[Spaceships] Are spaceships unrealistically cheap?

Michael Thayne · 07-22-2017, 07:03 AM

Now I'm curious if we can actually model missiles with scaled-down SS rules. There are going to be issues with e.g. the fact if the jump in delta-V between 28cm and 32cm is due to more stages, damage should temporarily plateau due to a smaller warhead, but let's see how close we can get.

A 24cm missile, as a spaceship, would a 2dHP impactor, because it does 6dx6 damage and collision damage is 6d x 3 x dHP. It weights 1/4 of a ton loaded into the battery. That's approximately SM+1, which ought to have 5 dHP. So the impactor should have an SM 2 levels lower than the missile loaded into the battery.

If the warhead is itself a single SM+1 system, then at TL7-8 a single-stage design has sixteen fuel tanks (plus two engines, the warhead, and a control room), for 4.8 mps delta-V, below the Spaceships 3 performance. But a TL9+ HEDM design needs 2.5 engines for 5G acceleration, so it has 15.5 fuel tanks, and 13.95 delta-V—better than the stats given in Spaceships 3!

If the warhead + control systems are a full upper stage (six systems), instead we have 11.5 fuel tanks for an HEDM missile with 5G acceleration, which together give 8.05 mps delta-V. Packing 2 mps delta-V into the upper stage, however, only requires devoting about a third of the upper stage to engines / fuel.

So not sure spaceships missiles can quite be built with spaceships itself, but it feels like we're within the realm of "generous rounding" here. The vast cost mark-up is hard to justify. The lower stage of our HEDM missile is only going to cost around $10k per ton of complete missile, so unless warheads are very expensive or the markup for a slightly more compact design is 100x, the numbers just don't work.

(Actually, I'd never done the price math explicitly before, it looks worse than I'd thought.)

07-22-2017, 07:03 AM	#12
Michael Thayne Join Date: May 2010	Re: [Spaceships] Are spaceships unrealistically cheap? Now I'm curious if we can actually model missiles with scaled-down SS rules. There are going to be issues with e.g. the fact if the jump in delta-V between 28cm and 32cm is due to more stages, damage should temporarily plateau due to a smaller warhead, but let's see how close we can get. A 24cm missile, as a spaceship, would a 2dHP impactor, because it does 6dx6 damage and collision damage is 6d x 3 x dHP. It weights 1/4 of a ton loaded into the battery. That's approximately SM+1, which ought to have 5 dHP. So the impactor should have an SM 2 levels lower than the missile loaded into the battery. If the warhead is itself a single SM+1 system, then at TL7-8 a single-stage design has sixteen fuel tanks (plus two engines, the warhead, and a control room), for 4.8 mps delta-V, below the *Spaceships 3* performance. But a TL9+ HEDM design needs 2.5 engines for 5G acceleration, so it has 15.5 fuel tanks, and 13.95 delta-V—better than the stats given in *Spaceships 3*! If the warhead + control systems are a full upper stage (six systems), instead we have 11.5 fuel tanks for an HEDM missile with 5G acceleration, which together give 8.05 mps delta-V. Packing 2 mps delta-V into the upper stage, however, only requires devoting about a third of the upper stage to engines / fuel. So not sure spaceships missiles can quite be built with spaceships itself, but it feels like we're within the realm of "generous rounding" here. The vast cost mark-up is hard to justify. The lower stage of our HEDM missile is only going to cost around $10k per ton of complete missile, so unless warheads are very expensive or the markup for a slightly more compact design is 100x, the numbers just don't work. (Actually, I'd never done the price math explicitly before, it looks worse than I'd thought.)