I could be wrong, but here is what I understand.
The part labelled "PPSD" contains the ignitor of the 1st pulse & a cap that separates the 2 pulses. The 1st pulse is the bigger of the 2. This will provide the kinetic energy needed to catch up to the target. The missile will coast for a while until the missile seeker catches up to the target. Then the 2nd pulse will be ignited, the ignitor is marked as "PRSM". The burning gasses from this pulse will blast open the cap that physically separates the two pulses.
The cap is like a one-way valve. Pressure from the 2nd pulse can open it, but pressure from the 1st pulse in the opposite direction won't budge it. Don't know how this cap is designed, made, what material is used etc.
The Astra Mk1/2 are good missiles, but it still has some way to go. I would like to see the big cruciform wings reduced in size or at least be foldable. This configuration is okay for external carry, but not good for internal carry in a IWB. The Mk3 will also have the same problem. There it is the ducted intakes, not the fins, that will cause this problem.
