<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Uh, the engine I mentioned in that book didn't need an oxidizer. The fuel was the same type of fuel used in normal solid fuel rockets, but in pellet form. The pellets enter the chamber via the same type of mechanism used by pellet stoves. <br />Posted by willpittenger</DIV></p><p>A concept of that basic sort has been considered, for a very small rocket motor of the station keeping type. It has all sorts of problems and virtually no advantages.</p><p>You could not use the pellet stove mechanism for two reasons. First, rocket motors operate at high pressure, and you want all of the gas to go out the nozzle and not back through an open feed channel. Second, those hot gasses going back through the feed channel would set off all of the pellets in your hopper at once, and that would get really exciting -- loud noises and pieces flying around at high velocity. You need a tight gas seal between the pellet magazine and the combustion chamber. That sort of mechanism can get to be very complicated and that complication eliminates the advantages of a solid fuel rocket.</p><p>A complicating issue is that solid fuels are basically explosives, some more so than others, and small pieces having a combined high surface area can react very violently to certain stimuli -- friction, impact, electrical discharge. So you need to be very careful in handling pellets, and among things make sure that you create no dust or anything that might behave like dust. If you started binding or grinding anything in the auger of your pellet feeder it could get real bad. Continuous mixers using a screw mechanism have been used for making solid propellant, and there have been some fairly spectatular fires as well. It can be done but it takes some expertise to do it.</p> <div class="Discussion_UserSignature"> </div>