Navigation in space

[steve_bank]

On Star Trek the captain commands 'all stop!'. The navigator relies 'forward motion stopped captain'.

A practical question for space travel. If you think you are stopped in deep space, how do you know?

In the solar system going from Earth to Moon is based on known relative velocities and positions relative to solar system coordinates.

It would be the same question for alleged ET visitors performing precision navigation over light years distance in a constantly changing galaxy.

 

[Jimmy Higgins]

Presumably the transmission is set to the "P" symbol.

 

[skepticalbip]

Star Trek writers (like most people) saw the universe as a Newtonian frame where there was a fixed background or universal reference frame against which all motion was measured. Either that or Sulu deployed the Enterprise's space anchor to be sure that they stopped.

 

[Politesse]

On Star Trek the captain commands 'all stop!'. The navigator relies 'forward motion stopped captain'.

A practical question for space travel. If you think you are stopped in deep space, how do you know?

In the solar system going from Earth to Moon is based on known relative velocities and positions relative to solar system coordinates.

It would be the same question for alleged ET visitors performing precision navigation over light years distance in a constantly changing galaxy.

Perhaps the ability to sense and manipulate this "subspace" dimension would give one useful information as to absolute position? Presumably, the time distortion created by movement would be easy enough to notice with Starfleet's tech.


But on the other hand, what benefit would there be in "stopping" in space? Why bother? It is useful to enter orbit around a planet if you are near one, to avoid object collision and make shuttle transport simpler to arrange. But otherwise, "stopping" or "going" is an irrelevant distinction at sublight speeds.

 

[steve_bank]

It us a serious question for those who think we will leave the solar system.

In Dune after years of taking a drug and mutating into a different creature there were those who could think their way through another dimension dragging a ship along witj it.

In the 60s relativity and relative motion was known.

You could head to a star constantly correcting. That would mean a curved trajectory.

 

[fromderinside]

Develop capability to bend (fold) time then straight trajectory possible.

 

[skepticalbip]

It us a serious question for those who think we will leave the solar system.

In Dune after years of taking a drug and mutating into a different creature there were those who could think their way through another dimension dragging a ship along witj it.

In the 60s relativity and relative motion was known.

You could head to a star constantly correcting. That would mean a curved trajectory.

If someone wants to get to a distant star system then it is easy to measure the relative motion of that system with respect to our system. Once relative motion is known, the thrust that will be applied to the ship, the mass of the ship, etc. then physicists can fairly easily calculate where the distant star system will be when the ship will get there. So they can aim the ship at where the distant system will be, not where it is now. If you have ever tried skeet shooting, you know to aim at where the clay pigeon will be when the shot gets there...(it's called, "leading the target"). If you aim at where the clay is when you pull the trigger then you will miss the clay..

 

[fromderinside]

For short, those with which the eye can track, distances I'd use a lazar gun. That is I'd chose the proper device for the current situation and circumstances.

 

[Jimmy Higgins]

Probably also need to note that there is no real science in Star Trek's technology, it just exists. Which is perfectly fine.

I do wonder if there is a basement for a speed that can be measured in space though. Going 55 mph in space probably isn't measurable unless a ridiculous amount of accuracy with red/blue shift maybe.

 

[skepticalbip]

Develop capability to bend (fold) time then straight trajectory possible.

If the capability to bend or fold spacetime is achieved then a trajectory isn't necessary. The Navigators in Dune folded spacetime so that where their ship was and where they wanted to go was at the same place... sorta like putting a dot on each end of a sheet of paper then folding the paper so the two dots touched.

 

[Jimmy Higgins]

Develop capability to bend (fold) time then straight trajectory possible.

If the capability to bend or fold spacetime is achieved then a trajectory isn't necessary. The Navigators in Dune folded spacetime so that where their ship was and where they wanted to go was at the same place... sorta like putting a dot on each end of a sheet of paper then folding the paper so the two dots touched.

I'd imagine that it'd suck to be at some point in between when that happens.

 

[steve_bank]

From an initial point you can vclulate distance traveled by calculating change in velocity by integrating acceleration. Inertial navigation.

If you know the position of the Earth when you are in orbit in a solar system coordinate system and initialize there, you can navigate to any point.

 

[Shadowy Man]

Develop capability to bend (fold) time then straight trajectory possible.

If the capability to bend or fold spacetime is achieved then a trajectory isn't necessary. The Navigators in Dune folded spacetime so that where their ship was and where they wanted to go was at the same place... sorta like putting a dot on each end of a sheet of paper then folding the paper so the two dots touched.

I'd imagine that it'd suck to be at some point in between when that happens.

If the fold is done right there are no points in between.

 

[Jimmy Higgins]

I'd imagine that it'd suck to be at some point in between when that happens.

If the fold is done right there are no points in between.

I can't see how that is possible. Firstly, we aren't talking about points in space but regions of space, and any displacement of a portion of space has to cross other space. Someone can drop an anvil on me if I'm incorrect.

It does make me think about a Kilgore Trout-esque sci-fi where a person invents a time machine that works! But he goes back in time, and Earth (well really the entire solar system / galaxy) is elsewhere, and they die from exposure to a vacuum.

 

[fromderinside]

Develop capability to bend (fold) time then straight trajectory possible.

If the capability to bend or fold spacetime is achieved then a trajectory isn't necessary. The Navigators in Dune folded spacetime so that where their ship was and where they wanted to go was at the same place... sorta like putting a dot on each end of a sheet of paper then folding the paper so the two dots touched.

I'd imagine that it'd suck to be at some point in between when that happens.

Why. If you were between when time folding took place you'd still be between only you'd be in folded time. Folding just makes getting somewhere practical no more than that.

 

[Jarhyn]

It us a serious question for those who think we will leave the solar system.

In Dune after years of taking a drug and mutating into a different creature there were those who could think their way through another dimension dragging a ship along witj it.

In the 60s relativity and relative motion was known.

You could head to a star constantly correcting. That would mean a curved trajectory.

If someone wants to get to a distant star system then it is easy to measure the relative motion of that system with respect to our system. Once relative motion is known, the thrust that will be applied to the ship, the mass of the ship, etc. then physicists can fairly easily calculate where the distant star system will be when the ship will get there. So they can aim the ship at where the distant system will be, not where it is now. If you have ever tried skeet shooting, you know to aim at where the clay pigeon will be when the shot gets there...(it's called, "leading the target"). If you aim at where the clay is when you pull the trigger then you will miss the clay..

The problem is not just knowing where it will be but matching its motion in space when you get there. You can't just fly by, unless you are tagging the system with something small, like spores; you have to actually stop there.

To that end, you will always have to approach on a curved trajectory.

If you lead the target here, you will pass by the target unless you manage to get so close to a body you can use atmospheric or gravitational braking.

And, you have to spend extra delta-v to stay out of the curved path produced by distorted spacetime. It's literally not worth the energy to go straight.

 

[skepticalbip]

It us a serious question for those who think we will leave the solar system.

In Dune after years of taking a drug and mutating into a different creature there were those who could think their way through another dimension dragging a ship along witj it.

In the 60s relativity and relative motion was known.

You could head to a star constantly correcting. That would mean a curved trajectory.

If someone wants to get to a distant star system then it is easy to measure the relative motion of that system with respect to our system. Once relative motion is known, the thrust that will be applied to the ship, the mass of the ship, etc. then physicists can fairly easily calculate where the distant star system will be when the ship will get there. So they can aim the ship at where the distant system will be, not where it is now. If you have ever tried skeet shooting, you know to aim at where the clay pigeon will be when the shot gets there...(it's called, "leading the target"). If you aim at where the clay is when you pull the trigger then you will miss the clay..

The problem is not just knowing where it will be but matching its motion in space when you get there. You can't just fly by, unless you are tagging the system with something small, like spores; you have to actually stop there.

To that end, you will always have to approach on a curved trajectory.

If you lead the target here, you will pass by the target unless you manage to get so close to a body you can use atmospheric or gravitational braking.

And, you have to spend extra delta-v to stay out of the curved path produced by distorted spacetime. It's literally not worth the energy to go straight.

I think you are confusing moving between planets in a system and interstellar travel. The most fuel efficient Earth to Mars trip would be arced because it is an orbital - thrust is applied at the start which puts the ship into a stretched elliptical orbit about the Sun which will intercept the orbit of Mars. This transfer orbit is a 'straight line' through curved space. Thrust is only applied to start the trip and again to stop by applying thrust to match the orbit of Mars.

The most fuel efficient interstellar trip would also be by only using thrust to start then thrust to stop. Coasting between those two applications of thrust would be along a 'straight line'.

 

[Gun Nut]

On Star Trek the captain commands 'all stop!'. The navigator relies 'forward motion stopped captain'.

A practical question for space travel. If you think you are stopped in deep space, how do you know?

In the solar system going from Earth to Moon is based on known relative velocities and positions relative to solar system coordinates.

It would be the same question for alleged ET visitors performing precision navigation over light years distance in a constantly changing galaxy.

Perhaps the ability to sense and manipulate this "subspace" dimension would give one useful information as to absolute position? Presumably, the time distortion created by movement would be easy enough to notice with Starfleet's tech.


But on the other hand, what benefit would there be in "stopping" in space? Why bother? It is useful to enter orbit around a planet if you are near one, to avoid object collision and make shuttle transport simpler to arrange. But otherwise, "stopping" or "going" is an irrelevant distinction at sublight speeds.

Considering the speed at which most objects we know of are moving in relation to each other in the universe, "stopping" sounds like a very dangerous idea. Best to keep moving with the same vector as the most gravitationally relevant object at that point in space... and call that state "stopped".

Right now, I am almost perfectly still, sitting in a chair... despite the fact that I am actually moving about 1000 miles per hour along the gravitational plane of our sun... which itself is moving at some ludicrous speed with respect to other stars.

Earth is the most gravitationally significant object from my perspective, so sitting here with no relative change in position with respect to the Earth is as "stopped" as I can reasonably be.

 

[Jarhyn]

The problem is not just knowing where it will be but matching its motion in space when you get there. You can't just fly by, unless you are tagging the system with something small, like spores; you have to actually stop there.

To that end, you will always have to approach on a curved trajectory.

If you lead the target here, you will pass by the target unless you manage to get so close to a body you can use atmospheric or gravitational braking.

And, you have to spend extra delta-v to stay out of the curved path produced by distorted spacetime. It's literally not worth the energy to go straight.

I think you are confusing moving between planets in a system and interstellar travel. The most fuel efficient Earth to Mars trip would be arced because it is an orbital - thrust is applied at the start which puts the ship into a stretched elliptical orbit about the Sun which will intercept the orbit of Mars. This transfer orbit is a 'straight line' through curved space. Thrust is only applied to start the trip and again to stop by applying thrust to match the orbit of Mars.

The most fuel efficient interstellar trip would also be by only using thrust to start then thrust to stop. Coasting between those two applications of thrust would be along a 'straight line'.

You have to account for relative motion still: it's not enough to be able to intersect the moving target, you have to actually adjust velocity to match the moving target.

And interstellar travel is still orbital. You're just not going to be orbiting the same thing as you were.

 

[Politesse]

On Star Trek the captain commands 'all stop!'. The navigator relies 'forward motion stopped captain'.

A practical question for space travel. If you think you are stopped in deep space, how do you know?

In the solar system going from Earth to Moon is based on known relative velocities and positions relative to solar system coordinates.

It would be the same question for alleged ET visitors performing precision navigation over light years distance in a constantly changing galaxy.

Perhaps the ability to sense and manipulate this "subspace" dimension would give one useful information as to absolute position? Presumably, the time distortion created by movement would be easy enough to notice with Starfleet's tech.


But on the other hand, what benefit would there be in "stopping" in space? Why bother? It is useful to enter orbit around a planet if you are near one, to avoid object collision and make shuttle transport simpler to arrange. But otherwise, "stopping" or "going" is an irrelevant distinction at sublight speeds.

Considering the speed at which most objects we know of are moving in relation to each other in the universe, "stopping" sounds like a very dangerous idea. Best to keep moving with the same vector as the most gravitationally relevant object at that point in space... and call that state "stopped".

Right now, I am almost perfectly still, sitting in a chair... despite the fact that I am actually moving about 1000 miles per hour along the gravitational plane of our sun... which itself is moving at some ludicrous speed with respect to other stars.

Earth is the most gravitationally significant object from my perspective, so sitting here with no relative change in position with respect to the Earth is as "stopped" as I can reasonably be.

In fairness, that momentum becomes a going concern when you try to launch or land a spaceship on said surface! But yes, I tend to agree, it is more useful to be in synchrony with the nearest large object than to be "stopped" (if such a state is even possible in a constantly expanding universe). And in deep space, simply irrelevant.