Editing Hybrid-propellant rocket (section)

===Disadvantages of hybrid rockets===
Hybrid rockets also 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. However, for a well-designed hybrid, O/F shift has a very small impact on performance because <math>I_{sp}</math> is insensitive to O/F shift near the peak.
* Poor [[Hybrid Rocket Fuel Regression|regression]] characteristics 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.<ref>{{cite web |title=Wax Hybrids |department=Science@NASA |publisher=National Aeronautics and Space Administration (NASA) |url=https://science.nasa.gov/headlines/y2003/28jan_envirorocket.htm |url-status=dead |access-date=June 1, 2009 |archive-url=https://web.archive.org/web/20090523003320/http://science.nasa.gov/headlines/y2003/28jan_envirorocket.htm |archive-date=May 23, 2009}}</ref>
* Compared with liquid-based propulsion, re-fueling a partially or totally depleted hybrid rocket would present significant challenges, as the solid propellant cannot simply be pumped into a fuel tank. This may or may not be an issue, depending upon how the rocket is planned to be used.

In general, much less development work has been completed with hybrids than liquids or solids and it is likely that some of these disadvantages could be rectified through further investment in [[research and development]].

One problem in designing large hybrid orbital rockets is that [[turbopump]]s become necessary to achieve high flow rates and pressurization of the oxidizer. This turbopump must be powered by something. In a traditional liquid-propellant rocket, the turbopump uses the same fuel and oxidizer as the rocket, since they are both liquid and can be fed to the pre-burner. But in a hybrid, the fuel is solid and cannot be fed to a turbopump's engine. Some hybrids use an oxidizer that can also be used as a [[monopropellant]], such as [[hydrogen peroxide]], and so a turbopump can run on it alone. However, [[hydrogen peroxide]] is significantly less efficient than [[liquid oxygen]], which cannot be used alone to run a [[turbopump]]. Another fuel would be needed, requiring its own tank and decreasing rocket performance.