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 Rear	Starboard Rear	Stern Thruster	Bow Thruster	Port Front	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.

 

Dev Notes

 

The calculations required to work out how the thrusters effect the ship will take time. Therefore they will only be ran when the mass of the ship changes (due to damage?) and they will be ran on a separate thread.First off teh calculation will find the center of balance of the ship (both lengthwise and width wise). We did think of applying a factor based on distance from the center of balance but have decided against it. We will assume that the thruster nozzles rotate to counter whether they are close to the center or far away from it.

Thhruster values are cumulative, but must be balanced to provide smooth movement. For example: If both the port and starboard rear thrusters are working at 100%, and they can work together to roll the ship at 10° per second (one firing down, the other firing up). However if the port thruster is only operating at 50% percent efficiency, then in order to roll smoothly the starboard thruster will have to output 50% power as well otherwise the excess thrust will push the starship up or downwards.

It’s worth explaining that last phenomenon as it is very important in spaceship physics. With a sea bound ship on earth thrusting starboard from the bow of the ship would rotate the ship because the resistance of the water is stopping the rear of the boat from moving as quickly. However there is no resistance in space, so firing the bow thruster to starboard will just move the whole ship sideways (with no rotation). In order to rotate the ship we would have to fire an equal amount of thrust from the rear of the ship in the opposite direction to cause it to rotate around its center point. If we can only push half the thrust out of the rear, then we will still rotate (at half the speed) but the excess thrust from the bow thruster will move the ship sideways (which of course will be a changing vector as we are now rotating, thus moving the ship in an arc).

 

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Like most ships systems the systems start at 100% health. Reduction to this health through lack of maintenance or damage will reduce the efficiency of the thruster which may make the ship hard to manoeuver. Thruster efficiency is reduced at the rate of 2% reduction for every 1% health lost. i.e. A thruster with 75% health would only be able to provide 50% of it's full power rating. When a thruster reaches 50% health it is inoperable and must be repaired.

 

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For every 1 minute of operation for each thruster there is a 1% chance that its health will drop by 1% due to wear and tear. This is reflective of the fact that the thrusters are not meant to be used as a long term method of transport.

The comms protocol from the user interface will allow either manual thruster control for programs that wan that refinement or automated thruster control - such as move the ship forward 100 metres at docking speed (i.e. very slowly and accurately).

Something we need to consider is where we are measuring the ship from. i.e. If the ship is docking with another ship we need to select the two docking ports we want to match up so that maneuvering can be carried out relative to them. First off would be "Match Speed". Then "Close to 5 metres". Then "Close to 1 metres" then "Close to 0 metres".