Vacuum-firing motors?
 

Hello All,

As part of educational demonstrations of model rocketry, has anyone ever fired commercially-available model rocket motors in school laboratory vacuum chambers? Either the 6 mm "1/8A" Quest MicroMaxx motors or the Estes 13 mm mini motors (particularly "1/4A" mini motors) appear to be ideal for this type of experiment.

Mounted on the ends of a balanced, rotating arm, two such model rocket motors (or perhaps just one motor, with a counterweight [mass] on the opposite end of the arm) could be used to demonstrate the fact that rockets work (and in fact work more efficiently) in a vacuum. The vacuum chamber pump could probably more easily deal with the exhaust gas from a "1/8A" MicroMaxx motor because there would be less exhaust gas that would have to be evacuated from the chamber to maintain a vacuum inside.

I'm not much of a chemist, but will a model rocket motor even BURN in a vacuum? Does it contain it's own oxidizer?

It better! How could it possibly get a source of O2 to come through the nozzle so the propellant could burn?

Didn't NASA use something like an Estes D engine in space for something once, or is that one of those urban legends?

I don't know. Like I said, I'm not much of a chemist. :)

The saltpeter in black podwer contains all the oxygen needed to support combustion of the sulfur and charcoal. For composite motors, the perchlorate provides the oxygen.

Goddards Lab, at the Hutchinson Cosmosphere does it all the time, to show people about thrust in a vacuum.

This is good to know, and I thank you for this information! I had asked because I'm helping a store in my neighborhood, whose owner (from my suggestion) carries model rockets. She has many customers who are teachers (just yesterday she got a request for 30 kits with motors for a school session!), and a vacuum-firing demonstration would be a dramatic demonstration that Newton's three laws of motion (including the third law of action and reaction) really do operate in empty space.

Dr. Goddard fired small powder rockets in vacuum chambers, and for at least one demonstration to a college physics class soon after the New York Times ridiculed him, be used a pistol (a revolver) mounted on the end of a rotating, counter-weighted arm set up in a vacuum chamber. (I wonder if this would be legal on any college campus today...) The blank cartridge in the gun's chamber was set up to be fired electrically, and when he fired it and the arm spun around several times, the students were impressed. Dr. Goddard remarked, "So much for the New York Times."

It's a major part of the definition of "rocket motor." It is what distinguishes rocket motors from jet engines. The latter draw oxygen from the atmosphere to support the fuel burning, and therefore have another opening for air intake. The only opening in a rocket motor is the exhaust nozzle. The oxygen can be in solid, liquid or gas form in a rocket motor; it can be present as a solid in suspension in the propellant grain, as in solid rocket motors, or as a liquid form and fed in from a tank, as in liquid-fueled rocket motors. In hybrid motors, the oxidizer is in a gaseous state and is also fed into the combustion chamber from an on-board tank.

Has anyone ever static fired a model rocket motor inside a glass aquarium that was filled with water? I recall reading a post, probably on this forum, a long time ago in which someone described doing this for a science fair exhibit.

I remember that one - I think it may be on You Tube. They were simulating a Polaris Missile undersea launch with a clear plastic walled chamber filled with water. I think they had to isolate the motor from the water (not only does water do bad things real quick to BP motors, but it tends to short out the igniter as well). I specifically remember the smoke filling the void in the water before it could collapse back on itself.

Greg