Star Grain

[daviesca14]

Anyone have any tips on learning how to cut a star grain?

 

[djs]

Are you talking about cutting a star grain in half (through the width), or by taking a solid grain and coring a star through it?

Normally these kind of questions belong in the Research forum. What exactly are you trying to do here?

 

[daviesca14]

Taking a solid grain and coring a star through it. Similar to what they do in commercial motors.

 

[dhbarr]

Taking a solid grain and coring a star through it. Similar to what they do in commercial motors.

Most of the stars / finocyls I've seen are cast in place. Cutting rubber that precisely isn't something I'd particularly like to attempt.

 

[djs]

Normally in the hobby rocketry world, this is done with using a star based mandrel and casting the grain around it. Probably the closest you could find is the finocyl mandrel that tru core used to sell (I don't think they do anymore):

https://www.rocketsaway.com/html/finocyl.html


Are you making your own propellant? What's your experience here?

 

[ttabbal]

You mean it's not done on a laser cutter? Boring. I don't want them anymore.

In case that was insufficiently snarky, that would be a very bad Idea.

 

[DavidMcCann]

I know Loki uses a mandral-

It's tapered-

 

[djs]

I know Loki uses a mandral-

I know I've seen this before- which motor is this?

 

[byoungblood]

If you want to see an interesting core configuration, look up the booster of a Talos missile. That must have been fun to cast!

 

[DavidMcCann]

I know I've seen this before- which motor is this?

J820 LW, I believe the only one he makes. I've seen test video for a blue I think... but nothing certified.

Looks like this when you turn it on-

 

[Winston]

If you want to see an interesting core configuration, look up the booster of a Talos missile. That must have been fun to cast!

Just had to look that one up. Glad I did.:

History of the Talos Booster

https://www.okieboat.com/Booster History.html

About those resonance rods:

Another problem that arose was resonant burning in the long tubular cavities in the grain, called "L* instability." Instead of even burning along the full length of the exposed surface the flame would oscillate between the middle and ends of the cavities, setting up strong resonant vibrations that could crack the grain. If the grain cracked the burning area would increase suddenly, possibly creating enough pressure to explode the booster. 3, 10

Several approaches were tried to suppress this problem.4, 12 The solution was installation of small diameter steel resonance rods in the cavities in the grain. These are the narrow white rods shown in the cutaway drawing. The rods were coated with a flame-retardant material such as an ethyl-cellulose binder containing potassium sulfate that vaporized in the hot exhaust gasses and prevented them from re-igniting.6, 9 In essence, the material acted as a fire extinguisher. In addition, the rods absorbed resonant energy in the combustion gasses and stabilized burning.

 

[Dave A]

I know Loki uses a mandral-

It's tapered-

That Loki J-820 star grain throws our 7.5" off the pad like a beast!