U1 through U3 are 555s due to inherent switch bounce advantages. All circuit components from V1 to the right are in the flare. V2 and the "Flare release SW" are on the launch platform. V1 and V2 voltage levels are arbitrary. Follow best circuit design criteria for 555s chosen.
The initial "SAFE" state of the circuit would be:
"Arming SW" OFF. "Flare release SW" ON, "DISABLE LINE" attached to flare circuit (this forces a positive bias on the trigger of U1, ensuring NO OUTPUT from U1 on power up).
Theory of operation:
Time -1 - "Arming SW" closed. U1 ONLY powered up.
TIME 0 - Device release. A switch (or plug removal) removes the +12vdc bias on the trigger of U1, forcing its output HIGH which immediately:
TIME 1 - powers up U2 and U3.
TIME 2 - U2's output goes HIGH for a duration determined by R4 and C5. When U2 times out:
TIME 3 - U2's output goes LOW which puts a negative pulse on U3's trigger, forcing U3's output HIGH, which:
TIME 4 - has a duration (to ensure the flare's proper ignition) set by R6 and C7. This output would feed a small relay or transistor/FET switch enabling a separate, isolated third power source for the ignition heater.
If something other than ignition delay after launch is needed, this circuit will have to be modified.