IMPORTANT!

The craft contains 3 main parts - the vacuum drive, the atmosphere drive and a navigation computer. The latter contains a program that calculates a brachistochrone trajectory (AG7) to the selected target (it uses vizzy++ bc I couldn't find a way around it). Basically, it has the craft accelerate halfway and decelerate the other half, accounting for the relative speeds. The program isn't perfect so if you end up too far from your desired location you can activate the computer again to move closer (don't worry, it has a failsafe so as not to crash into planets). When making a ship make sure that it can accelerate at 10m/s^2 or more and can turn around in less than 30 seconds.
The atmospheric engine has an aerospike nozzle and so has around 100 000 Isp at any altitude. The vacuum engine performs much better in a vacuum at around 1 000 000 Isp but is trash in an atmosphere (don't worry, those are realistic numbers, I checked). The invisible engines are there for the visuals, they provide nearly 0 thrust. Also, both engines work during timewarp and the program drops you out of it automatically when required.
There is also a script that maxes out your acceleration to 10 m/s^2 (1g) for crew safety. AG6 allows you to accelerate at up to 10g for when you need to (provided you have enough TWR).
If you encounter any bugs in the program or find ways to make it better please let me know)))