The best shape for Massive ships

[mdiinican]

Well shoot now I am planning on two Massive spaceships... Original one using "Magic Tech" from Starwars, super shields, armor, engines etc.
But now one utilizing much of the more 'reality' based ideas that have been floated. largely as they are MUCH more interesting then the magic tech stuff!

Well if you want some more "reality based" tech for your ship, you could use a highly advanced thermoelectric generator in the ship to convert the bulk of your ship's waste heat into electrical power, vastly reducing the need for radiators. Current state of the art is ~15% waste heat recovery IIRC. Your sufficiently advanced civilization could maybe have achieved say 75+ percent. I'm afraid I don't know the theoretical maximum efficiency of such a system so the number is really just made up. Then there are metamaterials which have all kinds of fun properties. You could make your ship invisible to certain kinds of EM radiation, create all kinds of optical systems that simply aren't possible with actual lenses, there are a ton of possibilities there. Right now we can only manipulate light with long wavelengths, like infrared, and only in 2 dimensions, but I haven't read anything other than positive news regarding building visual light cloaks that work in 3 dimensions (just way in the future) with our current tech being the only limitation.

Unfortunately, the efficiency of such a thermocouple or similar device is limited by the Carnot cycle efficiency for heat engines. Because it is essentially a kind of heat engine. The theoretical maximum is 1 - the temperature of the cold reservoir/the temperature of the hot reservoir. Thermocouples and things like stirling engines do not create electricity from heat per se. They create electricity from a heat gradient. The bigger the difference between the hot side and the cold side, the more efficient they can be. The device itself doesn't help at all at keeping the cold side cold. In space, using a thermocouple would pretty much entail sticking one side on what needs to be cooled, and the other side on a big friggin' radiator and radiating as much heat as possible as fast as possible. In order to be efficient, a heat engine has to move as much heat as possible from somewhere hot to somewhere cold. This is not conductive for stealth.

[Sarevok]

To be fair there is a difference between being found and being tracked. It is very difficult to find an object the size of a typical wet navy warship in space. We at present have not even cataloged the majority of asteroids over 300 m that entails the NEO moniker. Detecting previously unknown astronomical objects is a painstakingly slow process. A warship in powered down state could stay hidden for months or years right near an enemy homeworld. It would take some lucky optical sensor system looking at the right spot in space at the right time to find it.

On the other hand once a ship is detected there is no escaping tracking. Even present ground based telescope operating under Earth's prohibitive atmosphere can follow tiny moons and asteroids across the solar system.

So in short better not to invest much in stealthing because the chances of initial detection is low. But once detected meaningful evasion is almost impossible. So better gear up for the fight instead.

[Sarevok]

The difficulty of detection means there'll be difficulty in tracking too. If you move and they aren't sure just how you moved, being lost is a possibility.

Only if the enemy is stupid enough to treat a warship like an inert rock that does not change velocity. Tracking a warship 24/7 is not a problem at all even with present day telescopes.

Being found may be physically impossible too depending on a number of factors. If you keep your emissions low, it is very hard to be seen. (I know there's some fucktards on this site who think you can see things without photons triggering your receptors, but those people are fucking retards.)

Yeah instant detection of a shuttle sized object half way across the solar system, like some believe, is stupid. But at that range space combat is not possible. At ranges where realistic weapons work you are not sneaking up at all.

Of course, your emissions aren't necessarily under your control... the enemy might have big honking space radars, or the bloody sun might be lighting you right up.

Radar would kick ass within a few thousand kilometers. But beyond that ? I reckon optical and IR search and tracking would be better.

[Crossroads Inc.]

Well shoot now I am planning on two Massive spaceships... Original one using "Magic Tech" from Starwars, super shields, armor, engines etc.
But now one utilizing much of the more 'reality' based ideas that have been floated. largely as they are MUCH more interesting then the magic tech stuff!

Well if you want some more "reality based" tech for your ship, you could use a highly advanced thermoelectric generator in the ship to convert the bulk of your ship's waste heat into electrical power, vastly reducing the need for radiators. Current state of the art is ~15% waste heat recovery IIRC. Your sufficiently advanced civilization could maybe have achieved say 75+ percent. I'm afraid I don't know the theoretical maximum efficiency of such a system so the number is really just made up. Then there are metamaterials which have all kinds of fun properties. You could make your ship invisible to certain kinds of EM radiation, create all kinds of optical systems that simply aren't possible with actual lenses, there are a ton of possibilities there. Right now we can only manipulate light with long wavelengths, like infrared, and only in 2 dimensions, but I haven't read anything other than positive news regarding building visual light cloaks that work in 3 dimensions (just way in the future) with our current tech being the only limitation.

Unfortunately, the efficiency of such a thermocouple or similar device is limited by the Carnot cycle efficiency for heat engines. Because it is essentially a kind of heat engine. The theoretical maximum is 1 - the temperature of the cold reservoir/the temperature of the hot reservoir. Thermocouples and things like stirling engines do not create electricity from heat per se. They create electricity from a heat gradient. The bigger the difference between the hot side and the cold side, the more efficient they can be. The device itself doesn't help at all at keeping the cold side cold. In space, using a thermocouple would pretty much entail sticking one side on what needs to be cooled, and the other side on a big friggin' radiator and radiating as much heat as possible as fast as possible. In order to be efficient, a heat engine has to move as much heat as possible from somewhere hot to somewhere cold. This is not conductive for stealth.

Keep mind as a 100km Generational Command ship "Stealth" isn't high on the priorities I do appreciate all the ideas, I am really fleshing out the 'reality' based ship. So far what I have is a 80km "RAMA" type ship with a long drive section and engines and power reactors at the far end separated from the central habitat area. ALso incorporated a lot of the armor ideas into immense rotating plates that can double as radiators.

[avatarxprime]

^^

I am afraid the electricity you produce from waste heat conversion would again become waste heat. That is ignoring the fact that thermocouple junctions are hideously inadequate. They suffice as heat detection elements for various sensor equipment and producing minute amounts of power for long endurance observation posts or satellites. But they are not good for "cloaking" a ship in the IR part of the spectrum.

It seems both you and mdiinican thought I was saying that the waste heat reclamation could be used in acheiving some kind of stealth in space, I did not meant that at all and considered the two (metamaterial applications vs waste heat recovery) as two separate subjects. I apologize if that was not clear in my earlier post.

Anyway, as to the waste heat, if you're converting it into electricity then can't you just store it in a battery (until needed) or expend it some other way? Then if you have an electrically intensive system, like an ion rocket, or weapon systems, you can use these to essentially dump excess waste heat from the reactor in the form of electricity. The energy content remains the same, but the actual amount of waste heat that needs to be dealt with at any given time is reduced. At least, that was how I was thinking of it, please correct me if I'm wrong. Also, here is the article that first got me thinking along these lines, its about thermoacoustic devices being used to convert waste heat into electricity. It also mentions using the converting technology to cool down things (admittedly they are talking about laptops) but I would think the potential is there to expand such a system to handle larger issues. The article mentions the idea of "cool[ing] large, industrial sources of waste heat." As to their usefulness at being a means of generating power, this article discusses using heat engines for "utility-scale" level power generation. Although, the means in both are different, I guess I shouldn't have been as specific as saying "thermoelectric."

For the IR cloaking, metamaterials would cloak a ship from outside IR detection, and that was just one example I thought would be cool to put down for what metamaterials can do to get people, and specifically Crossroads Inc. thinking of the possibilities. Since metamaterials hold the potential to essentially redirect EM waves wherever you want them to be they have all kinds of potential and useful applications. Protect your crew from cosmic radiation by making your ship essentially invisible to it. Worried about your engine's strong magnetic fields (assuming VASMIR style ion rocket) affecting the rest of the ship? Shield the area with metamaterials that steer the fields away, or simply insulate the area. Need better resolution on that scope? Create a superlens and get past that pesky visual light diffraction limit. There is even research into using such material to shield buildings from the vibrational effects of earthquakes, a concept that I imagine would be useful in helping to protect sensitive bits of the mega-ship Crossroads Inc. proposed. There are just so many other applications beyond "Oooh, it's invisible."

[Sarevok]

I think you are ignoring how thermocouples work. They exploit temperature difference between two regions to produce a current. So in order for them to work at all you need a hotspot on your ship which as mdiinician explains defeats purpose of stealth entirely.

Now I understand you are not focused on stealth entirely but making use of waste heat. Well there are ways to do that. Combined cycle gas turbines use waste heat to generate even more power. They are effective as means of land based power generation and naval propulsion. Depending on type of nuclear thermal propulsion used maybe something similar could be invented. But I am not sure if it would be worth the extra weight. On a powerplant serving a moon or an asteroid base ? Sure you could try to recover every joule you can but in a combat space craft every extra pound has to be justified meticulously.

[Ellindsey]

Sadly, the brutal and uncompromising laws of thermodynamics say you can't get rid of waste heat, no matter what you do. Heat wants to flow from highly concentration to low concentration: the hot parts of your ship will want to radiate their heat out into the cold background of space. The purpose of radiators is to speed this process up, by giving the waste heat a highly conductive path to a large surface area so as to more efficiently radiate. Heat engines (no matter what type) work by exploiting a difference in temperatures, generating energy from the flow of heat from a hot source to a cold sink. They don't reduce the amount of heat in the process, but merely spread it out and make it less concentrated. You want to remove the heat from the hot parts of your ship in the first place, but a heat engine is actually a less effective conductor than something designed merely to conduct heat would be, so you are actually impairing your cooling systems by trying to recover waste heat. In the end you'll need even larger radiators to try and keep the operating parts of your ship at acceptable temperatures and a sufficient difference in temperature across your waste-heat-recovering heat engine.

[Nyrath]

You could also use many overlapping lengths of cable in each run; then the loss of any one section isn’t critical.

For additional redundancy, you can make the cables Hoytether.
http://www.tethers.com/Hoytether.html

[mdiinican]

I don't know if you could use metamaterials to protect against cosmic radiation. It's mostly particle radiation, specifically mostly protons and alpha particles. Those have absurdly short wavelengths via Schrodinger's equations, and I'm not even sure if it would work even if you could make a metamaterial with a wavelength that short. Do particles even refract when they run into other matter?.

[Sarevok]

Why bother with metamaterials when magnetic shielding is available ?