Editing Hybrid-propellant rocket (section)

===Advantages compared with liquid rockets===
* Mechanically simpler – requires only a single liquid propellant resulting in less plumbing, fewer valves, and simpler operations.
* Denser fuel – fuels in the solid [[phase (matter)|phase]] generally have higher density than those in the liquid phase, reducing overall system volume.
* Metal additives – reactive metals such as aluminium, [[magnesium]], [[lithium]] or [[beryllium]] can be easily included in the fuel grain increasing [[specific impulse]] (<math>I_{sp}</math>), density, or both.
* Combustion instabilities – Hybrid rockets do not typically exhibit high frequency combustion instabilities that plague liquid rockets due to the solid fuel grain breaking up acoustic waves that would otherwise reflect in an open liquid engine combustion chamber.
* Propellant pressurization – One of the most difficult to design portions of a liquid rocket system are the [[turbopumps]]. Turbopump design is complex as it has to precisely and efficiently pump and keep separated two fluids of different properties in precise ratios at very high volumetric flow rates, often cryogenic temperatures, and highly volatile chemicals while combusting those same fluids in order to power itself. Hybrids have far less fluid to move and can often be pressurized by a blow-down system (which would be prohibitively heavy in a liquid rocket) or self-pressurized oxidizers (such as [[nitrous oxide|N<sub>2</sub>O]]).
* Cooling – Liquid rockets often depend on one of the propellants, typically the fuel, to cool the combustion chamber and [[nozzle]] due to the very high heat fluxes and vulnerability of the metal walls to oxidation and stress cracking. Hybrid rockets have combustion chambers that are lined with the solid propellant which shields it from the product gases. Their nozzles are often graphite or coated in ablative materials similarly to solid rocket motors. The design, construction, and testing of liquid cooling flows is complex, making the system more prone to failure.