There are no known laws prohibiting the design or construction of rocket engines, rocket vehicles or accessories, in the United States. However, certain communities do have laws prohibiting the operation of rocket motors or engines or the free flight of rocket powered vehicles. Prior to actually firing a rocket engine the amateur builder should make certain that he is not violating established ordinances. If ordinances prohibit local testing, a remote site may be needed.
The amateur builder should keep in mind that a rocket engine, even a small one, is an extremely noisy devlce. If local ordinances permit testing in a populated area, the amateur should consider the effect of engine operation on his neighbors before the initial firing. The noise of a rocket engine comes from the shearing action between the high velocity exhaust jet and the surrounding atmospere. Some of the noise can be eliminated by firing the engine into a water-cooled duct. Ample quantities of water must be sprayed into the exhaust duct to rapidly cool the rocket exhaust stream and to protect the duct itself. However, this technique restricts viewing of the rocket exhaust plume and eliminates one of the unique features of rocket engine operation.