In the early years, from Aspire 1 through to ASRV2, Aspirespace rocket vehicleswere powered by solid rocket motors. At the time, this was an ideal source of propulsion as such motors are commercially available and do not require any specialist knowledge of rocket motor design.
However, there are disadvantages associated with the use of solid rocket motors by amateur rocketry groups such as Aspirespace, due to the need to handle and store large quantities of explosive substances.
Concerns regarding safety and the desire to develop our own propulsion system, led Aspirespace to switch from solid motors to hybrid rocket engines. Since 1995 Aspirespace has built and tested several designs of hybrid engine, namely the H0, H2, H20, and experiments with wax hybrids.
We've developed sophisticated hybrid engine simulation software that allows us to design bespoke hybrids to our requirements. The software models the physics of the emptying oxidiser tank, the flow through the injector, a chemical analysis and heat released within the combustion chamber, and then the flow dynamics through the nozzle with real nozzle effects such as the effect of changing altitude during the burn. The software then produces tabular outputs such as a thrust curve, and a graph of the hybrid Centre of Gravity movement with time during the burn.
Click on this picture to show a video of the H2 hybrid rocket engine firing.