Stars, planets and other Sci-Fi peeves

Regarding the sizes of ships, the number of people in hallways, and the number of crew: there's no reason to think that much of the ship is not only automated, but inaccessible (or at least no run through will commonly used hallways. These ships are often portrayed as having "turbolifts" or other sorts of high speed transport through them, so the distances travelled may be large but the actual space that people use might be quite small. Take a turbolift from one side of the ship that has some need for crew to another part where the crew-quarters are, but the area in between may be just be fuel storage tanks, for instance.
 
There is something of a fandom argument in Star Trek at least as to where exactly the "Jeffries Tubes" (small, half size access hallways and chutes we see on the show) actually fit into Federation Starships and where exactly they go to.

But yeah it makes sense, especially on ships like the Enterprise-D that has a very distinct administrative/science section and engineering section, that the part we see most of the time is the most "livable" par of the ship.
 
On the transporters, I think the energy requirements are dwarfed by the computational issues. Oddly the computers seem to have the capacity to do that and effectively run AIs in the holodecks but lack capacity in other ways.
 
Tying in with another recent topic of mine: the trope that black holes are magical vacuum cleaners that just suck in everything in sight. (As seen in, for example, Wing Commmander. Though Interstelllar does get points for not doing that.)

Thanks to Newton's theorem (in classical gravity) and the Birkhoff version (for generalized relativity) basically a spherical mass (or close enough) creates the same gravity outside as the same mass concentrated in a single point in the centre of the sphere. I.e., as a singularity, therefore as a black hole of the same mass.

If you concentrated the mass of the Sun into a black hole, the gravity you see from Earth (or even closer up from Mercury) would be the exact same as before. Because it's the same mass creating the gravity. Sure, Earth would be a colder and darker place, but it would orbit in the same place as before. It wouldn't just suck everything in.

In fact, you could go a LOT closer without anything special happening. If you were driving a ship about 2 million km from the black hole -- which is somewhere between 20 and 30 times closer than Mercury is to the Sun -- the pull would be only just a little over 3g, i.e., 3 times times the surface gravity of Earth. Even chemical rockets will get you out of there.

Just becoming a black hole doesn't turn it into a magical cosmic hoover.

But let's take a more common example. The smallest black hole that can form out of a star is about twice the mass of the sun, which basically doubles the pull calculated above. But generally, most are somewhere between that and 10 solar masses.

But let's go big. Let's go 100 solar masses on our black hole. Well, ok, it's nowhere near BIG by black hole standards, but bigger ones tend to also be less abundant, unless you go through the centre of a galaxy. Anyway, if you get as close to it as Mercury is to the sun -- which is REAL close at astronomical scales -- you'd experience a pull of less than 1g. Quite a bit less in fact. If your spaceship is able to land and then take off on a planet the size of Earth, it will have no problems accelerating away from that black hole.

You might get a dose of radiation from the accretion disk at that distance, mind you, but you won't be already doomed by just being anywhere near the system.
 
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Actually, while I'm at it, here's another stupidity: black holes suck in and/or trap ships capable of faster-than-light travel. (As seen in Wing Commander, ST Voyager, etc. Though Voyager gets points for having nothing noticeable happen at the event horizon.)

But the event horizon is nothing special per se. It's the distance at which the escape velocity is the speed of light. If you can go faster than the speed of light, you can actually be already a ways behind the event horizon and still get out.

Essentially if you do the equations for a given escape velocity v, the radius from which you can still escape is:

r = 2MG/v2
Where:
- M is the mass of the object you're trying to escape (you know, the escape in escape velocity)
- G is the gravitational constant
- v is your velocity, assuming you have the engines off

If you're above that r, and going at v, you're scott free even without engines.

The event horizon is just where you make v=c, i.e., you're going at the speed of light. So it's 2MG/c2
BUT if you can go, say, twice the speed of light -- which is quite modest actually for SF -- you can go three quarters of the way into a black hole (i.e., down to a distance from the centre equal to a QUARTER of the radius of the event horizon) and still be able to get out just fine.

But, as I was saying, that would be modest by SF standards. The top speed of the Intrepid class (the class of the USS Voyager) is anywhere between 1000 and 3000 times the speed of light. Even taking the lower one, you could be down to a millionth (!!!) of the Schwarzschild radius from the centre, and still be able to just warp out like a bat outta hell.

Basically if it plunged right into the supermassive black hole at the centre of the galaxy (and incidentally the most massive black hole anywhere in the galaxy), you could literally get to 7.4 miles from the centre and still have no problem getting out if you can do 1000c. (Withstanding the tidal forces at that distance is a different question.)

Also, no, you don't even need to hit it at any special angle or do technobabble tricks with the deflector shield or anything. Just point in any old direction away from the centre and hit max warp. That's it.

Basically what I'm saying is that I wish more people thought about even the most trivial implications of their SF technology. Using FTL to get away or even OUT of a black hole is one such trivial implication.
 
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HansMustermann said:
.... If you concentrated the mass of the Sun into a black hole, the gravity you see from Earth (or even closer up from Mercury) would be the exact same as before. Because it's the same mass creating the gravity. Sure, Earth would be a colder and darker place, but it would orbit in the same place as before. It wouldn't just suck everything in.

In fact, you could go a LOT closer without anything special happening. If you were driving a ship about 2 million km from the black hole -- which is somewhere between 20 and 30 times closer than Mercury is to the Sun -- the pull would be only just a little over 3g, i.e., 3 times times the surface gravity of Earth. Even chemical rockets will get you out of there.

Just becoming a black hole doesn't turn it into a magical cosmic hoover.
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Damn, of course. I never thought about it but it's so obvious when you point it out. :thumbsup:
 
Klimax said:
Not that hard. If planet is in database then computer already ahs all the info it needs for adjustment. If unknown then calculate one from rotation of planet and then adjust to whatever locals use for UTC-equivalent.

And computer is far more powerful and per technical manual is in its own warp field to further increase speed of calculations.
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It would be the right time somewhere on the planet.
 
Seismosaurus said:
Examples of giant ships?

Take the star destroyer. They're one mile long. If anything they're larger than a scaled up aircraft carrier, because they're far wider for a given length. So projecting 600,000+ crew for a star destroyer would be extremely conservative. Yet they only have a crew of 35,000. A carrier crewed to that density would have about 250 people on it.

The Executor Super Star Destroyer was 1,600 times bigger than a Star Destroyer. Yet it only has a crew of 280,000, eight times as many. If it was populated like a present day carrier is, it would have a crew of close to one billion people. Or alternatively, a modern carrier crewed to the density that an SSD is would have a crew of two people, at most. Two!

Similar story with the Enterprise-D in Star Trek. Though it's much, much smaller than the above ships, a Galaxy class ship is still huge - on the order of fifteen times the size of an aircraft carrier. Yet the war version of the ship in Yesterday's Enterprise can only carry six thousand troops, and is very crowded. With six thousand people aboard, that ship would feel practically empty. With the normal 1,000 crew, it should be a great rarity to see anybody walk past anybody else in a corridor - something that happens all the time.

Hell, Dax said that they "pack them in" on a Constitution class, which is over half the volume of a carrier but has a twelfth of the crew aboard


The problem is that that's exactly what we would expect these huge ships to be like - flying cities, with tens of millions of people in them and all that comes with that. But in reality we almost never see them treated that way. Being Captain of an SSD wouldn't even be like being the mayor of a town, it would be more like being the President of a country three times the size of America - and the Captain and his deputies would have as much involvement in the day to day running of any given department of the ship as Trump has in running any given state in the US.
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Why would they need to be crewed at a 'density' similar to a present day Aircraft Carrier?
Lots more automation, service droids etc would mean a smaller crew was required.

Even today that's happening. When I was in the RN the Leander Frigates had a crew of 260, they were 370ft. New Type 26 Frigates have a crew of 118 and are 492 ft long.
We were stuffed in to the ships like sardines, modern crews have a lot more space to live. Helicopter hangers and flight decks are bigger, machinery spaces don't require you to be a contortionist or midget to get around. Fuel bunkerage is bigger, stores are bigger and so on.
 
HansMustermann said:
...snip...

Basically what I'm saying is that I wish more people thought about even the most trivial implications of their SF technology. Using FTL to get away or even OUT of a black hole is one such trivial implication.
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Lots of science fiction that isn't just magic with technobabble does often deal with this by muttering about "gravity wells" and so on affecting the ability to go to FTL. And it can make some sense in the context of the story's technology - so if the FTL drive "warps" space to go FTL it could be that it doesn't have the "energy" required to do this in a deep gravity well.
 
With the Transporter and Replicator technology available in Star Trek the ships could be constantly modified and adapted with whatever configuration or equipment they needed for specific missions. It could almost be dynamic, grow extra engines or extra cargo capacity. Boost the shield generators, spawn a squadron of fighters or shuttle craft.
You get the idea.
 
Darat said:
Lots of science fiction that isn't just magic with technobabble does often deal with this by muttering about "gravity wells" and so on affecting the ability to go to FTL. And it can make some sense in the context of the story's technology - so if the FTL drive "warps" space to go FTL it could be that it doesn't have the "energy" required to do this in a deep gravity well.
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True enough, not every SF does the exact same mistakes.

Edit: The problem though wouldn't be energy, or not without turning into just a different technobabble. Gravity is quite literally just acceleration.

More realistically, if anyone wants to put a more scientific rationale in their SF, a justifiable reason would be tidal forces. Basically space isn't uniformly stretched around mass, but is more stretched (higher gravity) closer to it, and less stretched farther away. Worse, yet GR is a non-linear system, so two deformations don't just superpose. When your own engines rely on deforming space A LOT, and they're not placed exactly around the centre of the ship, you can at least hand-wave some rationale like that the combined effect of the two would pull the ship apart. Which incidentally, it actually might, since your warp would create one hell of a gravitational wave.
 
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Since people are still at huge ships, and I'm at tidal forces, let's combine the two: the Roche limit. Well, Mr Roche says that big huge ships are dumb.

People who know physics will know what I'm talking about. It's why Saturn has rings, basically.

The thing is, in a gravity well, the more curved it is (read, closer to the source) and the bigger you are, you start experiencing tidal effects. The bits of you closer to it are pulled in harder than the bits of you that are on the other side.

Really, just think of tides on Earth. The water closer to the Moon is pulled in harder towards the Moon, than the water on the other side of the Earth. So the water rises on the side closer to the moon. Well, the Moon has a weak gravity, but it shows that tidal effects exist.

But bigger gravity sources cause bigger tidal forces. And the closer you are to it, compared to your own size, the more tidal effects you would experience. And that's where that Roche limit comes in: if a moon (or other object that takes a few spins) of a given size and density comes closer than a limit calculated for those parameters, over time those tides will pull it apart. And this time we're talking about tides in rock, not water.

It doesn't even have to take a long time. The Shoemaker-Levy 9 just made a close pass with Jupiter and it was broken into 21 fragments, which then fell into Jupiter. It's exactly those tidal forces that broke it.

Now why does it matter? Well, take the second Death Star. At the scale and distance shown in the movie, even the weak gravity from the moon of Endor would pull it apart. (Though, commendably, the smaller scale listed on Wookiepedia would actually survive.)

Well, you might say, BUT welded metal is stronger than agglomerated silica or ice. It's not pulled apart so easily. And you'd be correct too.

BUT that uneven pull would still cause your Death Star to warp and buckle. Just turning slightly to better aim your weapon, would cause stresses in the metal and stuff like floor tiles coming off (because the floor just buckled a little) and doors not closing right any more. Cables running through the walls would get stretched and compressed. Etc. You get the idea.

But moons like Endor aren't the biggest things you might get close to in SF. You routinely see spaceships going just a bit into a gas giant (ST Enterprise did it more than once), or close to a sun (ST:NG even had it go INTO a sun) or the aforementioned black holes, or stuff like that. Well, the bigger your ship, the bigger the tidal forces that warp and buckle it.

But it gets even more perverse than that. If your propulsion depends on warping space-time, if that distortion isn't PERFECTLY uniform, the bigger the ship the more that bubble itself will create tidal forces in your hull. And not just the hull, really, or you could just make the hull really thick and strong. Floors, walls, power cables, etc, would be subjected to to the same forces.

So, yeah. Hundreds of miles long ships? Bad idea.
 
Hmm, that's actually getting me thinking about engineering large ships to be able to deal with tidal forces. Perhaps compartmentalizing them to allow for stretching, each compartment connected through some flexible membrane? As long as the compartments are small enough and the connections flexible enough to allow for the space between compartments to grow with greater tidal forces, that should do it.

Large ships would then look sort of like trains with train cars, and actually for a similar reason.
 
Roboramma said:
Hmm, that's actually getting me thinking about engineering large ships to be able to deal with tidal forces.
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If you have artificial gravity, then (depending on the specifics, of course) you might well be able to use it to manage the tidal stresses.

I'm thinking of an artificial gravity system in which individual areas can have the gravity turned off, reversed, etc. In such a system, if you had a central computer managing thousands (millions?) of individual gravity generators in a ship, it could probably compensate. It would be an interesting problem to see if it could reduce the hull stresses without having very uncomfortable gravity for the people; I'm picturing something like the Death Star flying near a planet and the agrav system invoking +3G on one end of the ship and -2G on the other.

Barring something like that (and I've very dubious about the prospects for a flexible, general-purpose artificial gravity like that), the next SF options would be some field-reinforced structure or some very strong exotic materials.

Slightly more exotic (!) but certainly in-bounds: if your FTL drive involves distorting space, you could simply use it to cancel out the tidal distortion in the vicinity of your ship. Of course, in the event of a drive failure near a planet, your ship would break apart.

[aside]Now that I think about it that way, that anti-gravity and that FTL drive look like different engineering implementations of exactly the same underlying technology. If I were writing an SF series . . . Hmmm. [/aside]

Perhaps compartmentalizing them to allow for stretching, each compartment connected through some flexible membrane? As long as the compartments are small enough and the connections flexible enough to allow for the space between compartments to grow with greater tidal forces, that should do it.
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Those would allow some flexing, but the forces would be persistent.
 
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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Roboramma said:
Hmm, that's actually getting me thinking about engineering large ships to be able to deal with tidal forces. Perhaps compartmentalizing them to allow for stretching, each compartment connected through some flexible membrane? As long as the compartments are small enough and the connections flexible enough to allow for the space between compartments to grow with greater tidal forces, that should do it.

Large ships would then look sort of like trains with train cars, and actually for a similar reason.
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Hmm... I like that idea, actually. A bunch of compartments with the joints being flexible and compressible/extensible enough could probably help a lot.
 
BTW, about huge ships, while momentum has been mentioned already, let's put some numbers on it.

Let's take a wee little ;) ship, just a little over 240 km in length. It's barely 150 miles for you imperials. It sounds big, but it's not even the size of an Ultra Star Destroyer, which is 260km. An Ultra is what I'm basically building it to be like, but I'm going for round numbers for my back of the napkin maths. So basically 120km in each direction from the centre.

I'll also want it to be able to turn in a circle in, say, two minutes? Not very nimble. I'll even allow it to do so in the most economical way, which is to say, accelerate constantly for a minute and decelerate for another minute.

I'll aso pretend that PI is about 3, because it willl make no big difference for what I'm about to do.

Well, a full circle is 2*PI, so about 6 radians. Doing the full circle in 120 seconds, gives us an average angular velocity of about 6/120=0.05 radians/sec.

BUT we said it will accelerate half the time and decelerate the other half, so that means a top angular velocity of about 0.1/sec when it's turned 180 degrees.

BUT, now comes the fun part. Linear velocity is angular velocity times radius. Well our radius on either end of the ship is 120,000m, so we're peaking at 12,000m/s. We're accelerating to that speed in a minute, so divided by 60s, that gives us an acceleration of about 200m/s2 or about 20g. Not very easy on the crew, let's just say, nor cheap in terms of energy.

But that's not the funniest part yet. Sure, 20g is bad, but maybe you can put the crew around the middle and store the fuel and stuff at the ends where it gets that bad. But it gets funnier.

The funnier part is torque: each kilo of mass at either end, will push back with a force of 200N or so. On a lever 120,000m long. So that's 24,000,000 Nm. Yep, TWENTY FOUR MILLION. For each kilo of mass at the ends alone.

That's just short of 10 million lbft for EACH pound of mass at the ends, for you imperials.

Yeah, I'm not going to integrate that over the shape and mass of one, but you get the idea. Not sure what materials they make it of, that it doesn't even buckle, much less break as you'd expect.
 
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