Liquid-Propellant Rocket Engines
Engines that store fuel and oxidiser as liquids and feed them into a combustion chamber.
Reference
Rocket Engine Library
A high-level educational overview of major propulsion families. Content explains principles, advantages, limitations, and typical applications. It does not provide construction recipes, propellant formulations, or hazardous testing instructions.
Solid-Propellant Rocket Motors
Motors in which fuel and oxidiser are mixed in a solid grain that burns from exposed surfaces.
Hybrid Rocket Engines
Systems that typically combine a solid fuel grain with a liquid or gaseous oxidiser.
Monopropellant Thrusters
Thrusters that decompose a single propellant, often over a catalyst, to produce hot gas.
Bipropellant Spacecraft Engines
In-space engines that burn separate fuel and oxidiser for higher performance manoeuvres.
Cold-Gas Propulsion
Simple thrusters that expand a stored pressurised gas through a nozzle without combustion.
Gas-Generator Liquid Engine Cycles
Open cycle in which a portion of propellants drives a turbine and is exhausted separately.
Staged-Combustion Engine Cycles
Closed cycle in which turbine drive gas is routed into the main combustion chamber.
Expander-Cycle Engines
Cycle that uses heat absorbed in the cooling jacket to drive the turbopumps.
Cryogenic Propulsion
Propulsion using liquefied gases stored at very low temperature, typically LOX and liquid hydrogen or methane.
Kerosene/LOX and Methane/LOX Propulsion
Hydrocarbon liquid engines pairing RP-1 or methane with liquid oxygen.
Hall-Effect Thrusters
Electric thrusters that ionise propellant and accelerate ions using a combination of electric and magnetic fields.
Gridded Ion Engines
Electrostatic thrusters that accelerate ions through a series of high-voltage grids.
Resistojets and Arcjets
Electrothermal thrusters that heat a propellant electrically before expansion through a nozzle.
Electrospray and Field-Emission Thrusters
Micro-propulsion concepts that accelerate charged droplets or ions from a liquid surface.
Nuclear Thermal Propulsion Concepts
Concepts that use a nuclear reactor to heat a propellant (typically hydrogen) which then expands through a nozzle.
Nuclear Electric Propulsion Concepts
Systems that use a nuclear reactor to generate electricity for high-power electric thrusters.
Solar Sails and Propellantless Concepts
Propulsion that uses radiation pressure or other external forces without expended propellant.
Comparison
High-level performance orientation
Approximate ranges for orientation only. Actual values depend on design, mixture ratio, expansion ratio, and operating point. Do not use for design decisions without primary sources.
| Family | Typical Isp (s) | Thrust class | Throttle / Restart | Primary use |
|---|---|---|---|---|
| Solid motors | ~250–300 | High | Limited / No | Boosters, tactical |
| Liquid bipropellant (storable) | ~280–320 | Medium–High | Yes / Yes | Upper stages, spacecraft |
| Liquid cryogenic (H₂/LOX) | ~420–460 | Medium–High | Yes / Yes | Upper stages, main engines |
| Hybrid | ~280–350 | Medium | Partial / Yes | Sounding, experimental |
| Monopropellant | ~180–250 | Low | Yes / Yes | RCS, station-keeping |
| Cold gas | ~40–80 | Very low | Yes / Yes | Small RCS |
| Hall thruster | ~1,000–3,000 | Very low | Yes / Yes | Orbit raising, deep space |
| Gridded ion | ~2,000–5,000+ | Very low | Yes / Yes | Deep space |
| NTP (concept) | ~800–1,000 | High | Design dependent | Crewed planetary (studied) |
Glossary
Key terms
- Thrust
- Force produced by the engine, typically measured in newtons or pounds-force. Determines acceleration capability for a given vehicle mass.
- Specific impulse (Isp)
- Measure of propellant efficiency: thrust per unit weight-flow of propellant, expressed in seconds. Higher Isp means less propellant mass for a given velocity change.
- Thrust-to-weight ratio
- Engine thrust divided by engine weight (or vehicle thrust-to-weight for the whole system). Critical for liftoff and manoeuvrability.
- Restartability
- Ability to shut down and reignite the engine in flight. Essential for many upper stages and spacecraft.
- Throttleability
- Ability to vary thrust level in a controlled way. Important for landing, structural loads, and trajectory shaping.
- Reusability
- Design intent to recover and fly the same hardware again. Affects margins, inspection, and propellant choice.
- Mission suitability
- Match between propulsion characteristics (Isp, thrust, restart, storability) and the delta-v, timeline, and operational constraints of a specific mission.
Selected references
- NASA — official educational and technical resources on space propulsion.
- ESA — European Space Agency public information on launchers and propulsion.
- NASA State of the Art of Small Spacecraft Technology — propulsion chapter (public reports).
- Public domain and educational overviews of chemical, electric, and nuclear thermal concepts.
All performance figures are approximate and for educational orientation only. Verify against primary technical sources before any engineering use. This page contains no construction or hazardous-operations instructions.