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Artist's conception of satellite with a tether Space tethers are cables , usually long and very strong, which can be used for propulsion, stabilization, or maintaining the formation of space systems by determining the trajectory of spacecraft and payloads . [ 1 ] Depending on the mission objectives and altitude, spaceflight using this form of spacecraft propulsion may be significantly less expensive than spaceflight using rocket engines . Four main techniques for employing space tethers are in development: [ 2 ] [ 3 ] Electrodynamic tether This is a conductive tether that carries a current that can generate thrust or drag from a planetary magnetic field , in much the same way as an electric motor .
Hydrogen and oxygen can be combined in a fuel cell to produce electrical energy. A fuel cell uses a chemical reaction to provide an external voltage, as does a battery, but differs from a battery in that the fuel is continually supplied in the form of hydrogen and oxygen gas. It can produce electrical energy at a higher efficiency than just burning the hydrogen to produce heat to drive a generator because it is not subject to the thermal bottleneck from the second law of thermodynamics . It's only product is water, so it is pollution-free. All these features have led to periodic great excitement about its potential, but we are still in the process of developing that potential as a pollution-free, efficient energy source (see Kartha and Grimes).
Fritz Haber, 1918 The Haber process , also called the Haber–Bosch process , is the industrial implementation of the reaction of nitrogen gas and hydrogen gas . It is the main industrial route to ammonia : [ 1 ] N 2 + 3 H 2 → 2 NH 3 (ΔH = −92.22 kJ· mol −1 )