3 ms·
"""It would also need to be big – some 200 metres long and 12 metres in diameter – and powerful, requiring 165 megawatts of power to generate just 1
by fao_ 7y ago
"""It would also need to be big – some 200 metres long and
12 metres in diameter – and powerful, requiring 165
megawatts of power to generate just 1 newton of thrust,
which is about the same force you use to type on a
keyboard. For that reason, the engine would only be
able to reach meaningful speeds in the frictionless
environment of space. “The engine itself would be able
to get to 99 per cent the speed of light if you had
enough time and power,” says Burns."""
So it falls into the same "impractical except at very high speeds for long, long, long journeys" category with "we can explode nuclear bombs on one end of the ship and use the explosion against a giant shield, to speed us up".
In other words, it's no Alcubierre drive.
- gbrown 7y agoThe bombs actually seem more practical.
- fao_ 7y agoThey seem so at first glance, but you have to build a couple of sheilds -- one for nuclear debris and the other for interstellar debris. There are also other problems with emission, fuel, etc. Issac Arthur has a good video on it (https://www.youtube.com/watch?v=3aBOhC1c6m8 https://www.youtube.com/watch?v=3aBOhC1c6m8). All of Issac Arthur's stuff is, quite frankly, amazing. He has a clear understanding of the material and manages to convey it in a way to laymen, like no one else.
- thelazydogsback 7y ago> requiring 165 megawatts of power to generate just 1 newton of thrust Not my field, but with that power, wouldn't an old-fashioned ion drive give you a lot more thrust than that?? [after some searching] With 165MW is looks like you could run hundreds of existing ion engines to get you to about 1/2C speed with a thrust measured in 1000's of newton's. https://en.wikipedia.org/wiki/Ion_thruster https://en.wikipedia.org/wiki/Ion_thruster
- readams 7y agoIon drive requires propellant. But it would be similar to a photon drive.
- skykooler 7y agoWith ion engines, you need fuel to be ionized - usually xenon. The faster you want to go, the more of your energy just goes toward accelerating the fuel in your tank. The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C.
- adwn 7y ago> The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C. That is not correct. The delta-v of a rocket (i.e., the maximum speed it can reach) depends on the effective exhaust velocity and on the mass fraction of its propellant; see [1]. For example, a rocket which is initially 90% propellant, can reach a velocity ~2.3 times its effective exhaust velocity. [1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
- skykooler 7y agoFair enough. Either way, the fuel requirement makes it pretty much impossible to reach a significant fraction of the speed of light with ion engines.