Hybrid rockets have been a concept for the last 75 years, and are becoming more popular, even being in use in the Virgin Galactic SpaceShipTwo. Simply put, hybrid rockets are rocket engines that use both solid and liquid fuel.

RocketMotorTwo Edit

Scaled Composites has developed hybrid rocket motor which is safer and more controlable and contains four main features.

Pro's of Use Edit

  • Mechanically simpler - requires only a single liquid propellant resulting in less plumbing, fewer valves, and simpler operations.
  • Denser fuels - fuels in the solid phase generally have higher density than those in the liquid phase
  • Metal additives - reactive metals such as aluminum, magnesium, lithium or beryllium can be easily included in the fuel grain increasing specific impulse($ I_{sp} $)
  • Higher theoretical $ I_{sp} $ obtainable
  • Less explosion hazard - Propellant grain more tolerant of processing errors such as cracks
  • More controllable - Start/stop/restart and throttling are all achievable with appropriate oxidizer control
  • Safe and non-toxic oxidizers such as liquid oxygen and nitrous oxide can be used

Disadvantages of Use Edit

  • Oxidizer/Fuel ratio shift during fuel burn and variable Oxidizer/Fuel ratio along motor length, resulting in degradation of specific impulse
  • Difficult to re-load propellant, especially if partially depleted (same re-loading procedure as with solid-fuel rockets)
  • Hard start (same as with solid rocket motor), placing additional stress on launch vehicle