Realistic spaceships, mecha, and other sci-fi goodies

[Holeypaladin]

I know some of you are probably thinking.. "But wait? Aren't sci fi and fantasy inherently unrealistic?"

Well... yes and no. Fantasy is inherently unrealistic, but sci-fi can vary (as discussed in my topic on sci-fi hardness).

The purpose of this topic is to discuss how to make spaceships, mecha, and other stuff applicable in a realistic setting that is somewhat believable and plausable, if not necessarily feasible by current reckoning. When coming up with a good sci-fi universe for stories, you really need to start from the ground up. When multiple writers are involved, people may have very different views of what they find "cool" when it comes to sci-fi, and without a universal standard, it becomes an inconsistent space opera, like Star Wars... fun, but not realistic at all.

So how to design ships, mecha, and everything else while keeping it realistic? Well, it's largely up to the GM to set the standards. Realistic sci-fi universes require a lot more GM regulation than unrealistic ones. Since I use a more realistic setting than most, I figure I'll share some ideas.

Spaceships.
A lot of people like to imagine spaceships as being huge, massive pieces of metal slowly drifting through space, except when they go FTL. This is far from accurate, in a realistic setting. If you look at modern ships... they're actually quite small and compact in comparison. And that's comparing spaceships to ocean-navies... a very bad comparison. About half of a naval warship is submerged under the ocean, and they have to worry about drag and current much more than a spaceship does. They're also quite slow, whereas a spaceship must be FAST... because space is BIG.

A more accurate comparison would be aircraft. While aircraft still have to worry about atmospheric drag, they're built for speed, compact in size, and highly maneuverable. Increase their altitude by a few thousand miles, and you have spacecraft. Such as the space shuttle, or Saturn rocket. Currently, no one has build anything much larger than the Saturn rocket designed for high-speed maneuverability in space... but you can imagine it would have a more compact design, with a lot of thrust from the engine. Since speed is determined by thrust divided by mass, you actually want as little mass as possible in order to achieve high speeds. The best ways to reduce mass are either to reduce volume or reduce density. Reducing density involves adding in a ton of empty space, which is highly inefficient. Reducing volume makes the ship much smaller than what you would see in Star Wars or WH40k.

Another thing writers often overlook is the fact that reality is three-dimensional. They measure ships by length. Length is NOT a good way to measure a ship.. as it's only one dimension. Mass is a function of volume, which is a function of three separate dimensions. To double a ship's length is to increase their volume and mass by 8. To multiple a ship's length by 10 is to increase the volume a thousand times over. That Executor from Empire Strikes Back? Yeah, it's a thousand times the mass of a star destroyer. In a realistic setting, it would take the combined firepower of a thousand star destroyers to match it. I didn't see a thousand star destroyers in that fleet... couple dozen or so, maybe even a hundred, but not a thousand.

A lot of people like to measure the "length" of ships in kilometers. This is not a realistic measurement for many different reasons. The physics reason is that according to square-cube mechanics, the thrust of a ship that massive should disintegrate it. The economics answer is that it's just too bloody expensive. Take for example the Imperial-class Star Destroyer. It's something like 1.6km in length. Now, compare it to a space fighter (which is very realistic in space) which costs the equivalent of, say, $50 million and is 16 meters in length (also pretty realistic). Using those same dimensions, the star destroyer is 100 times the length, or 1 million times the volume (100 cubed). Even if you halve the cost of the fighter, you're still looking at a single ship that costs $25 trillion.. nearly half the GDP of Earth. To make anything several kilometers in length? Do the math, remembering to cube the dimensions, and you'll find out that it's just not realistic.

Keeping in mind how MUCH space is out there, it's likely that battles between space fleets will involve hundreds if not thousands of warships. Because a space empire needs to be able to defend a vast amount of territory. The number of ships can be reduced for smaller scale space empires.. such as between single-system countries, but the actual size of most warships is unlikely to be affected much... larger empires will simply have more of them, as they have more space to cover. Ships the size of modern navy ships are much more realistic for space combat. Get too much bigger than a Nimitz-class supercarrier, and you're stretching the limits of what is realistically feasible.

Mecha

The very concept of Mecha is that they are based on "rule of cool" mechanics. Because what's more cool than a giant humanoid robot blowing up another giant humanoid robot with a giant space gun? Two giant humanoid robots blowing up two other giant humanoid robots, that's what!

However, mecha by their design are inherently unrealistic. This does not mean that they can't exist in a setting... they just wouldn't be the super-weapons that they are often portrayed as in anime. Pieces of military equipment is all they'd really be... real-robot genre rather than super-robot genre, basically.

But even real-robot genre can be unrealistic. There are several factors to overcome when making mecha to begin with.

First off, standing on two legs is inherently unstable. Ever try to make a two-legged table, or a two-legged chair? It requires amazing balance just to be able to stand upright... and it's also very easy to knock a two-legged object down. Bigger feet do add to stability, but more feet adds much more stability. However, since most people thing of humanoid mecha when they think of mecha, I'll focus primarily on two-legged mecha.

A stable robot might use three or more legs for increased stability. Or if you want to make them cool, just give them large enough legs and feet to support their massive size. Square-cube mechanics make it difficult for huge robots to stand on two feet without collapsing under their own weight, so the legs would likely be proportionally larger than human legs.

Another thing to consider is that standing upright makes you a larger target. One of the first thing soldiers do in combat is drop to a prone or kneeling position, making themselves a smaller target, and take cover behind objects. Upright mecha would have much greater difficulty in doing so, as large size makes them inherently unwieldy. Not to say it can't be done, but it takes longer.

Also, the humanoid form has a great deal of surface area... apparently evolved due to the fact that the tropical environment of Africa where humans are said to have originated from is super hot. Also the reason we have to wear jackets in the cold... too much heat escapes from our high surface skin. The problem with having a high surface area is that it is difficult to put armor on a humanoid form. Since armors protection is measured by its thickness, in order to provide sufficiently thick armor on a humanoid from, it has to be a whole lot more massive than, say, the same thickness on a sphere. So mecha are likely to be fairly lightly armored... not heavily armored. Or else they'd collapse under their own weight.

There are many other examples to consider when designing realistic mecha, but suffice to say that they're very different than what most people think of. They can be done, but a lot of realistic-setting countries probably wouldn't bother... tanks are more efficient, if less maneuverable.

Of course, you might also consider removing the humanoid form from mecha entirely and just use multi-legged mecha. Spiders and Scorpions are rather efficient designs, many legged and easily armored. Send in the spider mechs! Take on the roboscorpions!

[Foster]

Rockets are more like skyscrapers on a flying roller-coaster... while being shot-at by artillery... Or being crashed by jetliners...
-Length = good is a holdover at best from the idea of a tiny umbrella of radiation-shielding that only protected the crew, anything that lingered about 15 meters from the hull was probably going to glow blue from radiation.

~Problem is that the length also means the same challenges as building a tall skyscraper in terms of G-loading from the main-engine, plus 'wind' in the form of things hitting it. So consider the engine mounts as the only parts touching the ground.

Mechs... um... depends on where you wanna draw the line between an assault-vehicle and an assault-spacesuit.
-And at what points are people willing to ignore physics for dashing metaphors.

[Goldmarble]

Need to use a multi option poll.

And I like large ships at long range. I like fighters at long range. I mean, really, as soon as lasers become viable weapons in a sci-fi setting, they basically replace missiles at any range: Can't really intercept a laser, it covers 300,000,000 meters in a second. Dog fighting would eventually be pushed out to ranges of what? 300,000 - 600,000 KM using lasers as we used machine guns back in WW2. It becomes a war of who has the best sensors, or best stealth. The first to see and identify their target, is the first to get their shot off. And if there is no "technobabble subspace detection", then he who fires first, wins. Simply because you will never know you are being fired upon, until you are turned into a ball of plasma and shrapnel if your sensors don't know there is even anyone else out there. Which is sort of a reason to not build fighters.

Hell, in a realistic setting, you could make spaceships quite a bit larger than a air-craft carrier of today. Hell, Freighters are bigger. The current biggest was the Seawise Giant oil tanker, that was 458 meters long, and had a displacement of 646,642 tons in full load (Next biggest is under construction, and will be 488m long). Nimitz class is 332 meters long, with a displacement of 106,300 tons. Naval vessels have to take into account the stress of the sea, which has broken many a ship just by wave action alone. Space? Far, far fewer structural stresses. Are kilometer long ships possible? Definitely. Would the engines needed to move them, tear them apart as you suggest? No...Hell, you could strap a model rocket engine onto a ship 1 kilometer long, and it would move it. Very, very slowly, but it would, because engines in space are not so much about speed, but acceleration. Because there is no resistance from particles until you start hitting measurable fractions of relativistic velocity. Until that point, if you could fuel an engine the size of a model rocket for long enough, it would eventually get you going that fast. Because in space, away from gravity wells; there is nothing to impede your acceleration. Hell. Make an engine that is capable of 0.4-1.0g acceleration, suddenly you have artificial gravity all over the ship. So long as you keep accelerating, you have gravity.

Space ship design will probably remain cylindrical. Since the circular outer hull retains pressure the easiest, and would be pretty damn easy to armor.

Real-Robot mechs are fun to a degree, but Super-Robot mechs just.....don't work for me at all. Like Gundam. If this magic armor is so great, why not use it on tanks where it will be even more effective, while using less armor overall? Why are your mechs gaudy bright colours with chrome bumpers? If radar is useless, infrared blurred, and even visual light affected...because of particles then visual camouflage becomes more important than ever! How can the recoil of 130mm gatling cannons mounted to the shoulders of a mech...that is only 23 metric tons (oh dear god, I just hate Gundam the more I read of the idiocy...this was new to me), not knock it over on 1 shot, let alone sustained firing that would rip apart a 23 ton tank? The only way to mount a 120mm cannon on a 23-30 ton vehicle today is to use a long recoil length, to distribute the recoil force over time to the chassis, slowing the rate of fire of the weapon. Gatlings can't do that. They do high rates of fire...Oh...god...my head hurts already.
If the Minovsky Ultra Compact Reactor can power a gundam and it's beam cannon...why not throw it into a tank where it can put even more power to the beam cannon?

.....Yeah. Fuck Super-Robot because nothing ever makes sense, and the sheer amount of fucking stupid exuded hurts my head

[Foster]

Light-speed lag.
-Because just like PvP over dial-up, lag kills.

Because at one light-second away (convienently, 1 AU) you've got two seconds of time between what you've seen the ship doing, and the laser going where you pointed the darn thing.

And when ships are moving at speeds measured in km/sec, and can start accelerating at 100m/sec/sec (10 Gs [this will put stress on not only the crew, but the 100-meter ship as well*]), that means the target could be 200 meters from where you wanted to shoot (but 75% of the time, it'll be within 100 meters of your POA).

And there are ways to mitigate the effects of lasers.
Spinning or rotating to present a fresh hull-plate (like ERA) can reduce effectiveness just like waving your arms and throwing debris in their LOS.

*To get the picture, please drop a destroyer -bow-first- into the water from 75 meters. Or ram a dockyard @ 30 kts. It'll have to sustain these forces for an indefinate amount of time w.o tructural failure, even with a massive hole blown into it by a laser.

And Marble, guess what I did to a tank-platoon in a Gundam-thread?
-I mounted scrap-mech parts on them. They could fly.

[Goldmarble]

Space fighting just...starts to hurt my head after a while. Yeah, sensor lag and weapons lag would be fun, though computers can compensate for some of it, especially if the enemy is unaware of your presence. Know the acceleration vector, calculate path, fire. Win. Use a laser system that is embedded in the craft with a port so that the single laser can target an entire hemisphere. Depending on the re-charge rate, you could lay out a grid of beams in the 90% area of hitting the target and just wash them in laser fire.

Course, laser counter measure could equal a mirrored hull, literally reflecting the bulk of the energy instead of absorbing it.

And mechs....yeah, just saw that....It was like you were trolling them and they didn't realize it....

[Foster]

I just got lucky and found someone who admited that the Mech-pilots in that show were for all intents and purposes... spoiled children with no combat-experiance.

Enter a pack of wolves in 'outdated' tech that actually knew what it was doing...

Hovercraft-tanks are cool for load-carrying and all... but they're kinda easy to mobiilty-kill...
-Down the transports, and you instantly troll them into a drag-out fight of your choosing, because their damaged units ain't going anywhere.

Tactics, they work.

[Kadaeux]

I know some of you are probably thinking.. "But wait? Aren't sci fi and fantasy inherently unrealistic?"

Well... yes and no. Fantasy is inherently unrealistic, but sci-fi can vary (as discussed in my topic on sci-fi hardness).

The purpose of this topic is to discuss how to make spaceships, mecha, and other stuff applicable in a realistic setting that is somewhat believable and plausable, if not necessarily feasible by current reckoning. When coming up with a good sci-fi universe for stories, you really need to start from the ground up. When multiple writers are involved, people may have very different views of what they find "cool" when it comes to sci-fi, and without a universal standard, it becomes an inconsistent space opera, like Star Wars... fun, but not realistic at all.

So how to design ships, mecha, and everything else while keeping it realistic? Well, it's largely up to the GM to set the standards. Realistic sci-fi universes require a lot more GM regulation than unrealistic ones. Since I use a more realistic setting than most, I figure I'll share some ideas.

*Gets warpaint on.*

Spaceships.
A lot of people like to imagine spaceships as being huge, massive pieces of metal slowly drifting through space, except when they go FTL. This is far from accurate, in a realistic setting. If you look at modern ships... they're actually quite small and compact in comparison. And that's comparing spaceships to ocean-navies... a very bad comparison. About half of a naval warship is submerged under the ocean, and they have to worry about drag and current much more than a spaceship does. They're also quite slow, whereas a spaceship must be FAST... because space is BIG.

A more accurate comparison would be aircraft. While aircraft still have to worry about atmospheric drag, they're built for speed, compact in size, and highly maneuverable. Increase their altitude by a few thousand miles, and you have spacecraft. Such as the space shuttle, or Saturn rocket. Currently, no one has build anything much larger than the Saturn rocket designed for high-speed maneuverability in space... but you can imagine it would have a more compact design, with a lot of thrust from the engine. Since speed is determined by thrust divided by mass, you actually want as little mass as possible in order to achieve high speeds. The best ways to reduce mass are either to reduce volume or reduce density. Reducing density involves adding in a ton of empty space, which is highly inefficient. Reducing volume makes the ship much smaller than what you would see in Star Wars or WH40k.

Incorrect. You can make a Starship 5 meters long or 5000 meters long, and so long as they have the same percentage of mass in fuel and engines (and engine efficiency) their acceleration will be identical. Indeed, if the big ship has MORE engines for its mass than the small ship does for it the larger ship will accelerate faster.

Another thing writers often overlook is the fact that reality is three-dimensional. They measure ships by length. Length is NOT a good way to measure a ship.. as it's only one dimension. Mass is a function of volume, which is a function of three separate dimensions. To double a ship's length is to increase their volume and mass by 8. To multiple a ship's length by 10 is to increase the volume a thousand times over. That Executor from Empire Strikes Back? Yeah, it's a thousand times the mass of a star destroyer. In a realistic setting, it would take the combined firepower of a thousand star destroyers to match it. I didn't see a thousand star destroyers in that fleet... couple dozen or so, maybe even a hundred, but not a thousand.

Incorrect. Length is a perfectly acceptable way to measure a ship because saying "it's a 150'000 tonne ship" doesn't tell anybody anything about the ship.

But in a realistic scifi length will in fact be meaningless as all ships would be spheres.

A lot of people like to measure the "length" of ships in kilometers. This is not a realistic measurement for many different reasons. The physics reason is that according to square-cube mechanics, the thrust of a ship that massive should disintegrate it. The economics answer is that it's just too bloody expensive. Take for example the Imperial-class Star Destroyer. It's something like 1.6km in length. Now, compare it to a space fighter (which is very realistic in space) which costs the equivalent of, say, $50 million and is 16 meters in length (also pretty realistic). Using those same dimensions, the star destroyer is 100 times the length, or 1 million times the volume (100 cubed). Even if you halve the cost of the fighter, you're still looking at a single ship that costs $25 trillion.. nearly half the GDP of Earth. To make anything several kilometers in length? Do the math, remembering to cube the dimensions, and you'll find out that it's just not realistic.

You want to build a 16 meter fighter, no... a SPACE fighter... for 50 million and call it realistic? Put on this straight jacket and proceed straight to the mental care ward. Do not pass go. Do not collect $200.

Square-Cube mechanics do not, nor have ever, forbidden a vessel that large. Not would the thrust disintegrate it.

Keeping in mind how MUCH space is out there, it's likely that battles between space fleets will involve hundreds if not thousands of warships. Because a space empire needs to be able to defend a vast amount of territory. The number of ships can be reduced for smaller scale space empires.. such as between single-system countries, but the actual size of most warships is unlikely to be affected much... larger empires will simply have more of them, as they have more space to cover. Ships the size of modern navy ships are much more realistic for space combat. Get too much bigger than a Nimitz-class supercarrier, and you're stretching the limits of what is realistically feasible.

Entirely false. A space battle between hundreds to thousands of warships is completely unrealistic. And your artificial ship size limitations are borne of your own ignorance.

*SNIP*

I'll just skip the mech part.

- - - Updated - - -

And I like large ships at long range. I like fighters at long range. I mean, really, as soon as lasers become viable weapons in a sci-fi setting, they basically replace missiles at any range: Can't really intercept a laser, it covers 300,000,000 meters in a second. Dog fighting would eventually be pushed out to ranges of what? 300,000 - 600,000 KM using lasers as we used machine guns back in WW2. It becomes a war of who has the best sensors, or best stealth. The first to see and identify their target, is the first to get their shot off. And if there is no "technobabble subspace detection", then he who fires first, wins. Simply because you will never know you are being fired upon, until you are turned into a ball of plasma and shrapnel if your sensors don't know there is even anyone else out there. Which is sort of a reason to not build fighters.

Stealth is not possible in space. See the Link Below.
http://www.projectrho.com/public_html/rocket/spacewardetect.php#id--There_Ain't_No_Stealth_In_Space

Also. Lasers are NOT the be-all end all. They have to maintain the beam on a singular point over an extended period of time. Over light-second+ ranges lasers become easy to avoid.

Hell, in a realistic setting, you could make spaceships quite a bit larger than a air-craft carrier of today. Hell, Freighters are bigger. The current biggest was the Seawise Giant oil tanker, that was 458 meters long, and had a displacement of 646,642 tons in full load (Next biggest is under construction, and will be 488m long). Nimitz class is 332 meters long, with a displacement of 106,300 tons. Naval vessels have to take into account the stress of the sea, which has broken many a ship just by wave action alone. Space? Far, far fewer structural stresses. Are kilometer long ships possible? Definitely. Would the engines needed to move them, tear them apart as you suggest? No...Hell, you could strap a model rocket engine onto a ship 1 kilometer long, and it would move it. Very, very slowly, but it would, because engines in space are not so much about speed, but acceleration. Because there is no resistance from particles until you start hitting measurable fractions of relativistic velocity. Until that point, if you could fuel an engine the size of a model rocket for long enough, it would eventually get you going that fast. Because in space, away from gravity wells; there is nothing to impede your acceleration. Hell. Make an engine that is capable of 0.4-1.0g acceleration, suddenly you have artificial gravity all over the ship. So long as you keep accelerating, you have gravity.

All true.

Space ship design will probably remain cylindrical. Since the circular outer hull retains pressure the easiest, and would be pretty damn easy to armor.

A space warship would adopt a more Spherical design. It is far more efficient, easy to armour, provides the most sensor coverage, best thruster coverage, best centre of gravity etc.

[vangelis]

-snip-

QFT.

[Foster]

Actually, more of an teardrop-shape because of the thrust-loading on the outside, otherwise it' may be more likely to buckle and crack, lika an egg.

Spliting the difference, would be a sphere on a stick with a load-bearing hub&spoke keelframe.

But to get the necessary re-mass, it's easier to use gigantic containers, which may as well be conforming to the overall package of a thinly-clad cylinder veneer behind the trans-hab pressure-sphere.

Because when you've got a terrawatt-class reactor riding on your ship's ass, distance is your friend.

Ther's also a billion more problems with fabbing a sphere over a simple cylinder (it also makes load-balancing easier).

[Holeypaladin]

The main problem with huge ships is not the size limitation, nor are they inherently slower (but tensile strength IS a measure of surface area, NOT volume, so there IS a point at which the thrust will disintigrate due to insufficient tensile strength)

The problem is economics.

Remember, for the price of a single Executor, I could field a thousand Imperial-class star destroyers.

For the price of a single Imperial-class, I could field a thousand 160-meter cruisers.

People don't consider this in many settings. A lot of people thing twice the length means twice as big. It doesn't.

As for space fighters being unrealistic? That's completely wrong. We have fighters now, all you have to do is modify them to suit vacuum, replacing their engines with something that works in space, and you have space fighters. The US Navy claims that the F-18 hornet costs $29-$52 million. And it is 17.1 meters in length. I did NOT make these figures up when doing the comparison.

As far as first shot first kill weapons... that only applies if you have weapons powerful enough to kill in one shot. If you allow technology such as force fields and advanced armor (technology is one of those areas where we can't say whether or not it's realistic, it's one of the universal consistencies), then firing a laser at long-range probably won't be a one-hit kill, as laser beams widen with range, being dispersed over a wider surface.

Stealth in space is another one of those technology things. Our current technology forbids it. Doesn't mean you can't add tech to the setting to make stealth more possible. Especially considering space is not a true vaccuum.

Spherical spaceships... actually have both strengths and weaknesses. What's easier to hit with a gun, a circular target, or a long piece of tape? If a ship is designed to be facing its target and attacking in a single direction, as well as taking damage from a single source, it's harder to hit, and harder to get a non-glancing blow, on a flat wedge-shaped ship than it is on a sphere. But that wedge-shaped ship is vulnerable to attacks from above and below.

A sphere is amazing at fighting in all direction at once. But when firepower is focused from a single direction, there are more efficient shapes. Look at a modern tank... it's designed to take hits to the front. And its armor is angled to deflect hits to the front. It makes a good design for a spaceship designed to take hits to the front, as well.

EDIT: There is one factor to consider when deciding ship sizes. The fact that we already have WMDs capable of destroying a ship in one shot. How does that 10-km long ship like it when a 100 megaton bomb explodes it to pieces in one hit?