Disadvantages of hybrid rockets
Hybrid rockets exhibit some disadvantages when compared with liquid and solid rockets. These include:
- Oxidizer-to-fuel ratio shift ("O/F shift") - with a constant oxidizer flow-rate, the ratio of fuel production rate to oxidizer flow rate will change as a grain regresses. This leads to off-peak operation from a chemical performance point of view.
- Low regression-rate (rate at which the solid phase recedes) fuels often drive multi-port fuel grains. Multi-port fuel grains have poor volumetric efficiency and, often, structural deficiencies. High regression-rate liquefying fuels developed in the late 1990s offer a potential solution to this problem.
For a well-designed hybrid, O/F shift has a very small impact on performance because Isp is insensitive to O/F near the peak.
