On Monday, February 18, the team went to the propulsion’s laboratory to conduct a half duration test fire of our experimental propulsion system, HM-8. This hybrid motor uses solid HTPB fuel and liquid nitrous oxide oxidizer, and this year we have been developing a self-pressurized system, where instead of having nitrogen gas as a back pressure to keep nitrous oxide flowing like we had in HM-7, the nitrous oxide evaporates and is used as back pressure. This idea was developed as a possibility to reduce our rocket’s weight. Our previous data from flow tests indicated that the self-pressurizing system had comparable flow rates and pressures to our previous system, so we moved forward with the test fire.
However, we ran into new problems, where because we no longer had an inert gas (nitrogen) to put out the fire after the liquid nitrous oxide burn, the gaseous nitrous oxide continued to let the fire burn slowly. This fire burned through the rest of the fuel, the epoxy liner, and melted the aluminum combustion chamber at a point of high pressure.
We learned the importance of having an inert gas to back pressure our system, and we are going through a redesign process to get rid of using an oxidizing gas to back pressure the system.