Liquid-propellant rocket
A rocket that burns liquid fuel and oxidiser fed into a combustion chamber. The burn can be throttled, stopped and restarted.
Solid fuel such as gunpowder, once lit, cannot be stopped until it has burnt out. With liquids, pumps and valves vary the flow and so the thrust. Robert Goddard discussed using rockets to observe the upper atmosphere in a 1919 paper[1], and in 1926 flew the world's first liquid rocket, burning gasoline and liquid oxygen. It rose about 12.5 metres.
Liquid hydrogen with liquid oxygen gives the highest exhaust speed of any chemical fuel and has been used in upper stages such as those of the Saturn V that carried Apollo. It has to be kept extremely cold, which complicates the plumbing and pumps. Transferring propellant from one vehicle to another in space is key to plans for the Moon and Mars, but has yet to be demonstrated at scale.
Related terms
- Rocket equationThe equation stating that a rocket's gain in speed depends on its exhaust velocity and on the ratio of its starting mass to its burnt-out mass.
- Multistage rocketA rocket that sheds the parts whose fuel is spent as it flies. With that weight gone, the remaining stages accelerate faster.
- Reusable rocketA rocket that is recovered after launch, serviced and flown again. Not throwing the vehicle away brings down the cost of launch.
On the timeline
Sources
- R. H. Goddard, “A Method of Reaching Extreme Altitudes,” Smithsonian Miscellaneous Collections 71(2) (1919).