An ongoing debate between Nephtys and I revolves around our two differing perceptions of not only what is generally more efficent, but more aesthetically pleasing and useful in terms of a hypothetical starship combat scenario.

In her case, she wants Torchships with long endurance able to race out with a few potent guns--beams perhaps--and a supply of nuclear missiles. Engaging at long range and at high speed, they change course with heavy thrusting gear so that a foe that fires back has to choose a sphere of possible targets and spread the hurt around through there. Fast, accurate tracking weapons and a slim little fishbone or needle-like profile make it an ultralight, balsa-weak target that just tries never to be hit. The idea is, by moving fast enough and engaging at a long enough range, small changes in course make the small ship so hard to hit that it's nearly impossible to catch, but that it can continue to fire and choose soft targets.

In my case, I want an armored brick with a long body, thickly armored head to just shrug off whatever's thrown at it, and the weapons behind panels along the sides. Flat, ugly armor, possibly with a layer of graphite and a lot of structural support, designed to have hard-to-break sensors and enough heat soak to lessen the need for radiators. Half of the thing by mass is going to be reactor and engine anyway, but it'll be large enough to carry a variety of weapons much like a ship might. Some anti-missile lasers also useful for cooking annoying corvettes, rockets, kinetic weapons and maybe a few potent little automated kill vehicles like a combat wasp to make sure you hit something when you need it. The idea is, in space, any ship that's long range (and not a torch) is going to be a little slow to juke, so it's better to accept a few stray hits, protect against nukes and wide lasers, and drop enough dirt-cheap semi-seeking ordinance into the way of the enemy that he'll get hit badly enough to go down.

Now, the real thing is that when these two paradigms meet up, the results are always odd. Either my brick is unable to connect at all with it's weapons due to the Torch-juking and my sensors are slowly melted away until I'm blind (or she manages to get a nuke through my PD and blast it off with a hull hit), or some buckshot coilguns with seekers slam into her nimble needle and turn it into shrapnel.

After another round of debate, I decided to just ask the OSF bunch for opinions, science, and feelings on the subject. The harder the sci-fi the better I suppose, but she's already asking for High-Thrust, High-Exhaust Velocity, High-Endurance Torch drives so I felt that this meant that to even the field the brick needed to have some sort of fancy doohickey, and that I'd just leave that up to the board.

So, what do you think is a more reaAn ongoing debate between Nephtys and I revolves around our two differing perceptions of not only what is generally more efficent, but more aesthetically pleasing and useful in terms of a hypothetical starship combat scenario.

In her case, she wants Torchships with long endurance able to race out with a few potent guns--beams perhaps--and a supply of nuclear missiles. Engaging at long range and at high speed, they change course with heavy thrusting gear so that a foe that fires back has to choose a sphere of possible targets and spread the hurt around through there. Fast, accurate tracking weapons and a slim little fishbone or needle-like profile make it an ultralight, balsa-weak target that just tries never to be hit. The idea is, by moving fast enough and engaging at a long enough range, small changes in course make the small ship so hard to hit that it's nearly impossible to catch, but that it can continue to fire and choose soft targets.

In my case, I want an armored brick. Flat, ugly armor, possibly with a layer of graphite and a lot of structural support, designed to have hard-to-break sensors and enough heat soak to lessen the need for radiators. Half of the thing by mass is going to be reactor and engine anyway, but it'll be large enough to carry a variety of weapons much like a ship might. Some anti-missile lasers also useful for cooking annoying corvettes, rockets, kinetic weapons and maybe a few potent little automated kill vehicles like a combat wasp to make sure you hit something when you need it. The idea is, in space, any ship that's long range (and not a torch) is going to be a little slow to juke, so it's better to accept a few stray hits, protect against nukes and wide lasers, and drop enough dirt-cheap semi-seeking ordinance into the way of the enemy that he'll get hit badly enough to go down.

Now, the real thing is that when these two paradigms meet up, the results are always odd. Either my brick is unable to connect at all with it's weapons due to the Torch-juking and my sensors are slowly melted away until I'm blind (or she manages to get a nuke through my PD and blast it off with a hull hit), or some buckshot coilguns with seekers slam into her nimble needle and turn it into shrapnel.

So, after another round of debate, I decided to just ask the board for their opinions of the outcome. Who do you think would win this matchup? If we assume they both 'cost' the same, to be defined by you, which is more reasonable? Practical? Useful? What are some of the best examples of these matchups? And what would be some ways to improve on either one of these designs? I added a poll just for the basic question of who you think would win in the least specific terms, kinda like a Raptor vs. T-Rex poll, but I'm actually looking for people's opinions both as folks with some understanding of science and plenty of experience with science fiction. Come up with some ground rules, some scenarios, and weigh in on the immortal battle between speed, offense and armor!

Woah, you managed to double-post in one post!

That aside, I'm going to have to go with the Brick as the better choice in the situation you laid out. If we go by the results from single-ship fights that you described, then in fleet-engagements, sheer volume of fire is going to cut through the Torches simply because a large number of Torches won't be as able to effectively evade fire as they would in one-on-one battles and their weapons won't be able to put the hurt on a Brick fast enough to make the N^2 effect even-sided.

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Dark Heresy: Recondite War - Mercurius Haxtes, Techpriest
STGOD2k8 II - Dawns Star Empire
BM

On the brick. The fast ship can be overwhelmed with mass fire from the big ship.

Now what if in this situation, its just like modern warfare where it only takes one hit to kill something? The brick's just floating around, the small needle is barely noticeable, the needle shoots a missile and before the brick can do shit, it's dead?

The needle could maneuver to an angle where the fat brick has less guns, shoot a missile, and blow the brick up. Isn't this the reason why we don't have anymore giant battlecruisers festooned with giant phalluses, cannons and such?

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Yeah sure, as long as "awesome" is some kind of Shroomy code-word for "fucking stupid". - DW
shroom is a lovely boy and i wont hear a bad word against him - LUSY-CHAN!
Shit! Man, I didn't think of that! It took Shroom to properly interpret the screams of dying people - PeZook

What's to stop you from making torch drive missiles/drones and laughing as the Needle is chased down and destroyed.

Also, this is hard sci-fi, right? No inertial compensators/artificial gravity? Here's a hint: the needle will be just as fast as the brick, because both will be limited by human tolerances.

Have a very nice day.
-fgalkin

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The brick had better have good stealth systems, else it's dead meat. In space warfare, there is nothing that cannot be taken out fairly quickly and simply. When you throw missiles with AM or slugs at near relativistic velocities, the big brick with all its armour is just a bigger target.

The smaller, nimbler ship should be a better choice by simply being a smaller target, not just the agility.

At high enough velocities the torch isn't going to be able to get out of its own way. Since you achieve course changes by applying tangential accelerations . . . if you've got enough base velocity, not even a hundred-gravity (entirely unachievable in hard sci-fi, you can define 'enough' base velocity for ten gravities or one gravity of acceleration) burn is going to do much to change your heading in short periods of time. Of course, in a realistic sci-fi setting the torch is going to be crippled by its lack of internal bunkerage. If you tack on high-energy lasers to the torch, it's going to use its fuel even faster.



In a realistic sci-fi setting, you couldn't possibly build an armor capable of shrugging off a nuclear bomb, a laser of sufficient wattage, or a kinetic projectile with sufficient momentum and sectional density. At least not on anything you'd actually like to move. Sure, you could convert a sufficiently large asteroid into a warship, and rely on hundreds of meters of rock to soak up damage, but your asteroid-ship is going to have handling characteristics rivaled only by those of municipal stadiums.

As far as the brick's other defenses go, sure you can stop a nuclear bomb before it goes off in prime detonation range, but you're not going to be able to easily stop a laser beam, much less see it coming before it's too late. And you can't stick on too many point-defense turrets on your ship, otherwise you'd have no room for sensor clusters or maneuvering thrusters. Not to mention all those holes you need to poke into your armor to support a lot of point-defense. A brick or space battleship is going to be more vulnerable than you seem to be thinking it'd be.



Again, it depends on how realistic the sci-fi is. If there's something a brick should have lots of, it's internal bunkerage. Lots of cubage for fuel and warheads. A needle isn't going to have that, so the commander of a brick need only stay outside of the range of the needle's refueling depots and lob missiles in on ballistic trajectories. Sure the commander of the needle can catch you if she's willing to go ballistic, but she's not going to have a lot of maneuvering time on her clock, and her maneuvering options are limited unless she's decided killing you is more important than having enough fuel to make the return trip to base. But, as spaceships in a harder sci-fi are going to be bloody expensive, such kamikaze tactics will generally be frowned-upon by the higher-ups.



The harder the sci-fi, the less feasible an overgrown space-fighter becomes. Since, in order to get high performance, you must be willing to expend a lot of reaction mass per kilogram of ship, and to get high endurance, you must be able to carry a lot of reaction mass, which boosts he power requirement of your motors in order to push all that extra mass around, which requires more reaction mass to feed those beefier motors which . . . . .

On the other hand, the harder the sci-fi, the less feasible a heavily armored brick becomes. It already has a lot of non-propellant mass to shove around, so its peak acceleration will be severely limited. And since you can't build an armor strong enough, yet light enough to field on a mobile platform, to stop the sorts of weapons you could throw around in even harder sci-fi, there comes a point where a large enough ship becomes nothing but a big target for enemy gunners.



Any reasonable navy would probably use both, in different roles. A small, fast, lightly-armored needleship isn't going to have the endurance for long-range missions, and is going to get shredded by anything heavier. After all, to maximize performance, you're minimizing armor, which means a heavier ship with a lot of weapons emplacements needs to get lucky only once. On the other hand, a heavy space-battleship is going to take its sweet time getting anywhere, and while getting into its weapons range is going to be tantamount to suicide, anything lighter is going to be able to outrun it, and its mass isn't going to make it significantly more combat-survivable than a lighter unit like a space cruiser.

I think GrandMasterTerwynn did a good job of covering how the two compare in a hard sci-fi setting. So I'll approach it from a soft sci-fi perspective.

If we go by the typical conventions of soft science fiction or science fantasy, the the brick would be the premier platform. The reason is simple, we're typically dealing with energy shields and weapons, things that depend on the reactor's power output. This favors larger ships, as doubling the dimensions of the reactor squares its volume. The same applies for ammo magazines, strike-craft hangars, fuel bunkers, engines, weapon emplacements, sensor systems, EC, ECCM, etc. A small ship might be much faster and maneuverable, but it will have to deal with it's opponent's much superior volume of fire, and possibly longer firing range.

Awesome responses, I gotta say. Terwynn especially--I love poking holes in either extreme, and look for where the more efficent design actually lies.

Is there any way for someone who does want to emphasize armor to be able to? A ship made out of orion pusher-plates would be able to survive nuclear impacts, but what about everything else?

Let's say we take the brick and armor the prow still, so the front end of it is set up to withstand heavy impacts, and maybe both ends are orion thrust systems for accel and de-accel... but remove all the armor on the sides. This gives it approach capability and assuming it can inertially slide effectively to keep one of the pusher-plate armor blocks between it and a target, the ability to avoid a lot of relativistic beam fire without as many messy effects.

Such a ship would certainly be faster and more nimble, but the question was raised by others, how much armor are you going to need--and of what material--to make it not worthless in the face of space-age weaponry?

Removing side armor is suicide. You can't expect your ships to ALWAYS get the drop on the enemy-- if it's the other way around, the enemy will pump your sides full of laser beams/missiles/rail gun projectiles.

Besides, there's a limit on how many weapons you can pack on the front of a ship. Unless the ship's a LOT wider than it is long, you'll end up relying on broadsides as a battle drags on-- another reason to have good side armor.

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Please do not make Americans fight giant monsters.
Those gun nuts do not understand the meaning of "overkill," and will simply use weapon after weapon of mass destruction (WMD) until the monster is dead, or until they run out of weapons.

They have more WMD than there are monsters for us to fight.
(More insanity here.)

Agreed--but the usefulness of armor at all was called into question by some folks, so here's I suppose the smarter question to ask: if you wanted a heavily armored ship, with the idea that it may be slow but it can form the heavy support, expensive weapon carrier portion of a fleet that also includes smaller, faster vessels... how much armor is optimal? If my brick is too much, how much should I have?

Terwyn is right. Whatever technology is available will dictate which of the designs is most effective.

For instance, 'thick armour' is utterly worthless if it's not effective against weapons, and agility is worthless if there are fast-tracking weapons. The faster ship will be able to dictate the entire fight, and simply flee when it's weapons are expended. Further, saying a ship with significantly more mass 'costs the same' as a small torchship is absurd, even without going into endurance and target profile.

Really, your thought-experiment is a common one, but flawed. Without magic armour, armour is basically worthless and certainly a major limiting factor (since it'll slow your ship down, reduce mass for fuel/weapons etc). Until you have magictech like Star Wars, slow is bad, and who shoots first wins. Your competing designs have vastly different technology requirements, thus they should never compete.

We're getting off topic, so I'll be brief: you need a ship whose armor, armament, and speed is somewhere between that of the needle (high-speed torpedo boat) and the brick (fast battleship). For a destroyer or cruiser, its armor should be strong enough to survive multiple hits from the needle's weapons, while its speed should be high enough to let it outrun from a brick.

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Please do not make Americans fight giant monsters.
Those gun nuts do not understand the meaning of "overkill," and will simply use weapon after weapon of mass destruction (WMD) until the monster is dead, or until they run out of weapons.

They have more WMD than there are monsters for us to fight.
(More insanity here.)

In space, there is no stealth. Modern Earth sensors could detect the space shuttle's main engines somewhere out around Pluto and its maneuvering engines out by Ceres. An ion engine is detectable at 1 AU (~8 light-minutes). Even if you "run silent," you have to have a habitable module, which is "only" 282 degrees (Kelvin) hotter than space. The brick will be detectable at 2 or 3 light-minutes even with its engines off. The needle won't be much better (slightly, due to lower surface area, but not much).

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BattleTech for SilCore

There is a tendency to assume a large space warship must be far slower than a smaller ship. That is invalid.

A heavily armored space warship can be almost as fast as a smaller unarmored one. The performance of an engine can be described as its combination of specific impulse ("fuel efficiency") and thrust to mass ratio. These characteristics mainly depend upon the engine type rather than the size of the spaceship. For example, if a ship has 1 million sec Isp and an initial propellant mass fraction of 50%, the rocket equation gives the same final velocity whether it is 10 tons, 10000 tons, or 1 million tons. As a different example, if a warship's mass is increased 50% by adding armor, there is not an order of magnitude reduction in obtainable acceleration but just a 33% reduction.

The greatest armor protection could be concentrated on the head of an elongated warship oriented towards the enemy. Surprisingly thick armor is practical with only limited tradeoffs. For example, consider a moderate sized ship of 10,000 metric tons with an average density of 1000 kg per cubic meter (like that of a terrestrial submarine). If it is mostly cylindrical with a length to diameter ratio of 10, then 20% of its mass would be enough for a frontal steel armor plate 3 meters thick. Some type of composite material might be superior to steel on an equal mass basis. In that case, lower density material might allow up to 10 meters armor thickness for same mass. Such could be literally thousands to billions of times more resistant to enemy laser fire than a conventional design with a hull millimeters to centimeters thick. A narrow single laser pulse needs far more than 1000 times as much energy to penetrate 10-meter thick armor than to penetrate 10-cm thick armor. For example, for a blast producing a half-spherical crater, to make one 10-meters deep requires disintegrating a billion times as much mass of material as to make one 10-cm deep.



Without effective stealth or a FTL jump drive, warships will tend to approach each other starting from millions to billions of kilometers apart.

As a thought experiment, consider two laser-armed ships approaching each other to fight. To keep this simple, consider lasers only, no missiles.

Unarmored Warship A has a hull a centimeter thick.

Heavily armored Warship B has an armored frontal plate ten meters thick. It would also have lesser armor elsewhere, but that is irrelevant for this.

For now, suppose everything else is equal.

Both have lasers with the same power output.

Both ships are assumed to be constantly unpredictably accelerating to throw off enemy fire with the help of the light-speed lag. Suppose a shot from one of the lasers has a 50% chance of hitting an enemy warship at 100,000 km range. Without FTL, there will be a range at which there is only a 50% chance of hitting simply due to light-speed lag. Even the best fire-control computers will only be able to guess the future position of a target with unpredictable acceleration. The 100,000 km figure is arbitrary, but there will be some limit.

Though this is doubtful, for the sake of argument, suppose the lasers are so powerful that a single shot readily penetrates meters thick armor like that on Warship B.

So, weapons so outclassing armor means the armor is useless, right?

No!

Warship A must fire full-power narrow-beam shots to penetrate the armor of Warship B. However, Warship B can take the same laser beam energy and scatter it into a "shotgun pattern" consisting of 10000 segments each 1/10000th of total power. A laser capable of blasting through 10-meter thick armor is so powerful that 1/10000th as much energy would be more than enough to blast through the 1-cm hull of Warship A and destroy it. For example, Warship A may need to aim with an accuracy within a few meters, but Warship B can fire spraying its "wide beam" pattern over areas up to kilometers in diameter.

As a result, Warship B has at least a 50% chance of destroying warship A per wide beam shot at a range of 1 million kilometers. Essentially, it is as easy to hit an accelerating target with a 1-kilometer diameter shot pattern at 1 million kilometers as to hit the 10-meter diameter target with one narrow beam pulse at 100,000 km. The preceding calculations make use of a formula here, where a large laser pattern is equivalent to the target having greater cross-sectional area to hit.

Warship B has effectively 10x the range, not because its lasers are more powerful but because its unarmored opponent is effectively orders of magnitude more fragile. Warship B will win the engagement, destroying Warship A before the unarmored ship even has a chance.

The preceding was supposing everything else was equal. Realistically, Warship B should have a tradeoff compared to Warship A of less acceleration capability. The preceding sample design had 20% of ship mass be the frontal armor plate, corresponding to 20% less acceleration. This reduction in the unpredictable acceleration of Warship B means that Warship A has a 50% chance of an effective hit at 110,000 km instead of 100,000 km, again using the formula. The preceding does Warship A no good when Warship B can destroy it from an order of magnitude farther away.

At this point, one may object that the lasers are implausibly powerful. That was only specified to illustrate the situation if lasers greatly outclassed armor, being so powerful that one shot was like a nuclear blast able to go through 10 meters of solid armor. For more realistic weaker lasers, Warship B would not be able to produce so much wide-beam destruction, but that doesn't matter. With weaker lasers, the 10 meters of armor on Warship B would instead simply be invulnerable to Warship A's laser fire.

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The preceding is an idealized approximation.

For example, obviously ships might begin firing long before they had a 50% chance of a hit each shot, but that was enough to illustrate the principles. Though the frontal armor should be thickest, any armored warship would also have some armor on all sides. Such would be needed if engaging multiple enemy ships firing on much different vectors.

The situation becomes far more complicated if there are missiles to consider rather than just lasers.

However, in a realistic hard science fiction universe, the warships with the longer engagement range will usually win. Against beam weapons, a warship best harms the enemy's engagement range by combining acceleration capabilities with armor protection, finding an optimal balance. Even against missiles, armor may still be beneficial. If it takes a nuclear warhead to penetrate a ship's hull instead of a far tinier submunition, the chance of point defenses succeeding may be far higher.

Both armor and unpredictable acceleration capabilities are critical. For example, without soft science fiction technologies, planetary defenses would typically be sitting ducks. Warships could fire upon the planetary surface from a range of any number of light-minutes, maneuvering enough that any return laser fire would miss. There is no fundamental limit on laser engagement range against immobile targets like planets.

An unarmored warship is not best. Neither is an immobile one. The battlebrick is closer to optimal than the needleship. Most likely, the best design will be have its armor mass and engine/fuel mass be comparable, each a large fraction of total mass.

EDIT:
As a minor correction, the above is meant to be as follows:

A narrow single laser pulse needs far more than 100 times as much energy to penetrate 10-meter thick armor than to penetrate 10-cm thick armor.

For example, for a blast producing a half-spherical crater, to make one 10-meters deep requires disintegrating a million times as much mass of material as to make one 10-cm deep.

Wow Sikon, that's really great! I'd never even thought about setting my lasers to wide-beam settings, just the ordinance in my hypothetical cannons. I see you too enjoy the armored prow! That's the best part, I think, it trades a sexy firing profile for a riot shield to close some distance unmolested.

But the laser tactic makes perfect sense. Getting tight beams is hard enough, so by deliberately fanning it you can cause enough damage to cook heat sinks and blind sensors easily--and if the enemy is also attempting to engage me with lasers, there's a chance I'll be able to more likely strike their laser lens with my beam. Afterall, they need to fire longer and with a tighter beam, making them more of a target with less of a chance of them accidentially frying one of my lasers. That'd sure give their ship a nasty suprise!

Those are sensors that can be easily trimmed off in an ensuing fire-fight. The stealth aspect can come from decoy and ECM/ECCM suites, where obviously you won't be invisible, but you can make it a lot harder to be hit without resorting to more delicate antennae to scan around for. It won't be perfect, but it should buy time. You'll never be invisible that way, though nor are stealth aircraft today. They just try and make it a lot harder to get a good lock before they're toast.

This, of course, assumes near future technology. I've already mentioned in the past about possible workarounds that negate the IR, radar and even mass readings.

As for the lasers, yes, a good tactic is to blind the enemy with decent, wide-beam shots first. Even a transmission laser would be good for the delicate sensors at close enough range. For armour, the best way to deal with that is usually with KE from nice EM accelerated slugs. When you're close enough to use such weapons, they'll offer far better results than the comparative laser. Particle beams are also better for armour, though I expect spaceships to really have less armour than you'd expect on any naval vessel on Earth today. Armour costs a lot in terms of energy to move, and even a larger vessel only has so much reaction mass and energy, added to the fact that it's a far bigger target to boot (speed and acceleration redundant for the reasons stated in above posts).

This is a simple matter of physics. In order to propel a given mass to a given velocity requires an input of at least 0.5*m*Vf^2 (non-relativistic, assuming 100% efficiency) units of energy. Joules being the most common unit used. So to drive a given rocket to, say 1% the speed of light (too much more than this and the relativistic KE equation comes into play,) and one gets the following numbers:

10 tons = 4.94E+16 J
10000 tons = 4.494E+19 J
1000000 tons = 4.494E+21 J

Thus, one has to do more two orders of magnitude more work to get a megaton battleship up to 1% c than they would a 10 kiloton destroyer. This is just the KE of the vehicle, and doesn't include the total energy expended in getting there, which is quite a bit higher.

So, for the brick versus needle, which are orders of magnitude apart, one will be orders of magnitude slower on the helm than the other. Sure they might have the same final velocity, but the a smaller ship will be able to get to its final velocity much faster than a larger ship. This means that over the timeframes of a space battle (assuming similar initial velocities,) the smaller ship will, in fact, be noticably faster than the larger one. Even if the difference in accelerations is only 30%.



The problem being, of course, that a long cylinder tends to be hard to turn, especially if you're concentrating more of its mass at its ends. Sure its nose may laugh off your high-energy lasers, but if you can't keep your heavily armored bow between your enemy and your vital bits, then that armor isn't going to mean much when he jams lasers into your less-protected broadside.

I'll address the second half of this post later today.

Yes, a ship 100 times as massive requires 100 times the energy to reach a given speed, but it also would tend to have 100 times the fuel and 100 times the power output.

If for some reason the larger ship had much lower power to mass ratio, then it would be much slower, but there is no reason that has to be the case. Whether chemical, nuclear, or antimatter, engines based on real-world physics tend to have specific impulse performance primarily independent of mass. The specific impulse is the exhaust velocity and hence corresponds to the energy given per unit mass of fuel.

Take your examples. For the 10 ton rocket ship to obtain 4.9 E+16 J means that it must have fuel giving substantially more than 4.9 E+15 J per ton. Yet if the 10000 ton rocket ship has the same fuel, then proportionally it should obtain the 3 orders of magnitude higher energy needed.

Take my arbitrary example with a spaceship having 50% of initial mass propellant and 1 million sec Isp. As derived in detail at this website, the ideal rocket equation is

delta u = V_eq ln (m_f / m_e)

which is stating that the change in velocity (u) from a rocket engine firing is the exhaust velocity Veq (corresponding to the specific impulse of the fuel) times the natural logarithm (ln) of (m_f / m_e), where m_f is mass fueled and m_e is mass empty. In my example, m_f / m_e equals 2. As V_eq = 9.8 E+6 m/s, delta u = 6.8 million m/s. The change in velocity is usually called delta v instead of delta u.

In my example, all three ships reach 6.8 million m/s velocity.

Some high-performance forms of propulsion like nuclear engines can in fact be hard to scale down to a low size.

For example:

Like Covenant, the opening poster of the thread, I like the Orion concept for warship propulsion. It has a rare combination of real-world plausibility, high specific impulse, and good thrust-to-weight ratio. The Orion nuclear pulse propulsion designs tended towards higher obtainable velocity with greater size. A concept like antiproton-initiated microfission/fusion might make smaller variants more practical, but a bigger ship can still reach as high velocity as a smaller ship.


A ship orders of magnitude more massive would be orders of magnitude slower than a small ship IF both had same mass engine/fuel. Sure, one could have a 1000-ton ship with a 500-ton propulsion system, then have a 100,000-ton ship with the same 500 tons of engine and fuel mass. However, they wouldn't if I was designing them. I don't think a future military would do so either. If the 100,000-ton ship instead has a 50,000-ton propulsion system, it would not be orders of magnitude slower.

You said slower on the helm, so you might be referring instead to the speed at which the ship can be rotated. A ship 3 orders of magnitude more massive would tend to be 1 order of magnitude longer than a smaller ship, so, yes, it would rotate slower. A question is how much is that a disadvantage. See a later part of this post.


Not necessarily. See above. There are some material limits that would come into play at extreme sizes, not directly limiting velocity but limiting acceleration. However, whether 10 meters, 100 meters, or 300 meters in length, the ships are not so astronomically huge for structural strength to be the probable limit on acceleration. More likely, for hard science fiction engine performance, the limit will be either the thrust-to-weight ratio of the engines, the fuel supply for prolonged acceleration, or the acceleration tolerance of the crew.


Engagement ranges are going to tend to be at least thousands or million of kilometers. A realistic hard science fiction battle would be nothing like Star Trek or Star Wars. There will be no ships zooming around dogfighting at a few kilometers range, as any ships trying that would be destroyed long before they were that close. The tendency will be for it to take either minutes, hours, or days for ships to close their distance, while the elongated warship can turn in a matter of seconds.

For my sample 10000-ton ship, it was 110 meters long if I recall correctly. To turn it in a matter of seconds requires no more than tens of m/s velocity. Have an appropriate set of thrusters mounted on rotating mounts at each end under computer control. Rotating a ship at tens of m/s is trivial compared to having engines capable of accelerating it at multiple-g's to many thousands or even millions of m/s.

Frankly, I am no more sure the warship should have 10:1 length to diameter ratio than for it to have 20:1 or 5:1. That was an arbitrary example. It depends upon assumptions like whether the enemy will usually come from multiple directions, the relative effectiveness of direct-fire weapons (i.e. lasers) versus weapons able to curve around to hit the sides (missiles), etc.. However, I am sure some elongation will be helpful to allow extremely thick frontal armor.



Okay. I enjoy debate. Just to be clear, the big example is using arbitrary figures to illustrate its point. It uses implausibly powerful lasers. The range figures are arbitrary. I am sure combat ranges will be thousands of km at a minimum, but the 100,000 km is just a random example.

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Regarding larger ships versus smaller ships:

The main potential disadvantage of a larger ship is simply cost. A 1-million ton ship may cost as much as a large number of 10,000-ton ships. This is complicated. There is sometimes a certain economy of scale from making large ships. There may be fewer parts per unit mass, reducing the expense per unit mass.

An extreme example is illustrated by present-day rockets, where the difficulty of extreme miniaturization can make a small rocket sometimes cost as much as large one:


source

On the other hand, the above quote is obviously only illustrating an unusual case. Alternatively, smaller ships might be more easily mass-produced, and sometimes nothing is more effective than mass-production at dropping costs.

I don't know the optimal warship size. However, if small warships are the best choice, it will be despite having no orders-of-magnitude advantage in obtainable velocity.

I forgot the opening post here, which specifies both the needleship and battlebrick are to be treating as having the same cost.

This little bit is mostly to remove a length discussion about battleships versus rowboats, really. A torch drive, advanced sensors, tiny and high-powered lasers all run by some incredibly small but incredibly energetic fuel source is what is required for the small ship to attain the characteristics that Nephtys put forth to me. She wanted something that had long endurance, high thrust, and high impulse. Such a drive may not be theoretically possible, but if it was, I assume it'd also be more expensive.

I on the other hand am happy to devote 50-75 percent of my brick to engine and power production, have rugged but otherwise large construction, and am willing to settle for low thrust on the main engine with a seperate system like Orion for slowing the ship (IE, a prow-mounted orion and pusher plate), gathering additional combat acceleration, and not bothering to dodge around. So in my mind, my ship is based on simpler, more cost efficent technology that may simply require more space, if at all, and would be much cheaper to produce and have much higher tolerances for stress.

Otherwise it's mostly a problem of "all eggs in one basket" rather than the efficency of design. I don't want an Executor vs. A-Wing debate. Now, if you want, think of the two ships as dirt cheap, or highly expensive top-of-the-line warships. I encourage that, because maybe we would discover that at an arbitrarily high tech level, while it's cheaper to make several small bricks, the flashiest and best ships would be needles---or the reverse!

That sounds good.

It is fascinating how much miniaturization and demanding high performance relative to mass can drive up costs. For example, in the present-day space program, once a craft costs thousands of dollars per pound overall, it becomes desirable to shave weight off just about everything at astronomical cost.

Example:
Suppose one was an engineer working on part of the Space Shuttle and had a choice between buying a commercially available pump for $1000 or developing a special super-lightweight pump for $100000. Unfortunately, if all else is equal, one would have to logically choose the latter if it would weigh even 1 pound less. Such would have to be chosen because it would allow 1 pound more of payload on each of a number of flights, and Space Shuttle payload costs are tens of thousands of dollars per pound (per flight).

The problem is that then almost everything may cost up to orders of magnitude more than it could otherwise.

Returning directly to the battlebrick versus needleship debate, you definitely are right that a super lightweight needleship could easily end up costing as much to develop and/or produce as a battlebrick without such extreme weight-saving measures. For example, trying to produce lightweight needleship lasers able to destroy a heavily armored ship many times more massive at sufficiently long range could get expensive.


Though I am not sure what you mean by not bothering to dodge around, at least some unpredictable acceleration would tend to be important. At ranges of a few light-seconds or greater, even a small fraction of one-g of unpredictable acceleration could make nearly all single narrow-beam laser shots miss. If the ship's course is too predictable, it could be hit by enemy fire-control computers from almost unlimited range, giving the enemy the range advantage, which would be a problem.

However, you suggested 50+% of the battlebrick mass being the propulsion system, so you could readily have enough unpredictable acceleration.

Overall the design seems much more practical than the needleship.

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When I did an earlier example, I did it with two ships having the same laser power, just with one having more armor.

However, for the battlebrick versus the needleship, the situation may have a still bigger difference. The battlebrick may be able to hit the needleship from farther away due to the needleship being more fragile and vulnerable to "spraying" beam weapons. However, in addition to that, the battlebrick could also benefit from greater beam weapon output power.

As a random example with arbitrary figures, suppose the needleship is 100 times less massive, and little armor makes it in total 1000 times easier to destroy. By that, I mean suppose 1000 times less laser energy is needed for destruction. The ratio of battlebrick laser power to needleship vulnerability might not be simply a result from the needleship being 1000x more fragile. It may be more like a factor of 100,000 from the battlebrick having 100 times the laser power plus the needleship being 1000 times more vulnerable to a given amount of laser power.

As a result, the battlebrick could potentially have more than an order of magnitude advantage in the effective range of its beam weapon, provided that the battlebrick appropriately unpredictably accelerates ("dodges") much like the needleship.

Such might be practically undefeatable against the needleship, unless the latter managed to get a nuclear missile or the equivalent past point defenses.

A decoy will be just about as expensive as a ship. You need to simulate heat, radiation, surface area, and thrust/mass ratio, meaning your decoy is as large as your ship, generates as much waste heat as your ship, and basically is another ship. Or it's not a decoy.

Stealth aircraft today generally don't have to deal with the fact that their cockpit is a hundred times the ambient temperature around them. They're also in a far more high-energy environment (on average) that has more quirks and anomalies to distract enemy sensors. Airplanes also require "wasted" mass on lifting surfaces and atmospheric controls that the spaceship won't need, limiting their sensor capabilities (or weapons, et cetera). The extra mass won't translate into better stealth, as for radar it's purely a matter of shaping, and for IR it's a matter of stealth not existing in space. A single FLIR (small target, would fit on the nose of a helicopter) will see the spaceship's heat signature from absurdly far away. Any decent-sized spaceship could carry a few dozen.

Radar's not hard. IR is very difficult unless you have perfect intelligence (which by default does not exist). Mass is (with current physical knowledge) impossible without technomagic, in which case we need to go over to Fantasy to hold this discussion.

Assuming the sensors are that delicate, and assuming you don't got blown apart by a focused blast first. Doubling the area of the beam quarters the energy. A "wide-beam" at range will be the equivalent of shining a flashlight on a battleship. It lets them know you're there, and doesn't do much more than tickle.

For once, I agree. Railguns or coilguns are among the more probable realistic weapons, given the lack of atmospheric drag and the lack of beam dispersal. Charged particle beams will be extremely short ranged (like charges repel, remember?), have the nasty side effect of charging your ship (leading to all sorts of problems, not least of which is the possibility of electric discharge from space into the ship), and aren't terribly useful against a truly thick-armored spaceship, as they tend to rely on re-radiation effects. Neutral particle beams are a PITA to generate. True. Any mass used for armor is mass lost for supplies, weapons, fuel, engine size, et cetera, ad nauseum. There might be some light anti-radiation armor, but I doubt there'd be much in the way of massive armor plates.

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BattleTech for SilCore

As has been pointed out, you can forget about stealth in space. You can also forget about ECM and decoys: the fomer simply makes you stick out to ARM missiles, you may as well just paint target rings on your ship. The latter is unfeasible because a tiny decoy will never be able to effectively simulate a full-scale spacecraft; it's far lower heat-signature will give it away in an instant.

And barring some massive advance in propulsion technology and the discovery of a very high-energy density storage medium, you can forget about spacebricks and spaceneedles as well. For anything that can be realistically envisioned, you're talking about spacecraft which are 80-90% fuel in terms of mass and as lightweight a structure to contain that fuel as possible. The mass penalty factor precludes armour, and the range limitation factors preclude any craft which cannot carry sufficient fuel to cover AU-range distances and safely return. High energy weapons like lasers are also out, since those will gobble up fuel not only to fire but simply to carry around —two objections which would probably preclude railguns as well.

If you want a realistic picture of a feasible space battleship/fighter, think of a big flying gastank with miniguns and/or missiles. Or a sailcraft with miniguns and/or missiles. And with the sort of very lightweight material you'd need for either, you needn't worry about damage as one good hit or two will probably kill you that instant.

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