If we assume we are in a perfect vacuum in space, where there’s no friction or anything to slow us down, at what point would bursts of fuel from thrusters stop increasing our speed? And would they even?
Now, I understand that by einstein, we need infinite energy to accelerate to speed of light, but i cant intuitively see how a rocket wouldnt constantly speed up in a vacuum when given constant bursts of rocket thrust. Im sure im missing something pretty simple here, but nevertheless.
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First of all you need to understand how does the rocket accelerate:
Controlled explosion, if you make a controlled explosion in the opposite side of the rocket u will start moving forward due to the “For every reaction there’s an equal opposite reaction”.
Taking that into account the amount of power that the explosion has is the “top speed” it can achieve, in a extremely perfect scenario the maximum speed will be the speed of the expansion of the explosion.
I want to mention I didn’t use any numbers due to the different fuels and mixtures u got which I’m no expert on.
Since we’re having a discussion about physics I feel I need to be precise here. The question you ask is about acceleration. As a measurement acceleration is just a measurement of how much force is added to something per a given time. If I am falling at terminal velocity towards earth my acceleration is 0m/s² but my velocity about 56 m/s. This means I’m gaining no more velocity but i am still travelling at a really fast rate.
So to answer your question literally, the max amount of acceleration a rocket can produce is based on how much fuel it can burn and expel as gas.
What I believe you’re asking is if there is a top speed that a rocket can get an object to in space. Max speed is governed mostly by how much force a rocket can produce and how long. There are theoretical rocket engines that don’t produce much thrust, but they “burn” for so long (years on end) that they accelerate the space craft to a significant fraction of the speed of light.
So the max top speed of a rocket is a combination of how much force it can produce per second and how many seconds have passed.
Well, there is a top speed in the sense that eventually the rocket will run out of fuel. But if the rocket got more fuel, then no, there’s no maximum speed. Burning more fuel will always make it go faster.
So, why can’t you go faster than the speed of light? Well, it’s complicated, but the short answer is relativity. When you go faster, two things happen: [time slows down](https://en.wikipedia.org/wiki/Time_dilation) and [lengths in the direction of motion shrink](https://en.wikipedia.org/wiki/Length_contraction).
So, while burning more fuel will make you go faster, to an outside observer, the faster you’re going the smaller the acceleration will be.
> at what point would bursts of fuel from thrusters stop increasing our speed?
When the fuel runs out. In discussions about rockets, fuel is often talked about in terms of “delta v”, which is the total change of speed that the engine could produce with a given amount of fuel in the absence of gravity or air resistance. This depends mainly on the mass of the rocket, the energy density of the fuel, and the efficiency of the engine.
> we need infinite energy to accelerate to speed of light, but i cant intuitively see how a rocket wouldnt constantly speed up in a vacuum when given constant bursts of rocket thrust.
As the name suggests, in relativity, the key theme is that things are relative. The rocket does not have an absolute speed – from the perspective of someone on board the rocket, it isn’t moving at all, while from the perspective of another rocket moving in the opposite direction, it’s going very fast.
But in relativity, speeds do not add together linearly. If, from my perspective, there is one rocket travelling at 90% of the speed of light in one direction, and another rocket travelling at the same speed in the opposite direction, then from the perspective of one of these rockets, the other one is still travelling at less than the speed of light.
If you travel away from earth with an incredibly powerful rocket that keeps pushing you forwards with the same force, then from the perspective of someone on earth, your acceleration will gradually slow down and you will never hit the speed of light. But that isn’t because you somehow have to work harder to attain higher speeds – it’s just because of how your reference frames relate to each other.
There’s several good comments here (and one wildly inaccurate series) but, to directly answer your question, there is no maximum speed to which a rocket can accelerate other than the speed of light.
If you keep running the engine you will keep accelerating. For most designs, you’ll accelerate *faster* the longer you go as you burn up fuel and get lighter (same thrust, less mass = more acceleration).
In virtually all real-world circumstances the limit is how much fuel you have. When you run out of fuel you run out of thrust and stop accelerating.
You are not missing anything; in a vacuum with constant thrust a rocket will constantly speed up.
Kind of. The fuel’s *specific impulse* is a measure of how quickly the fuel could make its own weight go. You might think you can’t make it go faster than that.
However, by adding more stages, the rocket can go faster. If your specific impulse is 1000m/s then 1000 tonnes of fuel can make 1000 tonnes of stuff go at 1000m/s. But that 1000 tonnes of stuff could be another rocket with 500 tonnes of fuel moving 500 tonnes of stuff, at 1000m/s faster than how fast the first rocket made it go. And so on.
But then again, it’s exponential. If you *double* the weight of the rocket it only goes 1000m/s faster again, and that’s the theoretical limit. So if you want it to go 100,000m/s you’re out of luck. You can’t make a rocket that big.
It also explains why they want to make satellites and space probes as lightweight as possible, because at the bottom of this stack of rockets – and the deciding factor for the overall weight of the stack – is the thing you’re actually trying to get into space. If you can halve the weight of that you can use that extra weight to make a small rocket and then you can delete the biggest rocket from the stack – halving its weight
You need more energy to achieve the same acceleration at some point, even if your rocket fuel is infinite the maximum thrust of the rocket does limit the top speed. Relativity speeds and its are effects are far beyond this
This is because the energy difference between 21000mph –> 22000 mph is smaller than the energy difference between 63000 mph –> 64000 mph. Even in vacuum this counts.
The real question is, does this approach a limit when t –> infinite
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