Delta-v calculations and mixed fuel loads/engines

[ElWanderer]

Two linked issues:

1. Refuelling by hand often leaves an uneven mix of fuel/oxidiser. Our delta-v calculator assumes all that fuel is usable and gives an inflated impression of the delta-v available as a result. This is even more true when launching a spaceplane where you may aim to have plenty of LF leftover (or indeed end up with an excess of OX due to underestimating how much LF would get used during ascent).

2. The calculator does not understand that if you have a mix of LF/OX and a mix of nukes/other engines, that there is effectively a staging event once the OX runs out. In this case, it underestimates how much delta-v is available. Mixed loads such as running Ion engines alongside anything else would be another case of this, though one I'm happy to ignore for now.

The first of these was mentioned in #164, though it wasn't tackled then. Since I've started messing about with spaceplanes, it seems a lot more important.

[ElWanderer]

If we have an engine, e:

LOCAL all_consumed_resources IS e:CONSUMEDRESOURCES.
FOR key IN all_consumed_resources:KEYS {
  LOCAL cr IS all_consumed_resources[key].
  LOCAL fuelName IS cr:NAME.
  LOCAL fuelRatio IS ROUND(cr:RATIO,5).
  LOCAL fuelMassFlow IS cr:MAXMASSFLOW.
  // store the total mass flow (excluding intake air)?
  // store the mass flow for each engine?
}

From there, it's a case of working out how much mass we want for each resource. The total mass requirement for each fuel can be used to determine which fuel we will run out of first. The combined fuel-rate is also useful for the delta-v calculation.