How do spacecraft propel themselves if outerspace is a vaccum?

Answer 1

Newton’s law of “for every action there is an opposite and equal reaction” is what propels spacecraft. They can do it without rockets.

It is not gravity and those that said rockets don’t explain how something like an ion engine works.

The best example for this is to put yourself in a rowboat with a bunch of large stones. If you throw a stone out behind you then the action of throwing it out will propel you forward. The splash that it makes in water is only secondary. Keep throwing out more stones and you will keep moving forward. Once you overcome your inertia then you can use additional stones to accelerate; providing more thrust.

What is happening inside a rocket is that the engine is pushing out a lot of gas at a very high speed, through a narrow valve. I had a toy rocket that used water and air for fuel, but nothing ever burned; it was only is a pressurized container of water. You simply partially fill the plastic rocket with water (about 75%) and then using a simple bicycle pump you add air pressure. The pressurized air would propel the rocket once released by pushing the water through a narrow valve. The air pressure is over that of the outside pressure so it pushes the water out the back end, through that narrow valve, and that propels the rocket forward. If it was simple air like a balloon then the thrust would be less. But, water is an incompressible liquid that is fairly dense, so pushing that out the rear gave the rocket more power. A balloon of the same size would go a few feet, but this water propelled rocket went several dozen feet into the air.

In a normal rocket, similar to what NASA uses, the fuel is hydrogen or a very flammable gas like kerosene (as in the Saturn 5 for the Apollo program) and liquid oxygen. The oxygen is liquidized so more of it can be stored at a higher pressure. When the solid rocket boosters of the shuttle or of the toy model rockets are made they use a solid mix of a highly flammable fuel with an oxidizer in the mix converted to a solid which makes a more stable engine. The problem is that a solid fuel rocket engine can’t be shut off once it is started and it is less efficient than a straight hydrogen and oxygen liquid oxygen. Liquid oxygen and liquid hydrogen is what is used in the main tank of the space shuttle to fuel the shuttle’s engines. The throwing out of the rocket fuel provides lift, the explosion of that fuel provides even more lift, but the action that starts it is the simply Newtonian action of throwing something away. Remember that force and matter are related by E=mc^2 (Energy = mass X speed of light squared). Now a rocket engine’s thrust is no where near the speed of light, but the energy of the chemical reaction of burning the fuel becomes thrust; the more violent the burning the more energy, the more thrust. This is all calculated with the formula F=ma (Force = mass X acceleration).

Lifting off from the earth is hard to do; it takes a speed of at least 25,000 mph to escape the gravity of the earth. We launch space craft near the equator so that we can use the additional rotational speed of the earth to help the rocket. Even then it takes a lot of energy to move the spacecraft from low orbit to a higher orbit. All of our probes to our moon and other places where only put into space by a rocket; moving them out into a higher earth orbit and away from the earth required gravity assist orbits with simple orbital corrections administered by pressurized jets.

The spacecraft is lifted into orbit and then gravity causes the spacecraft to fall. A stable orbit is called free fall because you are falling around the object that you are orbiting. The gravity on the Space Station is called microgravity because it is so faint that it is almost undetectable. The mass of the Space Station provides more gravitational attraction to the astronauts than the earth, so they float. But, the gravity of the earth still holds the station in its orbit. Once you are in a stable orbit then the gravity of the object you are orbiting has very little effect on you. This is why people don’t get pulled off the face of the earth by the attraction of the moon or the sun. However, both of those gravitational forces create our tides.

The New Horizons Pluto Probe uses a revolutionary new engine; an ion engine. In this case it provides a very little propulsive force over a long time and at a constant acceleration. Although the New Horizons Probe was only launched a few years ago it is the fastest moving man made object ever created. That record used to be held by the space craft Voyager and both of them got most of their propulsion from a gravity assist maneuver.

In the case of the New Horizons Probe the engine uses a fuel that holds an electrical charge. As the charged powder is thrown out the rear of the engine it provides more thrust. Since the powder is electrically charged and more energetic it provides a little more thrust. However, this thrust is very small; it couldn’t lift a rocket from the face of even the moon. With the New Horizon Probe in deep space the small thrust of the ion engine can provide a constant acceleration. Since the powder and the tiny electrical generator are small and light the space craft can use only a little force to keep accelerating it. This brings in one more of Newton’s Laws: “Any object in motion tends to stay in motion.” In space the friction is very small, so only a tiny thrust can provide a lot of acceleration.

One of the most powerful forces in the universe is gravity, it is how the sun keeps the earth and the other planets in orbit, it forms a black hole, and it crushes collections of gas and dust into planets, and larger collections into suns. The force of gravity is so strong that hydrogen fusion is possible inside of a star. The star’s great mass causes a huge amount of pressure at its core, which then creates more heat, which only adds energy to the equation to create fusion.

If a spacecraft is orbiting around the earth then it can use a dive maneuver to draw force from the earth’s orbital speed to propel the spacecraft. This maneuver is called a gravitational assist. The voyager space craft took a gravitational assist around the earth to start it on its mission. Then it took a gravitational assist around Venus, the Sun and the planet Jupiter all to give it enough thrust to move it out into the outer system. So the gravity assist maneuver has sent our spacecraft further than any rocket has.

Rockets work by dumping mass out the rear of the spacecraft though a narrow valve (the engine), which gives it thrust. Exploding that mass only increases the thrust; this is how rockets work. Ion engines are far weaker, but can provide a steady acceleration over a long period of time, thus more acceleration. The gravity assist maneuver uses the orbital speed of a planet to provide extra energy to propel the spacecraft. Spacecraft thrust comes from more than just rockets. We have to use rockets to put our spacecraft into orbit because it requires a violent (powerful) thrust over a very short time to get the high acceleration needed to defeat the gravity at the surface of the earth.

Answer 2

The rocket doesn't really propel itself the same way as a boat or an airplane, it gives off little Co2 impulses to give the craft inertial momentum in any given direction. They even put in big gyroscopes to maintain a stable spin and trajectory.
There is no atmosphere in space, so no friction to stop the motion of the ship, or satellite.
Also nothing to propel against.
The Co2 tanks blast the compressed gas at high speeds through a nozzle, forcing a backwards pressure against itself.
A tiny blast is all it requires to give it motion in any direction, usually several of them counteracting one another, until the gyroscope says they've reached stability. The force of pulling away from the Earths gravity keeps them on course, as they can't really stop due to inertia and momentum.

Answer 3

Same reason a bullet shoots out of a gun. A higher pressure trying to escape to a lower pressure area. Behind a rocket's engine is a high pressure area, the rocket is trying to get away from it. The outward expansion of gases causes the rocket to be pushed forward. Because there is virtually no friction in space it doesn't take much to push the rocket. Get your mind around this. Earth's atmosphere is around 14.7 psi. If you were on a planet with an atmospheric pressure of 75,000 psi that gun wouldn't even fire. The pressure of the bullet trying to leave is not greater than the outside pressure of the air. This is why things get crushed inside gas giant planets like Jupiter. Hope this helps.

Answer 4

Its pushing against the burning fuel. It doesnt need atmosphere to push against like its pushing off of a wall. Imagine a 10 kg ball of liquid (somehow) rolling along at 1 meter a second. Then suddenly, 1kg of the liquid is ejected out of the front at 1m/s. This will act against the inertia of the orignal moving ball of liquid, so slowing it down slightly. Now imagine youre back on the spacecraft, throwing the stuff out of the back of the craft, consider this. Every action will have an equal and opposite reaction. So, throwing the fuel out of the back of the spacecraft at 1000m/s, even while very light compared to the spacecraft, at that speed, make a lot of inertia. Thus the equal and opposite reaction is pushed against the spacecraft.

Answer 5

Outer Space Craft

Answer 6

Imagine if you had a tube with no air and you made a bubble of air in the middle. What would happen?


The air would go all different ways and disperse. When the rocket combusts the fuel, think of the rocket as an air particle. The rocket goes one way and the burning fuel travels in an opposite direction in an attempt to disperse.

Answer 7

Why shouldn't they be able to? Vacuum has nothing to do with the action/reaction principle.

A rocket works on Newton's law of that says "for every action there is an equal and opposite reaction".
So as the rocket exhaust moves one way, the ship moves in the opposite direction.

Answer 8

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Answer 9

The fuel for the rocket is used to propel it fast enough to escape Earth's gravity well. Then, remaining fuel is used to push it away from itself away from the expanding heat through an affect called, "centrifugal force."

Centrifugal force is a force pushing something away from... So, it doesn't require much rocket fuel to push objects in space because they are weightless. In fact, to push something in space requires less energy then it takes for someone on Earth to bend paper.

Gravity is another force that is used for space travel once we stop using the fuel. Space crafts or satellites are programmed to borrow the gravity of another planet to create trajectory. The trajectory increases velocity (speed without fuel) to push the object to its next destination.

The larger the mass, the more it attracts objects through gravity so the trick is to program the satellite or space craft to use it without getting so close to the planet that it falls back into the planets gravity well.

That is how astronauts went to the moon and back. It wasn't all fuel. It was a well planned trajectory to take advantage of the gravity of the moon and earth to fling the space craft and its precious cargo out to space so that it could make its 8 day journey with no fuel.

Man made satellites that are left long enough in Earth's orbit eventually succumb to Earth's gravity and are consumed by the atmosphere and mistook as meteorites. They just simply wear out and its becoming more common as we send more out to space for military, cell phone, and media purposes.

Answer 10

Believe it or not, it's easier to move in a vacuum. There's no air, so no friction, so nothing to stop you. Basically, all you need to do is give one burst of thrust and you'll go on forever until something stops you.