RCS - why use it?

[EasyAce]

Hi guys,

Probably this has been mentioned before, but couldn't find it.

I've made some probes and ships but never got further than Minmus. Reason is that I like to "do it real" by establishing Communications and safe travels for my Kerbals before launching them on Hazardious missions. Thanks to RemoteTech, several other Mods and the update frequancy of the game, I never have found the time to travel further before I need to start over. (Patches)

Anyway, that was a digression, what I've noticed is that I do not need RCS at all... my probes and ships is able to turn in space even without RCS thrusters.

(Maybe I haven't built big enough...)

Why???

Is it a glitch? Is it one of my Mods that makes is possibe?

I whish it wasn't possible. I sort of makes the game somewhat unrealistic for me.

I do understand it is possible in the atmosphere... and by using gimbal engines... but what annoys me is that I am able to turn outside the atmosphere and with no engine active.

Do someone have any comments about this?

[Aphox]

The SAS logic in the next version may or may not change your experiences with turning.

However, RCS is predominantly used for translation (movement) in space, usually to dock. Using engines to dock is painful because you have to spin back and forth and it takes time that you don't have doing close maneuvers like that.

Unless you're a psychopath and have engines pointing both directions.

But yeah, RCS is more for docking than turning. But it really helps on large vessels. There's a lot of designs you'll discover that require RCS to turn around.

[SargeRho]

Reaction Wheels. Plenty of probes and sattelites use those IRL.

[bsalis]

It's not a bug. RL craft use reaction wheels too.

Don't attach RCS if you don't need it.

[EasyAce]

The SAS logic in the next version may or may not change your experiences with turning.

However, RCS is predominantly used for translation (movement) in space, usually to dock. Using engines to dock is painful because you have to spin back and forth and it takes time that you don't have doing close maneuvers like that.

Unless you're a psychopath and have engines pointing both directions.

But yeah, RCS is more for docking than turning. But it really helps on large vessels. There's a lot of designs you'll discover that require RCS to turn around.

Reaction Wheels. Plenty of probes and sattelites use those IRL.

I didn't know about Reaction Wheels before now

Looked it up on wikipedia and it seems pretty ordinary.

Ok, so I guess my time attaching RCS and RCS Thrusters to small probes, that are not intended for docking, is over.

RCS for docking is, as you say, very much needed.

Weight saved is TWR and dV gained

[Domfluff]

Docking and turning large ships are the main reason - especially large unmanned vessels, since the probe bodies have far less torque.

RCS can also be very handy for orbital maneouvres, especially with small craft - each radial fuel tank masses 0.235 tons and each RV-105 block masses 0.05 tons, so you can easily build for tight tolerances, if you needed a probe to rendezvous, or change their orbit - say, launch to LKO on a small booster, air-launch or SSTO, then boost itself up to geostationary (keostationary?).

Early on, I also found linear thrusters to be extremely useful for accurate landings on the Mun. This became less important as I improved, but if you wanted to land *on* something (say, another vessel) then that's the most sensible option.

Edited July 17, 2013 by Domfluff

[ASnogarD]

I found a few of my rockets dont turn well at all without RCS, mostly the unmanned ones but a few manned ones as well... the 'magic torque' wasnt enough, even with extra SAS modules. These craft were heavy bruisers though, about 100 - 130 tonnes fuel delivery ships (3 full orange tanks full , 3 nukes each with a FT800 tanks to fuel them).

My docking practise craft has a emergency retro rocket system, small rockets that are toggled with a action group that switches off one set of engines and fires another set (so if you were firing mains and hit the action group button, it would switch off the mains and fire the retro rockets, and visa vera... no chance of firing both sets at the same time). I put that in just as a means to try avoid collisions with the station I used to practise docking with, its not much use as a retro grade burn engine as the retro rockets are a bit small for full burns.

My RCS is used mostly for docking, I cant even use RCS for Mun landings as I always forget which way to fire the RCS to correct and found it easier to use the landers main engines to cancel lateral movement instead.

[stupid_chris]

I found a few of my rockets dont turn well at all without RCS, mostly the unmanned ones but a few manned ones as well... the 'magic torque' wasnt enough, even with extra SAS modules. These craft were heavy bruisers though, about 100 - 130 tonnes fuel delivery ships (3 full orange tanks full , 3 nukes each with a FT800 tanks to fuel them).

That's because probe cores produce much less rotational power than command pods do and because SAS modules produce no torque whatsoever to help turn your ship around. Just magic stuff to help it stop when you activate them.

[SRV Ron]

My biggest probe rockets need thrusters for maneuvering during the early stages of a long range interplanetary mission. Otherwise, the ASAS can handle the job in the later stages when most of the launch vehicle has been discarded. I keep a thruster pack and tank on the probe stage and can use that for small moon landings with thruster fuel to spare. I use a second tank on the upper stage for the rocket maneuvers but need to disable the probe tank so that it doesn't get drained first during those maneuvers.

[Sma]

As others have said, it's not really needed for smaller probes, but it does help you turn faster with bigger ships/probes/stations(on the rare occasion you want to reposition it). They do also help a lot when docking or landing on low gravity bodies, like Minmus. I think I also read about landing purely on RCS I think at Pol or Bop, forget which one. I haven't been out much further than Minmus my self.

[Moon Goddess]

If I understood the notes about .21 correctly we'll be getting proper gyros soon, so we'll not really be needing RCS as much except for translation.

[bsalis]

If I understood the notes about .21 correctly we'll be getting proper gyros soon, so we'll not really be needing RCS as much except for translation.

It's just pod torque renamed to reaction wheels. Details to be seen.

What we do know is that they will require electricity, so RCS may be more important than before.

[The Lone Wolfling]

RCS in real life is used to desaturate reaction wheels / CMGs.

In KSP, gyro saturation isn't modeled, so they aren't as needed.

That being said, RCS is invaluable for docking.

[Vanamonde]

For very small probes, you can use RCS as your main propulsion, even if you don't need it for attitude control.

[SlyReaper]

Unless you're a psychopath and have engines pointing both directions.

I have done this.

[Francesco]

also, RCS is handy for fine-tuning your orbit, for example during interplanetary transfers which involve aerobraking/aerocapture, for which a high degree of precision in setting your periapsis is required.

[Mr Shifty]

Other uses:

* I've used RCS as secondary propulsion when my fuel ran out. Made it from a suborbital Moho liftoff to orbital rendezvous at 10km using only RCS one time.

* I also often use it for de-orbiting fuel tanks; that way I don't have to leave a tiny bit of liquid fuel in them.

* It can be useful for re-positioning landers on low-grav worlds particularly if your engines are high-thrust.

* And I've used it to fine-tune geosynchronous orbital periods to the second.

[spikeyhat09]

Other uses:

* I've used RCS as secondary propulsion when my fuel ran out. Made it from a suborbital Moho liftoff to orbital rendezvous at 10km using only RCS one time.

* I also often use it for de-orbiting fuel tanks; that way I don't have to leave a tiny bit of liquid fuel in them.

* It can be useful for re-positioning landers on low-grav worlds particularly if your engines are high-thrust.

* And I've used it to fine-tune geosynchronous orbital periods to the second.

i landed a probe on Dres using only RCS for the whole mission

[BubbaWilkins]

Most of my larger craft have too much mass for pod torque or reaction wheels to significantly control them. RCS is a requirement on anything of sufficient size.