Reserve monopropellant for translation

[THX1138]

I have a limited amount of monopropellant which I want to reserve for translation. I want the attitude to be controlled using reaction wheels since the electrical supply is renewable. I want SAS to control the attitude while I translate using my limited monopropellant supply. I don't want SAS dipping into my monopropellant supply when the electrically powered reaction wheels should be adequate. Am I alone in this? Currently I have to switch off SAS, switch on RCS, do some quick bursts, switch off RCS, switch on SAS; repeat x 50. Is there some way to cut off SAS' access to the RCS system?

Edited January 10, 2015 by THX1138

[Taki117]

Unfortunately there is not as far as I know.

[Anquietas314]

In short, no. It's all or nothing with RCS/SAS, at least for now. It's possible there's a mod out there somewhere, but in my experience unless you're flying some absurdly large ship, it shouldn't be a serious issue to just leave both on while docking. It's rare that I don't have craploads of spare RCS fuel if I add RCS tanks to the ship - if I don't, then usually I can dock with just the capsule's fuel, but the margin's generally too close for my liking. The trick's to be careful and not overdo it

EDIT: I should add that you don't often need RCS at all for most designs unless you're docking. Very large ships are obviously an exception, but in most cases one or two reaction wheels appropriate to the ship size are more than sufficient for maneuvering.

Edited January 10, 2015 by armagheddonsgw

[LethalDose]

I want the attitude to be controlled using reaction wheels since the electrical supply is renewable. I want SAS to control the attitude while I translate using my limited monopropellant supply.

I have wanted this feature for almost as long as I've played the game, and this isn't the first time I've seen it mentioned. Tweakables would be perfect for this, e.g. tweak RCS engines to activate on translation and/or attitude adjustment.

[Red Iron Crown]

If you are a MechJeb user there is a function that does exactly that. Agree it would be useful stock functionality, I made a suggestion thread about this very thing.

[tater]

You can hold the f key while you are using RCS, as that kills SAS while held down, right?

[Anquietas314]

You can hold the f key while you are using RCS, as that kills SAS while held down, right?

Technically yes but then you have a problem if you're using a USB keyboard and want to press 3 keys at once other than F (for example, to move up, left and forward at the same time).

[Red Iron Crown]

You can hold the f key while you are using RCS, as that kills SAS while held down, right?

Still using monoprop for attitude control then. OP wants attitude control by reaction wheel only but RCS for translation. Only way in stock is to toggle R as needed.

[LordFerret]

Curious about this, I just now tested something out... and it worked. I assigned all reaction wheels (capsule, SAS) to Action Group 1, and then assigned all RCS ports to Action Group 1 also. Then, out on the launchpad, prior to launch, I manually clicked on the capsule and SAS and toggled them off... actually, I had to do it twice... but the end result was (with RCS "R" key and SAS "T" key turned on) I could toggle the states - one on with the other off - with a single keystroke.

Does that help any for what you're looking for?

[tater]

Oh yeah, forgot about that. That'd only turn it off for translation, then it uses both for attitude.

[Anquietas314]

LordFerret: OP basically wants to be able to leave SAS on, but have it use the reaction wheels only, even with RCS active, with the idea being to have SAS hold the ship still "for free", while using translation controls to move left/right/etc.

[LordFerret]

Oh yeah, forgot about that. That'd only turn it off for translation, then it uses both for attitude.

No, in one state only reaction wheels work... in the other state only RCS thrusters work. One or the other.

- - - Updated - - -

LordFerret: OP basically wants to be able to leave SAS on, but have it use the reaction wheels only, even with RCS active, with the idea being to have SAS hold the ship still "for free", while using translation controls to move left/right/etc.

Yes, I understand that. But being that can't be done, I figured the next best thing was to reduce the 'turn this on that off, then that off this back on' to one keystroke. :/

[OhioBob]

I want the attitude to be controlled using reaction wheels since the electrical supply is renewable. I want SAS to control the attitude while I translate using my limited monopropellant supply.

I don't want SAS dipping into my monopropellant supply when the electrically powered reaction wheels should be adequate. Am I alone in this?

You're not alone. I always prefer SAS for attitude control. I'll include RCS only when translation is needed.

Currently I have to switch off SAS, switch on RCS, do some quick bursts, switch off RCS, switch on SAS; repeat x 50.?

I don't see the need to switch off the SAS. I usually keep the SAS on all the time while I toggle only the RCS on and off.

Is there some way to cut off SAS' access to the RCS system?

One thing you can try doing is to not use the 'RV-105 RCS Thruster Block'. Instead use the 'Place-Anywhere 7 Linear RCS Port'. Place four of them around the ship's center of mass pointed radially outward to provide translation. With this positioning the thrusters don't provide any rotation, thus they won't fire when rotating.

[Anquietas314]

One thing you can try doing is to not use the 'RV-105 RCS Thruster Block'. Instead use the 'Place-Anywhere 7 Linear RCS Port'. Place four of them around the ship's center of mass pointed radially outward to provide translation. With this positioning the thrusters don't provide any rotation, thus they won't fire when rotating.

I'll just add that this only works if your center of mass won't shift (much) due to fuel consumption, or you can accurately predict where it will be when you're docking. I have used that thruster arrangement a few times though with varying degrees of success , though I used the thruster blocks (RCS thrusters are expensive... linear ones more so).

[THX1138]

I don't see the need to switch off the SAS. I usually keep the SAS on all the time while I toggle only the RCS on and off.

I have to switch off the SAS because if I don't it will be using my monopropellant until I disable RCS. The SAS is really inefficient on my large rockets.

A suggestion thread already exists for this request so if you also want this feature, please leave a comment in that thread so maybe it will be considered for inclusion.

Edited January 10, 2015 by THX1138