So during my free-time I've thought up of a total conversion. The premise is to give a player a greater range of freedom as to how they will colonize Mars and to add more realism as well as feel you are running a space company.

The main focus would be the tech-tree, in the start you would only start off with late 1960's, early 1970's technology, which would comprise of a small impactor probe, an early digital camera, an SSTV transmitter, and a rocket capable of taking the probe to the moon.

You will progress by first building orbiting satellites then sending probes and finally landers and rovers to map out and research the locations on the targetted body, then you you have to unlock Mars, and do the same. Finally you will have other targets you can unlock and explore like Vesta, Venus, Phobos, and Titan (as well as the other locations already in game) which would also can send satellites, probes, and landers to.

Venus wouldn't be accessable to manned missions simply due to how horribly corrosive, hot, and thick the atmosphere is combined with its near Earth-like gravity. It wouldn't be worth it or safe in the time-frame of this game.

As you progress through tech levels you will unlock 4 different manned exploration programs that you can research depending on how eager you are to send manned missions out:

-The first option will allow you to research and send a manned mission to the moon to build an outpost with 70's-80's-early 90's tech which will then after a few missions develop into a moon base and allow you to research and build a mass driver to send manned missions to Mars and else-where. There would be no 3D printers so you would have to rely inflatable habitats, supply missions and eventually build bulky mining, refining, and part making machines to supliment. (until you later research the 3D printer)

-The second would be like the first only with 90's to modern day technology, again you would not have a 3D printer and would have to rely on supply runs, inflatable habs and large equipment to make parts.

This would also let you develop the Mars Direct sub-plan, if you choose to, that would allow you to skip building a mass driver and go directly to Mars where you would build an outpost which would eventually become a full fledged base. It would be based around the Mars Direct plan.

-The third option would be a Mars One like option, it would be near future and be cheap compared to the others but would consist of you being dropped off on Mars with meager supplies, a small lander, and a 3D printer and told good luck. :P

-The forth would be a near future focus and include the vanilla game tech.

The end game would be building a craft on Mars, Phobos, or Deimos which will take a manned mission to Vesta and Titan. Titan would be resource and fuel rich but you would have to be cautious with the Methane atmosphere since if your base or pressurized vehicle was to leak, a fire or spark could trigger a catastrophic explosion that could rip the entire base apart.

Some other things the mod would have is that you would have to test out landers, rovers, and manned craft at either the Mars Yard or at a desert or artic location since you wouldn't want to send an expensive craft out into the unknown not knowing if it even works. :P

(More ideas, crafts and locations that could be used will be posted here later on.)

=Edit: I removed the Soviet/NASA design proposal since that would add too many craft and would have to be a mod itself. Plus I started to feel it wouldn't fit in with the concept of the game.