Wednesday, March 13, 2013

Solar Electric Propulsion [SEP] - Ion Propulsion [IP]

An alternative to chemical combustion propulsion for Space travel.

This month's issue of the 'Aerospace America' magazine carries an interesting article on the development of Solar Electric Propulsion [SEP], popularly referred to as Ion Propulsion. The technology is still in a state of relative infancy, with the propelling force around one-tenth that of a corresponding sized chemical thruster. Efforts are on to increase the power obtained, from the present 3-4 KW to around 300 KW as a long term goal, making it possible to power spacecraft that could perform unmanned spaceflights, especially ferry services. In the meantime, NASA hope to achieve a target power output of 30 KW by the end of this decade.

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An interesting application envisaged for Ion Propulsion-based space crafts is to use it to nudge asteroids away from trajectories that would lead to its collision with Earth. The rationale being that the gravitational forces exerted by the mass of the spacecraft on interaction with the asteroid's mass [Newton's law of gravity] would be sufficient to slightly alter the orbit of the asteroid. Ion thrusters, with their low but sustained propulsion1 are perfectly suited to maintain position of the spacecraft in vicinity of the asteroid, nudging it away. In fact, Astronomers announced that one such asteroid could very well hit Earth in 2036. Possibility of it occurring depended on how close to the Earth would it fly past in 2029. Fortunately, recent calculations revealed that in 2029, it would be flying past Earth at a distance that would prevent it from hitting Earth in 2036. However, in the intermediate period between the announcement and calculations, one of the solutions proposed to avert disaster was building such an Ion Propulsion powered Gravity Tractor.


Related: Space Station: since the ages & in the future

1 = As mentioned in the article, for NASA's Dawn mission, the Ion Propulsion thrusters operated continuously for 4 days. Fuel in a chemical propulsion-based system would have run out much earlier. NASA successfully ran its NSTAR engine for 3.5 years without failure.