THERE ARE NINE PLANETS IN THIS SOLAR SYSTEM DO ANY SUPPORT INTELLIGENT LIFE?
There are four categories of propellants, although there are some combinations which do not fit neatly into any category. Solid propellants are compounds or a mixture of oxidizer and fuel which is solid at normal temperatures. Liquid propellants are well, liquids. They are usual kept separate until they meet in the combustion chamber. Hybrids combine a liquid and a solid. Monopropellants are so unstable that they react all by themselves. As there are innumerable combinations of propellants, I will only discuss those that are in wide use or of amateur interest. There are five common solid propellant combinations;
* Nitrocellulose /nitroglycerine - this is a cast version of smokeless gunpowder, and as such is very dangerous. With the proper inhibitors, stabilizers, and plasticizers, it produces high impulse (270) and long burn duration, and is used in many military rockets and some upper stage engines.
* Ammonium perchlorate /polybutadiene /aluminum - this is the propellant combination used in the Space Shuttle SRBs. It is somewhat safer (?), and has an ISP of 260. An ammonium perchlorate explosion obliterated the solid propellant plant outside Henderson Nevada. Left a really BIG hole in the ground.
* zinc /sulfur - used to construct amateur rockets, although I would not consider it to be safe. Using amateur assembly methods the rate of combustion can vary wildly, meaning that the vehicle will either be dangerously under powered or explode, whichever will cause the most damage or loss of life. ISP is about 50 which is low, but sufficient for sounding rockets. A mixture of 2/1 is best.
* Potassium Nitrate / Sugar (or Sorbitol ) - readily available and used to construct amateur rockets. It has a little better ISP of about 130. But it must be melted to be cast, which can be dangerous. A ratio of 65/35 is normally used.
* Ammonium Nitrate / Rubber - Another amateur combination which has an even better ISP of around 240, but the ammonium nitrate absorbs water from the air.
The problem with solid propellants is controlling the combustion rate. A slight increase in combustion temperature will cause an increase in the combustion rate, which in turn will cause an increase in combustion temperature. It takes a good chemist to keep the thing from becoming a BOMB. Also flight stresses and combustion temperatures can cause cracks to form in the propellant structure, also causing an increase in combustion rate, etc. There are so many propellant combinations and mixtures that experimentation, which is always risky, is required. A high level of quality assurance and safety are essential.
Solid propellant rockets have many military applications because of their high thrust, and simple operation. The Generals usually don't care if some of the troops are killed in accidents. The current altitude record for a single stage rocket is held by a solid propellant sounding rocket based on the second stage of the minuteman ICBM at 256 miles.