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Ion thrusters have two major considerations however. The first is that they take a lot of energy, partly to ionize the materials, but most especially to accelerate the ions to the extremely high speeds. Exhaust speeds of 30 km/s are not uncommon. This compares well with the 3-4.5 km/s for chemical rockets in terms of propellent usage. However, since energy consumption is proportional to exhaust velocity squared and the thrust per kg of fuel is only proportional to exhaust speed, the overall thrust for a given amount of energy is inversely proportional to exhaust speed (see also the energy computed from the rocket equation). Thus, in practice, it turns out that with currently practical energy sources, masses, and vehicles, only extremely modest accelerations are feasible, typically of order a milligee.
The second consideration is the relatively short life of the thruster. The ions often hit the grids on their way through the engine, which leads to the decay of the grids, and their eventual failure. Smaller grids lower the chance of these accidental collisions, but decrease the amount of charge they can handle, and thus lower the acceleration.
The Hall effect thruster is a type of ion thruster that has been used for decades for station keeping by the Soviet-Union and is now also applied in the West: the European Space Agency's satellite Smart 1 uses it.
Of all the electric thrusters, ion engines have been the most seriously considered commercially and academically in the West. Ion engines are best used for missions requiring very high ΔV (the overall change in velocity, taken as a single value), interplanetary missions, for example.
interplanetary missions. This engine was tested in the highly successful space probe Deep Space 1. Hughes has developed the XIPS ( Xenon Ion Propulsion SystemXIPS A method of electrical propulsion where Xe+ ions ( xenon atoms with one electron removed) are accelerated electrostatically through an electric field to velocities of about 30 km/s. There is a positive grid with an electric potential of +1090 V and a) for performing stationkeeping on geosynchronous satellites.
In 2003 NASA ground-tested a new version of their ion engine called High Power Electric Propulsion , or HiPEP. The HiPEP engine differs from earlier ion engines because the xenon ions are produced using a combination of microwaveThis page is about the radiation; for the appliance, see microwave oven. Microwaves are electromagnetic waves with a wavelength longer than infrared light, but shorter than radio waves. Microwaves, also known as Super High Frequency (SHF signals, have wavs and spinning magnetThis article is about magnetized material. Magnet is also the name of a commune in the Allier departement, in France A magnet is an object that has a magnetic field. A so-called permanent magnet is made of a ferromagnetic material. Such materials consists. Previously the electrons required were provided by a cathode. Using microwaves significantly reduces the wear and tear on the engine by avoiding any contact between the speeding ions and the electron source.
Most other electric spacecraft engine designs are based on the same principles, but attempt to avoid the problems with grids with a combination of other electric or magnetic fields.
JP Aerospace has been working to build an orbital airshipThe orbital airship also called the space blimp is a proposed space transportation system that carries payloads to and from low Earth orbit. In the Airship To Orbit (ATO) design envisioned by JP Aerospace, there are three components. A conventional airshi, which uses a combination of a balloon and ion thrusters to achieve orbit without any use of conventional rockets, for roughly one dollar per ton per mile of altitude.
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