Reaction Control System

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The Reaction Control System, or RCS, is a set of monopropellant-fuelled (with the exception of the Vernor Engine) thrusters primarily intended for vessel orientation in a vacuum. It is toggled on and off by pressing the R key (default key binding). In order to use RCS, a part containing monopropellant along with at least two RCS thrusters are needed. The fuel tanks for monopropellant are different from solid or liquid fuels tank, and currently come in five options, one for each radius, and two side-mounted types. Apart from the dedicated tanks there is some monopropellant also in command pods but not probe cores.

It should also be noted that the SAS system will make use of the thrusters. To avoid a constant drain of RCS fuel, it is recommended to not have both the RCS and the SAS systems enabled at the same time, unless you need to keep your ship dead level and/or have RCS fuel to spare.

In real life the RCS is used to control the attitude of a spacecraft rather than its orbital velocity.

Placement

The thrusters can be located anywhere on a ship. Unlike jet and liquid fuel engines, there is no need to place RCS thrusters on RCS fuel tanks or manually run fuel lines to them. The thruster block can provide full rotation control, whereas the linear port can only provide thrust in one direction. It is advisable to place the thrusters as far away from your centre of mass as possible, thus maximising the torque (turning force) they generate.

For the most effective control, it is typically most practical to place RCS thrusters with four way symmetry. In theory, you can provide suitable roll, pitch and yaw control with just one set of four way thruster blocks. Translation maneuvers are much easier when the thrusters for a specific direction are evenly distributed on both sides of the center of mass so they don't apply torque. This is usually accomplished with one set at the top and another at the bottom of your rocket. The SAS may dampen unintentional changes of heading during translation movement.

Beware, they will be fatally damaged if they brush against the ground.

Trivia

Between their introduction in 0.11 and 0.17.1 (including the old 0.13.3 demo), all RCS thrusters were massless and dragless, despite the CFG file values. Between 0.18 and 0.23 (including the 0.18.3 demo), RCS thrusters have the expected mass values. They were explicitly made massless parts again in 0.23.5.

Fuel

RCS Fuel Density is 4 kg/unit Mass
(t)
Monopropellant
(Units of fuel)
Image Part Radial size Cost
(Funds)
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
FL-R10.png
FL-R10 RCS Fuel Tank Tiny 200
(176)
0.10 0.02 2 000 12 50 20
FL-R25 FT.png
FL-R25 RCS Fuel Tank Small 330
(186)
0.56 0.08 2 000 12 50 120
FL-R1 Yellow.png
FL-R1 RCS Fuel Tank Large 1 800
(900)
3.4 0.4 2 000 12 50 750
Mk2 Monopropellant Tank.png
Mk2 Monopropellant Tank Mk2 750
(270)
1.89 0.29 2 500 50 50 400
Mk3 Monopropellant Tank.png
Mk3 Monopropellant Tank Mk3 5 040
(2 520)
9.8 1.4 2 700 50 50 2 100
Stratus-v roundified monopropellant tank.png
Stratus-V Roundified Monopropellant Tank Radial mounted 200
(176)
0.10 0.02 2 000 12 50 20
Stratus-V Cylindrified.png
Stratus-V Cylindrified Monopropellant Tank Radial mounted 250
(190)
0.23 0.03 2 000 12 50 50


Thrusters

Image Part Radial size Cost
(Funds)
Mass
(t)
Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
Thrust
(kN)
Fuel
(Units of fuel/s)
Isp (s) (atm) Isp (s) (vac)
RV-105.png
RV-105 RCS Thruster Block Radial mounted 45 0.04 1 500 15 50 1.0 0.11 100 240
Linear RCS.png
Place-Anywhere 7 Linear RCS Port Radial mounted 25 0.02 2 600 15 50 2.0 0.21 100 240
Vernor.png
Vernor Engine[Note 1] Radial mounted 150 0.08 2 000 15 50 12.0 0.94 140 260
  1. The Vernor Engine uses a liquid fuel/oxidizer mixture.


See also