FTL rate of movement for GURPS SPACESHIPS

[Rupert]

It will certainly encourage the use of message torpedoes/probes. If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible. For military purposes, the small ships are even more strongly selected for - missiles make ships eggshells with hammers, so you want each egg to be as cheap as possible.

The proposed FTL system hammers this home, even with a relatively slow loss of speed with increasing mass.

It would likely kill carrier+fighter and carrier+rider concepts, because the big carrier would be strategically slow compared to a fleet of small ships.

It would make small PC-owned ships faster than the lumbering great warships of the Evil Empire. However, if two FTL drives means you go twice as fast, a 30,000 ton ship with two drives is very nearly as fast as a 1,000 ton ship with just one, which might not be a strong enough speed difference to really differentiate ships by speed.

[David Johnston2]

Originally Posted by Rupert

It will certainly encourage the use of message torpedoes/probes. If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible. For military purposes, the small ships are even more strongly selected for - missiles make ships eggshells with hammers, so you want each egg to be as cheap as possible.

The proposed FTL system hammers this home, even with a relatively slow loss of speed with increasing mass.

It would likely kill carrier+fighter and carrier+rider concepts, because the big carrier would be strategically slow compared to a fleet of small ships.

It would make small PC-owned ships faster than the lumbering great warships of the Evil Empire. However, if two FTL drives means you go twice as fast, a 30,000 ton ship with two drives is very nearly as fast as a 1,000 ton ship with just one, which might not be a strong enough speed difference to really differentiate ships by speed.

Assuming that you include the defense favouring switches then it creates the early 20th century paradigm of battleships for heavy firepower, destroyers for speed and cruisers to catch destroyers.

[Rupert]

Originally Posted by David Johnston2

Assuming that you include the defense favouring switches then it creates the early 20th century paradigm of battleships for heavy firepower, destroyers for speed and cruisers to catch destroyers.

While these classes had differing tactical speeds, where their strategic speed varied it did in ways you might not expect - for long distance movement destroyers were often quite slow because they were small (making them uneconomical at quite quickly as their speed rose, and they lost speed in bad weather) and carried little fuel (so they had to travel slowly to conserve fuel if they were moving long distances between bases). Cruisers were only faster than battleships if they had reasonably close bases for the same reason. However, these things varied a lot depending on the exact time - before reduction gearing was used the only steam turbine ships with good range were ones with 'cruising' turbines, and that limited them all to quite slow cruising speeds.

Also, if you're using that naval model, destroyers are fleet boats and FTL that's faster than that of the battleships is wasted, as they'll be moving as a group. Cruisers are the scouts and would need fast FTL speeds, but destroyers wouldn't.

[Agemegos]

Originally Posted by Rupert

If you use Spaceships there's already incentive to use many small ships over few large ones, even for civilian use - the cost per ton is the same, the payload per ton is the same, and the 'small ship fleet' is more flexible.

On the other hand, the larger ships don't need engine rooms and can be automated more cheaply. I recently did a cost study for a particular set of assumptions, and found that a highly-automated SM+12 ship came in 30% cheaper per ton-lightyear than an SM+9 ship with an engine room.

[Rupert]

Originally Posted by Agemegos

On the other hand, the larger ships don't need engine rooms and can be automated more cheaply. I recently did a cost study for a particular set of assumptions, and found that a highly-automated SM+12 ship came in 30% cheaper per ton-lightyear than an SM+9 ship with an engine room.

I assume that's including crew salaries and life support costs, etc. Did you try a SM9- ship with Total Automation of the Engine Room?

I'm curious as to whether the high cost of total automation would be worthwhile in this case.

[ericthered]

I suspect you get better results if you cap the speed gain from size at some point. That sort of thing happens all the time, as different limiting factors take over.



If you want to create a fighter and carrier paradigm, increasing the FTL speed of the fighters is a little odd, unless you intend for battles to be fought with carriers parked in different systems sending fighters back and forth to each other. Also, with many paradigms you end up with the "Carriers" being nothing more than fuel tankers and cargo ships, so watch out for that.

[Agemegos]

Originally Posted by Rupert

I assume that's including crew salaries and life support costs, etc.

Yes, and propellant, insurance, amortisation, depreciation. Also maintenance, repairs, and overhauls of the reaction and FTL engines based on engine hours.

Did you try a SM9- ship with Total Automation of the Engine Room?

No. It seemed to me that total automation is so expensive that you would need really, really low interest rates, insurance rates, and depreciation to let it compete with crew salaries, quarters, and life support.

I'm curious as to whether the high cost of total automation would be worthwhile in this case.

At 8% interest, insurance, & depreciation (which was as low as I dared to go) each workspace totally automated costs G$400,000 per year. Spaceships 2 suggests a crew employment cost of $67,200 per year for base-level crew, plus which it costs G$150,000 (G$12,000 per year) to give them a cabin, $75,000 to give them a shared stateroom or couchette, or $37,500 a bunk in a bunkroom. And $730 per year for consumables. High automation is really marginal at 8%, even with comfortable long-occupancy crew quarters. Only adding foremen to large crews puts it firmly over the top.

If I had ships with very small payload fractions it might be different: total automation of all workspaces and NAI "officers" might mean having no crew habitat at all. But I was at a payload mass fraction of 70% or better, so it obviously wasn't going to work.

I'll take a look after breakfast and get back to you.

[khorboth]

I would expect a couple of interesting results:

1: Carriers would become a real big deal.

2: Ships would have some kind of connection device or coupling connection.

For some applications, staying together is much more important than speed. You don't want your big ship to jump in-system with no support, so attach a few (dozen) small ships to it's hull and have them ready to detach. This is not necessarily a military application, but for an exploratory mission, everybody may want to arrive together and not 3 days ahead of the supply cruiser.

Similarly, having all the ships show up at the same time may be better than being fast. Even with an exponential slow-down, having all 30 invading ships show up at the SAME time instead of over the 5-minute span which is the closest you can get with careful weighing may be worth a full 2-day delay in the plans. Even with careful weighing and math, it may be impossible to time things better than a few hours when systems are days apart. And that can be an eternity in battles.

If these connections double as some kind of emergency towing and/or rescue attachment and are standardized, that's a bonus.

[Agemegos]

My small freighter cost G$207,307.69 per "compartment" of cargo space, and the large freighter G$189,233.33 per "compartment"; the passenger ships cost G$368.846.15 per passenger compartment and G$358,677.78 per passenger compartment. So total automation is more expensive than more/bigger ships as a way of increasing payload, in the situation I modelled.

[Rupert]

Originally Posted by Agemegos

If I had ships with very small payload fractions it might be different: total automation of all workspaces and NAI "officers" might mean having no crew habitat at all. But I was at a payload mass fraction of 70% or better, so it obviously wasn't going to work.

I'll take a look after breakfast and get back to you.

I had a feeling it probably wouldn't be worthwhile. I do wonder how removing the engine room entirely changes things - it reduces crew requirements, and frees up space for more payload. The question is how much the -1 HT and the annoyance of having to do maintenance from outside the ship costs compared to the savings, and I have no idea how best to assess that.