Since sulfur starts melting at 112°C, zinc-sulphur propellants can also be used as cast grains. It is less well understood than the powder but bears many advantages : the grains are very hard and strong, the density of the propellant is very high (generally between 3.5 and 4.4 g/cm³) and a wide variety of thrust curves and buring times can be produced.

The aim of this zinc-sulfur project is to further investigate the behaviour of the propellant and to come up with higher specific impulses (mostly through the addition of aluminium) and longer buring times. In the longer run the propellant will be used to boost a single stage rocket to an altituted of 7 to 10 km This will be made possible thanks to the very high propellant density and the higher specific impulses (up to 60 s). . The booster will be about 160 cm long and 10 cm in diameter.

So far we have measured specific impulses around 60 s. With better chamber isolation and the use of nozzles with small inlet and outel angle, we may be able to reach 65s. We have also control over the burning rate which, depending upon the propellant composition, can range from about 3 to 10 cm/s. Different types of grains have been tested : cigarette, bates,…

A book titled "Understanding Zinc-Sulfur Propellants" descibes the results of about 35 years of experience with this propellant and is available at VRO.

Test results and pictures of past statical tests:

Thrust curve ZAS5-1 motor. end-burner

Thrust curve ZAS5-4 motor: internal burning tube