For Questions That Don't Merit Their Own Thread

[Kryten]

If they measured the velocity and direction carefully, and then worked backwards while taking stellar motion into account, they could have a pretty good go. If that does ever happen, that diagram probably won't be accurate by then.

[Mazon Del]

One issue with time dilated wormholes however is they would become unstable - when their field radiation propogates far enough to be able to travel through both, energy cycling through repeatedly would drain the wormhole's energy and cause it to collapse, so this would also be a very time-limited technique.

My understanding is that this has only been shown to be mathematically true in the case of one dimensional wormholes. Either the additional dimensions of higher dimensional wormholes somehow fixes this issue, or the math hasn't been done yet. Uncertain which.

[gooddog15]

If they measured the velocity and direction carefully, and then worked backwards while taking stellar motion into account, they could have a pretty good go. If that does ever happen, that diagram probably won't be accurate by then.

I was meaning it's position on the plaque, with its antenna pointed towards earth (as it was argued that aliens wouldn't know what the arrow was).

However what you said is extremely interesting!

[shynung]

Warp to a remote location, accelerate to near light speed away from Earth (using reaction drive, not warp), warp back to Earth, decelerate. As you can see, it's practically impossible even if you have FTL.

P.S. Essentially, it's the same reason FTL + wormholes give you time travel. The extreme acceleration you need to pull this off causes extreme space-time curvature from perspective of the pilot. (Gravity indistinguishable from acceleration, etc.)

So, is it safe to say that a non-torch-drive ship (not able to accelerate to near-light-speed without 'warp' drive) can warp all over the solar system without experiencing significant time-travel effects (that is, not larger than a few hours) throughout its mission?

[K^2]

So, is it safe to say that a non-torch-drive ship (not able to accelerate to near-light-speed without 'warp' drive) can warp all over the solar system without experiencing significant time-travel effects (that is, not larger than a few hours) throughout its mission?

Without significant acceleration, it's safe to say that it won't experience any.

What I'm more interested in is sub-light warp. Inductively, I would, inductively, expect sub-light warp to be possible using positive energy density only, since negative energy density seems to be very consistently associated with CTCs. However, Alcubierre geometry requires negative energy even for sub-light warp, and I haven't been able to find any reference to a specific geometry that allows sub-light otherwise.

[Mazon Del]

K^2: One of the somewhat big points of the current experiments (well, current as of my last bit of info about them which isn't very recent. New's kinda suddenly died...) from White's warp field lab is that if the system ends up proving that we can warp space with significant power densities, then even if we cannot figure out the negative matter backside thing, we might have proven that we should be able to create a sub-light drive that 'pulls' you in.

[problemecium]

Thanks for the input. It's about what I would have guessed, so I can rest assured the guy who told me other shapes are impossible is being closed-minded.

Now about sound in space. They say there is no sound in space, but what they mean is that the density of the interplanetary or interstellar medium is so low that sounds attenuate to below audible levels very quickly, so unless you're right next to that TIE Fighter when it blows up, you'll be lucky to hear it at the volume of a bubble popping.

But here's the part I wanna know. In water, sounds sort of get a "bass boost" because low frequencies attenuate less in the denser medium. Is it the opposite in space, i.e. the TIE Fighter explosion will sound tinny like an old radio for lack of bass? Or, since they say bass sounds travel farther in general, will it sound like a very quiet underwater explosion?

[Whirligig Girl]

Why is the spray-on foam insulation used on the fuel tanks of rockets orange?

[Skyler4856]

Why is the spray-on foam insulation used on the fuel tanks of rockets orange?

http://upload.wikimedia.org/wikipedia/commons/1/16/STS122_Atlantis.jpg

http://www.daviddarling.info/images/Delta_IV_Heavy_launch.jpg

https://photos.travelblog.org/Photos/127635/416489/f/4024811-Saturn-V-rocket-fuel-tank-2.jpg

Apparently the Polyurethane foam shifts to an orange color when placed in the presence of UV rays

[Newt]

I am pretty sure the shuttle ones had been previously painted white (why I do not know), but the decision was made to leave them orange, as to save mass.

[Iskierka]

Now about sound in space. They say there is no sound in space, but what they mean is that the density of the interplanetary or interstellar medium is so low that sounds attenuate to below audible levels very quickly, so unless you're right next to that TIE Fighter when it blows up, you'll be lucky to hear it at the volume of a bubble popping.

But here's the part I wanna know. In water, sounds sort of get a "bass boost" because low frequencies attenuate less in the denser medium. Is it the opposite in space, i.e. the TIE Fighter explosion will sound tinny like an old radio for lack of bass? Or, since they say bass sounds travel farther in general, will it sound like a very quiet underwater explosion?

There is genuinely no sound in space - sound is generated by being able to pulse waves of pressure from a source, but at the low densities of orbit, there is genuinely so little material that air-air collisions are so rare they could not propagate a sound's pressure wave. Something exploding would generate its own gasses and thus pressure, which would hit you with a thud-like sound, but it would sound very different to a conventional explosion, as it would simply be particles hitting you in one burst and bouncing away immediately.

As for the "bass boost", I believe that's more due to the inter-particle dynamics of water absorbing higher velocity differences, which is due to the particle of water itself, rather than the density. I don't believe higher or lower pressure air would significantly affect the dominant frequencies that air can carry, beyond some very high extremes (likely hundreds of atmospheres). A plane's engine certainly sounds basically identical at surface and less than 1/3rd pressure, excepting rpm changes.

[zekes]

I am pretty sure the shuttle ones had been previously painted white (why I do not know), but the decision was made to leave them orange, as to save mass.

It was UV protection, which they found to be unnecessary. Saved 660 pounds.

[Robotengineer]

What is the ∆v in m/s of the Endurance from Interstellar?

[Newt]

That, is a difficult one, RobotEngineer. There are a couple of things that make it so.

We know that it got to Saturn, that it entered Saturn orbit without apparent aerocapture, and we know that it took about two years to do this. It is possible to calculate such an orbit, and how much ∆v is needed to do so. Off the top of my head I have not calculated that, but let me tell you that it is a lot of acceleration. Cassini spent seven years going to Saturn, and slower most often is cheaper.

When it gets really difficult is when they go through the wormhole, on the water planet the ship did station keeping for about 20 years. That is not much, but I am sure it adds up, and without good information about the local environment, ship's interaction et cetera and drag parameters, it is essentially impossible to do. Further, they fly about between these different planets, of unknown orbital parameters, of to us unknown positions, and around a black hole, the mass of which we can speculate but not know for sure. We also do not know how efficient of orbits were used for this purpose, although aerocapture and gravity assist maneuvers appeared to not be performed. Finally, they somehow blasted themselves into a doomed orbit around the black hole, after the horrible docking event. This changed the mass of the ship, may have cost them fuel, and probably impacted performance to some degree. But really, that does not make that part of the calculation any more difficult, we knew so little before.

Other ways to do it seem difficult to do. We know neither how much fuel they had, nor what sort of fuel it was, really. It did not seem to be nuclear, or ion, but perhaps chemical of some sort. But who knows? We may be able to estimate a lower limit of the ∆v, by adding up some actual numbers and estimations, but I think that really the film gave us too little information to do something that can be answered with any certainty.

Thus in sum, the Endurance had a ton of ∆v. More than any spacecraft to date. But how much is a very speculative matter. I think that your best bet is to peer at some screens during the film and try to see if any of them give better data than the audience was given directly.

[Robotengineer]

We do know it had Magnetoplasma engines, which according to Wikipedia have an exhaust velocity of 15-60 Kilometers/second. But I can't find anything about the weight of the Endurance though.

[gooddog15]

If the launch vehicle was a Saturn V (which people assumed was the rocket seen in the movie), we could estimate how big the spacecraft was.

I could be very wrong though, as I've neglected to see the movie yet.

Also, I would think that this thread would be stickied permanently by now

Edited December 13, 2014 by gooddog15

[Hary R]

Hello,

Here is one I need to ask.

In Halo the marines fly their dropship on Halo like a normal airplane and I was wandering, how would an airplane behave in a ring shape colony in real life?

We assume the colony have atmosphere of course.

So, on earth, lift counteract gravity and gravity counteract lift (keeping airplane more or less straight) but on a ring shaped colony, gravity will be generated by the rotation of the ring so if you fly above the surface, you wont experience gravity at all. Then what will counteract the lift once the airplane leave the ground. Will the plane just lift infinitely to the "sky"? will everyone on board experience zero gravity? Would it be flyable?

That's a a lot of question.

Edited December 13, 2014 by Hary R

[Z-Man]

In Halo the marines fly their dropship on Halo like a normal airplane and I was wandering, how would an airplane behave in a ring shape colony in real life?

Almost just like here. If the artificial gravity comes from the ring's rotation (I'm not into the Halo canon enough to know), it does not stop if you lift of as long as the speed relative to the surface is small compared to the ring's rotation speed. Essentially, if you drop a brick from the flying airplane, it would go on in a straight line all right, but the ground would accelerate towards it. The net effect is the same as if there was gravity: ground and brick accelerate towards each other.

[Iskierka]

The major differences with rotational gravity is that if you drop from a significant fraction of the radius, you will have a lower velocity and the ground will appear to accelerate below you, and in a very small structure the human ear can detect the rotation when turning around. However, the Halo structures are very large, so neither of these would be noticeable effects - the only things that would affect aircraft at all is that flying higher would reduce gravity at a slightly faster rate, and if you flew at very high speed against the rotation gravity would appear to increase. But, at any low speeds, it would be imperceptible.

[andrewas]

So, on earth, lift counteract gravity and gravity counteract lift (keeping airplane more or less straight) but on a ring shaped colony, gravity will be generated by the rotation of the ring so if you fly above the surface, you wont experience gravity at all. Then what will counteract the lift once the airplane leave the ground.

That depends on your motion relative to the ground. If you fly counterspinward, the apparent gravity decreases, and on a small enough ring it might be possible to get close to zero gravity than thus get into space for very little fuel. Fly spinward, and the apparent gravity increases which could be dangerous if the pilot isn't anticipating it. Again, this is more important on a smaller ring since the tangential velocity is lower and the crafts own motions have more effect.

[gooddog15]

Is it possible to stop the orbiting electrons of atoms to attain the lowest speed ever?

[K^2]

They aren't exactly orbiting. Quantum Mechanics, etc. And the angular momentum of the ground state of hydrogen is already zero. So they are already "stopped". Or rather, as still as they are going to be.

Good Wikipedia article to start with.

[shynung]

Suppose somebody built an indestructible probe and plunge it into Jupiter. What would the probe encounter, from the atmosphere down to the surface? Will it ever actually reach any definite surface?

[K^2]

There won't be a gas to liquid transfer. Hydrogen's critical point is 32K. Meaning, above 32K, there is no fluid to gas transition. As you increase pressure, the supercritical hydrogen simply gets denser and denser. Helium's critical point is even lower. I don't recall what the rule for critical point of mixtures is, but either way, Jupiter's atmo seems way supercritical.

The first real phase transition you should hit, with a definitive boundary, is hydrogen to metallic hydrogen. Here, things start to get murky. I've seen a lot of contradicting predictions for properties of metallic hydrogen. They range from ordinary fluid, to superfluid, to supersolid, to ordinary solid. All that anyone really agrees on is that metallic hydrogen is wickedly weird. If it is, indeed, a fluid of some kind or a supersolid, the probe will keep sinking. In fact, in superfluid or supersolid it will be almost dropping as it would encounter a very sudden reduction in viscosity.

If you keep sinking through metallic hydrogen, eventually you will hit a solid core. The outer layer will most likely be solid helium. Bellow it, there is likely to be a rocky core as well. But that layer of solid helium is likely to be the first definitive "surface" of Jupiter.

[Yru0]

Could Orion get to the moon now? With existing rockets such as the Delta IV and its current design? Not necessarily a landing, but a flyby perhaps?

If not, what would it take? Will such a mission be capable with the initial version (as we expect it to be) of the SLS? If THAT'S the case then how come a possible lunar mission is so far away? I'd have thought such a thing would've been high on the list, if only for the prestige factor. After all, if we have the technology and all that jazz.