Colony mass driver (aka space guns)

[Strawberry]

There's been a lot of talk regarding space infrastructure, such as space trains or space elevators. Personally I dislike most of these proposals because they tend to circumvent game features more then they expand on them. Instead of designing a rocket to send materials up to orbit, you just select the space elevator launch pad and you're in orbit now. Space train falls into this issue as well because it'd be hard to make a space train designer that's integrated with the rest of the game. I do think there's one major piece of space infrastructure that can integrate itself with a lot of game systems organically though.

Mass drivers/space guns have been a frequently discussed topic for sending large amounts of payloads up to orbit cheaply. These are large and expensive pieces of hardware, but capable of saving loads for resources. Personally, I think this game would benefit from two types of mass drivers, but first lets establish some commonalities in function between the two. The first commonality will be some colony behavior.  When fired, mass drivers will consume large amounts of energy and produce lots of heat all in a short burst. This means you have to build the infrastructure to support the energy and thermal loads from a mass driver. Launching from a mass driver will be as simple as selecting the mass driver launch pad, you can also select the exhaust velocity of the mass driver with power consumption scaling alongside it. Each type of mass driver will have a mass and/or size limit as well. A spacecraft will first spawn in/on the mass driver, with the same orientation as how the mass driver is pointed.  Then, the mass driver will simply make the spacecraft move with the exhaust velocity of the space gun in the direction of the orientation. This means that if you do this in an atmosphere, if you're not careful you can overheat your spacecraft. Now, with all the common behavior established, lets get onto the differences.

The first space gun you will unlock will be a light gas gun in the style of project harp. This part is expensive but requires simple materials.  The barrel (thus max exhaust velocity), is constant. This space gun needs hydrogen to fire. This space gun will consume any excess power to pressurize this hydrogen to get the gun ready to fire, when fired this hydrogen will be gone.  This means the demand for the burst of power is lessened, thus less energy infrastructure is required, however the inefficiencies in this will lead to more heat being generated. This space gun can also be reoriented freely, giving it a lot of versatility. With the small barrel, the spacecraft has tight size and mass restraints, with the max diameter being 1.25 meters. The fast acceleration of this means that any craft will have to be unmanned. This gun is best suited for the early days of colonies, requiring minimal infrastructure to support it, however its versatility with orientation gives it a unique edge later in the game when you want to do things like a single launch to get from a moon to a planet.

The second mass driver you unlock will be a linear railgun. This railgun will be expensive, and require fancy materials to make. This railgun would be modular, you can add additional railgun units to the end of it to increase the length thus the max velocity. This railgun has a few downsides. It accelerates much slower then a light gas gun, meaning you need a longer track. It is also linear, the direction it is constructed will be the only direction it can launch a vehicle at, this means that this works best when built around slopes. The railgun only consumes energy as well, this is both an upside as it means you don't need to waste hydrogen, but its also a downside as it means you need more energy infrastructure to support it. To make up for this, this comes with plenty of upsides as well. The size requirements are practically removed, allowing much larger launches. This gun is also more energy and heat efficient compared to the light gas gun. The lower acceleration also means that you can allow kerbals to fly on this thing without them turning into mystery goo. The railgun is best suited for built up colonies, the linear nature could in some situations could require colonies built on the slope of craters just for launching goods, and the increased need for energy infrastructure can complicate things. However the increased energy efficiency means that it can increase the efficiency of orbital delivery, and the ability to launch large manned missions from this is also very useful. This would also be highly useful to launch planes as well.