Last year, billionaire SpaceX founder and space-fan Elon Musk delivered an expansive, hour-long presentation, outlining his ambitious plan to get humanity to the Red Planet. Musk has recently published a research paper adapted from that presentation entitled "Making Humans a Multi-Planetary Species".
The 15-page paper, published in the journal New Space, and available for free until early July, doesn't offer a great deal of new information that wasn't presented last year, but it certainly reads like a solid manifesto from a man who is very serious about colonizing our solar system.
"So how do we figure out how to take you to Mars and create a self-sustaining city," asks Musk, "a city that is not merely an outpost but which can become a planet in its own right, allowing us to become a truly multi-planetary species."
The paper is certainly a compelling read, covering in reasonable detail the engineering challenges in getting to Mars and the realistic costs per person. Musk also reiterates several exciting benchmarks in his timeline that will take us to Mars, with the first unmanned payloads being delivered to the Red Planet within the next two years.
"We are going to try to send something to Mars on every Mars rendezvous from this point on," predicts Musk. "We plan to send Dragon 2, which is a propulsive lander, to Mars in a couple of years, and then probably do another Dragon mission in 2020."
Musk is nothing if not ambitious, and his paper goes even further to examine the potential for traveling beyond just Mars. He envisions a series of in situ propellant depots, from the asteroid belt to Europa or Titan, allowing humanity full access to the greater Solar System.
"Therefore, you could travel out to the Kuiper Belt, to the Oort cloud," writes Musk. "I would not recommend this for interstellar journeys, but this basic system –provided we have filling stations along the way – means full access to the entire greater solar system."
Interestingly, Musk's paper does not investigate where geographically on Mars he proposes to start his settlement. Considering he may only be a few years away from beginning to transport payloads to the surface of the planet ahead of human visitation, this is presumably a vital detail to consider. Our investigations last year found three promising spots that could be ideal for humanity's first footprints.
While the paper is still probably a bit more utopian sci-fi than hard science, it is a great deal more detailed than the usual 140 character tweet-prophecies we usually get from Musk. Time will tell if Musk actually gets to Mars, but it is clear this is a man very excited about the prospect of taking humanity off-Earth, and he's willing to put his money where his mouth is.
Source: "Making Humans a Multi-Planetary Species", New Space
This module and associated experiments were cancelled: https://en.wikipedia.org/wiki/Centrifuge_Accommodations_Module
We should do such experiments first before even considering sending humans to Mars especially for long term stays.
If it turns out Mars gravity is insufficient then it is better to consider human colonies in various orbits than on the surface of Mars. With our current tech levels it is easier to fake suitable gravity in orbit/"space" than on the surface of Mars. In this scenario there wouldn't be much point orbiting Mars. You might as well orbit a suitable asteroid or the Earth.
The 5km/sec escape velocity of Mars and near zero atmosphere also will make it more expensive for trade and supplies.