Probes launching off of main ship with no fuel or mono

[queloggs]

I built a long range ship that launches multiple probes. My problem is that when my probes launch, there is no fuel or mono in them. I do not have external fuel lines running to them (next course of action) so I suspect that they are being drained in the stage. Going to try external fuel lines but does anyone else have a suggestion in case this does not work. Thanks for the suggestions! Once I get these last bugs taken care of I'll post design to the ship exchange thing.

[The_Rocketeer]

Beginning with the obvious...

Does the large ship definitely have fuel/monoprop remaining when you launch your probes? If so you can top up the probe tanks by alt-right clicking the tanks and doing a manual fuel transfer.

If you haven't already invested a lot of time in the mission, you could start again from launch and make sure that the tanks in question are shut off, also by right-clicking the part and clicking the little button next to the fuel level indicator.

Unless it's been changed in a recent patch, fuel/monoprop shouldn't cross over decouplers, so if you're using docking ports you could consider replacing them.

A few pictures of the craft in question showing how the probes are undocked and the respective tank levels would be an advantage.

[cantab]

For monopropellant, the game tries to drain the lowest stages first. Fuel lines have no effect. That's fine for a single rocket, but will cause decouplable probes to lose their monoprop before the main ship. The resolution is to disable fuel flow from the probes' monoprop tanks, by right-clicking them (either in the VAB or flight) and changing the green arrow to a red no sign.

[bakanando]

This happens when the ships are docked to the main ship. The fuel of this probes will normally be further away than most other tanks and thus the ship will use it's fuel before other ones. There are some solutions to this:

You can disable this in the dock, but it's not persistent.

Another solution is to trasfer the necessary fuel before undocking (mod+click on both parts, check the wiki).

You could also just disable every tank in the probes before launch so their fuel is not spent until you need it.

[LethalDose]

Unless it's been changed in a recent patch, fuel/monoprop shouldn't cross over decouplers, so if you're using docking ports you could consider replacing them.

Monoprop will cross decouplers. It's been that way since at least 0.24, and I think 0.23.5. Cantab is correct that it drains from lower stages first.

The fuel (presumably LF/O) issue sounds like a docking issue, it does not cross over decouplers. The best solution is, again, what cantab suggested: lock the fuel and oxidizer tanks.

[Claw]

The fuel (presumably LF/O) issue sounds like a docking issue, it does not cross over decouplers. The best solution is, again, what cantab suggested: lock the fuel and oxidizer tanks.

Fuel actually will transfer through a decoupler, if the child part connected to the decoupler allows crossfeed and is not a fuel tank. The decouplers are actually crossfeed capable, but have a small bit of special case logic that stops the crossfeed if it's a fuel tank connected to the jettison side. This is something that often bites people when they use things like cubic struts to connect to a decoupler.

Monopro has been a "transfer to anywhere on the ship" type resource for many versions. It wasn't until recently (either 0.23.5 or 0.24) where it was set up so that it drains from the latest stages first. Xenon works the same way.

Cheers,

~Claw

[bakanando]

Fuel actually will transfer through a decoupler, if the child part connected to the decoupler allows crossfeed and is not a fuel tank. The decouplers are actually crossfeed capable, but have a small bit of special case logic that stops the crossfeed if it's a fuel tank connected to the jettison side.

You learn something everyday.

Is this mentioned/tested anywhere? Never heard of it before.

[Red Iron Crown]

You learn something everyday.

Is this mentioned/tested anywhere? Never heard of it before.

In this thread. An example here.

I believe it only applies to radial decouplers, but am not 100% sure.

[LethalDose]

Fuel actually will transfer through a decoupler, if the child part connected to the decoupler allows crossfeed and is not a fuel tank. The decouplers are actually crossfeed capable, but have a small bit of special case logic that stops the crossfeed if it's a fuel tank connected to the jettison side. This is something that often bites people when they use things like cubic struts to connect to a decoupler.

Im not going to argue the point, because I trust both Claw and RIC on this.

But this is some serious WTF logic. The devs really need to clean up their code.

[DeathSabre]

I've had problems with cargo ssto's using fuel from their cargo in the past. the best solution I had was to clip your camera through the cargobay/ or open it on the runway/launchpad.

and disable the fuel in them so nothing can use that fuel.

just be careful if you disable electricity on your probe. that you re-enable it before undocking/decoupling your probe from the SSTO or you will have an unusable piece of junk in orbit.

[cantab]

Last I checked you could enable and disable resources without control, or has that been changed?

[Claw]

Last I checked you could enable and disable resources without control, or has that been changed?

I also have not checked recently, but as far as I know it hasn't been changed.

Cheers,

~Claw