To prevent the solid rocket motor from premature ejection charge from firing a proper delay grain must be integrated between the propellant and the ejection charge. this video will show the evolution the reusable recovery device went through from the time of no delay to the point of a forty seconds delay timer. This single device consists of three parts welded together to form a single unit. The upper portion is what contains the ejection and is the last part that fires with a hot flame, the middle part is a repurposed diesel fuel injector where the delay grain enters. Surrounding the injector is a circular steel case closed on the side facing the propellant grain except for the whole reading to the delay grain as shown in the video.
As the propellant burnout, the delay grain takes over which much slower burn rate until it reaches the ejection charge which then shoots out a hot flame in from of the motor. The delay goes quicker when epoxy is not added

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