What is the RCS for?

[Sprachenheitz]

I'm not sure if someone asked this question before,but what is the RCS for

so far I have no clue on what it does and I' not sure what it is for 

P.S thank you for the answers

LIVE WELL AND PROSPER FELLOW KERBONAUTS!!!

 

[Superfluous J]

There is too much, so I'll just link you to the wiki page on Reaction Control Systems for KSP.

[Venusgate]

Short answer: Controlling which direction your craft is pointing through RCS ports fueled by monopropellant. Sort of like SAS, but using monopropellant instead of electricity and magic

[Starhawk]

RCS is used for controlling the attitude of vessels in vacuum.  RCS thrusters placed in combination as well as some RCS propellant will allow the vessel to turn in space without the engine running.  Reaction wheels are also used for this purpose and turn the vessel at the cost of electricity instead of RSC propellant.

RCS thrusters are also used to translate the vessel while docking.

Happy landings!

Edited May 4, 2016 by Starhawk

[Plusck]

R.C.S. - Reaction Control System.

Basically - small rockets using reaction force (i.e. expelling propellant at high speed) to push the rocket the other way.

A mini version of spacecraft RCS is what a jetpack is - tiny rockets pushing your astronaut about in space (see the film Gravity).

It is used mainly for attitude control (rotation of the ship) and translation (going sideways).

Before you get to use RCS, rotation is done using fins (in the atmosphere) and torque wheels in the cockpit (most useful in space), and by directional thrust from the main engines. However torque wheels are not very effective on anything but the lightest of ships, the main engines have to be running to have any effect, and fins are useless in space.

RCS is more powerful, and has the added advantage of allowing movement in all directions.

 

To use it, you need Monopropellant - basically a propellant that contains both fuel and oxidiser together which burn when passed over a catalyst. It's slightly less powerful than LF-O per unit of mass, but more convenient in the small quantities required for RCS.

And for very small probes (and Kerbals on EVA), it can replace engines entirely, especially if you dont have any tiny rocket engines available and don't want to go too far (because again, it is always somewhat inefficient, and monoprop is heavy).

Finally, RCS also requires little plumbing, so can be attached anywhere on a ship and will use whatever monopropellant you have on board. Just press "R". Then use WASD for rotation and IJKL HN for translation (IK: up down; JL: left right; HN: forwards backwards).

Edited May 4, 2016 by Plusck

[Wemb]

10 hours ago, Sprachenheitz said:

I'm not sure if someone asked this question before,but what is the RCS for

 

As the others have said - It's designed (invented) for fine control of translation and rotation that generally cannot be done, or be done easily, with the main engine. It's principal application is for assisting with docking where extremely accurate control of attitude and velocity is vital, but it can be used to help in many other areas such as landing, launch stability, or even to replace a main engine if needed.

This is a brilliant video of the Soyuz TMA-19M mission to the ISS last year where the automatic docking failed and had to be done manually by the commander.  you can see at  ~3:50 onward the RCS thrusters on the soyuz capsule firing to help keep the capsule aligned in the right direction for docking, and at 4:35 firing to reverse the capsule and back away from the ISS.

 

Wemb

Edited May 4, 2016 by Wemb

[Servo]

RCS is a stronger method of controlling how your ship points/moves. You fuel RCS thrusters using monopropellant (which cone in manned pods and in special tanks), and the thrusters can be placed anywhere on your vessel.

RCS has two main purposes: control and docking.

Most large ships are unwieldy and hard to control without lots of SAS wheels. Using RCS thrusters, it can be turned easily. R turns on the thrusters, and WASDQE control the ship's rotation.

The other function is docking. RCS allows for precision control in three dimensions. Docking is a thing for another time, but using IJKLHN, you can translate your ship up/down, left/right, and forward/backward.

[Foxster]

Just for info...I never use RCS except for docking. I prefer to use reaction wheels for attitude control on every type and size of craft. They are light and don't run out of fuel ever - as long as you have enough electrical power, but that's what RTG are for. 

It's pretty essential for docking though. With RCS jets fore and aft you can move the craft sideways and backwards+forwards in small amounts. 

[bewing]

One caveat, though: RCS is nice, but it is not absolutely necessary. It is possible, once you are quite good at piloting and docking, that you can do all your maneuvers with only reaction wheels and your main engine.

[Wemb]

Not in the strictest sense, no.  The problem comes if you get any sort of off-axis translation when you're trying to dock - and if your vessels are moving in circles round planets, this is quite likely. Correcting for this with a reaction wheel and main engine isn't so much difficult as very time consuming and unwieldy as it requires you rotate the entire ship in the opposite direction of the drift and then burn to correct and then turn back to the target.  Attempting to do this when you're 10 seconds from a docking is almost certain to be disastrous in some way. 

Wemb

[Plusck]

2 hours ago, Wemb said:

Not in the strictest sense, no.  The problem comes if you get any sort of off-axis translation when you're trying to dock - and if your vessels are moving in circles round planets, this is quite likely. Correcting for this with a reaction wheel and main engine isn't so much difficult as very time consuming and unwieldy as it requires you rotate the entire ship in the opposite direction of the drift and then burn to correct and then turn back to the target.  Attempting to do this when you're 10 seconds from a docking is almost certain to be disastrous in some way. 

Wemb

This is one reason to put docking ports on the bottom on your landers, since that makes it easier if you want to make do without RCS.

One of my proudest moments: no RCS, having to slide by another ship with only inches to spare due to docking port location, and in the dark. proof!

Edited May 5, 2016 by Plusck

[bewing]

4 hours ago, Plusck said:

One of my proudest moments: no RCS, having to slide by another ship with only inches to spare due to docking port location, and in the dark. proof!

I hate how 50% of the time, you have to dock in the dark! Sheesh. Or maybe it's more like 80% of the time. It certainly feels like more than 50%. I'm coming in nice, and suddenly *poof!* There goes the sunlight.

Somebody needs to make all the planets transparent.