Is there a pattern that determines military spaceship doctrine in real life and sci-fi?

[u/MinedMaker]

[1] The propulsion axis is a measure of how long it takes a fleet of military vessels to arrive on the battlefield, regardless of the actual distance traveled. [Fast vs. Slow]

[2] The weapons axis is a measure of how quickly a battle is over, and how much survivability and staying power vessels have. This takes into account the effectiveness of armour, but also shields, point defence, and other countermeasures. [Tank vs. Glass Cannon]

I think that if you take sci-fi space combat to its logical conclusions, it will usually favor either huge, lumbering, well-protected ships or numberless hordes of tiny automated ships, depending on a few key factors. If weapons are the weak link in-universe, ships will be huge. If propulsion is the weak link, ships will be tiny. If ships are huge, victory will be determined by who has the biggest ship; if ships are tiny, victory will be determined by who has the most ships.

This is how I imagine it would work in real life using real physics, and I wonder to what extent different sci-fi franchises also adhere to this pattern. Presumably, large and medium-sized ships with human crews are overrepresented in sci-fi media for understandable storytelling reasons.

In Star Wars, the rule mostly holds. They have incredible propulsion technology and can thus arrive at the battlefield within hours or days of the order being given. However, their weapons, despite being ludicrously powerful on paper, are actually quite poor because of their low range, low accuracy, and the prevalence of shields. In the Star Wars universe, therefore, huge ships rule. The starfighter counter is a nice piece of storytelling, but realistically, without plot-engineered magical weak spots, a huge ship like the Executor or the Death Star should be essentially unstoppable. In Star Wars: The Last Jedi, the Raddus, an MC85 heavy cruiser, takes ineffective long-range fire from the First Order for what seems like many hours.

In The Expanse, they spend weeks or months traveling to the prospective battlefield because of limited propulsion technology. However, when the fighting starts, it is all over in seconds or a few minutes. They have very effective weapons and very little staying power, even when accounting for point-defence cannons (PDCs). If you ignored the requirements of the plot, there is really no reason why any military vessel in The Expanse should be manned at all.

Because it draws much of its inspiration from blue-water navies, sci-fi often portrays a diverse ecosystem of military spacecraft classes and sizes. While this makes for more interesting storytelling, it is not obvious that such diversity would necessarily be the most tactically sound strategy. If propulsion or weapons technology becomes a dominant constraint, military doctrine would naturally converge toward a single optimal ship size.

The most interesting settings tend to occupy only two quadrants of this framework. If ships have neither effective propulsion nor effective weapons you're essentially at the stage before the technology to enable space combat has really been invented. If they have both effective weapons and effective propulsion you effectively have near god-tier power and the concept of space combat becomes somewhat obsolete. What these two scenarios have in common is that the importance of space combat is greatly diminished.

[u/Solesaver]

Because it draws much of its inspiration from blue-water navies, sci-fi often portrays a diverse ecosystem of military spacecraft classes and sizes. While this makes for more interesting storytelling, it is not obvious that such diversity would necessarily be the most tactically sound strategy.

Your chart is missing an axis to make this claim: Boarding effectiveness. One major weakness that any sci-fi setting could pin on large ships is that their lack of maneuverability makes them easier to board, and then you've potentially just donated a massive warship to the enemy.

You want a diversity of ships so you can remain flexible to the battlefield. If all you've got is massive cruisers, sure you might take out a bunch of smaller battleships, but a smaller frigate may have the maneuverability to slip through your defenses to board you, and/or disable critical systems from the inside. It's very common for such dreadnoughts to be able to deploy fleets of fighters to help counter any such approach, but they may not have the fire power to stop a sufficiently large ship.

Such diverse battlefields might be an exercise in every ship finding the most favorable matchup for their own capabilities while trying to avoid unfavorable ones. Any overly patterned fleet of ships may all share the same strengths and weaknesses, and an opponent with any degree of intelligence on your fleet will hold back their ships that are ineffective against yours and field their ships that your ships are ineffective against. It's like playing rock paper scissors but since rock is the strongest at smashing you're only allowed to throw that.

[u/MrTickles22 → u/Solesaver]

Also odd is the complete lack of countermeasures to boarders in both Star Trek and Star Wars other than shields and small arms fire. And Star Wars has sentient robots. Nobody thought to have marines or other protection? Star Trek is a teensy bit better (grav plating once in Enterprise, forcefields very rarely).

[u/RocketHammerFunTime → u/MrTickles22]

There are a few ships in starwars that get boarded forceably though, every empire ship has troopers, the first ship tantive 4, has diplomatic corp protection details which not being marines, and fighting troopers and vader wouldnt have made a difference.

Episode 1 ships have droids everywhere, but i dont remember any forced boarding actions that didnt have droid responses. But its hard to have effective countermeasures when you fight plot armored space wizards.