I was thinking a bit
(..I hate when that happens) to come up with special situations where definitely each of the 3 possible calculation routes would be practical.
Maximizing for speed:
- Fighters that operate in a mothership's active sensor coverage. Here you have a pretty set range (to the edge of the given sensor range, back, and then a tiny bit extra), and the propulsion mass assignment is likely predetermined already too, because the weapons take a fixed part. I would actually need that for my current game.
- In case of a game with a working interstellar fuel network or sizable oiler fleets: Military ships would need only need a very low fixed range here (much lower than than the usual 20-30% fuel in the propulsion part), so maximizing the speed with that low requirement will provide fruitful.(and is otherwise difficult to determine by hand - ..you end up wasting research into engines that weren't quite fitted)
Minimizing mass assignment(/maximizing mission tonnage):
- Ships that operate in a fleet. If you have to cross-sync different designs of cruisers, destroyers and frigates, it could be a waste to have them go at different speeds or ranges. So to give them equal capacities and then figure out how to maximize their mission component tonnage, this is very useful.
- Generally the way of choice if one has very organized fleets and likes round numbers.(my current capital{+survey} ships for example all aim for exactly 5kps speed and about 300b range, so here I would apply this calculation)
Maximizing for range:
- Small jump or stealth scouts whose size is predetermined through the jump engine or cloak size, and the mission component size is fixed as well. The remaining percentage of mass needs to be ideally utilized in right fuel:engine ratios and power factors, so that you get the most out of the scouts.
- A speed goal comes up, because of observation on enemy designs. Ships get readjusted to have pretty much the same design in matters of total mass and engine to mission ratios, but you need to figure out how exactly to rework the already known propulsion part so that the speed goal is achieved.
There are likely more uses, and occasionally even normal design routines can use one or the other. Missiles specifically can easily fall in any of the three. LR Torpedoes might for example be more a case for the speed solver, because a range requirement and payload is likely already set, but generally every missile could be eligible for any case.(I assume most will do either speed or range optimization, because the payload needs to be determined so accurately {/squares} in most cases)
As stated by Vandermeer, the 5/7 rule of really just something to go by to simplify things. If we were to try and get an exact answer here, it would be tough, due to circular referencing.
This happens because the total engine size is based on the total mass wanted minus the mass of the fuel. To find the mass of the fuel, you need to find the EPH, and to find the EPH, you need a per engine size, which is based on the total engine size. This just keeps looping on itself, which can cause calculation errors.
Oho, but wait, that was the point there in my answer from above: It is possible. The circular reference is often a nuisance, but in this case for once it can be bridged with the method I described above and also put to paper(?) in the other calculator. The reason this works is because maximized single-engine-sizes
always lead to the better solution (since the fuel ratio is always better), so no need to worry about fields of answers or circular recalculation. You just make a list where that maximum possible single engine component is determined for every power factor, and then
