Resupplying big badass starships

[Coalition]

I would look at it where larger vessels can have more flexibility in what they carry for spares/repairs. This allows larger vessels, with the same mass fraction allocated to repair equipment, longer endurance than smaller vessels.

I.e. Space Navy Coalitia has allocated 1% of all ship masses to repair systems. This is in the form of raw materials, tools, tooling equipment, spare parts, etc.

A 1 ton courier ship to ship courier boat only has 10 kg to work with, so it would only have a basic tool kit. A hammer, gauges, small welder, etc. This limits its endurance to what can be repaired by the tool kit.

A 100 ton frigate has 1 ton allocated to it. It can have a tool kit easily, plus some spare pipe, and a machine to cut and form the pipe to proper dimensions. The endurance of this vessel is slightly longer.

A 1 megaton dreadnought has ten kilotons of tooling and parts. It can afford the tool kit, pipe materials, small reactor assembly, and possibly the materials to make a new machine if necessary. The ship has a much longer endurance due to greater variety of internal tools.

Of course the larger vessel also spends a larger mass fraction on internal structure than a smaller vessel, slowly canceling out the savings in endurance. Still, the several orders of mass advantage allows for a greater variety of tooling to be carried on board.

So if you get bored, you can look a series of various repair toolkits, and give a rough idea of what mass is necessary for XX amount of time for endurance. I.e. a 200 kiloton vessel with the same ten kilotons of repair equipment as the 1 megaton dreadnought above will have a similar endurance (ignoring the fact that it only needs 1/5th the repair parts), because of the variety of tooling equipment.

Short version = Order of magnitude in repair equipment mass would lead to a linear increase of endurance time.

[Darth Smiley]

Short version = Order of magnitude in repair equipment mass would lead to a linear increase of endurance time.

I actually get the feeling that repairs are really not the limiting factor in starship endurance. Your 'big, badass starship(tm)' is going to run out of delta-V and munitions long before repair really become an issue.

That's not to say that repair is not important, particularly for military starship, just that it's really not the limiting factor when it comes to endurance. This goes double for starships that have large crews - food and life support are going to eat up more mass than repair equipment, and are consumed at a more or less constant rate, rather than only really being an issue if something fails.

For our hypothetical 100 ton frigate, with a crew of 10, for a 90 day voyage, we'll need about 2250 kg of food and water - not counting oxygen. It's easy to see that it's really pointless to invest significant proportions of the ship's mass into repair - if the ship is well designed at all, you'll run out of food before you run out of screws.

Supply, for a starship, can be divided among three categories - fuel, hardware, and life support.

Fuel can be gotten around a variety of different ways. Aside from the obvious tanker solutions, a huge amount of 'fuel' can be attached to the starship prior to launch in the form of boosters, giving it a decent outbound vector and enabling it to use it's internal stores more liberally.

Hardware shouldn't be a major problem, with the major exception of weapons. A military starship could run out of missiles really fast, but there really seems no point in creating colliers - why not just make the colliers missile pods, and have the ability to saturate the enemy's point defenses while you're at it?

Life support is the problem. I frankly don't see any way around this, save creating supply ships, or delivering supplies via magnetic cannon.

My own universe uses 'tenders' - which are lightly protected ships with high Isp/low thrust, few defenses, and tons of supplies + dV, that push the real ships around, and when the going gets tough, the tenders get the hell out of the way, and let the high thrust / low mass ship that was piggybacking on it the whole way do the fighting. It neatly avoids quite a few logistical and engineerings, in particular the difficulty of getting both high thrust and huge dV without the Magical Fusion Torch.

[Junghalli]

I actually get the feeling that repairs are really not the limiting factor in starship endurance. Your 'big, badass starship(tm)' is going to run out of delta-V and munitions long before repair really become an issue.

Precisely. The only application where an onboard machine shop really makes sense is a ship that's designed to operate on its own for years or decades, like a long-range explorer or an STL colony ship. For a military ship an onboard machine shop just eats up delta V for a function that can be easily taken care of when the ship refuels, something that it almost certainly must do long before parts breakdown becomes a serious issue.

Although some basic machine tools might be useful in an extreme emergency, so on a really big ship I could see a couple being thrown in.

[Genii Lodus]

I would have thought life support would be much less of a problem since it's relatively easy to turn waste into food again, though the idea's a bit unpleasant.

I suppose if you had relatively advanced manufacturing technologies and FTL was neither very fast nor that common it would be easier to just make your own widget than wait for the logistics chain to deliver one.

In my own sci-fi I gave most cruiser+ size their own machine shops but nothing dramatically complicated just enough to fabricate simple metal panels etc. Intended for it to be used to patch the ship up after battle until they returned to a shipyard. I have mobile shipyards and factories in my universe so anything more involved can be handled by one of these if the ship was operating far enough from friendly space.

[Darth Smiley]

I would have thought life support would be much less of a problem since it's relatively easy to turn waste into food again, though the idea's a bit unpleasant.

For very long trips, like exploration missions where the travel times measured in years, then creating a closed ecosystem is mandatory. However, the recycling equipment takes up mass and space, so for shorter trips, it's just better to carry rations - not to mention the effect on moral. It is probably possible to create a hybrid system, that recycles some of the food and uses some consumables, in order to maximize efficiency on medium voyages.

[Sea Skimmer]

Precisely. The only application where an onboard machine shop really makes sense is a ship that's designed to operate on its own for years or decades, like a long-range explorer or an STL colony ship.

Really? Then please do explain just what this guy is doing working in a machine shop on USS John C. Stennis, a ship which operates for no more then six months at a stench, with almost daily COD flights and regular visits by a supply ship?



The answer? He’s making a brass fitting for a fire main pump.

Reality is that a ship has a shit load of small metal parts, and after a certain fairly low threshold it’s much more economical to have a machine shop and metal blanks then to carry a whole stockpile of different parts. Because of its complexity stuff breaks on a ship all the damn time, not just after its years out of dock. Aircraft carriers also have numerous other repair shops to service there weapons and aircraft, which actually take up a fair portion of the entire volume of the hanger deck. Any warship over a few thousand tons is going to have significant repair facilities. IF said warship is going to travel out into space, when it might be pelted by meteorites at any time, and when a single broken pipe could leave it crippled these facilities are going to be by far more vital then they ever would be on earths surface.

[Junghalli]

It is probably possible to create a hybrid system, that recycles some of the food and uses some consumables, in order to maximize efficiency on medium voyages.

Recycling air and water but not food would make sense. Air and water is much easier to recycle than food.

IF said warship is going to travel out into space, when it might be pelted by meteorites at any time, and when a single broken pipe could leave it crippled these facilities are going to be by far more vital then they ever would be on earths surface.

Yes, I conceed some machine tool capacity is useful. Though I still think it will be mostly geared toward light and emergency repairs. For anything else it makes more sense to put the machine shop on the space stations the ship gets resupplied at: the space station, unlike the ship, can be as heavy as it wants to be.

[Nyrath]

Recycling air and water but not food would make sense. Air and water is much easier to recycle than food.

Technically true, but food isn't particularly hard to recycle. A tank of algae could do it.

[Typhonis 1]

Nyrath? Food poroduction could be part of the life support structure. It can clean and recycle the air and water .