I work on rockets with my best friend every year. She is a Physics Professor at Madison-I do the rocket fuel-she does the propulsion…..
What propels a rocket is Newton's third law of motion, for every force acting on one body there is an equal and opposite force acting on another. When the rocket burns its fuel the expanding gases thus created create a force that shoots these gases out the back end of the engine.
This force create a second force that pushes the rocket in the opposite direction (forward). So, the rocket is pushing against the gases that it shoots out the back. At the same time, these gases are pushing on the rocket. This cause both to move in opposite directions.
1) You can move through a vacuum. (Well, it will then no more be a vacuum, because you are inside it...)
For instance, the photons of light move through the vacuum of a light bulb, or through intergalactic space. Objects moving through vacuum follow inertia, gravitational fields, and other kind of fields.
The greatest problem is, not to follow this given way. To lose this problem is the purpose of spacecraft propulsion.
2) Spacecraft propulsion:
"When in space, the purpose of a propulsion system is to change the velocity v of a spacecraft. Since this is more difficult for more massive spacecraft, designers generally discuss momentum, mv. The amount of change in momentum is called impulse. So the goal of a propulsion method in space is to create an impulse."
"The law of conservation of momentum means that in order for a propulsion method to change the momentum of a space craft it must change the momentum of something else as well. A few designs take advantage of things like magnetic fields or light pressure in order to change the spacecraft's momentum, but in free space the rocket must bring along some mass to accelerate away in order to push itself forward. Such mass is called reaction mass.
In order for a rocket to work, it needs two things: reaction mass and energy. The impulse provided by launching a particle of reaction mass having mass m at velocity v is mv. But this particle has kinetic energy mv²/2, which must come from somewhere. In a conventional solid, liquid, or hybrid rocket, the fuel is burned, providing the energy, and the reaction products are allowed to flow out the back, providing the reaction mass. In an ion thruster, electricity is used to accelerate ions out the back. Here some other source must provide the electrical energy (perhaps a solar panel or a nuclear reactor), while the ions provide the reaction mass"
"Rather than relying on high temperature and fluid dynamics to accelerate the reaction mass to high speeds, there are a variety of methods that use electrostatic or electromagnetic forces to accelerate the reaction mass directly. Usually the reaction mass is a stream of ions. Such an engine requires electric power to run, and high exhaust velocities require large amounts of energy."
"The law of conservation of momentum states that any engine which uses no reaction mass cannot move the center of mass of a spaceship (changing orientation, on the other hand, is possible). But space is not empty, especially space inside the Solar System; there are gravitation fields, magnetic fields, solar wind and solar radiation. Various propulsion methods try to take advantage of these. However, since these phenomena are diffuse in nature, corresponding propulsion structures need to be proportionately large."
Source and further information:
http://en.wikipedia.org/wiki/Spacecraft_propulsion http://en.wikipedia.org/wiki/Spacecraft 3) Further information:
- about vacuum:
http://en.wikipedia.org/wiki/Vacuum - outer space:
http://en.wikipedia.org/wiki/Outer_space - space travel:
http://en.wikipedia.org/wiki/Intergalactic_travel http://en.wikipedia.org/wiki/Interstellar_travel http://en.wikipedia.org/wiki/Interplanetary_travel
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