any way to set exact amounts on fuel transfer?

[king of nowhere]

so i am assembling a big ship in orbit, and i am using recoverable launchers to do the trick. they get into orbit as ssto with a 20 ton payload, i take the payload, deorbit and recover them.

some of the payloads weren't exactly 20 tons, or perhaps i did fly them especially well, anyway, i still have a couple tons of fuel in them. i want to transfer them to the orbiter before undocking. but i don't want to drain the tanks completely, as the launcher still needs enough to deorbit and get recovered.

and here is the difficulty. because when i start the fuel transfer, the numbers zip by very fast, and i can't stop them with any reliability. i would live to leave 45 fuel and 55 oxidizer in the launcher (which uses rockomax jumbo tanks), while transferring everything else in the orbiter (which uses many mismatched tanks in the 5-20 ton range).

it took me a dozen tries of transfer, stop, reverse, stop, transfer again, stop again, always trying to hit the right moment, until i eventually managed some satisfying results: 40-44 in one launcher, 45-56 in the other. but i really think there should be a better way to set up fuel targets during transfer.

is there a better way?

 

P.S. i now realize i also have a small 1-ton tank on a probe attached to the main ship, i could empty the launcher completely, then refill it with the whole content of the small tank, then refill the small tank from one of the larger tanks. still not ideal. and considering the bug every time you transfer fuel, which in my case requires reloading to fix, this method is also time consuming.

[Grogs]

33 minutes ago, king of nowhere said:

so i am assembling a big ship in orbit, and i am using recoverable launchers to do the trick. they get into orbit as ssto with a 20 ton payload, i take the payload, deorbit and recover them.

some of the payloads weren't exactly 20 tons, or perhaps i did fly them especially well, anyway, i still have a couple tons of fuel in them. i want to transfer them to the orbiter before undocking. but i don't want to drain the tanks completely, as the launcher still needs enough to deorbit and get recovered.

and here is the difficulty. because when i start the fuel transfer, the numbers zip by very fast, and i can't stop them with any reliability. i would live to leave 45 fuel and 55 oxidizer in the launcher (which uses rockomax jumbo tanks), while transferring everything else in the orbiter (which uses many mismatched tanks in the 5-20 ton range).

it took me a dozen tries of transfer, stop, reverse, stop, transfer again, stop again, always trying to hit the right moment, until i eventually managed some satisfying results: 40-44 in one launcher, 45-56 in the other. but i really think there should be a better way to set up fuel targets during transfer.

is there a better way?

 

P.S. i now realize i also have a small 1-ton tank on a probe attached to the main ship, i could empty the launcher completely, then refill it with the whole content of the small tank, then refill the small tank from one of the larger tanks. still not ideal. and considering the bug every time you transfer fuel, which in my case requires reloading to fix, this method is also time consuming.

As far as I know, no. Maybe some mods will let you do do that.

I usually try and have a small tank on my stations for just the purpose you're describing. Maybe something that's about 10% of the size of my fuel tankers seems to work pretty well. Then I can completely drain the tanker, fill the small tank, and transfer from the small tank back to the tanker. That's about enough to get the tanker from say LKO back to Minmus to refuel. The fuel transfer bug makes it more of a pain to be sure.

[jimmymcgoochie]

I would suggest you add a small additional fuel tank to the launcher which contains just enough fuel to deorbit it, then set that to not get drained during the ascent. The extra mass might hurt your payload capacity slightly, but it also means it’s really easy to fill up just enough fuel to return to the surface without a complicated juggling act.

Or you could try using a mod to record a launch and then reuse the recorded flight instead of having to fly each mission yourself. You would only have to get it right once that way and then you’d be able to automate it in future.