you know I may have just figured this out,. Attached is a drawing I made back in 2005 when I was pondering how to stage composite motors... It's a total rough draft but bear with me.
Composite Motors 101:
As we all know when you ignite a composite motor you also ignite the delay train at the top of the core. This delay has 2 functions:
1. act as a delay train and
2. act as a pressure seal
So the delay train can only be so thin as to contain the combustion chamber pressure and ie you get thrust in return.
so the delays equal the burn time of the motor in question along with the actual delay time. Looking at ATQ's Master Motor listing I notice that only a handful of motors have a 3 sec delay while the biggest number of engines have a 4 sec delay.
this tells me this is the minimum delay time length that can be used by these motors is on the order of 2 to 3 sec max. this also defines the minimum length of the delay train that can contain the chamber pressure.
so if you look at my drawing here's how I would ignite an upper stage motor.
notice that you have a tube that goes through the middle of the delay train...... this tube could be made out of whatever material that might be suitable. this tube would have a faster burning delay train in it than is currently used. the length of the tube and it's diameter would determine it's burn rate.
The actual delay train in the boost engine could be removed entirely and replaced with a circular plug in place of the actual delay train which would hold in the pressure.
But the small diameter delay train would be ignited when the boosted stage engine is ignited at it's top as usual.
The small diameter tube would basically be a composite igniter and it would burn hot enough to ignite the upper stage propellant/delay train as would an electrical igniter.
The question is what composite propellant to use in this composite engine igniter.
It would have to adhere to the sum of the engine burn time plus maybe 1/2 second.... so it would have to be a fast burning composite, perhaps warp 9 or a derivative of this.
Another question is: what do you make the composite igniter tube of? Something strong enough to contain the composite delay train burning pressure but also would be incinerated upon the upper stage igniting and not clogging up the nozzle....... so maybe some kind of coating instead of a physical tube.
Now, this design technique would work on RMS but then there's a question of how you would implement this on single-use motors. I'm sure using this idea as a baseline that something could be worked out.
I will expect royalties if this idea works.
