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Dec19-10, 10:12 PM
P: 64
Quote Quote by mheslep View Post
My first thought when I saw the OP's part about a fixed planetary laser propelling a spacecraft was not momentum transfer from photons but a photoelectric energy capture, which then is used to produce thrust via some high velocity acceleration of on board matter, plasma, etc. Seems like that's more likely to be successful, at least superficially.
but it is said laser and solar sails can propel themselves from EM pressure

Quote Quote by D H View Post
To illustrate the silliness of this idea, let's up the ante a bit. Well, not just a bit. A whole lot. How about a laser that consumes, without any losses, the equivalent of the entire world's electric energy production? That was about 6.251019 joules for 2005, or about 2 terawatts. The thrust produced by a 2 terawatt laser: 6,700 newtons.

A spacecraft that produces 6,700 newtons of thrust and contains a 2+ terawatt power plant and a 2 terawatt CW laser will not go anywhere.

Ion thrusters accelerate slowly but they do gain in speed through time. In space one may assume the object will tend to remain in motion, and even small acceleration should add up over long periods of time. Also fission reactors need not be extraordinarily large, and shielding requirements depend upon the construction of the ship.

The trade-off for the high top speeds of ion thrusters is low thrust (or low acceleration). Current ion thrusters can provide only 0.5 newtons (or 0.1 pounds) of thrust, which is equivalent to the force you would feel by holding 10 U.S. quarters in your hand. These thrusters must be used in a vacuum to operate at the available power levels, and they cannot be used to put spacecraft in space because large amounts of thrust are needed to escape Earth's gravity and atmosphere. -link
nuclear waste from which no more energy could be extracted could also be expelled to supplement efforts by reducing mass and providing additional propulsion