Staging HPR Motors

[majordude]

I was at a launch over the weekend and witnessed blow through on a two-stage HPR rocket. I've never staged composites but I presume it needs electronics to do so.

So, since the explosion propelled a fireball and the 2nd stage into the air but then it fell to the ground without igniting. How?!!

 

[Jmhepworth]

An overpressure can cause blow through and put out the motor. It happens on the ground as well. But it’s not nearly as spectacular as an overpressure that throws flaming grains in all directions.

 

[rfjustin]

Any pics or video available for additional context?

 

[Charles_McG]

I'm thinking that a CATO in the booster is unlikely to light the sustainer. Composite motors are ignited from the top. The fireball might go up by the nozzle, but it would have to compress the air inside the motor to get up to a flammable surface. I bet its much more likely to pop the sustainer off.

 

[Titan II]

If the interstage coupler went with the sustainer the motor is totally closed off from the fireball. Even if not, the sustainer motor nozzle is frequently taped up to hold the igniter in place. Also.....what Charles said.

 

[David_Stack]

Lots of possible explanations for why that occurred, and without additional details on the electronics on that rocket, difficult to answer definitely.

In addition to the prior comments about how composite motors are lit from the top...

It could be that the sustainer was to be ignited from electronics in the booster, and when the booster motor CATO'd it damaged those electronics or broke the connection from the booster to the igniter in the sustainer motor. If the sustainer motor was to be lit from electronics in the sustainer, that altimeter/computer may have been configured with various inhibits or lockouts, if those criteria are not met then it won't fire the sustainer motor.

Suggest reading through this thread for an active discussion about sustainer ignition, inhibits, timing, etc.: https://www.rocketryforum.com/threads/ignition-timing-vs-tilt.174675/