Some thoughts on mining kethane from Asteroids.
Right now, it's possible to just give asteroids a flat amount of kethane storage, although it is not aware of the size of the asteroid. Hopefully, a workaround will eventually exist, and it could potentially add some degree of randomness, since some asteroids should have lots, and others might have none. However, I decided to work out how much kethane asteroids could conceivably hold.
I assume for this that asteroids have a consistent density and that all asteroids of the same class have about the same volume. I also assume that the outer 2.5 meters of rock, no matter how solid it is, will eventually lose all its kethane to evaporation/sublimation. The remaining body of the rock might be up to 25% "kethane slush" by volume (as I've determined through the highly scientific method of "guessing"), and I assume that any displaced mass is present as either denser surrounding rock or projections of stone on the surface.
A and B class asteroids are too small to retain kethane, but that's only if we assume that kethane requires 2.5 meters of solid rock to stick around. Since we really can't assume much about the orbits asteroids take- players might send them solar skimming, frankly- I'm not going to do blackbody radiation calculations to determine how much kethane they should contain. If you want to give it a try, go right ahead. If you estimate one meter of surface rock, then even A-classes can have a little kethane.
Class C asteroids mass 100 tons- using the average density (derived from the information on the wiki), that's a diameter of 9.3 cubic meters. Subtracting 5 (For a 2.5 m thick layer), that's 4.3m, or 333 cu. m of gas storage space. That works out to about 1.3 orange tanks worth of kethane, which sounds about right.
Class D asteroids mass 400 tons, with a diameter of about 15m, porous d of 9.7, which is 3823 cu. m, about 15 orange tanks.
Class E asteroids are 3000 tons, and have a D of 30. That works out to 65450 cu. m, which is about 250 orange tanks. Yes, 250.
That's all assuming the absolute maximum total capacity. I'd assume that there would be a bell curve of most asteroid having about 50% capacity, with a few that are naturally empty, and a very rare set that are naturally full.
You can use similar calculations to derive the amount of ore from extraplanetary launchpads. I'm assuming that about 10% of the average asteroid by mass would be rich enough to qualify by ore (I know that many asteroids are c-type asteroids with no iron or other ores, EXPL uses one type of ore for everything so we obviously are dealing with some simplifications), so that means that an A-type is 0.04% of a full storage tank, B-type is 10%, C-type is 66%, D-type is 2.5 tanks, and E-type is 20 tanks. However, these aren't maximal values; In fact, having asteroids have wildly varying ore densities, they could have anywhere from 0% to 100% ore; there's quite a few naturally occurring asteroids that are made entirely of nickel-iron. Finding a Class-E motherloade would be a fun event, assuming you can find a way to slow 6000 tons of high-grade ore.