Rcandy Mixing

[jthompso]

In the book Amatuer Rocket Motor Construction, Sleeter discusses a pressed fuel grain consisting of Potassium Nitrate and Sugar, but he also presents two characteristics of this fuel that make it unsuitable for use in a rocket motor that must sit for longer than 48 hours.
1. The fuel is hygroscopic (which is simple to get around by sealing the motor or putting it in a container with dessicant.
2. The fuel and oxidiser will continue to mix just sitting in close contact to eachother which will serve to shrink the grain and increase chamber pressure.
For these reasons Sleeter advises that KnS rocket propellants be fired within 48 hours of making the motor, however I have a question. I am planning on building a cast KnS propellant grain of the "Nakka" style, but I'm wondering if this continual mixing occurs even in a heat-casted propellant grain. Anybody with experience in the matter please chime in.

To paraphrase: Will a heat-casted KnS grain continue to mix after being cast, and if left for 48 hours (or indefinitely) cause a CATO?

[jthompso]

Thanks for the reply Ben, I was thinking I'd never get a response, I'm planning on experimented with a ducted-rocket motor and knowing that I shouldn't have problems storing motor grains is very helpful. And in case you're wondering Sleeter tamps the two powders into the casing but says that the seperate components crystal structures will actually merge together the longer they sit together which serves to shrink the grain. I had assumed that a heat-casted grain wouldn't show this characteristic so thanks again for the good news!