactly, but it is BAD. A CATO generally means you are picking up pieces of your rocket once the smoke clears.
The problem is even worse with the ammonium perchlorate propellants. That stuff must be pressurized in order for combustion to take place. If you advance past caramel candy motors into perchlorate motors, you must buy a vacuum pump to place your fuel slugs under vacuum--voids in the perchlorate-type propellant can lean to cracking, and if the fuel slug cracks, your expensive reloadable casing could end up being a casualty as well as the rocket.
Reloadable casings are manufactured by several companies, and the technology is mature enough to be safe. The only time I ever used a reloadable motor, I didn't assemble it correctly. I had an o-ring fail. My rocket--a nice scale model of a Phoenix missile--got about 15 feet in the air, and then the nose cone blew off, followed by an enormous gout of flame. I safed the range and ran to my rocket to make sure there was no grass fire starting; the glue in the body tube had melted, and as I watched the thing sagged into a vague oval shape. The interior structure of the rocket was entirely destroyed. There was almost no damage to the paint or decals, except on one side, where the paint had bubbled and the decals charred.
Then we have hybrids. The most common is nitrous oxide and HTPB. It's a good, safe combination; Rutan's Space Ship One used just that to fly 52 miles up. Hybrids are expensive to buy when you first get involved with them, but economical in the long run, and the fuel slugs are utterly inert without the nitrous oxide around. They'll burn, but they'll burn like rubber rather than like rocket fuel. This makes UPS and FedEx a lot happier to ship them.
The guys who are into high-power rocketry had, for years, to do their own thing when it came to motors. No one made anything bigger than Estes' D12 rocket motors; if you wanted to launch a big rocket you had a lot of engineering to do.
The basic know-how of the typical American hobbiest always astounds me. There's that guy who built a flamethrower from stuff he bought at the hardware store. There have always been kids who were into chemistry, and could do all kinds of crazy things. Did you know that, if you wanted to, you could build your own goddamned particle accelerator for about a thousand dollars and a few months' worth of evenings spent on construction? Tabletop fusion made the news last year--inertial confinement fusors are mainly useful as neutron sources, but still--!
But if you want to make rocket fuel you learn about making explosives, too. It's not hard to make stuff explode. The hard part is making a high-energy reaction which does not explode.
It turns out that you can buy two innocuous household chemicals off the shelf. They come from separate parts of the typical grocery store, but most stores carry these two chemicals. Mixed in the right proportions, these two chemicals will react to produce a white precipitate. (What's left in the jar after the reaction is done is just toxic waste.) That white precipitate, once dried, is a high explosive--and the people who set off the bombs in the subways of London made their bombs from that stuff.
If you can acquire a quantity of a certain refrigerant and subject it to high heat, it forms phosgene gas, which is a type of nerve gas.
Ammonium nitrate mixed with diesel oil forms an explosive known as "ANFO": Ammonium Nitrate Fuel Oil. It's what Tim McVeigh and his buddy used; it's what the terrorists used in the first attack on the World Trade Center, in 1993. ANFO is dirt cheap and easy to make, and powerful; the amount you can stuff into a typical 1/2-ton truck is more than enough to bring down a typical office building. Add a few pounds of nails for extra shrapnel.
If you know chemistry at all, you don't need to buy your components from a traceable source. Just walk into a grocery store and buy some sundries and pay cash. Go to the hardware store for some fertilizer and pay cash. You can buy diesel at the gas station. Any hobby store which stocks model rocketry stuff can sell you as many black powder rocket motors as you need to build detonators. If you have a gun owner's ID card--or a convincing fake--you can buy black powder and fuse at many gun stores; and if any mining occurs nearby you can probably just steal detonation cord.
For $400 you can build a one-use EMP generator which will wipe out every computer and magnetic domain (video tape, hard drives, credit cards, etc, etc) in a half-mile radius surrouding "ground zero". Cars stop running, electricty stops working, all businesses inside that area are utterly screwed for days.
A Boy Scout, messing around with salvaged smoke detectors, managed to make a garden shed dangerously radioactive. Someone could make a radiological bomb using the same methods. Forget stealing radioactive materials; just make your own using salvaged smoke detectors and aluminum foil! You'll probably die of radiation poisoning, but you'll probably be able to hand-trigger your dirty bomb before that, anyway....
This kind of puts the problem of preventing terror attacks into perspective, doesn't it? Most people who are apt to be terror operatives are largely uneducated, which really works in our favor. Consider the fact that methamphetamine can be made in a garage by people who dropped out of high school, and that our government can barely stop them--what about people who have basic training in counterdetection techniques and a serious desire not to be caught coupled with the willingness to die for a cause?
Make no mistake about it: the people who are actually perpetrating the terror attacks against us and others are largely ignorant savages, people who have been duped into being kamikaze bombs by evil men who have twisted a religion beyond recognizable shape. The people (cowards) in charge go nowhere near the "front lines" of this asymmetrical war.
Ultimately, this is good for us: the educated ones don't have an opportunity to put that education to use. Meanwhile, if anyone tries to invade the US, I can just about guarantee that hobbyists all over the country would immediately go to work on building remote-controlled, flame-throwing robots with chainsaw arms.
And that is just one of the things which make America the great country it is.