Reaction Control Thrusters
Ships use Reaction Control Thrusters to manouver when in space.
The engines (Warp and Impulse) just provide thrust in one direction, the Reaction Control Thrusters allow the ship to turn in space so that the engines point in the correct direction. Typically the power provided by the thrusters is very small compared to the main engines.
When thrusters are placed on the outer hull they are capable of pushing away from the ship in any direction.
If there are enough this will allow the ship to be maneuvered in pitch, yaw and roll (all blue arrows) and to slide (green arrows) on the x, y and z planes.
These thrusters can provide movement in the following directions:
- Roll Port/Starboard
- Pitch Nose Up/Down
- Yaw Port/Starboard
- Slide Up/Down (Z axis)
- Slide Port/Starboard (Y axis)
- Slide Forward/Backwards (X axis)
Adding more thrusters will allow the ship to turn faster. Damaged or missing thrusters may affect maneuverability. Re-routing power to other systems may also hinder the maneuverability of your ship.
These are fired in groups to provide the following motions:
Note: Direction of thrust will produce movement in the opposite direction (i.e. firing a thruster up will cause the ship to be pushed down).
Desired Movement |
Port |
Starboard Rear |
Stern Thruster |
Bow Thruster |
Port |
Starboard Front |
Roll - port |
Up |
Down |
|
Up |
Down |
|
Roll - starboard |
Down |
Up |
|
Down |
Up |
|
Pitch nose up |
Up |
Up | Up |
Down |
Down |
Down |
Pitch nose down |
Down |
Down | Down |
Up |
Up |
Up |
Yaw - port |
Port |
Port | Port |
Starboard |
Starboard |
Starboard |
Yaw - starboard |
Starboard |
Starboard | Starboard |
Port |
Port |
Port |
Slide up |
Down |
Down | Down |
Down |
Down |
Down |
Slide down |
Up |
Up | Up |
Up |
Up |
Up |
Slide forward |
Aft |
Aft | Aft |
Aft |
Aft |
Aft |
Slide backwards |
Forward |
Forward | Forward |
Forward |
Forward |
Forward |
Slide port |
Starboard |
Starboard | Starboard |
Starboard |
Starboard |
Starboard |
Slide starboard |
Port |
Port | Port |
Port |
Port |
Port |
The above table shows the standard firing sequence of the thrusters in order to achieve the desired movement. There is nothing to stop the bridge officer from firing different thrusters manually which would produce a more complex maneuver (turning and sliding upwards for example). The simulator will work out all of the various thruster vectors to provide the final ship rotation and movement vectors. Some combinations may be counter-productive, such as firing the rear thrusters aft and the front thrusters forwards. Assuming that all thrusters are working at 100% health, the thrusters will cancel each other out and the ship will not move.
Furthermore each group has Primary Thrusters (powered from the ships power grid) and much less powerful Auxiliary Thrusters (powered by their own micro-fusion chambers).
The thrusters are used to turn the ship at impulse speeds or to perform precise maneuvers at slow speeds (such as docking with a starbase).
There is no reason that the layout of the thrusters has to be even. For cost or weight saving reasons, the ship could be configured to turn to port much faster than to starboard. This would allow faster evasive maneuvers in combat, but only to the port side.
Damaged thrusters will still operate but much less efficiently and will cause the ship to turn at a slower rate (compared with undamaged thrusters).
In case of total thruster failure, each primary thruster also has an auxiliary thruster backup. The auxiliary thrusters are capable of applying thrust equal to 1/20th of the thrusters normal maximum power.
These can be used in conjunction with the primary thrusters, but are usually left offline. The auxiliary thrusters are powered by their own micro-fusion chambers and do not need external power to operate. Damage affects them in exactly the same way as the primary thrusters (i.e. 2% reduction in efficiency for every 1% of damage), however they do not suffer from the same wear and tear issue that the primary thrusters have.
Power Requirements
Thrusters come in different sizes. To turn our 500 tonne ship 90 degrees to starboard in 10 seconds (assuming the ship is 100 metres long) the fore and aft thrusters would have to move 250 tonnes (assuming a 50-50 split in weight) through (2*pi*50)/4 = 78.5 metres in 10 seconds. Assuming 5 seconds of acceleration and 5 of deceleration we would need to achieve an acceleration/deceleration rate of 78.5/5! = 0.654 metres per second per second.
Assuming the thrusters have 50% efficiency this would require 0.654 * 250000 * (100/50) = 327 KW. To perform this maneuver we would need equal forces fore and aft, so the total power draw would be 654 KW for the 10 seconds of turning.
Doing the same calculation for our 1,000,000 tonne ship that is 600 metres in length we get.
Distance = (2*pi*300)/4 = 471 metres.
Acceleration/Decceleration = 3.925 metres per second per second
Power = 3.925 * 500,000,000 * (100/50) = 3.9 GigaWatts per thruster or 7.8 GigaWatts in total.
Realistically a large ship would have multiple thrusters, so it stands to reason that the maximum thruster size might be 1 GigaWatt.
The auxiliary thrusters are self-powered and do not require any external power.
Thrusters can be improved through technology and increase their efficiency (from 50% up to 100%), their weight, their resilience or the efficiency of the auxiliary thrusters.