Propulsion Methods
How spacecraft push off from nothing — electric propulsion and its nuclear-electric, VASIMR, arcjet and resistojet variants; the propellant-free solar sail; mono- and bipropellant chemical systems; and the waste-nothing staged-combustion engine cycle.
- Arcjet ThrusterPropulsion method
An electrothermal thruster that passes propellant through an electric arc, heating it far beyond what a chemical reaction alone allows before it expands through a nozzle. Arcjets have flown operationally for satellite station-keeping, offering higher exhaust velocity than cold-gas or simple resistojet systems.
- Bipropellant PropulsionPropulsion method
A chemical system that burns a separate fuel and oxidiser, releasing far more energy than a monopropellant and delivering higher exhaust velocity. Bipropellant engines — from hypergolic storable combinations to cryogenic hydrogen–oxygen — power launch vehicles, orbit-insertion burns, and deep-space main engines.
- Electric PropulsionPropulsion method
A family of thrusters that accelerate propellant using electrical energy rather than combustion, reaching exhaust velocities several times higher than chemical rockets. The trade is thrust: forces are gentle — millinewtons to newtons — so electric propulsion excels at station-keeping and patient deep-space cruises, as NASA's Dawn demonstrated in reaching both Vesta and Ceres.
- Monopropellant PropulsionPropulsion method
A simple chemical system in which a single propellant — classically hydrazine — is decomposed over a catalyst bed to produce hot gas, needing no separate oxidiser or ignition. Monopropellant thrusters are workhorses for spacecraft attitude control and small maneuvers, valued for their simplicity and quick, repeatable pulses.
- Nuclear Electric PropulsionPropulsion method
An architecture that pairs a space nuclear reactor with electric thrusters: the reactor generates electricity, which drives ion or Hall thrusters. Unlike solar-electric propulsion it is independent of distance from the Sun, making it a candidate for crewed missions to Mars and the outer Solar System. No nuclear-electric system has yet flown; it remains a design and technology-development goal.
- Resistojet ThrusterPropulsion method
The simplest electric thruster: propellant is warmed by flowing over an electrically heated element and then expelled through a nozzle. Modest but reliable, resistojets have long been used for satellite attitude control and station-keeping, bridging cold-gas systems and higher-performance electric propulsion.
- Solar SailPropulsion method
Propulsion with no propellant at all: a large, lightweight reflective sail is pushed by the momentum of sunlight itself. The thrust is minute but continuous and free, building up large velocity changes over time. Japan's IKAROS proved the principle in interplanetary space in 2010, and The Planetary Society's LightSail 2 demonstrated sail-raised orbits around Earth.
- Staged-Combustion CyclePropulsion method
A high-efficiency rocket-engine power cycle in which propellant burned in a preburner drives the turbopumps and is then routed into the main chamber, so almost none is wasted. It is harder to build than the simpler gas-generator cycle but yields higher performance; the Space Shuttle's RS-25 used it, and SpaceX's Raptor uses the even more demanding full-flow staged-combustion variant.
- VASIMRPropulsion method
An electric-propulsion concept that heats propellant to a plasma with radio waves and confines and exhausts it with magnetic fields, in principle allowing the exhaust velocity to be tuned in flight. It has been tested on the ground but has not flown in space, and operating it at useful power levels would require an electrical source far beyond today's spacecraft.