Capstone Tank Design Project

endcap internal view endcap real life image At Oregon state University there are several rocketry teams, I was part of the Hybrid Propellant Rocket Team, our goal was to build a hybrid propellant Rocket to reach the Karman Line. I was part of the propulsion team, and was the lead designer for our oxidizer tank.

We had to design a pressure vessel to meet several requirements:

  • maximize propellant volume (no hemispheric tanks or tank ends)
  • have attachment points for several sensors at fittings, including:
    • Temperature sensor
    • Pressure Sensor
    • Capacitance Sensor
    • Filling port
    • Drain port
    • structural connections for motor tube struts
    • emergency venting port
    • radial rocket tube interfaces
  • Mainly student manufacturable
  • quick assembly and disassembly for cleaning and transport
  • hold liquid Nitrous Oxide at its room temp vapor pressure
  • at a factor of safety of at least 2 for yielding

These requirements forced us to innovate. We had to abandon regular hemispheric tank ends due to space and fixture constraints, even though they have nice stress characteristics. We simply couldn’t justify the waste associated with buying a large piece of aerospace grade aluminum stock and machining 99% of it away. Just one set of end caps would put us over budget, and would leave no room for error.

We designed an internal ribbing structure to prevent excessive end cap bending, and tested it using finite element analysis before consulting with our faculty advisors or manufacturing. Additionally, we decided to fix our ports to the sides of these ribs to reduce weight while maintaining rigidity.

We also had many discussions as to the sealing method for our tank. in previous years, we had issues with our O-rings being cut during assembly. this was due to the rings passing underneath the machine screw holes we used for fixing the cap to our previous setup. in order to mitigate this issue, we decided to use a 2 pronged approach. First we have an O-ring that will pass underneath the bolt holes normally. If this is cut, the machine screws we use will have O-rings at the base of their threads, providing an alternate sealing method along with the second O-ring.