beneficial to future mission applications. Chemical propulsion A large fraction of the rocket engines in use today are chemical rockets; that is, they obtain the energy needed to generate thrust by chemical reactions to create a hot gas that is expanded to produce thrust. Many different propellant combinations are used to obtain these chemical reactions, including hydrazine, liquid oxygen, liquid hydrogen, nitrous oxide, and hydrogen peroxide for example. They can be used as a monopropellant or in a bi-propellant configuration. Green chemical propulsion The dominant form of chemical propulsion for satellites has historically been hydrazine, however this fuel is highly toxic and at risk of being banned across Europe. Non-toxic 'green' alternatives are now being developed to replace hydrazine. Nitrous oxide-based alternatives are garnering a lot of traction and government support, with development being led by commercial companies Dawn Aerospace, Impulse Space, and Launcher. The first nitrous oxide-based system ever flown in space was by D-Orbit onboard their ION Satellite Carrier (space tug) in 2021, using six Dawn Aerospace B20 thrusters, launched upon a Falcon 9 rocket. Reaction engines Reaction engines produce thrust by expelling reaction mass, in accordance with Newton's third law of motion. This law of motion is most commonly paraphrased as: "For every action force there is an equal, but opposite, reaction force." Examples include jet engines, rocket engines, pump-jet, and more uncommon variations such as Hall–effect thrusters, ion drives, mass drivers, and nuclear pulse propulsion. Rocket engines Most rocket engines are internal combustion heat engines (although non combusting forms exist). Rocket engines generally produce a high temperature reaction mass, as a hot gas. This is achieved by combusting a solid, liquid or gaseous fuel with an oxidiser within a combustion chamber. The extremely hot gas is then allowed to escape through a high-expansion ratio nozzle. This bell-shaped nozzle is what gives a rocket engine its characteristic shape. The effect of the nozzle is to dramatically accelerate the mass, converting most of the thermal energy into kinetic energy. Exhaust speed reaching as high as 10 times the speed of sound at sea level are common. Rocket engines provide essentially the highest specific powers and high specific thrusts of any engine used for spacecraft propulsion. Ion propulsion rockets can heat a plasma or charged gas inside a magnetic bottle and release it via a magnetic nozzle, so that no solid matter need come in contact with the plasma.