Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

Thanks. Understood.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

A lot, yes. Most of them are very simple if you wanted to do them, but they would add up.

The easiest approach would probably be to keep track of remaining delta-V and use that when needed to calculate remaining fuel fraction, then remaining total mass, then maximum acceleration.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

On the other hand the TL7 chemical rockets in Spaceships produce 0.15 mps/tank, implying an effective exhaust velocity of 3 mps. Rocketdyne F-1 engines had an effective exhaust velocity of 1.83 mps in vacuum (1.64 at sea level), which would give less than 0.1 mps per tank.

That comes down to the F-1 burning kerosene and LOX, whereas the TL7 chemical rocket is probably based on a LOX-LH₂ upper stage or shuttle main engine with less thrust but better specific impulse, more suitable to operations in space.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

TQ I love this kind of info.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

In general Spaceships is a tad generous with rocket performance, mostly because if you aren't generous it will be inordinately difficult to design something useful (in part because it really is inordinately difficult, in part because the design simplifications of Spaceships makes it even harder).

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

I've seen the SpaceX Merlin engine listed at 150 to 1.

There's also no magic in any given number of Gs. The shuttle had to throttel back when it hit 3 Gs because of mechical limits of the vehicle. A Titan II second-stage carrying a Gemini capsule ended its' burn at just under 7 GS. So did an X-15 rocket plane.

The msot important thing to remebr is that though Spaceships does give you a G number and a Delta-V figure that you can use in combat those things are mostly calculated on an average per mission basis not as second by second simulation.

What does Spaceships do to simulate how your Gs of thrust go up as you burn fuel and/or how your fuel use goes down as mass decreases while holding a given aceleration? It averages your acceleration and fudges your Delta-V with that adjustment in the Fuel tank section for the number of tanks.

Spaceships is a simple system, an abstact system and not a second by second simulation. Even Ve2 wasn't really and it was far more complex than Spaceships.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

There is a reason why 'rocket science' is an analogy for something that is really, really hard. It is a highly complicated field that has to take into account four dimensional space-time, material sciences, aerodynamic drag, gravitational drag, etc.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

This is another of those weird occasions where somebody tries to defend Spaceships by painting it as doing something much worse than what it actually does.

The text of Spaceships indicates to me a really clear understanding of the breakpoints and other factors that make a 'mission average' acceleration a largely useless number. Furthermore, if that's what it was trying to do it would be obviously doing it wrong since the mission average mass obviously depends on the fuel fraction while the Spaceships' acceleration values do not.

Deciding that key statistics will not be subject to frequent recalculation even if logic suggests maybe they 'should' is an understandable and familiar GURPS game design choice. It doesn't need to 'justified' as an ill-concieved 'abstraction' of things the game does not in any way treat as abstract.

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

When I've compared the figures of the engines from Spaceships with those of real engines from the Atomic Rockets website, Wikipedia, and my copy of Humble, Henry, & Larsen Space Propulsion Analysis and Design I've found that the figures in Spaceships are pretty accurate representations of some real engines, prototype, or detailed proposal. mps per tank is close to 1/20 times exhaust velocity; acceleration per system is close to 1/20 times thrust-to-weight. And that table for adjusting delta-vee for large propellant fractions has correct values from Tsiolkovsky's equation. That's all as it ought to be for the system to represent the performance of the spacecraft fully loaded. Delta-vee is adjusted for vessels with large propellant fractions, but acceleration is not adjusted for partly-unloaded vessels — probably because that would be fussy and complicated.

I've seen a couple of issues arise because of the choices of what engines to represent. In this case it seems that the figures are correct for a hydrogen-burning orbital engine, and so don't match a kerosene-burning launch engine (which might be represented as a sort of "high thrust" option). In a recent thread I found that the stats for the TL7 fission rocket match NERVA or Pewee (which reached test-firing prototype stage) but underestimate what was expected from DUMBO (which was cancelled because of a political decision).

Re: [Spaceships] It seems that TL7 Chemical Rocket's acceleration is an overspec.
 

hmm... well, I got it.