Generating Gravity

[Morat]

Suppose you've been assigned the task of designing a space ship that must carry humans for extended missions (on the order of several months) with no outside support. How would you deal with the problems associated with having humans in a zero gravity environment?

Would you forget about trying to generate gravity, and instead find ways to work around the problems (such as bone density loss and problems with mobility)? Would you include a rotating section on your ship? Or might you try to rotate the entire ship, all or only part of the time?

What if the ship were:
1. A warship the size of a large Aircraft Carrier?
2. A science ship for conducting exploratory surveys?
3. A colony ship that has to transport people to a neighboring star at sublight speeds?

[Perinquus]

I'm assuming that we have no kind of artificial gravity technology such as most sci-fi frachises feature.

The best way for a warship would probably be exactly the kind of vessels in Niven and Pournelle's The Mote in God's Eye - a roughly cylindrical configuration, and constant boost sublight drive. When underway, you normally cruise at 1g acceleration, and halfway to your destination, you turn the ship around and decelerate the rest of the way. This makes the bow "up" and the stern "down". When the ship is keeping station or in orbit, the entire ship rotates, and "down" is now toward the outer hull. The crew rigs the interior of the ship for each configuration as needed.

I think this approach presents the fewest difficulties. In the absence of any kind of technobabble "inertial dampeners" a constant boost propulsion will get you there faster than simply accelerating to a given velocity and cruising there. And this avoids the extra mechanical complexity of rotating sections, which have other associated problems. For instance, in Babylon 5, the earth ships have only one rotating section (including the Babylon station itself). In the absence of a counter-rotating section, the entire rest of the ship would spin in the opposite direction from your rotating section, unless you added a fuel wasting thruster to do the same work that a helicopter tail rotor does, and keep the rest of the hull from spinning. The only sci-fi movie I've seen get this right is "Red Planet" where they gave the ship two conter-rotating sections. (Actually, "2001: A Space Odyssey" does as well, though it's not apparent onscreen - I once saw a set of deck plans someone drew for the spaceship Discovery, and it featured a counter-rotating flywheel to compensate for the spin of the rotating drum of the interior crew section, but since both the drum and the flywheel are internal, you can't see this on screen.)

Rotating sections also opens the door to gyroscopic forces that may affect maneuverability. Also, in combat, if your rotation mechanism is damaged, and suddenly siezes up, all that momentum from the rotating sections will send your ship into an end over end spin, just like the Discovery was spinning in "2010: The Year We Make Contact".

[Durandal]

Suppose you've been assigned the task of designing a space ship that must carry humans for extended missions (on the order of several months) with no outside support. How would you deal with the problems associated with having humans in a zero gravity environment?

I'd ask, "Are you fucking serious?"

Would you forget about trying to generate gravity, and instead find ways to work around the problems (such as bone density loss and problems with mobility)? Would you include a rotating section on your ship? Or might you try to rotate the entire ship, all or only part of the time?

The only way to do it would be to incorporate rotational sections into the ship. There are a number of engineering and practicality difficulties associated with this, however.

What if the ship were:
1. A warship the size of a large Aircraft Carrier?

The power generation might be insufficient.

2. A science ship for conducting exploratory surveys?

Surveys where? Inside our solar system? We have probes for that.

3. A colony ship that has to transport people to a neighboring star at sublight speeds?

What's the point? The crew would die in transit, and they'd have no place to stop for resources if something goes wrong.

[Arrow]

Well, since rotating sections has been taken, I'd spend many more years researching strings and figure out a way to convert electricity into gravitions. From what I've read about strings (admittedly, its only a few issues of Scientific American and Hawking's Nutshell), this seems to be possible.

If thats not possible, I'd use dual rotation sections in a "P-38" design, such that the rotation of the sections cancel each others effects on the rest of the ship.

[SWPIGWANG]

JUST ROTATE THE WHOLE FVCKING SHIP

nuff said

[Kuroneko]

3. A colony ship that has to transport people to a neighboring star at sublight speeds?

What's the point? The crew would die in transit, and they'd have no place to stop for resources if something goes wrong.

Depends on the capabilities of that ship. Although far from the realm of modern engineering (but then, this is sci-fi), a ship that could maintain 1G acceleration for very long periods of time would be halfway across the galaxy in a mere decade.

[SyntaxVorlon]

3. A colony ship that has to transport people to a neighboring star at sublight speeds?

What's the point? The crew would die in transit, and they'd have no place to stop for resources if something goes wrong.

Depends on the capabilities of that ship. Although far from the realm of modern engineering (but then, this is sci-fi), a ship that could maintain 1G acceleration for very long periods of time would be halfway across the galaxy in a mere decade.

No ship could actually maintain 1 G for so great an amount of time, as they would have to brake for relativity.

A colony ship that would be working at sublight speeds would either have its population in hibernation or it would work as a very large contained ecology itself for the period in which it is required. In other words, it would be the home of serveral generations of people.
The fact that both of these would require large amounts of starting resources, hydrocarbons, plants, etc, reactive fuels, uranium, hydrogen, etc, and raw materials to be used in a manufacturing setting, should the need arise.
Colony ships have all been all or nothing. Where at sea did ships like the Mayflower have to stop off?

[Perinquus]

An interstellar colony ship will not be able to employ a constant boost drive unless it is going ta very nearby system, otherwise it will run into the problem of relativity (though realistically, fuel would probably an issue long before even that). For a warship or an intra-system exploration ship, constant boost would be the way to go. An interstellar colony ship that must cross to a very distant system will either have to have a crew in suspended animation, or else be a multi-generational ship.

[RedImperator]

You could partially solve the fuel problem by using solar sails, booster rockets, or laser-based propulsion to accelerate out of the Solar System without consuming any onboard fuel, and by making fuel tanks external and jettisonable once they've been drained, so your mass gets progressively smaller the further you go. I can't imagine how you could maintain continuous 1g acceleration across interstellar distances, though.

[Kuroneko]

No ship could actually maintain 1 G for so great an amount of time, as they would have to brake for relativity.

You're right, that's horrendously expensive. How about half year instead? After accelerating 1G for six months, the ship is traveling at almost half of lightspeed, with work done to accelerate it about 0.14 kg of mass-energy equivalent for each kilogram of the ship's mass.

The cost is still ridicuously high from a modern engineering standpoint. As far as the context of sci-fi, on the other hand, personally I find such a mechanism far more believable than 'warp drive' or 'hyperspace' or whatnot.

---
Edit: I was mistaken as to what the point was. Shame on me.

[Kuroneko]

An interstellar colony ship will not be able to employ a constant boost drive unless it is going ta very nearby system, otherwise it will run into the problem of relativity (though realistically, fuel would probably an issue long before even that).

Why is the nearby presense of a star relevant?

[Perinquus]

An interstellar colony ship will not be able to employ a constant boost drive unless it is going ta very nearby system, otherwise it will run into the problem of relativity (though realistically, fuel would probably an issue long before even that).

Why is the nearby presense of a star relevant?

Because if the distance is too great, you will either run into that problem of relativity or run out of reactant mass before you can cover it.

[Kuroneko]

Because if the distance is too great, you will either run into that problem of relativity or run out of reactant mass before you can cover it.

My apologies. I read your original post as 'being near a star system' rather than 'going to nearby star system'.

Hmm... this is the second time today I completely misread a post. I should really get some sleep before I make myself out to be even more of an ass.

[GrandMasterTerwynn]

I'm assuming that we have no kind of artificial gravity technology such as most sci-fi frachises feature.

Rotating sections also opens the door to gyroscopic forces that may affect maneuverability. Also, in combat, if your rotation mechanism is damaged, and suddenly siezes up, all that momentum from the rotating sections will send your ship into an end over end spin, just like the Discovery was spinning in "2010: The Year We Make Contact".

If one built a warship with rotating sections, I'd think that it'd be prudent to lock them down while in combat. The rotating sections would only be there to prevent the crew from losing their physical tone while in space. There's absolutely no need to have them up during combat, especially if the ship has to engage in radical maneuvering and acceleration.

[Arrow]

You could put an armored housing over the rotating section. I still prefer two rotating sections, one clockwise and the other counterclockwise, to cancel out the forces they place upon the rest of the ship, so that the rotation of the sections won't affect the ship's manuverability.

[NecronLord]

(Actually, "2001: A Space Odyssey" does as well, though it's not apparent onscreen - I once saw a set of deck plans someone drew for the spaceship Discovery, and it featured a counter-rotating flywheel to compensate for the spin of the rotating drum of the interior crew section, but since both the drum and the flywheel are internal, you can't see this on screen.)
It's throughorly apparent in the book

[NecronLord]

Those who suggested a one g drive, if it could be built it would take <50,000 years to reach the center of the galaxy, however time distortion would make it seem like twenty (turning and decellerating half way.) However, the little problem is that you WILL hit something

[Perinquus]

You could put an armored housing over the rotating section. I still prefer two rotating sections, one clockwise and the other counterclockwise, to cancel out the forces they place upon the rest of the ship, so that the rotation of the sections won't affect the ship's manuverability.

That means unecessary extra weight, both for the armored section, and for the rotating sections and motor, bearings, etc. For a warship I maintain that a constant boost vessel, cylindrical or conical in shape, and which will generate gravity when at rest by spinning the whole ship would be more practical. The only reason to have rotating sections is because you can't do constant boost, maybe because your engine technology isn't up to it (can't carry enough fuel, for example).

[jegs2]

Those who suggested a one g drive, if it could be built it would take <50,000 years to reach the center of the galaxy, however time distortion would make it seem like twenty (turning and decellerating half way.) However, the little problem is that you WILL hit something

I was thinking the same thing.

[Kuroneko]

Those who suggested a one g drive, if it could be built it would take <50,000 years to reach the center of the galaxy, however time distortion would make it seem like twenty (turning and decellerating half way.)

The ship-time would be the most relevant for the survival of the crew.

However, the little problem is that you WILL hit something

Going forwards shouldn't be too bad, as long as one keeps from going into any nebuli: very thick ice coating, for example. There's really not much interstellar dust normally. After the turn-around to decelerate, however, it would be a very large problem, unless the exhaust is dense enough and has enough energy to significantly slow down or stop incoming particles.

[Erwin Rommel]

you normally cruise at 1g acceleration

The problem with this as stated is relativity, which adds two problems, working the math quickly, and very poorly, you find that in order to maintain 1g (1g=9.8N, I used 10N for the sake of the twelve trees I would need to work out the math using 9.8N). 1N=1m/s^2/kg. The speed of light is VERY roughly 300,000,000m/s. So by doing simple math you'd conclude that to reach the speed of light you'd take 30,000,000s in a craft weighing 1kg that could maintain 10m/s^2. I can't remember Einstein's equation pertaining to increasing mass as approaching the speed of light but the increasing mass would also present a problem to your engine.


My solution would be to have one ship that could break into two during long voyages and using a tether rotate around a central point.

[Wicked Pilot]

You could try using electric and magnetic fields to simulate gravity. I'm not sure of what kind of power requirements and possible human side effects your looking at though.

[Kuroneko]

So by doing simple math you'd conclude that to reach the speed of light you'd take 30,000,000s in a craft weighing 1kg that could maintain 10m/s^2. I can't remember Einstein's equation pertaining to increasing mass as approaching the speed of light but the increasing mass would also present a problem to your engine.

You're confusing the frames of reference. 1G constant acceleration from the point of view of the ship does not necessarily translate into 1G acceleration from, say, Earth's reference frame.

Doing the math, at 1G = 1.03237 light-years per year per year acceleration for T = 3e7 s = 0.95 yr, the final velocity is v = tanh(0.95*1.03237), which is just barely above three-quarters of light-speed. For each kilogram of the ship, the ship now has about c^2*(1/sqrt(1-v^2)-1) = 4.68e16 joules of kinetic energy, which is about eleven megatons of TNT!

[Arrow]

You could try using electric and magnetic fields to simulate gravity. I'm not sure of what kind of power requirements and possible human side effects your looking at though.

I saw on PBS once that a researcher was using electromagnets to float organisms, such as spiders and insects. I think he said that he would need 12 to 20 megawatts to suspend a human in his device.

Also, you have to make sure that non of your equipment would be attracted to the electromagnetic fields your using to simulate gravity - picking a hammer off the floor would probably be a bitch.

[Wicked Pilot]

I saw on PBS once that a researcher was using electromagnets to float organisms, such as spiders and insects. I think he said that he would need 12 to 20 megawatts to suspend a human in his device.

Also, you have to make sure that non of your equipment would be attracted to the electromagnetic fields your using to simulate gravity - picking a hammer off the floor would probably be a bitch.

The good thing about the magnetic fields option is that the technology already exist. Of course there will be kinks to work out, but I think this is probably better than the rotating section option, and way better than the constant 1g acceleration/deceleration.