Reasonable Peacetime Space Navy

[Cycloneman]

What sort of space navy would exist for a interstellar polity facing no present or forseeable interstellar threats which has the following needs:

• Prevention of suicide bombing using civilian spacecraft
• Prevention of FTL fuckery via telefrags
• Showing how cool we are with a few really expensive fuckoff vessels
• Maintaining capacity for orbital bombardment and planetary invasion (one planet at a time)

and the following abilities:

• Alderson Drive FTL
• D-T fusion drives capable of mid-speed acceleration (maybe up to 1 or 2 Gs max, generally more like .5-1.5 m/s^2)
• Chemical coolant and radiator heat dispersion
• Effective laser, coilgun, and missile weapons systems
• Multistage planet-to-orbit capacity (railgun/turbojet/rocket), rather than space elevators
• Spacecraft not completely automated
• Necessity of switching out crews at least once every year to deal with bone loss due to microgravity.
• Other reasonable expectations of technology for a human civilization a century or two from now.

My expectation would be:

• Lightweight patrol craft, with a single high-powered weapon system (most likely missiles), 1-2 per system controlled.
• Large fleet of transit vessels, possibly used as some kind of merchant navy during peacetime. At least enough to effectively move several hundred thousand troops between planets on a single trip.
• Small fleet of bombardment-capable vessels (a few dozen? how many would be necessary for effective use as an aid to standard ground tactics?)
• Even smaller fleet (3-5) of extremely large, high-powered spacecraft, equipped with pretty much everything and a few dozen missile buses

Thoughts?

[Stofsk]

Why would you have anything other than patrol vessels and some kind of cruiser-analog for the 'bully planets from orbit' role? I don't see a reason to have battleships if there aren't any other rival nations to get battleships as a deterrent against.

You basically set it out that the hypothetical polity has no present or forseeable external threats to contend with. So it sounds to me like you'd want a big fleet of small patrol ships, with larger cruisers to act as flag vessels or carry out independent operations. In times of war you can have the cruisers act as the heavy hitters, and I suppose you might also have dedicated transport ships to carry your army around.

[Stofsk]

Missed the timing to edit. It occurs to me that the polity you describe would be somewhat unique as far as human history is concerned. No external threats would be something unparalleled to a human nation, from what I can tell. Is this a space empire? A Union of Federated Planets? You may not even really need a huge army to transport either. Your space navy may only really need to combat crime and piracy and if there are any ground forces, they'd probably be geared up to support those kind of missions.

[Cycloneman]

Why would you have anything other than patrol vessels and some kind of cruiser-analog for the 'bully planets from orbit' role? I don't see a reason to have battleships if there aren't any other rival nations to get battleships as a deterrent against.

Boondoggles?

You basically set it out that the hypothetical polity has no present or forseeable external threats to contend with. So it sounds to me like you'd want a big fleet of small patrol ships, with larger cruisers to act as flag vessels or carry out independent operations. In times of war you can have the cruisers act as the heavy hitters, and I suppose you might also have dedicated transport ships to carry your army around.

In (historical) times of war, military conflicts have been completely planetbound, so heavy hitters/cruisers don't have any use..

Missed the timing to edit. It occurs to me that the polity you describe would be somewhat unique as far as human history is concerned. No external threats would be something unparalleled to a human nation, from what I can tell. Is this a space empire? A Union of Federated Planets? You may not even really need a huge army to transport either. Your space navy may only really need to combat crime and piracy and if there are any ground forces, they'd probably be geared up to support those kind of missions.

It's a "voluntary" association of countries that share a unified currency and obey certain economic directives. The polity has no genuine threats, but it does occasionally engage in ground campaigns of conquest of (technologically unsophisticated) alien planets, and keeps its military ready for such events. That's its military's primary purpose, besides anti-crime stuff.

[Bakustra]

What they need primarily, as far as I can see, are 1) armed customs stations at the Alderson points with some medium-weight vessels with fairly low acceleration as backups, 2) lightweight patrol vessels to move in-system to deal with criminal activity, 3) specialized bombardment and invasion vessels, and 4) a merchant fleet.

If the goal is to capture planets fairly intact, then bombardment would be fairly difficult or incredibly situational given the situation you outline. If your vision of a plausible 23rd century incorporates pure-fusion nuclear weapons with minimal fallout, then bombardment becomes more useful but still somewhat situational.

Invasion vessels would need robust landers, possibly one-way drop ships, to build up temporary spaceports to move troops in in greater numbers. If that's not reasonable for the timeframes needed, then they require dropships and some way of reliably spoofing/evading ground-based anti-aircraft and anti-spacecraft weaponry on the way down.

Either way, relying solely on converted merchant ships is problematic unless there's some way to reliably control airspace and near orbit around planets without severely damaging the areas to be taken intact.

Heavy prestigious ships aren't really reasonable, and it's rare for nations to engage in dick-waving unless there's some other, metaphorical, penis to measure against. If we assume that this future nation is aristocratic and dysfunctional, then we could have modern equivalents of the "treasure ships", but those would hardly be warships.

If they have Alderson drive, "telefragging" is impossible, as ships don't move through the intervening space while using it for transit.

Fake Edit: How technologically unsophisticated are the third-worlders aliens that they invade the planets of?

[Starglider]

Boondoggles?

Aside from defence contractor lobbying, you may want to maintain the ability to build these in volume should a major threat appear, for which low-rate design and production is really the only way.

[Darth Tanner]

but it does occasionally engage in ground campaigns of conquest of (technologically unsophisticated) alien planets

How do they reconcile this with being a union of voluntary members? Most people today would object to the enslaving of alien civilisations so how are the invasions being sold to the public?

Main limiting factor is how big is this political body? Even with magical star wormholes to move about with we are nowhere near any magic tech that will enable us to terrorform planets on the scale to have a meaningulful star empire. Unless liveable planets are far more abundant than currently thought the main population centre is still going to be stuck at the bottom of the earth gravity well with only minor colonies numbering in the dozens for the resources/science projects.

Ultimately with the tech available within a couple of hundred years you’re going to have maybe a few dozen light patrol ships that double as rescue ships for the civilian traffic and some transports for supplies to the colonies/research outposts. The fact they have encountered aliens may mean they have some larger ships kept near earth but I'd imagine their limited to large missile racks with engines bolted on as an offensive platform and maybe orbital missile platforms with lasers bolted on for Earth.

In terms of conquering alien worlds, unless their sparsely populated I don’t see how you can have that many men and materials being transported to pick on some primitive society without magic means of getting out of the gravity well. The shear cost of running an invasion on a stellar distance would preclude it unless there’s special alien tech available (in which case their not the defenceless primitives) or the aliens can simply be intimidated by orbital strikes into surrendering which isn’t that believable, people at home would likely object to genocide.

At least enough to effectively move several hundred thousand troops between planets on a single trip.

How are these massive troop concentrations getting out of the gravity well? How are they kept supplied? Why is a peaceful government’s population ok with invading alien worlds light-years away?

How far away from the sun are the wormholes in Alderson FTL? Could mines/stations be constructed near them or is it too close to stay there for long.