does interstellar travel matter?

[cantab]

You could do this, although if you were coasting instead you could just use rotation of the place to create artificial gravity too.

That poses an interesting challenge. Can you make use of the acceleration gravity when under power, and a rotation gravity when coasting? They would be in completely different orientations, making it something of a challenge.

One way would be physically rotating cabins. Maybe something like a ring structure with several sections connected by suitable joints, which would accelerate along axis, then when coasting, rotate all sections through 90 degrees and spin the ring.

Another is simply designing the interiors to work with both gravity orientations. This would require cleverness for things like showers, cooking facilities, etc. Or you could just rotate individual fittings.

 

[MrIndigo]

That poses an interesting challenge. Can you make use of the acceleration gravity when under power, and a rotation gravity when coasting? They would be in completely different orientations, making it something of a challenge.

One way would be physically rotating cabins. Maybe something like a ring structure with several sections connected by suitable joints, which would accelerate along axis, then when coasting, rotate all sections through 90 degrees and spin the ring.

Another is simply designing the interiors to work with both gravity orientations. This would require cleverness for things like showers, cooking facilities, etc. Or you could just rotate individual fittings.

[/quote]

You can. The way to make artificial gravity by rotation is by making the normal force created by the rotation equal the gravity-based normal force on Earth. By adjusting the "floor" to be at an angle from the rotation plane, you can still have simulated Earth gravity with rotation. Changing thrust would require a change in the rotation speed of the wheels. You'd probably want different sections rotating in opposite directions for additional stability.

 

[cantab]

(My question in the previous post was rhetorical btw)

So you're suggesting that by changing the rotation speed of the ring as you change the (axial) thrust, you can make the direction of the perceived gravity constant? While that's correct, you then cannot control its magnitude; the rotation speed has to scale with the thrust to a positive power, meaning the resultant gravity would vary.

I don't think you need contrarotation. If anything, it would be detrimental, since it would actually destroy the gyroscopic stabilisation. Of course it's possible that you'd have too much stability, making manoeuvring difficult - the speeds involved combined with relativistic effects mean one has very little warning indeed of any upcoming obstacles.

(Indeed, the limit on maximum speed could come not from fuel or energy requirements, but from the need to be able to make evasive manoeuvres. The lateral and emergency braking engines would probably need to be capable of many orders of magnitude more thrust than the main engines, and then you start seriously stressing the material of the spaceship.)

 

[MrIndigo]

(My question in the previous post was rhetorical btw)

So you're suggesting that by changing the rotation speed of the ring as you change the (axial) thrust, you can make the direction of the perceived gravity constant? While that's correct, you then cannot control its magnitude; the rotation speed has to scale with the thrust to a positive power, meaning the resultant gravity would vary.

I don't think you need contrarotation. If anything, it would be detrimental, since it would actually destroy the gyroscopic stabilisation. Of course it's possible that you'd have too much stability, making manoeuvring difficult - the speeds involved combined with relativistic effects mean one has very little warning indeed of any upcoming obstacles.

No, you'd be more gyroscopically stable, but you're right about it being harder to manouver. Though I think if you were having rotating platforms at all you'd want the contrarotation for that stability, because otherwise you would get some EPIC conservation-of-L effects when you tried to turn. (Actually, that's almost enough reason not to have contrarotation :P)

My rotation-adjustment solution changes the direction of the simulated normal force at a given point on the surface of the toroid that forms the wheel, but keeps the magnitude controlled. You would need the ability for the "corridor" to be rotated in a controllable fashion around the center of the toroid's cross-section so the direction of the force can be kept constant relative to the "floor".

EDIT: In fact, this would mean you couldn't have a circular toroid; it would have to be a polygonal shape with a series of discrete cylinders with a "joiner" between the end of one and start of the next.

You'd also have an upper limit on your acceleration of 1g.

(Indeed, the limit on maximum speed could come not from fuel or energy requirements, but from the need to be able to make evasive manoeuvres. The lateral and emergency braking engines would probably need to be capable of many orders of magnitude more thrust than the main engines, and then you start seriously stressing the material of the spaceship.)

It depends on your wayfinding abilities, I think. How far away can you ping an object with light and "echolocate" it's distance and relative velocity?

 

[ultimifier]

assuming you got a vehicle of 1000kg (1 ton) into space and accelerated it to 0.9c (0.9 times the speed of light) it would take over 10^20 J of energy. That is a shitload of energy.

For a nifty comparison, to accelrate that car to 0.9c would take over 15% of the energy used by the ENTIRE HUMAN RACE IN THE YEAR 2008!!

and thats a car, accelerating a giant spaceship that weighed, lets say, 1 million tons to 0.9c would take 150,000 times the amount of energy the human race used last year.

so needless to say, interstellar travel at speeds approaching the speed of light is IMPOSSIBLE!

NOTE: if anyone wants to argue, please actually know something about relativistic calculations and not just talk out of your ass

EDIT: ok to people like mr. indigo. if you are going to argue with me, have a fucking counter arguement. dont just say random shit without any information to back it up. thank you

 

[MrIndigo]

assuming you got a vehicle of 1000kg (1 ton) into space and accelerated it to 0.9c (0.9 times the speed of light) it would take over 10^20 J of energy. That is a shitload of energy.

For a nifty comparison, to accelrate that car to 0.9c would take over 15% of the energy used by the ENTIRE HUMAN RACE IN THE YEAR 2008!!

and thats a car, accelerating a giant spaceship that weighed, lets say, 1 million tons to 0.9c would take 150,000 times the amount of energy the human race used last year.

so needless to say, interstellar travel at speeds approaching the speed of light is IMPOSSIBLE!

NOTE: if anyone wants to argue, please actually know something about relativistic calculations and not just talk out of your ass

It's unfeasible, not impossible.

 

[cantab]

assuming you got a vehicle of 1000kg (1 ton) into space and accelerated it to 0.9c (0.9 times the speed of light) it would take over 10^20 J of energy. That is a shitload of energy.

For a nifty comparison, to accelrate that car to 0.9c would take over 15% of the energy used by the ENTIRE HUMAN RACE IN THE YEAR 2008!!

and thats a car, accelerating a giant spaceship that weighed, lets say, 1 million tons to 0.9c would take 150,000 times the amount of energy the human race used last year.

so needless to say, interstellar travel at speeds approaching the speed of light is IMPOSSIBLE!

NOTE: if anyone wants to argue, please actually know something about relativistic calculations and not just talk out of your ass

EDIT: ok to people like mr. indigo. if you are going to argue with me, have a fucking counter arguement. dont just say random shit without any information to back it up. thank you

That is indeed a lot of energy.

One obvious source is nuclear fusion. Deuterium-tritium fusion gives us 3.5 MeV per fusion reaction (ignoring the energy of the neutrons; I'm not sure if it's possible to effectively use it). That works out at 6.7 * 10^16 joules per tonne of fuel. So we are indeed falling way short.

Antimatter annihilation will give us 9*10^19 Joules per tonne. Probably around about the ballpark for what we want, although it would still likely result in a craft with most of its mass as fuel.
Of course, for this to be feasible would require an efficient way to make antimatter. We currently have no way of doing that. (The original energy source could then be something like large scale solar power; the sun easily produces enough energy.) It might even be possible for the spacecraft to be able to produce its own antimatter for refuelling once in a stellar orbit - though I'm not sure the weight of the solar panels wouldn't be prohibitive.

The Bussard ramjet is an old idea. I'm not sure if it can reach very high velocities though.

Certainly, the energy requirements are greater than I had thought. It may require something beyond current physics to be feasible (and such an energy source, something offering greater energy per unit mass than antimatter annihilation, may well not even exist).

Power (in the strict sense), as well as energy, may be an isssue. Even in the Newtonian regime, for an engine to create a constant acceleration requires an increasing power. (I think; I'm not 100% certain on this.)

 

[MrIndigo]

That is indeed a lot of energy.

One obvious source is nuclear fusion. Deuterium-tritium fusion gives us 3.5 MeV per fusion reaction (ignoring the energy of the neutrons; I'm not sure if it's possible to effectively use it). That works out at 6.7 * 10^16 joules per tonne of fuel. So we are indeed falling way short.

Antimatter annihilation will give us 9*10^19 Joules per tonne. Probably around about the ballpark for what we want, although it would still likely result in a craft with most of its mass as fuel.
Of course, for this to be feasible would require an efficient way to make antimatter. We currently have no way of doing that. (The original energy source could then be something like large scale solar power; the sun easily produces enough energy.) It might even be possible for the spacecraft to be able to produce its own antimatter for refuelling once in a stellar orbit - though I'm not sure the weight of the solar panels wouldn't be prohibitive.

The Bussard ramjet is an old idea. I'm not sure if it can reach very high velocities though.

Certainly, the energy requirements are greater than I had thought. It may require something beyond current physics to be feasible (and such an energy source, something offering greater energy per unit mass than antimatter annihilation, may well not even exist).

Power (in the strict sense), as well as energy, may be an isssue. Even in the Newtonian regime, for an engine to create a constant acceleration requires an increasing power. (I think; I'm not 100% certain on this.)

This is part of why I think interstellar space travel will realistically be "big burst at the beginning, basically nothing for the rest of the trip".

Keep in mind that the energy from matter-antimatter recombination would need to be harnessed in some way, and we don't have 100% efficiency for that (e.g. gamma rays would just fly through the entire ship and escape into the void) or any other power generation effects (nuclear fission is really an elaborate large-scale method of boiling water).

@ulti: My point was merely a semantic correction, I wasn't disagreeing with you. Impossible has a different meaning in scientific use (i.e. the literal, not the figurative). Impossible means that there is no physical mechanism in the universe to achieve it. Unfeasible means that the material costs are so large that society is unlikely to achieve it.

 

[cookie]

You don't need increasing power, you just need consistent thrust. A good term to look up is specific impulse if you're discussing ways to achieve high velocities using rockets.

 

[Brain]

assuming you got a vehicle of 1000kg (1 ton) into space and accelerated it to 0.9c (0.9 times the speed of light) it would take over 10^20 J of energy. That is a shitload of energy.

For a nifty comparison, to accelrate that car to 0.9c would take over 15% of the energy used by the ENTIRE HUMAN RACE IN THE YEAR 2008!!

and thats a car, accelerating a giant spaceship that weighed, lets say, 1 million tons to 0.9c would take 150,000 times the amount of energy the human race used last year.

so needless to say, interstellar travel at speeds approaching the speed of light is IMPOSSIBLE!

You put a sweeping statement where you should be more precise and nuanced. Interstellar travel of heavy payloads at speeds approaching the speed of light seems infeasible by today's standards.

If an inordinate amount of energy must be expended to move a ton, obviously, research will focus on reducing the payload. Pack the strict minimum of people like sardines in hibernation chambers, carry the strict minimum to keep them alive. Still too heavy? Carry skinny teenage female dwarves, or better yet, genetically engineer smaller humans. Still too heavy? Extract the travelers' brains and discard their bodies in favor of lightweight machine bodies. If we went to that extreme (I believe we could), we could possibly carry hundreds of people (well, brains) in a spaceship weighing a ton.

If the point of the trip is to colonize another planet, you don't even need to man a ship - pack in a small autonomous robot that can build stuff (including duplicates of itself) using materials readily available at the target site, along with genetic samples and construct a society from there. It is not a far stretch of the imagination that we could eventually make small, lightweight robots sufficiently advanced to build what's needed and seed us somewhere else. And it could all fit in under a kilogram, for all we know. If the human race was in danger, would you really bother making a colony ship rather than just send a couple thousand "seeder" lightweight ships?

Basically, my point is that if we can't possibly produce enough energy to ship a payload weighing a ton at 0.9c to a distant system, we'll just work on removing everything in the payload that isn't absolutely necessary until it weighs little enough. There won't necessarily be political or economical incentive to do it, but it could happen, if only as a byproduct of compact, advanced AI technology.


This said, if we somehow figured out how to produce antimatter cheaply (I'm not sure on what grounds we could discard this possibility), large payloads might be reasonable. And we can't discount the possibility of fuel-less propulsion either. I'm not sure if large solar sails could somehow be used to attain great speeds spiralling out of orbit (the ship would fly out too early, but maybe we could use auxiliary propulsion as a sort of centripetal force? It doesn't sound like a good idea). Another possibly crazy idea would be to ship the payload from a distant outpost emitting a powerful laser or maser towards it. If the line of sight can be conserved (which in itself sounds like a difficult technical challenge), the ship would receive a constant influx of energy that it could use to accelerate or decelerate without it counting against its payload as fuel.

I mean, I will readily admit that I don't really know my shit here but what appears like an impossibility might just be a lack of inventiveness.

NOTE: if anyone wants to argue, please actually know something about relativistic calculations and not just talk out of your ass

EDIT: ok to people like mr. indigo. if you are going to argue with me, have a fucking counter arguement. dont just say random shit without any information to back it up. thank you

Don't be so pre-emptively defensive.