Is there a limit to propulsion in space?

Question

When a rocket is being propelled through space is there any limit to how fast it can go? Because the rocket is in a vacuum there should be nothing to slow it down, that being the case can the rocket increase in speed exponentially (or at least at a constant rate) as long as the thruster is activiated? It seems to me that a rocket with a continuous constant thrust would continue to increase in speed. That being said, it seems like space travel should be a lot faster. Does this have to do with the amount of fuel, or the rate of acceleration? Or can our rockets just not go that fast?

Answer 1

Yes, there are limits to propulsion in space.

1. Even though in the vacuum of space there are no friction due to air and no Earth's gravity to overcome, there is still inertia of the rocketship, meaning that the more massive an object is, the more force you will need to apply to push it into motion and to increase its velocity.
2. There is a limit to how much fuel you can carry on a rocketship to keep you moving. Chemical fuel is extremely inefficient. Remember, when a rocket launches into space, it burns all its fuel in a matter of a few minutes.
3. Then there is the laws of physics that will prevent you from getting anywhere close to the speed of light, because as you expend more fuel to increase your speed, and as you get closer and closer to the speed of light, relativistic effects kicks in and your rocketship becomes more and more massive, thus slowing it down.

Answer 2

You need a force to obtain an acceleration. So basically, the rocket will increase in speed so long as there is thrust being produced by the motor. once the motor stops, so does the acceleration. At that point the rocket will maintain a constant velocity.

So, a lack of FUEL is what eventually keeps the rocket from going faster.

If for some magical reason the rocket had an infinite fuel supply, then the speed of light would be its maximum velocity.

Answer 3

The problem initially lies with escaping earth's gravity well.This require IMMENSE amounts of fuel.If you could somehow "teleport" the space shuttle into interstellar space with a full complement of fuel you would get much better "mileage".Not as much gravity to escape from.But then if you could teleport why would you bother with rockets?
I don't know at what rate the shuttle burns fuel,but it's supply would be exhausted well before any significant rate of speed could be reached.Our methods of propulsion in space just aren't that efficient.
Ion drive seems to work well (on a fuel to thrust ratio),but the acceleration rate is so slow as to be negligible.Wouldn't be practicle for manned missions.
As for your claim that there is nothing to slow you down in the vacuum....not so.
Every particle in the universe is "gravitationally aware" of every other particle.This "pull" may be negligible in intergalactic space,but it is there just the same.

Answer 4

Force=Mass*Acceleration, so with mass not changing, and space (almost) a vacuum, a constant force (thrust) will yield a constant acceleration. Unfortunately, it takes a huge amount of energy to get to space where this works, so we are often left with little energy left once we get there. To take more fuel into space requires more fuel to get there, until we reach the point where the weight of the ever larger fuel tank negates any gains. What we need is either a lighter weight fuel (relative to its energy content) or fuel stored up in space for a 'second launch' in zero gravity.
If we were to launch in space, we would see a constant acceleration as long as we had fuel or until we reach relativistic speeds. As we approach the speed of light, Einsein's theory tells us that mass increases, which means acceleration decreases with a constant force. Because of this we cannot (based on our current understanding of physics) reach the speed of light.

Answer 5

You would be limited by how fast the thrust is being produced. If the burning or expanding gasses can only expand at... say 10000 feet per second, then your ship will only hit 10000 feet per second. (with no other outside influence on the ship)

Other types of propulsion are in development, but the basic principal is that you will only hit the same speed as what is being expelled backwards to provide thrust. You might not even be able to hit the exact speed of the propelling force....

The whole "speed of light" thing adds more problems, as written below by others.

Answer 6

The energy that propels it faster also makes it heavier. Einstein discovered that the energy of motion manifests itself as the mass of the object that is moving. Therefore the increased mass causes Resistance to any further acceleration. Its own mass resists it.

But it is also possible to travel faster than light. This comes about because the faster you go the slower your clock. So if your clock is going slow you have extra seconds in which to travel compared to light. The fact that clocks differ allow matter to go farther than light can by its clock.

Not to confuse people Einstein said that space shrinks along with time. So your new map would say you are traveling at less than light speed. In this way you really are traveling slower than light speed. It is only the difference in clocks that creates faster than light possibilities.

I hope this is understandable.

Answer 7

Yes, but eventually you will start to get closer to c (the speed of light). And when you get closer to c, you'll need more energy to accelerate. To actually reach c requires an infinite amount of energy. So there's a limit. Otherwise your reasoning was sound.

The main limitation with space travel is to get away from earths atmosphere. It's not a big problem to build huge rockets in space, the only problem is to get them up there.

Answer 8

This sort of depends if you are on the rocket, because of the time dialation. If you had reall good engines then you could get to another star in a matter of moments for you the passenger, but for the rest of us it would take a very long time.

In essence the limit is for the observer, not the passenger.

Of course you don't have to have a chemical rocket. You could try something more exotic like an engine that uses the Biefeld Brown effect.

Answer 9

Yes, available fuel...
Larry Niven the scifi author used a 'bussard ram jet', which was a vehicle, that would collect the gas in the path of travel and via nuclear propulsion get continuous thrust, thus having unlimited fuel.
He figured on a steady acceleration of 1 gravity.
The idea was accelerate halfway to the target and then to turn over and decelerate the second half of the way.
Because of (Einsteinian) time dilation, a trip to a star 200 light years away would take 9 subjective years, a trip to the center of the galaxy (33,000 light years) would take 19 years and a trip to Andromeda (2,000,000 light years) would take 29 years.
I calculated at the time that on the trip to Andromeda at the halfway mark, the speed would be just 0.3mm/sec short of the speed of light, and the time dilation (and increase in mass!) would be 770,000:1

Answer 10

There is actually a sign in space says " Speed limit C ".

In theory, there is no limit to propulsion. But it takes mass to acceleration and decelerate you in space using propulsion method.

To continue to accelerate for a long time, you need to carry a lot of fuel, that will slow the accerleration during the initial journey.