Okay, my little sister had a question about space shuttles so i'm not sure if this would be classified as a "stupid" question, we were just curious. If we want to travel using a space shuttle throughout outer-space, why can't engineers just build and design space shuttles that are powered by the sun? That way you wouldn't need fuel or anything, you could just use the solar power to power the space shuttle for as long as needed and then when the space exploration is done just, as she would say "fly it back around and put it down on the earth again?" Okay, sorry if we are supposed to know the answer for this. I assume that if such a thing could be done, someone would have done it by now. But we just wanted to know, why not?
Thanks! :]
Thanks! :]
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Propulsion systems are NOT exclusively about the energy source. Here on Earth, yes that is the case, because you can always "grip" some surrounding air, water, or ground against which to push.
But, in the middle of space, there is nothing around you to "grip". Nothing against which to push. You can attempt to put a turboprop on the spacecraft (powered by the system electric power), and that rotor will just spin in place laughing at you while you attempt to go forward.
Solar power in space is useful as a source of energy (which we INDEED DO for many satellites and surface probes), but not as a source of momentum. It could be useful as a source of momentum in the design of a solar sail. And there is an experimental spacecraft propelled by a solar sail called IKAROS. It isn't anywhere near comparable in payload (humans, instruments, supplies, etcetera) to the payload of the space shuttle...so it will be a while before solar sails become practical.
To put the challenge of a solar sail in perspective, a perfect reflection yields a radiation pressure of 9.1 micropascals at the Earth orbit distance from the sun. The problem of course gets worse farther from the sun. Compare this to 360 micropascals, as the sun-gravitational-field weight per unit area of the lightest paper in common production. That is, very light paper is FORTY TIMES heavier than the available support from the sunlight. And this is in the sun's gravitational field at Earth orbit...not the Earth's own gravitational field.
But, in the middle of space, there is nothing around you to "grip". Nothing against which to push. You can attempt to put a turboprop on the spacecraft (powered by the system electric power), and that rotor will just spin in place laughing at you while you attempt to go forward.
Solar power in space is useful as a source of energy (which we INDEED DO for many satellites and surface probes), but not as a source of momentum. It could be useful as a source of momentum in the design of a solar sail. And there is an experimental spacecraft propelled by a solar sail called IKAROS. It isn't anywhere near comparable in payload (humans, instruments, supplies, etcetera) to the payload of the space shuttle...so it will be a while before solar sails become practical.
To put the challenge of a solar sail in perspective, a perfect reflection yields a radiation pressure of 9.1 micropascals at the Earth orbit distance from the sun. The problem of course gets worse farther from the sun. Compare this to 360 micropascals, as the sun-gravitational-field weight per unit area of the lightest paper in common production. That is, very light paper is FORTY TIMES heavier than the available support from the sunlight. And this is in the sun's gravitational field at Earth orbit...not the Earth's own gravitational field.
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