11. AMROC developed the largest hybrid rockets ever created in the late 1980s and early 1990s. 12. HTPB is also used as a hybrid rocket fuel. 13. Environmental Aerospace Corporation ( eAc ) was incorporated in 1994 to develop hybrid rocket propulsion systems. 14. The hybrid rocket engine design was dropped in favor of a cluster of Orbitec's Vortex engines. 15. Several hybrid rockets have been successfully launched so far, reaching altitudes of 10 ~ 20 km. 16. ONERA, based in France, and Volvo-Flygmotor, based in Sweden, developed sounding rockets using hybrid rocket motor technology. 17. These could have included multi-pulse rocket motors, thrust vectoring, hybrid rockets , gel propellants, and ductless external combustion ramjets. 18. The polyamide hybrid rocket motor is a modified version of the polybutadiene version, with different oxidizer valve arrangement. 19. Nitrous oxide can be used as an oxidizer with various fuels; it is popular mainly in hybrid rockets . 20. Liquid systems enable higher specific impulse than solids and hybrid rocket engines and can provide very high tankage efficiency.
