Stars, planets and other Sci-Fi peeves

Actually, an even funnier idea hit me about turning a big ship. And it probably should have been obvious in the first place.

The centrifugal acceleration from the perspective of something at either end, is the radius multiplied by the square of the angular velocity.

Well, the top angular velocity above is 0.1/s, so the square is 0.01/s2. The radius is 120,000m at either end of the ship. So the centrifugal force it experiences is 1200m/s2.

That's 120g. Forget the 20g from the floor I calculated before, you're seeing 120g towards the end of the ship.

Every pound of mass at either end of the ship is trying to pull the ship apart with a force of 120 lb. The hull or chasis or hovever you build it would be pulled in both directions, by the whole mass in either direction, integrating that centrifugal force along its length.

So let's do some more maths.

Let's say the whole ship was just a solid bar of carbon steel. No space inside for crew, fuel, equipment, whatever.

It doesn't matter how thick a bar, actually. The mass of the bar in one direction is
m = density x volume = density x L x A

Where L is the length in one direction, and A is the cross section area of the bar.

so the force it pulls at the centre at, in Newtons, is F = density x L x A x acceleration.

integrating the force along the bar, well, it's linear so it's equivalent to that mass m being at half the length in one direction, so basically seeing 60g of force, or 600m/s2.

The elongation of a piece of metal the centre is dL/L[inf]0[/inf]=F/(E x A), where E is Young's modulus of elasticity. Substituting the formula above, and simplifying by the cross section area (told you it doesn't matter):

dL/L[inf]0[/inf] = density x L x acceleration / E

Well, E is about 200 for steel (which is actually very high), the density of steel is around 8kg/m3, and the L and acceleration we already have.

dL/L[inf]0[/inf] = 8 x 120,000 x 600 / 200 = 2,880,000

So basically the metal at the centre would stretch to almost 3 million times its original length. So we're not talking a littlle buckling or warping there. We're talking 3 million times.

Luckily it breaks long before that :p

But why is that number so insanely high? Well, because it's proportional to the SQUARE of the length. You see the L in the elongation formula, times the acceleration? Well the aceleration too is proportional to the length in that centrifuge. So you end up with L being squared in the final force at the centre.

What that means is that if you spin a bar of steel of the same diameter around at the same angular velocity, a 1km bar will generate a million times more centrifugal force than a 1m bar, and a 100km bar will generate 10,000 times more centrifugal force than a 1 km bar.

So the bigger you make the ship, well, your problems increase with the square of that size.
 
Conversely, let's say we want to turn that bar / ship around at a more reasonable rate, so at the centre it doesn't stretch more than 3% (which is still HUGE).

Well, we'll have to make that force 3,000,000 / 0.03 = 100,000,000 times smaller.

But the force is proportional to the SQUARE of the angular velocity, so we only have to turn the ship slower by a factor equal to the square root of that. I.e., only 10,000 times slower.

So now it will turn in a full circle in 20,000 minutes instead of 2 minutes. 20,000 minutes is 333 hours, or almost 14 days. That's how long it would take to turn that 240km ship around if it were solid steel. Not very nimble to say the least :p

This time though, your problems only increase linearly with size. So if you make it twice as long, well, better plan the whole february to turn it around. But at least it's not a whole season :p
 
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HansMustermann said:
This time though, your problems only increase linearly with size. So if you make it twice as long, well, better plan the whole february to turn it around. But at least it's not a whole season :p
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Star Trekking, across the Universe.
All aboard the Enterprise under Captain Kirk!
Star Trekking, across the Universe.
Always going forward 'cause we cannot find reverse.​
 
HansMustermann said:
Well, in ST they have a lot of technobabble, not the least being the inertial dampers. Which, if you think about it, what do they do?

Well, if the ship is going, say to impulse a mere 0.1, that is to say 0.1c, in one second, you have an acceleration of approx 3x107 m/s2. Well 1g is approximately 10 m/s2. (Or more than close enough for back of napkin calculations.) So it's accelerating at 3,000,000 (THREE MILLION!) g.

From the point of view of someone inside the ship, either the back wall is coming at them at 3 million g, or they're suddenly falling towards it at 3 million g.

To realize how dire that is, kinetic energy equals work, which is force times distance. And the force is the mass times acceleration. We're still going all classic Newtonian here, which is why I didn't give it half impulse or something. (Well, it may not be technically strictly true, but it's good enough for back of envelope maths.) If you're just 1m from the wall, each kilogram in your body would get a kinetic energy of 30 million Joules. If we took a lithe little cadet (I'm looking at you, Wesley!;)), let's say only 50 kg, he'd hit the wall with an energy of 1.5 BILLION joules, or about 360 kg of TNT.

Since it's all going in one direction, think more like a 360 kg shaped charge. Yeah, he's going clean through. Well, in the form of soup, but he is :p

So obviously you have to counter that 3 million g acceleration somehow, for the people and equipment inside. And it's not enough to brace them against the chair, because when your body weighs 150,000 tons suddenlly, you crush yourself just fine. You have to make it so every point inside sees an acceleration of zero.

How? Well, remember when I said that gravity is literally acceleration. So essentially you'd have to create a gravity field inside that pulls them with the same 3 million g towards the front of the ship. I'm not sure how, but that's basically what you have to do.

At which point it ties in with the question about artificial gravity plates. If you can create a 3 million g gravity to keep your crew from squashing, then 1g so they stay on the floor should be the very easy sub-case.
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You kind of have to if you want to save on the very long acceleration times you'd otherwise need.

And TOS wasn't as guilty of this as the succeeding series.
 
True on both accounts. Still, I got to do a thought experiment that involved punting Wesley through a metal wall, so it was worth it ;)
 
I wish more "Space exploration" science fiction wasn't focused on aliens / extraterrestrial life.

Space as a concept is interesting and fascinating enough. That's why, faults they might have had, I loved the Martian and Gravity.
 
JoeBentley said:
I wish more "Space exploration" science fiction wasn't focused on aliens / extraterrestrial life.

Space as a concept is interesting and fascinating enough. That's why, faults they might have had, I loved the Martian and Gravity.
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The Martian was pretty good. Haven't seen Gravity.

I like all sorts of sci-fi stuff. Aliens, space anomalies, cool tech and ships... actually, anything set in space is good for me.
 
Argumemnon said:
The Martian was pretty good. Haven't seen Gravity.
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Gravity is really solid. There's some nitpicking you could do about the orbits (Basically the plot requires the Hubble and the ISS to be on the same orbital plane) and it's in a some sort of alternative universe where we still have a shuttle program (and now I've made myself sad) but beyond that it's really good.

The film involves the shuttle on a routine mission to service the Hubble. While the Mission Commander (played by George Clooney) and a Mission Specialist (played by Sandra Bullock) are outside the shuttle during the servicing of the satellite they get word from Houston that a Russian test of an anti-satellite missile has gone bad, causing a satellite collision that has lead to a Kessler Cascade, leading to a huge mass of debris heading for them at orbital speeds.

The initial orbit of the debris field destroys the shuttle and knocks out communication with NASA and the two astronauts have to reach the safety of the ISS and the Soyuz it has docked there to get back to Earth.

Late in the film there's one piece of annoying... magical realism, the kind that Alfonso Cauron has to put in all his films for some reason but for the most part it's factually and tonally very well done.
 
Blue Mountain said:
Star Trekking, across the Universe.
All aboard the Enterprise under Captain Kirk!
Star Trekking, across the Universe.
Always going forward 'cause we cannot find reverse.​
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And you haven't linked that? :D


I sent it to Forumvision when forum was still under JREF...

Argumemnon said:
Anything that puts Wesley through pain, misery and death is good.
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Still don't understand such hatred for Wesley.
 
Btw, just to make it clear for whoever isn't that much into physics. When I say that gravity is literaly acceleration, I'm using "literally" very literally. That equivalence is the equivalence principle, which in turn is what the whole GR is based on.
 
But let's get back to kvetching about bad tropes, this time the pre-Galileo idea that a heavier object falls faster. You'd think it would be dead for 400 years now, but apparently some script writers never heard of Galileo.

Let's look at Wing Commander again, namely the black hole scene: The Kilrathi ship is faster, which in space means more acceleration, but heavier. The Human ship is lighter, but slower. When they get near a black hole, of course the Human ship gets out (because it's lighter!) while the Kilrathi ship gets sucked in like by a cosmic hoover (because it's heavier!). Which is beyond stupid.

Well, for a start, the WEIGHT, which is to say the force by which you're pulled by gravity, is proportional to your mass. But your ACCELERATION is that force divided by your mass, so your mass simplifies out. Two ships of vastly different weights will stil fall into a black hole with the same acceleration, which is to say, just as fast.

But if one ship can accelerate faster than the other, no matter its weight, then that one will be the ship that has an easier time pulling away from the black hole.
 
Klimax said:
Still don't understand such hatred for Wesley.
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Well, he started OK, but after Roddenberry died and they started jumping the shark for ratings without him firing script writers for going against his canon, Wesley turns into a complete Garry Stu. By the time even travelers from the future come to meet the legendary Wesley, and he creates sentient nanites in his spare time, and when he's the only one in the universe who can tunnel to a warp bubble went wrong. and whatnot... he starts actually getting in the way of suspending disbelief.

I mean, seriously, he out-Marry-Sues even Ballard from Voyager. And at least that one only went Mary Sue for one episode.
 
I like the character of Wesley conceptually. On a huge starship where families lived and that was (ostensibly) on a multi-year voyage bringing family members for routine jobs and familiarizing some of them with ship's functions wouldn't be the worst idea in the world.

Now even granting that you wouldn't have a kid, no matter how much of a prodigy, actually on the bridge maneuvering and piloting your exploration/warship, he'd be down in the 3rd Auxiliary Exo-biology lab as an intern or something but Star Trek strugged the same with giving established main characters who were Starfleet officers excuses to always be on the bridge (*cough*Troi*cough*) so whatever.

On that note if the Officer community on the Enterprise is anything like that of the US Navy and bridge time and bridge quals are as important to the career of a junior officer as they are in the US Navy there probably has never been a greater amount of pure, raw hatred ever produced in the history of any possible universe than the hatred the Enterprise-D's junior officers most certainly had for Wesley Crusher.

I think the big problem is that unlike the rest of the crew most all of Wesley's big plot lines happened in the earlier seasons where the writing was awful, the direction was really by the numbers, none of the main cast had really found their groove yet and the whole show was just a total mess. If you had to judge any TNG major character by only their Season 1 performances I don't think anyone would come out of that looking good.

When he came back as a guest star in later seasons I found him a lot more enjoyable. They were nowhere near the franchise or even the series's best but The Game, Final Mission, and The First Duty were all better than average and perfectly serviceable.
 
Still, as I was saying, as long as Gene was actually in charge of the show, that character was still palatable. Turning it to eleven and then some happened after Gene was dead. Not that it makes the character any less stupid in the end.
 
HansMustermann said:
Still, as I was saying, as long as Gene was actually in charge of the show, that character was still palatable. Turning it to eleven and then some happened after Gene was dead. Not that it makes the character any less stupid in the end.
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I'm still of the opinion that Gene wasn't necessarily a great influence for post-TOS Trek.
 
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