Following changes were made:

The nozzle was made shorter, essentially by shortening the graphite middle part ( with ca. 5cm ) such that the nozzle became more traditional in shape ;

• To come closer to the optimal ratio of Ae/At for zinc-sulfur powder 3/1, the outlet diameter was made smaller : from 70 mm to 60 mm ;
• The motor case was longer, with an effective length of 650 mm ;
• The propellant charge was this time not one single monolithic block but made of 3 different parts : starting from the nozzle :
  • A propellant grain of 270 mm length and 90 mm in diameter with a central hole of 30 mm, composed of 67,5% Zn, 28% S, 4,5% Al filled with zinc-sulfur powder 3/1 (left block painted in blue).
  • A cigarette block (end-burner) of 30 mm and also 90 mm in diameter with the same propellant composition (gray part in the middle ;
  • A cigarette block of 320 mm and 90 mm in diameter with the following composition: 70% Zn, 25,5% S en 4,5% Al (white painted block right), which is the same as for ZAS10-1.
  • The 3 block were glued together with Pattex Uni-rapide a cyanoacrylate.

The outside surface of all grains was painted with alkyd lacquer in order to stabilize the surface and assure a good contact with the coating.

The purpose of this approach is the following: although the burning rate of the propellant composition used in the ZAS10Z-1 is very fast (about 400 mm/s) a motor of 1500 mm (the final version) long would finally generate a working duration of 7 to 8 s (apart from the time needed for the flames to reach the end of the propellant grain we must also take into account the time needed for the combustion products to leave the motor). As a consequence we have to shorten the reaction phase. This can be done in making use of both internal burners and end-burners. The small end-burning grain of 30 mm long, burns about as long as the internal burner as they have the same propellant composition and the fast burning grain will only be ignited once both blocks are consumed.

Also the isolation has been changed. Instead of applying coating to the outer wall we have opted to pour a low viscous polymer (protoflex with a viscosity of about 2500 cp) between the grains and the wall (all grains were first coated with paint – reasons for the different colors). The fact that we dispose of about 4 mm between case and grain is sufficient to apply this method. A sufficient coating thickness was considered necessary given the experience with the ZAS10Z-1, where at different places the coating was burned away and the case overheated. Between grain and nozzle, silicone was used to protect the wall.