Propulsion Tech Tree

Propulsion technologies are absolutely essential to modern space exploration. Without these advances there would be no way for ships to get around, both at slower-than-light speeds and faster-than-light speeds.

## Technologies in the Propulsion Branch

#### Ion Drive

* Prerequisites: None
* Posts: 0
* Ion drives propel a ship by expelling ions out of the engine. They are extremely fuel efficient, but do not have much thrust.

#### Liquid Fuel Rocket

* Prerequisites: None
* Posts: 0
* A liquid rocket fuel is burned out of a nozzle, providing thrust. Extremely basic engines. They are not particularly fuel efficient, but provide a lot of thrust.

#### Gas Core Nuclear Rocket

* Prerequisites: None
* Posts: 0
* A powerful and efficient engine that uses the exhausted coolant of a gaseous fission reactor as a form of propulsion. There are two forms of Gas Core engines, open-cycle and closed-cycle. Open cycle engines do not contain the radioactive fuel within a vessel, and as such some fuel will leak out with the propellant - this makes open-cycle engines dangerous to operate close to planets because of the radioactive nature of the exhaust. Closed cycle engines contain their fuel inside of a vessel separated from the propellant, resulting in minimal fuel loss and little radioactivity of the propellant itself. The disadvantage of closed-cycle designs is that the material making up the vessel will eventually be destroyed due to the intense heat of the fission reactions taking place inside - as a result, the operating temperature (and therefore the power) is not as high as open-cycle designs because otherwise the walls would be destroyed too quickly.

#### Solar Sail

* Prerequisites: None
* Posts: 10
* Solar sails are a form of slower-than-light (STL) propulsion which rely on the solar wind of a star. The sails "catch" this solar wind and move the ship, much like how terrestrial sails would move the ship due to the terrestrial wind. This form of "engine" requires no fuel or power to use (and can in fact serve to generate power), but they are fragile when in combat and you are at the solar wind's mercy.

#### Fusion Rocket

* Prerequisites:  Fusion Reactor (Power technology), Plasma Containment (Weapons technology)
* Posts: 30
* Fusion rockets work by directing the exhaust products of a fusion reactor out of the engine. They are extremely fuel efficient and can generate high amounts of thrust, but require what is essentially their own personal fusion reactor (which cannot be used to generate power, only for the engine).

#### Warp Drive

* Prerequisites: None
* Posts: 20
* Warp Drive is a form of FTL travel which creates a "bubble" of distorted space-time around a ship, allowing for speeds exceding c (the speed of light) to be achieved. Inside the bubble, the ship does not actually exceed the speed of light. Early Warp Drive enables ships to traverse up to 0.4 LY/day. Not quite as fast as other forms of FTL, but by far the simplest and safest.

#### Interdimensional Drive Theories

* Prerequisites: None
* Posts: 15
* Investigations into the feasibility of FTL travel via other dimensions such as Hyperspace. While not enough to create functioning FTL of this type, it provides a way to get there.

#### Hyperspace Drive

* Prerequisites: Interdimensional Drive Theories
* Posts: 30
* A Hyperspace Drive pulls the vessel into a dimension called hyperspace, which enables the ship to travel faster than light. In hyperspace, ships are able to accelerate beyond c, and the effects of acceleration are greatly increased. As a result, vessels inside of hyperspace can theoretically accelerate to infinite speeds. Without vastly improved technology, however, the Hyperspace Drive itself will prove to be a bottleneck, because at high velocities the dimensional bridge which allows the ship to safely travel through hyperspace may collapse. In the best case scenario, this will result in the ship being ejected from hyperspace and the drive being "blown", requiring replacement. Depending on the speed of the vessel when the bridge collapses, however, it may result in the ship's complete destruction. Early Hyperspace Drives only remain stable up to speeds of 0.6 LY/day; ships can keep accelerating beyond that, but the faster the go, the more at risk they will be for destruction or stranding.

#### Ripspace Theory

* Prerequisites: Interdimensional Drive Theories
* Posts: 25
* Scientists have come up with a theory of an alternative dimension known as "Ripspace" in which the laws of physics are vastly different from our own. Ideas on how to open "tears" into Ripspace have been formulated, but attempts will prove difficult.

#### Ripspace Breaching

* Prerequisites: Ripspace Theory
* Posts: 30
* Crude methods of breaching the dimensional gulf between our dimension and the mysterious Ripspace have proved fruitful, as scientists succesfully create small, controlled Ripspace tears inside of laboratories. Accessing ripspace has proven extremely power-intensive, as well as hazardous due to powerful energy currents which are present at the "edge" of the tear. Scientists believe that Ripspace could be useful as a form of FTL drive.

#### Ripspace Drive

* Prerequisites: Ripspace Breaching
* Posts: 35
* Methods of opening large Ripspace Tears have been discovered and refined enough to be put to use as a form of Faster-Than-Light travel. The Ripspace Drive works by opening a tear into Ripspace and generating a protective Physical Field around the ship, which ensures that the ship itself continues to be subject to our laws of physics rather than those present in Ripspace, and protects the ship from the powerful and deadly energy currents. Venturing inside of Ripspace requires the use of active energy shields to protect against the massive amounts of radiation present inside. If the shields fail, the crew will be bombarded with gamma radiation at levels high enough to negate almost all radiation shielding. Communication is impossible with vessels outside of Ripspace. Ripspace travel, though highly dangerous and power-intensive, is very fast in comparison to most other FTL drive types. It also presents advantages in that pursuit through Ripspace is impossible if the pursuing vessel is not equipped with a Ripspace Drive and that the course of the ship cannot be determined via sensor scans. These early Ripspace Drives are only capable of sustaining the Physical Field at speeds of up to 0.8 LY/day.

#### Massive Engines

* Prerequisites: Massive Reactors (Power technology), Reinforced Superstructure (Industry technology)
* Posts: 30
* Allows the upscaling of existing engine technology to meet the needs of large ships.

#### Warp Bubble Geometry

* Prerequisites: Warp Drive
* Posts: 30
* The geometry of the warp bubble is further optimized, allowing for an increase in speed of Warp Drives to 0.7 LY/day.

#### Reinforced Dimensional Bridge

* Prerequisites: Hyperspace Drive
* Posts: 35
* The bottleneck of hyperspace travel is always the dimensional bridge which is required in order to link the vessel to hyperspace. The dimensional bridge would previously only be stable up to speeds of 0.6 LY/day before the possibility of collapse became a concern, but new advancements have served to strengthen the link between realspace and hyperspace. The bridge is now stable up to 0.9 LY/day.

#### Ripspace Navigation

* Prerequisites: Ripspace Drive
* Posts: 40
* Ripspace has long been difficult to navigate, with the powerful and deadly energy currents proving to be significant obstacles - vessels which went too fast were in danger of being unable to avoid them. New sensors allow for better navigation of the chaotic dimension, allowing safe travel up to 1 LY/day.