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Space battles, with huge/gigantic space ships shooting lasers, missiles and projectiles at each other, there's a lot of material regarding space battles (Movies, books, games), but there's something that's been bothering me for quite some time now...

Like how during and after WW2 they stopped producing large battleships (Bismarck, Yamato) in favor of air carriers and smaller vessels because of how vulnerable they are in the open ocean (easy targets).

There are no constraints regarding the technology/resources.

My question: Would future space admirals favor huge ships, or smaller ones?
The advantages and such..

Thanks for reading, and I hope for some good answers~

Edit
Wow, this question garnered more attention than I thought it would; here are a few more things I would like to mention:
one of the biggest problems in my question is this quote :

There are no constraints regarding the technology/resources.

What I meant by resources is that "money" (or space credits) is not a problem (keep in mind that rare resources still play a part in being "rare"), the only thing that would be "lost" if the ship is destroyed would be the amount of time spent to build one.

As for the technology, since there is so many material regarding space faring civilizations, and tech; it's very hard to specify which one specifically I'm looking for (sorry about that, but FTL is a must), but something realistically possible; and also commonly seen in sci-fi is fine.

As for the place of battle, most of the "massive" and "important" battles would be fought in interstellar space, away from planets and stars.

Also thanks for all the useful answers/comments~

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    $\begingroup$ Possible duplicate of How would space battles alter combat tactics? $\endgroup$ – Mołot Jun 20 '17 at 9:40
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    $\begingroup$ For ship sizes, you need to describe technology level. Where are these ships build? How good is their armor against lasers? Their anti-missile weapons? How big is missile and missile launcher? And so on, and so on. And even then, it will be in large part opinion of these admirals - historically not all opinions of military leaders was sane. $\endgroup$ – Mołot Jun 20 '17 at 9:53
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    $\begingroup$ This question is highly dependent upon the technological and political assumptions going in. What sort of propulsion technologies? What kinds of weapon technologies? Does point defense work? Are navies designed around symmetrical open warfare, or asymmetrical police/insurgent operations? Is the theater Earth orbit, the inner planets, the entire solar system? Are any science fictional technologies (FTL, shielding) in use? The answer could go either way depending on the context. $\endgroup$ – Catgut Jun 20 '17 at 12:24
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    $\begingroup$ Depends, do they have an exhaust port? $\endgroup$ – Kevin Jun 20 '17 at 16:15
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    $\begingroup$ If there are no constraints on either resources and technology... I don't know. As Arthur C. Clarke said, "To a primitive mind, any sufficiently advanced technology is indistinguishable from magic". If you handwave away technology and resource limits, you can do anything - even a planet-destroyer on the tip of a needle, and your shielding would be able to block just about anything. At such a time, if you want to cause any notable damage on something shielded, you would utterly destroy everything shielded. In the end: "A STRANGE GAME. THE ONLY WINNING MOVE IS NOT TO PLAY." $\endgroup$ – rytan451 Jun 21 '17 at 6:15

19 Answers 19

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Warfare in space is hard. Surviving it, that is. With any penetration of the hull, you'd be losing atmosphere. In a small spaceship, this is catastrophic. In a large one, it is easier to contain, but if it is not, it is catastrophic to a lesser degree. With this in mind, let's try to answer the question.

There are two main ways we can damage enemy spaceships. We either hit them with solid things (like bullets and missiles) or we hit them with directed energy (like lasers). The problem with solid things is that we already have defenses against them in our spaceships. If we send an explosive, it would be more damaging still.

On the other hand, explosives tend to be bigger. Think the size of a bullet verses the size of any high-explosive shell or high-explosive anti-tank warhead. Besides, a Whipple shield is already optimized for HEAT warheads, after all, they're spaced armor, which is the typical defense against HEAT warheads. An explosive is bigger and heavier; thus it would require more energy to accelerate to reach the enemy's spaceship before they have time to maneuver out of the way.

Directed energy weapons are much faster than solid objects. In fact, most of them travel at the ultimate speed limit of the universe: the speed of light. In some cases, it is because they are light. Because of this, they cannot be detected and then avoided. At most distances we are used to, light travels instantaneously.

However, in space, it is not infeasible for two battling spaceships to be light-seconds or even -minutes apart. In such a case, it is possible that the enemy's spaceship is maneuvering as soon as it is in range of our lasers (that is to say, if we can reliably hit a still target - there are limits to our minimum accurate angle we can turn our laser). In such a situation, they need to be in closer range before we can reliably hit and disable/destroy them. Otherwise, by the time the laser reaches their position, they would have already moved out of its way, without even detecting the laser.

Of course, maneuver is a lot easier when you're smaller and less massive, and you can get much closer to the enemy before it can hit you with their lasers.

On the other side of the equation, if we have a giant space station with the best armor, we would be able to withstand any and (nearly) all conventional and even nuclear attacks with only minimal damage. These types of ships are probably going to be extremely high on the target list due to their extreme cost of construction, and because they are probably containing the high-ranking officers in the army. Like your Admiral.

But if your weapons are strong enough, any amount of armor that we can afford to be placed on the giant space station would not be enough to protect the interior. In that case, it would be much more cost-effective (and effective in general) if your armed forces were to spend their money on manufacturing millions of tiny fighters.

In conclusion (TL;DR), the smallest spaceships equipped with lasers (and possibly a proton torpedo would be most effective, though if weapons are sufficiently weak and the armor sufficiently strong, large space stations like the Death Star and large ships like Star Destroyers would be likely also be utilized.

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    $\begingroup$ Welcome to WorldBuilding rytan451! Interesting start. If you have a moment please take the tour and visit the help center to learn more about the site. Looking forward to your contributions. Have fun! $\endgroup$ – Secespitus Jun 20 '17 at 10:47
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    $\begingroup$ What of a hybrid solution: a bit space ship that is mostly empty, and just use the external hull(s) to hide where its active parts are (and their spares), thus actually being closer to a hive of small ships inside? $\endgroup$ – Matthieu M. Jun 20 '17 at 15:19
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    $\begingroup$ If you know where a ship is going to be you can also just fire a lot of <some sized> particles from really far away and accelerate them to really fast. When you get hit by a shotgun that's moving half the speed of light it doesn't much matter what your ship was made of. $\endgroup$ – Wayne Werner Jun 20 '17 at 19:25
  • $\begingroup$ @WayneWerner Right, and the Whipple shield (linked in this post) won't help against a series of small particles punching holes in it followed by a big one. $\endgroup$ – maaartinus Jun 20 '17 at 20:48
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    $\begingroup$ And depending on how it works, the existence of FTL travel may mean that FTL weapons are a possibility. Specifically, if it involves somehow accelerating beyond lightspeed, e.g. by warping space around the ship. They may or may not be affordable or portable enough to use as weapons combat, but if they are, that's another difficulty with using larger ships - unless there is a specific countermeasure to that kind of spacial distortion. $\endgroup$ – Bemisawa Jun 22 '17 at 15:36
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It depends what technology you are using.

For example, a ship big enough to carry a nuclear reactor in the 100+ MW range and railguns/beam weapons powered by it is going to have a minimum size. If this weaponry can counter multiple missiles - or whatever the small ships were carrying - then the 'big ship' approach works best.

Look at it this way, from naval history..

  • In 1800, a 'big' 3-decker ship of the line could take on smaller ships with a very high chance of success - no asymmetric warfare.

  • By ~1850, a smaller ship with explosive shells could obliterate such a ship.

  • By ~1870, steel armor and big guns gave battleships advantages over smaller ships in almost any number.

  • By ~1880, quick-firing guns on small ships gave 'small' ships the advantage (in theory, never tested..)

  • By 1890, quick firing guns and better accuracy on the battleships swung the advantage back (but torpedoes.. The torpedo was the first true asymmetric weapon)

  • In WWI, big ships were mostly kept in port by the threat of submarines with torpedoes, only venturing out under heavy escort.

  • By WWII, big battleships were practically obsolete in the face of both submarines and aircraft. The new capital ships - Aircraft carriers - could only survive by virtue of their own 'small ships' (aircraft) in protection.

There have been very few naval engagements since. The Falklands suggested that missiles from 'small ships (planes)' could beat 'big ships'.. but anti-missile technology has come on since then.

So you have a fundamental problem. Can your swarm of small craft - in realistic numbers - land a fatal punch on the big ship before the superior firepower of the big ship takes them all down? Remember that in space, it's really hard to hide. You can't have a submarine, obviously, but also there is no horizon, no atmospheric distortion.. your big ship can spot incoming ships and ordinance from a huge distance.

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    $\begingroup$ In recent years, various articles and wargames have indicated that the defenses of aircraft carriers would likely be overwhelmed by a large number of small attackers. First reference that comes to my mind $\endgroup$ – Michael Vehrs Jun 20 '17 at 14:08
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    $\begingroup$ Indeed.. but all Earth-based ranges are effectively 'point blank' for a space battle. $\endgroup$ – Andrew Dodds Jun 20 '17 at 15:18
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    $\begingroup$ @MichaelVehrs I think part of Andrew Dodds' point is that the balance of technology changes over time, and that the truisms of contemporary wet navy warfare are no more likely to be perpetual than their late-1800s equivalents. $\endgroup$ – Catgut Jun 20 '17 at 15:24
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    $\begingroup$ As this answer implies, the answer to whether bigger ships would be better is dependent upon a lot of other questions about the various technologies involved, and about the nature of societies and economics in the world imagined, so that it may be more a question of deciding whether you want bigger or smaller ships, and working out the technologies to justify it. $\endgroup$ – bgvaughan Jun 20 '17 at 15:46
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    $\begingroup$ This. It all comes down to one thing: how big is the smallest platform from wich you can fire a weapon that will do substantial damage to your main target? If you need a big gun to punch a hole in the enemys main ships, you'll need a big ship to mount that big gun on. If a small missile will do the job, a swarm of light crafts wil be harder to defend against. $\endgroup$ – Guran Jun 21 '17 at 8:57
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Every such decision is a combination of two factors, the effectiveness of the ship in combat and the vanity of the admirals in charge of ordering the vessels.

During the age of ship to ship combat, a bigger ship with bigger guns, more range, more armour was an advantage. In the age of carriers, a bigger ship was a bigger more expensive target. The building of the Yamato was an exercise in vanity, and its demise showed the futility of that exercise.

Big aircraft carriers are now an exercise in vanity. They're about projecting power over the little people, not about symmetrical warfare. It's well known that a good submarine can easily knock out a carrier, but both such submarines and the big carriers are currently controlled by the same powers. Should symmetrical warfare break out between the submarine powers you're not going to see any carriers getting involved. Just as the Yamato didn't put to sea until the end of the war because she was too expensive to lose, the carriers would be kept well away from places the submarines could get to them. It's not so much about the cost of the vessel as the loss of prestige that goes with it.

Your fleet admirals would be making very similar decisions; how expensive is the ship; how vulnerable is it to the latest technologies; how good does it look on my resume to have commanded it; how bad is it going to look if we lose it; is my career over if I prang it in spacedock; does it actually carry enough firepower to be worth it.

There's no glamour in a missile boat, there's no pride in a kid sitting in a tent a thousand miles away with a joystick controlling a drone. Consider your technologies when you build your space battles, but also consider the vanity of the old guard. They want to see dogfights, they want to be launching manned fighters, they want to see the whites of the enemies' eyes, they want acts of romantic heroism. They don't want to be pushing buttons from a distance.

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    $\begingroup$ Need a source on any of the claims regarding carriers being 'an exercise in vanity' or vulnerable to submarines. Carriers use onboard ASW aircraft and the passive detection abilities of their attendant CVBG to detect and engage submarines, and their utility is the ability to rapidly project airpower from a mobile platform rather than the logistics nightmare of moving air operations between airbases. If vanity were the object, we'd still be cruising the Iowas around. $\endgroup$ – Catgut Jun 20 '17 at 12:16
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    $\begingroup$ @nefas, it's an example of the comparison of weapons and targets, maybe the bigger ship, bigger gun, more armor system just carries on in your universe, in my universe someone always works out how to stick a big gun on a small cheap ship and flies a couple of dozen at the behemoth. Losing that big flagship is a big loss of crew, prestige and moral, losing a bunch of little gunboats not so much. $\endgroup$ – Separatrix Jun 20 '17 at 12:43
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    $\begingroup$ "Why move a carrier group into an area?" Perhaps to have the ability to deploy somewhere north of a hundred combat aircraft and associated logistical support on a moment's notice? SLCMs, despite being impressive on paper, have limited utility, require external support for any kind of accuracy, and cannot be easily rearmed in the field. Carriers have been responsible for far more ordnance dropped over the last decade than SSGNs. Again, provide a source for your claims, they directly contradict military doctrine. $\endgroup$ – Catgut Jun 20 '17 at 13:00
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    $\begingroup$ @Separatrix It's not a secret that carriers are highly vulnerable, high profile targets. That's not what you're claiming in saying SCLMs can do everything a carrier can, and that the only reason carriers are in use is as useless symbols, neither of which are supported by the article you posted or by operational history. Again, I'd like to see a source for the claim that carriers are functionally redundant and maintained solely for appearances. $\endgroup$ – Catgut Jun 20 '17 at 15:16
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    $\begingroup$ @Separatrix Having yet to see any naval analyst argue that the operationally-limiting ski-jump/STOVL requirements of the Kiev-class, Queen Elizabeth-class, and other 'small' carriers are a cost-effective trade-off, no, I don't believe larger carriers were designed as such solely for the sake of vanity. I'd be happy to be proven otherwise if you would like to start providing actual sources for the substantial claim that vanity is a driving factor in naval procurement, rather than offering these random thought experiment examples. $\endgroup$ – Catgut Jun 20 '17 at 15:35
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Bigger ships are better in some areas, and worse in some others. They are, however, so ludicrously impractical to build that the bulk of any space fleet will be made out of smaller ships for sheer convenience. Consider a modern army: a tank is better than a soldier in every combat metric, but for every tank, there are probably about 1,000 soldiers, because people are so much cheaper.

Pros of a larger ship:

  • Intimidation factor. This is never to be underestimated when it comes to warfare. A squadron of fighters coming towards you = meh. An Imperial Star Destroyer coming towards you = oh crap.
  • You can fit bigger weapons/more weapons on it.
  • It can carry more cargo, be it food, fuel, troops, smaller spaceships...
  • Potentially greater durability - for example, if the hull is breached, then the larger the internal volume, the more air there is, and the longer it'll take before you're all suffocating
  • It's a status symbol. It says, "Look how rich and technologically-advanced we are!" It makes you look cool.

Cons of a larger ship:

  • Exponential increase in cost (raw materials, construction time, number of required crew members, fuel, maintenance...)
  • Exponential increase in power consumption (see: square-cube law, tyranny of rocket equation)
  • Much larger target
  • Much larger "space dock" required to hold it
  • You probably wouldn't be able to enter planetary atmospheres with it, whereas a smaller, more aerodynamic ship might be able to fight in the atmosphere as well as in space (I say "might" because you might not need or want that functionality at all)

So a space army will want at least one large ship, to act as a flagship and status symbol, but any significant number would be wholly impractical.

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    $\begingroup$ "Consider a modern army: a tank is better than a soldier in every combat metric" Except for one thing--the tank can't think. $\endgroup$ – Ambrose Winters Jun 20 '17 at 13:50
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    $\begingroup$ Admittedly not by itself, but it's manned by humans, who (generally speaking) can think. $\endgroup$ – F1Krazy Jun 20 '17 at 13:51
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    $\begingroup$ "People are so much cheaper" - This is a sad world where we live in, isn't it? $\endgroup$ – T. Sar Jun 20 '17 at 13:57
  • $\begingroup$ I would think the biggest issue would be whether there's anything in the ship that needs to be big. If any engine based upon XYZ, regardless of size, will require a 1000-meter-thick containment vessel, but will then be able to produce a really massive amount of energy, that would suggest that something like a Death Star™ brand space vessel could produce more power than a comparable mass of smaller ships. $\endgroup$ – supercat Jun 20 '17 at 16:46
  • $\begingroup$ @TSar no modern military thinks that. Watch any of the TV series where they embed with a unit for an extended period. They typically come back with 0 serious casualties and a very conservative approach to warfighting, where they often let the enemy get away rather than risk a soldier. People are not cheaper, they're expensive. $\endgroup$ – Harper Jun 21 '17 at 1:44
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Would future space admirals favor huge ships, or smaller ones?

I tend to think for warfare, large swarms of smaller ships would be better. There are many advantages to many smaller ships. For the sake of comparison; let us say we are talking about the same total tonnage of hardware; say a battleship or a fleet of 100 smaller ships that collectively weigh the same as the battleship. Note first, this can be more expensive, but the expenses add redundancies that are an advantage.

For example, you now have 100 engines, and 100 armament systems. You have infinitely more options in battle: A battleship is in one place; you have 100 ships you can arrange however you want. A battleship is hard and slow to move; 100 ships can be reconfigures into a front, a spear, with a mile between them (very easy communications distance even in poor weather) they can present a 100 mile wide search front. Unlike the battleship, you can sacrifice 10% of your ships to eliminate an enemy. A single torpedo, missile or Kamikaze bomber could sink (and has sunk) a battleship, or loaded with appropriate incendiaries start an inferno deck fire that disables the ship. But a Kamikaze doesn't sink a fleet, at best it sinks 1% of it: You have resilience.

Finally, big ships tend to have centralized resources and supplies of food, fuel, communications support, etc. A fleet of smaller ships will tend to result in decentralization of these resources and supplies, which is a good thing: You have backups, and therefore (again) resilience.

There are parallels IRL; in my field the modern supercomputer is actually a network of tens (or hundreds) of thousands of off-the-shelf Intel processors, the same ones you can put in a desktop or laptop machine. The chips themselves are typically up to 64 independent processors. If any fail to function, the controlling software can just not use that chip, we mark it as offline and get on with the day's work. The servers hosting this site are probably working exactly the same way: If a node fails, it is marked as offline and not used until a tech repairs it. A swarm of "small" ships (processors in a supercomputer) can do things impossible to do with a single large ship.

I haven't forgotten we are talking about space; all of these translate, with a few substitutions, to the space scenario.

There are some practical disadvantages; it is slightly more difficult to transfer personnel, move supplies and fuel around, etc. It probably requires more fuel. Storms that a big ship could ride out could sink some smaller ships (less of a problem in space; but translate perhaps to space debris).

Overall, by having 100 hulls, 100 engines, etc, the interior livable space could be much tighter than if all that material was used to enclose one giant space. The small ship fleet is not for the claustrophobic! But we are still talking about, say, 400 ton ships, so it isn't just a pilot's seat and a few jump seats. Think more like Submarine quarters; the crew can still sit around a table to eat or play cards; you still have a galley to cook in. A battleship has a crew of 2700, so the small ship crew is on the order of a squad of 27 or so people. Of course you can have highly trained specialists scattered throughout the fleet, electrical and mechanical engineers for example; you don't have to provide one for every ship.

I wouldn't rule out very strong network communications throughout the fleet and virtual reality or virtual presence. Small does not have to mean primitive.

Although each ship should probably have a ship-runner (person in charge), the chain of command doesn't have to be self-contained; e.g. personnel can report to both their ship-runner and a fleet-wide executive that is on another ship, and take their orders from that executive. A ship-runner may only be in charge in situations where the fleet-wide executive is offline, dead, or the ship's comm systems are disabled.

I think there are far more advantages to a fleet than there are to a monolithic ship, and the disadvantages of a fleet are manageable. Rationally speaking, I think I'd opt for the small ship fleet and the resilience it offers: If 50% of my big ass ship is blown to smithereens, I am probably dead. If 50% of my fleet is blown to smithereens, I can still win this thing.

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    $\begingroup$ Do like the answer.... another thing that occurred to me on these lines is there are greater economies of scale in mass producing lots of small fighters - so in the long term they're cheaper and easier to build... $\endgroup$ – 5Diraptor Jun 20 '17 at 11:59
  • $\begingroup$ Regarding debris, it's actually a con for big ships. Small ships can dodge debris, they just need to know where it will pass, a big ship will have a much harder time dodging, especially if debris is spread across a very large area. $\endgroup$ – Miguel Bartelsman Jun 20 '17 at 17:49
  • $\begingroup$ @MiguelBartelsman I was thinking, the big ship could have much heavier plating or armor to protect it from debris it might create itself by blowing up other ships. Maybe not high speed missiles, but a stray engine moving at a few hundred miles an hour, could be stopped by 12 inch thick plate steel. Certainly I'd think it could have much heavier plate armor than the smaller more maneuverable ships. $\endgroup$ – Amadeus Jun 20 '17 at 17:55
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    $\begingroup$ The thing is that space velocities are rarely in the range of hundreds of mph/kph, but in the range of the tens of thousands of mph/kph and beyond. An engine hitting you at orbital speed is likely to leave a pretty big hole in anything, and other than magically advanced and impractically heavy shielding, the only chance to stop it is to blow it up into smaller chunks. $\endgroup$ – Miguel Bartelsman Jun 20 '17 at 18:00
  • $\begingroup$ @MiguelBartelsman Not under the conditions I just stated, Miguel. If a big ship is in a fight with (or pursuing) another ship; they are effectively at rest with respect to each other. If the big ship blows up the small ship; the debris will be moving at normal explosive speed of tens or hundreds of MPH. Same is true for plowing through asteroids or satellites: if everybody is at orbital speed in the same direction, they are at rest with respect to each other. That is why our astronauts can dock with the space station slowly and carefully; they match speed and direction. $\endgroup$ – Amadeus Jun 20 '17 at 18:54
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One important thing to consider is travel time - you can't fight a battle if you can't get there. If you're on a small ship, it's going to be much harder to include all the resources you need for more than just a short trip. So if you don't have FTL, large ships will be an absolute necessity - you'd have a large carrier that houses the fighters as well as the food production, etc. necessary in order to travel a meaningful distance.

If you have FTL, then small vs. large ships is going to depend a lot the nature of the FTL drive. You could have a form that requires more and more energy the larger the ship, in which case large ships would be infeasible (I believe Alcubierre drives fall in this category). You could also have a form that is more efficient at larger scales (I want to say wormholes would fall in this category), which would naturally lead to larger ships being used at least for transport.

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  • $\begingroup$ This is exactly what I was going to say. It wouldn't be an either / or scenario, instead you would have both large and small ships. As in current navies the large ships would mainly be carriers (though with weapons of their own as well) used to transport the small ships to the battlefield. $\endgroup$ – adaliabooks Jun 21 '17 at 22:44
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Everything is going to boil down to a battle. But the war will be won with the supply chain. You simply can't resupply or replace lost units without big ships. You also can't effectively attack an enemy big ship from all sides without little ships. Supply and manufacturing depots will also need to be attacked. The power demand for large munitions and the agility provided by small crafts will be required.

To answer the question, A wise admiral will neither favor large or small ships but will use both strategically to achieve her/his current goal. Given all the excellent points in other answers, I believe you can easily deduce that neither ship type can be excluded.

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Due to the laws of physics, my instinct is that the destructive power of weapons will always exceed the defensive potential of armour and other defensive technologies. Therefore the escalation towards bigger, tougher ships is avoided and instead the priority is on nimbleness for evasion over tanking the damage.

However, on the flip-side of this is the problem of speed. FTL travel or no, you will likely require a much larger vessel for logistics and viable long-distance travel. More generally, there will always be tasks that favour one property over another, so it's difficult to favour one specific attribute as the one 'future' of space war. It's far more likely to develop a combined arms approach that uses a variety of archetypes.

The simplest one would be a combination of carriers/hive ships that provide all the qualities that favour larger sizes, combined with unmanned drones or nano-ships that encapsulate what's desired from smaller vessels.

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There is an incredible website somewhere out there dealing with all aspects of space travel, battle etc. in stupifying detail - sadly I lost the URL. From what I can recall, one thing about space battle is that many movies, books, etc. simply transport the concept of a ship to space - but that is the wrong concept.

A space ship does not need an outer hull. It would most likely consist of modules chained together by some skeleton structure. As such, the very idea of size begins to break down. The ship might have a length x width x height that is considerable, but most of the space inside that area is just empty space.

This design would also be advantageous in battle, because travelling at space speeds does not exactly allow for much maneouverability. Not being hit can more easily be accomplished by not having much to hit, while evasive action is largely impossible. Additionally, a modular structure will keep any damage local, maybe even allowing you to drop away a destroyed element of the ship.

Mass will be a much more important factor than size. Most likely, tons or kilotons or something like it will be the better measurement for the size of space ships.

That said, the answer to your actual question depends on other factors, namely size/mass restrictions of core components. In many stories, movies, etc. the capital ships are so big because, for example, warp drives are by necessity massive. This leads to the carrier design - capital warp-capable ships with smaller non-FTL crafts that dock with the capital ship for FTL travel.

If you want big ships in your story, all you need is to come up with a convincing restriction that makes their size necessary or advantageous in certain conditions. Maybe the most powerful weapons in your world cannot be miniaturized?

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There are a couple of issues with combat in space:

  1. Doing anything in space is expensive.
  2. Armor/shielding, as we currently understand it, is ineffective against military grade weapons.

So, you don't want to invest a ton of money into a large ship, because smaller ships will, if they ever get close enough, be able to destroy them with not much effort (even modern day bombers are able to carry nukes).

However, with 10 years or so, our laser technology will be so effective that we will be using them on surface navies to combat other ships/incoming missiles (there are already some systems like this in place, such as this). However, such a device requires a lot of power. Thus, you lean again toward larger ships with bigger power generation capabilities.

Ultimately, I think space combat will boil down to this: large ships with highly sophisticated sensors, covered in an array of point defense systems that can detect and eliminate small ships and missiles before they can even get close enough to pose a threat. The only reason energy weapons don't rule the day now is because of the energy requirements and the fact that atmosphere distorts the laser beam, robbing it of some of its energy. In space, that isn't an issue.

However, when you start talking battles between two large ships, directed energy weapons won't work as well. It takes a long time to melt through thick armor plating just with lasers, and energy shielding against pure laser attacks is already somewhat feasible. These larger ships might act as carriers for AI or remote piloted drones in an attempt to overwhelm the other's point defense/laser systems, but that probably isn't practical.

You would probably end up with large mass-driver weapons like railguns. If you accelerate a big piece of metal to a fraction of the speed of light and then successfully hit the other ship, it's going to cause very significant damage and will be almost impossible to stop with lasers.

So that's my prediction on what type of military ships we will likely end up with in space, given our current technological limitations. Obviously some of that technology needs to mature a bit, but we aren't too far off.

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Well, let's take a look at the scaling of a few vital numbers. If we grow the length (and width, and height) of a space ship by a factor of N, we grow

by a factor of N^3

  • its volume
  • its mass
  • its emergency energy production (energy production by heating some entropy containers)
  • its top laser based firepower

by a factor of N^2

  • its surface
  • its long term energy production (because this is connected to surface as we need to radiate away the entropy)
  • its propulsion force (bounded by energy production and exhaust area)

by a factor of N

  • its shield thickness

not increased at all

  • its top non-laser missile power, assuming the missiles are nuclear anyway

by a factor of 1/N

  • acceleration

Now, powerful lasers are certainly one of the best counters against incoming missiles, thus a really big spaceship can be expected to be able to defend itself against large missiles. The additional shield thickness also works to help it defend against smaller ammo. So, talking offensive vs. defensive, I believe that the big ship is better.

However, the size has the cost of reduced maneuverability due to the reduced acceleration.

A strategy a fleet of small ships could try against a single large space ship would be to try to exhaust their emergency energy production by launching a big number of nuclear looking missiles against them, forcing them to use their lasers to destroy the missiles, overheating their reactors. A last round of actually nuclear missiles could subsequently overwhelm the big ships defenses. This puts an upper limit on the usable size of space ships. So, sorry, no death star class ships...

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  • $\begingroup$ I disagree with acceleration scaling as 1/N. build N**3 times bigger engines, burn N**3 times as much fuel and get the same acceleration. $\endgroup$ – maaartinus Jun 20 '17 at 20:28
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    $\begingroup$ @maaartinus ... and get N^3 times the waste heat to cool away, for which you only have N^2 the surface. You may easily reach the same delta-v as with a small spaceship, since you can store N^3 times the amount of fuel, but you need to increase the burn time by N to avoid overheating. At least, that's what the physics say. Of course, you can always handwave such facts, but in hard science fiction, I expect the big space ships to be less maneuverable than the small ones. $\endgroup$ – cmaster Jun 20 '17 at 21:06
  • $\begingroup$ Right, I missed the heat. But it needn't be the limiting factor for maneuvering (as apposed to long term accelerating). As long as all you want is a small maneuver needed to avoid being hit, you can absorb the heat in your N**3 mass. Your engines may be also more efficient than smaller ones giving you even more maneuverability in the short term. Just an idea. $\endgroup$ – maaartinus Jun 20 '17 at 21:21
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The problem with this kind of space opera (I should note that I am a fan of this type of military sci-fi) is that it makes no sense.

First and most obvious: we're not ever going to have a space navy where sailors spend months or years in interplanetary space. A robot will be exponentially cheaper, safer, and more effective.

Second, dropping a rock onto your enemy (kinetic kill) is easy, if you have the propulsion technology which is assumed in the typical space battle. The only way (aside from magic force fields, tractor beams, teleportation gates, etc.) you can stop a rock is to detect it in sufficient time to change its momentum vector. Detection is nearly always assumed to be easy in space battles, while in the real world It. Is. Not.

Anyway, the assumption "Oh! They've got a spaceship! I should attack it!" is just plain silly. The typical reason given to attack an enemy ship is to gain control of a volume of space (especially a volume of space which includes a planet, or other large resource). What I'm saying is you can't "control" a volume of space: you can't defend it from a targeted attack.

The only realistic scenario is:

  1. To restrict access to space to a small group of superpowers (by definition) so that there will never be any question about who attacked you.
  2. Use a hidden network of doomsday devices, which will automatically attack the resources of the attacker, making the cost of any attack too expensive to contemplate (mutual assured destruction, MAD).

This is the only realistic scenario I can think of, given the most realistic situation where volume defense is generally impossible (with the possible exception of planets, which may have enough economic power to support orbiting (A.I. robotic) forts and defense systems).

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    $\begingroup$ Detection in space is quite easy. There is no atmosphere or horizon, so you can use the full EM spectrum to look in every direction; stealthing against that is tricky indeed. This in turn means that you have time to avoid very-high-speed projectiles. $\endgroup$ – Andrew Dodds Jun 20 '17 at 15:11
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    $\begingroup$ @AndrewDodds That's it, speed. If a missile is approaching with 0.999 c, then it leaves you no time to defend. Imagine detecting 1 cubic kilometer big missile approaching Earth at the distance of Pluto. If you could detect it instantly (at this distance!), there'd be 5.5 h to impact, out of which, you'd need the vast majority for signal transmission (assuming no FTL) leaving you just 20 seconds to react. Hitting such a small target could be hard, but even if you could do it, it could change its trajectory just a tiny bit (or split itself) and you'd miss it a by a few kilometers. Game over. $\endgroup$ – maaartinus Jun 20 '17 at 20:42
  • $\begingroup$ At high percentages of c, yes, the balance goes in favor of throwing rocks.. There is a balance here. What we call a hypersonic missile on Earth based battlefields moves at a crawl relative to, say, Earth-moon system distances. So as missile speeds increase, battlefield distances increase. $\endgroup$ – Andrew Dodds Jun 21 '17 at 7:46
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The use of small fighter craft in some space operas like Star Wars is based on the use of carrier and land based airplanes in naval combat in World War II.

A big part of the advantage of airplanes in naval combat is that they travel in a different medium which has less resistance and thus requires less fuel to travel fast in. Also the airplanes can vary their altitude while the surface ships cannot.

Thus carrier and land based planes can locate and attack surface ships while the surface ships are too far away from land or the carriers to attack them. The planes can attack from too high for the weapons of the surface ships to reach them, while gravity helps their weapons reach the surface ships. And the airplanes can travel several times as fast as the surface ships.

These advantages don't exist in space where every vehicle travels in the same medium or vacuum.

Thus space fighter craft and space carriers for them are unlikely. Space warships may range from space torpedo boats to space missile frigates to space destroyers to space cruisers to space battleships. And different technologies and sociological factors will determine what types a fictional space navy will build more of.

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I think the analogy from naval warfare to space warfare has several issues:

  1. Actual naval warfare is constrained by a curved earth, air resistance, and the asymmetry of water and air. So aircraft carriers have a huge advantage over battleships, not because of swarms of small vehicles, per se, but because the small vehicles travel over the horizon. Similarly, submarines lurk under the surface and fire torpedoes that you can't really hit from a surface vessel.

    On the other hand, a laser in space can hit a distant target far faster than a physical projectile.

    Not to mention that carriers may become obsolete as hypersonic missiles and torpedoes are finally perfected. So maybe future battleships will launch these -- or maybe they'll all be launched from land bases and targeted via satellites.

  2. The ultimate space weapons are launched from enormous "vessels", where we might loosely define a huge device and an entire solar system as a "vessel". Look up Relativistic Weapons in the fascinating Exotic Weapons page. (The exotic weapons page is absolutely worth a read... be prepared to spend some time there.) These are the ultimate, unstoppable weapons for destroying entire planets. Small targets would be hard to hit with one, of course, so a swarm of small spaceships might take out your launcher, but if you get a first shot you'll destroy their planets with no chance of them defending. Lots of luck with them surviving in a bunch of little ships with their home planet(s) gone.

  3. Space is larger than the ocean. Even at some FTL speeds, it'll take you longer to get to a battle than the days or even weeks it takes a ship to cross the Pacific. Which tilts things towards larger ships, I would say.

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Would future space admirals favor huge ships, or smaller ones?

Huge ships obviously. It's not a strategic choice but an ego thing. A huge ship is a massive show of power.

Now in space, huge ship would be preferable (like an aircraft carrier). The ship would actually be a giant factory, building and repairing drones. In battle the ship would hide and send the drones out on automated missions.

The only weapons the ship would have is anti drone weapons for last ditch defense. The ship in all likelihood would flee if attacked, leaving behind drones to aid the escape. Losing a capital ship is too expensive to risk it.

They wouldn't bother with giant space lasers like the Deathstar because destroying a planet doesn't require massive weapons. A simple vial of a lethal virus or self replicating nanites could destroy a planet. It's much cheaper and easier. The drones could also be used to accelerate and protect an asteroid to create an extinction level event.

As for where the battles are held, they will never be in wide open space. They will always be near planets because there is too much open space to ever be able to protect it.

The only way battles could be held in open space is if both sides agreed to the terms and created rules for warfare because damaging a planet was too risky and inhabitable planets were too valuable. The problem with this is if the sides are not equally matched, nobody will ever agree to rules that might hold them back.

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The main issue with large spacecraft using Plausible Mid Future levels of technology is everything is constrained by the rocket equation. Essentially every gram counts, so increasing the mass of the spacecraft comes at an ever increasing performance penalty. The ability to do tactical manoeuvre in the combat zone like instantaneous acceleration or "jinking" out of the way of oncoming missiles.

On the other hand, spaceships do need to carry massive shielding to protect the delicate humans aboard, not to mention the electronics and other systems which will be affected by exposure to radiation. Heavy armour also provides protection against laser and particle beam weapons, although not so much against hypervelocity kinetic energy weapons.

So perhaps the best solution would be to combine the two ideas. En route, the spacecraft are encased in a large honeycomb like hanger structure, which provides protection against radiation and small impacts (flecks of dust, small particles of gravel floating in space), while in the combat zone, swarms of small, manoeuvrable ships are released to create a spherical zone bristling with sensors and weapons.

The final factor to think about is what, exactly the premier weapons system is that you are fighting against. Massive Ravening Beam of Death (RBoD) lasers could theoretically be deadly out to a light second away (just under the distance from the Earth to the Moon) and escaping from that would be problematic with any sort of ship. Kinetic energy weapons like missiles or railgun projectiles generally would need larger vessels or installations to launch, but there should be sufficient time to detect oncoming rounds and evade at a light second. Nuclear driven weapons like CASABA Howitzers are an intermediate case, since they can project effects from 100km/sec (pellets from nuclear "shotgun rounds", to nuclear driven HEAT rounds projecting metal jets at 3% of c, to using the nuclear charge to crate a focused plasma jet moving at 10% of c. More information can be found here, and at the Atomic Rockets site in the section here.

Of course, being hit in either a large or a small ship is bad news, even something orbiting the Earth is already moving at more than 7km/sec, and objects moving at interplanetary speeds are moving far faster, so the kinetic energy of a strike could rival a nuclear explosion, even if the impactor is made of wadded up kleenex tissues. You will need to make the determination if it is more feasible to try to dodge the strike, or to be massive enough to absorb it.

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Just for kicks, let's consider a fairly extreme spaceship size... The Earth. Then, you can scale back and see if there's a good balance for your universe.

Advantages-

  • so large, it would be difficult to destroy with any kind of laser tech. Physical attacks would need to be massive, like tossing large asteroids
  • atmosphere and magnetosphere shield Earth from a lot of energy and physical damage "attacks".
  • underground / underwater bunkers and cities would exist for added protection during wartime, and travel.
  • enormous energy store, in the form of geothermal energy.
  • in carefully-regulated solar proximity, it sustains its own atmosphere, oxygen production, and water stores, pretty much indefinitely [though rebooting this after extra-solar travel would be quite a challenge]

Overall, the sheer size make it easy to attack, but difficult to damage significantly.

Disadvantages-

  • although the Earth is moving a high velocity through space, its mass and the laws of Inertia make any kind of steering or stopping nearly impossible.
  • the only way to achieve FTL would likely be a technology that enables re-positioning without the need for propulsion. Possibly some means to surround Earth with a field that "drops is into hyperspace", and then emerge elsewhere.
  • any travel anywhere away from our precise solar conditions would mean destruction of Earth's surface water, surface atmosphere, & surface life. It would still work as a vessel, but would have to be re-engineered for such conditions (subsurface reservoirs, oxygen production, etc)
  • so large, it would be difficult to defend without massively automated, widespread systems. Even with all inhabitants underground, a coordinated attack of landed vessels would be difficult to repel.

That example is a bit extreme but highlights some interesting possibilities and vulnerabilities of very large ship design.

Another possibility would be a ship that has different modes of operation. In travel mode, it's lightweight, fast, and decently cloaked - but vulnerable. In battle mode, it could fly into an asteroid belt and essentially construct a defensive shield. In that mode it's not mobile, but has camouflage and a heavy layer of physical shielding.

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A combination of different kinds units is always better than a single kind, so I guess you'd have both. Large ships are efficient carriers, so these would be useful to supply smaller ships with fuel and ammo, perhaps even carry them during long marches. Smaller ships are definitely better for scouting and surprise attacks.

It's worth noting that size is usually not a constraint for spaceships (only mass is), so truly huge ships could be build if needed. For example, a ship equipped with a huge radar locator would provide a noticeable advantage in reconnaissance without slowing down the army it supports.

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  • $\begingroup$ Does your answer bring anything new, that wasn't already explored in other answers? Accepted answer already considers when mix of large and small makes sense. $\endgroup$ – Mołot Jun 21 '17 at 12:50
  • $\begingroup$ @Mołot Really? It seems to be advocating either building Deaths Stars or "manufacturing millions of tiny fighters", depending of the strength of weapons available. $\endgroup$ – Dmitry Grigoryev Jun 21 '17 at 12:57
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I'm afraid the question makes assumptions familiar to most modern PC games and space movies - which are more like WWII films in space.

In reality, WWII thinking does not apply to space for 2 reasons:

  1. The vast distances involved

  2. Vast time scales involved

Our current understanding of cosmological science indicates that travel and even communications over interstellar distances is almost impossible - let alone militaristic conflict.

Travel to nearby star systems alone would take unbelievable amounts of fuel, and lots of time (timescales over 1000's of years, if not 100,000's or millions). Our recent visitor (our first observed interstellar asteroid) is theorised to have taken 45 million years to reach us, possibly violently ejected from a red giant star system, at a tremendous speed which will pass us by. Conflict at this timescale would not be feasible to have a navy, a civilisation, or even a species that last that long (our species has only recently evolved).

The only thing close to answering your question is what was previously theorised early in the last century as Von Neumann probes. This concept was developed as a thought experiment as to how to swiftly (in galactic timescales as in several million years) explore or colonise a galaxy by creating a self replicating probe, sending it to a nearby star system, which then replicates some more using local resources to then send onwards to other nearby star systems.

In this sense it is more likely that the probes would be very small - even just nano-probes, as for every unit of mass it requires much larger energy to travel. Arrival at a star system is still a major feat, but possible by small robotic, AI controlled craft.

In answer to your question, it is perhaps best to say that small ships are preferable to larger ones, perhaps even microscopic ones, due to smaller mass requiring less fuel and still retaining the ability to self replicate resulting in eventually trillions of probes, however for what purpose is the larger question. There is no sense to 'control' another star system in such a manner, as to what purpose is it being controlled if only by small machines? Especially if it takes many millions of years to reach star systems in our galaxy, after a time which we are likely all long dead.

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protected by Mołot Jun 21 '17 at 12:50

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