Tractor Beams

A starship uses tractor beams to manipulate objects that are in close proximity to it, such as towing other ships or bringing objects into the shuttle bays. The shuttle bays have their own tractor beams that are used to assist with launches and landings - these are separate from the systems described here.

Tractor beam emitters can be placed on the outer hull of the ship. Each emitter can only tractor one item at a time. Multiple emitters can be locked together to hand over items from one tractor beam to the next to allow for items to be moved around the ship. 

Objects that are under tractor beam control can be moved in any of the 3-axis (X, Y or Z). The operator can enter the desired co-ordinates either as part of the galactic grid or relative to the ship (e.g. 100Km off the port side). The tractor beam will calculate how fast it can move the object and will move it at the maximum possible velocity, up to a maximum of 100 meters/sec². This formula will also have to take into account decelerating the object as it approaches the desired location.

If an object cannot be moved (because of size/distance or because it has engines powerful enough to overcome the tractor beam), then the tractor beam will break off. Note: Speed is measured as relative to the player's ship. So if an object is stationary and the player's ship is traveling at high speed, then the ship might not be able to apply a sufficient change of speed in the object before it travels out of range.

Once an object is locked on by the tractor beam it can be rotated in any direction.

Each tractor beam emitter can be damaged. This has no effect on the system until the health drops below 50% at which stage that tractor beam will stop working.

Damage to the tractor beam emitters will cause a loss of efficiency down to 50% health (at which point it will stop working as mentioned above).

Power Requirements

Tractor emitters come in a variety of sizes from 100MW to 2 TerraWatts. They are 50% efficient - therefore if 1 GigaWatt of power is fed to the a transmitter, then the tractor beam will only have a strength of 500 MegaWatts. The power usage of the tractor beam can be restricted to conserve energy. 

Upgrades

Research can be used to increase the efficiency of the tractor beams.

Dev Notes

The shuttle bay tractor beams have a range of 10km and are capable of pulling and pushing objects to/from the individual shuttle bays. Any manipulation of the object being tractored (to bring it in the right way up) is done automatically (unlike the ship tractor beams which can turn the object as the operator wishes). Shuttle bay tractor beams are typically 1 GigaWatt maximum.

Before we discuss tractor beams we need to explain what we mean by force. The formula for force is mass times acceleration in Newtons. 1 Newton can accelerate (or decelerate) a 1 kg object by 1 meter per second, every second. That is if our 1 kg object was stationary and you applied a 1 Newton force to it for 5 seconds, at the end of the 5 seconds it would be travelling at 5 meters per second.

Most of the objects we deal with are measured in metric tonnes. A metric tonne is 1,000kg, and so would require 1,000 Newtons to change its speed by 1 meter per second, every second.

With 50% efficiency at turning power into the tractor beam force, for every Newton of force applied, 2 Watts of power need to be supplied to the tractor beam emitter.

The amount of force that can be exerted from the tractor beam is given by the formula:

Force in Newtons =  (PowerInWatts * Efficiency/100)/ Distance² (in KM)

If the distance is smaller than 1km then it is treated as 1km to prevent massive amounts of force being exerted on close objects. 

This means that a 2 GigaWatt tractor beam locked on an object with mass of 1,000,000 metric tonnes at 1km distance could be imparted with a change of speed of 1m/sec².

At a distance of 10km this would be reduced to

(2,000,000,000 * 50/100) / 100 = 0.01m/sec².

So the force drops off significantly with distance.

Of course for every action there is an opposite and equal reaction, so if we are applying the 1m/sec² acceleration to the object we are actually applying 0.5m/sec² acceleration to the object and 0.5m/sec² deceleration to ourselves (assuming our ship weighs the 1,000,000 metric tonnes). That would be a massive ship, so assuming the player ship is "only" 100,000 metric tonnes, then the target object would have it's speed changed by 0.1m/sec² acceleration and the player ship would be pushed away at 0.9m/sec² acceleration. The net result is a change of 1m/sec² acceleration as viewed from the players ship. 

This is un-important if we are using the tractor beam to move an object towards or away from the ship, but is of vital importance if for instance we are trying to change the course of an asteroid. 

In this scenario, thrusters or impulse engines would have to be used to offset this movement, especially if the player ship is significantly smaller than the object being tractored.

Now that we know how much force the tractor beam can apply, we need to understand how this relates to simulated objects. A Galaxy class starship has a mass of 397,805 metric tonnes. At a range of 1km the ship could use a 4 GigaWatt tractor beam to tow another Galaxy Class sized vessel at a maximum acceleration of 5 metres per second per second. In this scenario the tractor beam would be set to keep the distance between the two ships constant at 1km and the thrusters would be fired to provide acceleration to both vessels of 5 metres per second per second.

However using a 1 TerraWatt tractor beam would increase this value to 125 metres per second per second.

This effectively means that the tractor beam cannot restrain a large ship under its own impulse power, however it would be able to restrain a shuttle.