The use of zinc-sulfur powder, without the addition of aluminum (which will increase the pressure severely), is probably the most simple way to make a decent rocket. It yields sufficient performance to reach several kilometers of altitude.

Another major advantage is that when properly designed and built, it will never explode! This is due to the fact that the pressure in the motor will never exceed a given maximum value (about 100 to 120 bar under normal conditions). The conditions are that:

• the propellant is free from moisture (the presence of water may increase the pressure to very high values). Hence the propellant should be dry (like any propellant).
• the inner motor case is insolated to prevent severe heating up which may cause loss of strength of the metal. Cardboard, polyester, epoxy,...of 0.5 to 2 mm is used.

Cast zinc-sulfur grains can be tailored to burn quite slowly (a few cm/s) or very fast (up to 40 cm/s). Hence cigarette grains can be used which makes the construction easier.