Preserving monopropellant

[GungaDin]

Before I ever added rcs thrusters and monopropellant I was able to pitch and yaw just using the gimbal on my rear engine. Now that I've added the extra thrusters and some monopropellant - is there any way to preserve that fuel and save it for translating and braking? (I understand that I must use it when I press the IJKL keys.)

[Dave Kerbin]

As long as you don't turn it on it won't be used. Press R to toggle RCS on or off, you'll see the RCS indicator on the navball opposite SAS if it is turned on.

[Tank Buddy]

You also could set an action group to toggle the RCS, but that would be the same as pressing the R key.

[GungaDin]

As long as you don't turn it on it won't be used. Press R to toggle RCS on or off, you'll see the RCS indicator on the navball opposite SAS if it is turned on.

Ahhh! So stupid! Thanks. (Man these boards are great - I just got an answer in 5 minutes on a Saturday night!)

[RSwordsman]

Can't you also selectively disable RCS blocks? If you don't need all of them for rotation, this could also be an option. (I haven't done it personally so can't say for sure, but it stands to reason. )

[Captain Sierra]

Can't you also selectively disable RCS blocks? If you don't need all of them for rotation, this could also be an option. (I haven't done it personally so can't say for sure, but it stands to reason. )

This is true, and it can be done via right click, or via action groups for more symmetrical toggle.

[Claw]

But you can't disable them selectively for rotation vs. translation. You are only allowing or disabling a given port with the tweakables.

[undercoveryankee]

MechJeb's RCS balancer has a setting to use RCS for translation only. That's something like what you're looking for.

[Luckfish]

You can also attach monopropellant tanks in both lower and upper stages, and right-click to disable the upper stage tanks, effectively saving that fuel for later in the mission.

[eurybaric]

I like the idea of routing them to action groups ! havent thought of that! cool possibilities thanks guys!

Cheers!

[eurybaric]

But you can't disable them selectively for rotation vs. translation. You are only allowing or disabling a given port with the tweakables.

true, and that would be cool if there was a feature for that actually. But for now, you can do that if you build your own RCSystems using the linear ports... hmm... thinking outloud here hehe but I can see something cooking here

Edited February 16, 2014 by eurybaric
clarifying

[Dispatcher]

There are also reaction wheels in pods (or stand alone), which will allow you to save a little monopropellant.

[Kryxal]

If you want to use the linear port for forward translation and NOT allow rotation, you'll need to have the engines mounted off the centerline, of course ... or you can just say "I don't need RCS THERE, I have LOTS of thrust!"

[Geschosskopf]

Before I ever added rcs thrusters and monopropellant I was able to pitch and yaw just using the gimbal on my rear engine. Now that I've added the extra thrusters and some monopropellant - is there any way to preserve that fuel and save it for translating and braking? (I understand that I must use it when I press the IJKL keys.)

RCS has 2 primary uses: rotating huge, long ships and lifters, and translating small-ish ships for docking. Often, the same ship needs to do both at different points in its flight. In use, RCS draws fuel from all tanks equally so the issue is always making sure the payload keeps its RCS tanks full despite RCS use during ascent to rotate the lifter.

There are several ways to do this, all of which require some intervention on your part. But all methods require additional RCS tanks on the lifter, which supply the fuel for pre-docking RCS use.

Method 1: Tweakables

This method is stock. In the VAB, right-click on the payload's RCS tanks and turn them off. During flight, these tanks won't be used so the payload will have full RCS tanks upon separation of the final ascent stage. However, you'll now have to turn these tanks back on, either by right-clicking them or assigning that to an action group. NOTE: in the VAB, tweaking follows symmetry so if you have multiple tanks installed via symmetry, 1 tweak will turn them all off. But in flight, you have to turn on each tank individually with right-clicks unless you assign them all to the same action group.

Method 2: MOAR Boosters

This method is also stock. Make your lifter a bit over-powered so the last ascent stage is still attached to the payload after the circularization burn. Then, prior to jettisoning this stage, manually pump mono from the ascent tanks to the payload tanks. Has to be done individually for each payload tank. But OTOH, you can also put a probe core in the ascent stage, so that after separation, it can use its remaining fuel to deorbit, thus eliminating debris.

Method 3: Pumping During Ascent--STOCK

This can only be done stock if both the payload and the ascent stage have only 1 mono tank each, which normally means using the in-line tanks, which are way overkill for most purposes. Anyway, before launch, use ALT-right-click to set up mono to flow into the payload tank, then launch. The drawback here is, not only are you having to lift more weight than you need, but you'll have the ugly right-click menus on top of your rocket during the whole ascent, and you can't move the camera without stopping the process and having to restart it.

Method 4: Pumping During Ascent--Modded

Here, you have TAC Fuel Balancer or something similar. Before launch, set the payload's tanks to transfer in, then launch. The advantages over Method 3 are that this works regardless of the number of RCS tanks involved so you can use little ones, you don't have right-click menus visible the whole time, and can freely move the camera without stopping the pumping.

Note that in general, even mondo lifters won't need more than 2, maybe 4, of the small, roundified RCS tanks.