Two Stage Recovery with Redundant Deployment Charges

[jshattell]

I am designing a level 2 project which will use a two stage recovery system. I am planning on using redundant drogue deployment by utilizing both the ejection charges from the motor and a separate charge ignited by a two event recovery controller. For the main chute deployment, my intentions are to also use two separate redundant charges; one ignited by the two event recovery controller the other by a back-up single event controller.

I have two concerns. The first is, if both black power injection explosions should occur simultaneously at either stage of deployment, the full force of both charges might damage the airframe. My thought to prevent this, would be to stagger the ignition of the charges. For example, I would program the controller to ignite the drogue deployment charge at apogee, but use a long enough delay in the motor so that its charge goes off a bit after apogee. Likewise on the main chute deployment I would set one controller to ignite the charge at say, 500 feet, and the redundant controller to ignite a backup charge at say, 300 feet.

This staggering of ejection charges brings me to my other concern. Let's assume that all charges go off as planned. The result will be two of the charges igniting after separation. What affect will this have on the recovery descent? Could a redundant explosion after a separation damage the bridle cord, the parachute, or any part of the recovery apparatus?

Please respond with any comments.

[kgholloway]

First let me say that your recovery profile is one that I have seen used many times with success. For example 2 years ago our club project was a 11.5" dia. X 10' long upscale of the Estes' "Canadian Arrow". It flew on an older L-1120 motor using a MissileWorks RRC2 and a PML altimeter. Both were set to deploy the drogue at apogee and the main at either 1000' or at 800'. There was no problem with using two charges at apogee as no two altimeters will sense apogee at exactly the same time.

When the rocket was coming down under drogue we could distinctly hear the second charges going off. There was no apparent damage or problem with either of the redundant charges.
_________________
Kenneth G. Holloway
NAR #78336, L-II

[troj]

What you describe is a fairly common setup.

As you figured out, you don't want two charges going of simultaneously. The pressure can be a bit much.

A charge going while the recovery system is out doesn't do any harm. Redundant, staggered charges are very common.

-Kevin