I'm not sure he has a plan. In an interview he talked about dropping nuclear weapons on the pole, but it was an off the cuff remark which I am pretty sure was meant to be taken humorously. Many scientists pointed out soon after that it couldn't work, just not enough power in nuclear weapons to do it, even if there is enough ice / CO2 which is also unknown. This was my answer here on Quora which I also did as a science blog post.
He later on said that he meant lots of nuclear weapons exploding continuously to form a mini sun above Mars or some such, which is a way out science fiction idea we are nowhere near able to do at present. See Elon Musk Clarifies His Plan to "Nuke Mars"
Whether we can terraform Mars or not, the most optimistic estimates make it a thousand year process to get to the point where trees can grow there, which would however also involve some way of keeping it warm, as even an Earth pressure atmosphere of pure CO2 at distance of Mars would not keep it warm enough for trees to grow. You'd need to either use space mirrors comparable in area to the planet itself (which is possible perhaps using thin film mirrors, but a big mega project), or else, lots of greenhouse gases, really large scale production, mining cubic kilometers of material a century, every century, to make the gases and many nuclear power stations on Mars whose sole task is to provide power for making the greenhouse gases to keep the planet warm (which though a mega project again, may be easier than the idea of space mirrors of total surface area millions of square kilometers to double the amount of sunlight on Mars - cross sectional area of Mars is about 144 million square kilometers so you'd need at least that much by way of mirrors to double the radiation)
That's the conclusion of scientists who have studied this in some detail - especially Chris McKay has done some detailed papers on the requirements for terraforming Mars.
And it's also making some optimistic assumptions about the amount of CO2 on Mars. We only know of enough CO2 there to double the thickness of its atmosphere. To get started on a runaway CO2 warming would require ten times the thickness of its current atmosphere - and it can only get as thick as the amount of CO2 there permits. Based on what we know for sure at present, it could only get to 2% of Earth's atmospheric pressure. Well below the Armstrong limit of 10% below which humans need pressurized suits because even with oxygen masks the moisture in their lungs would boil and you'd die quickly without a pressurized suit. And because 1% is a point of stability then even 2% would not be a stable atmosphere - it would soon re-condense at the poles, so to keep it at 2% would require mirrors or greenhouse gases being produced continuously.
It's a big mega engineering project. And that's the "easy way" to do it. I think it is far too soon to think about actually starting on such a project, given that we find it hard enough to keep a space project going for a couple of decades never mind a thousand years.
There's also lots to go wrong. And the thing is, we could do things like accidentally introduce lifeforms to Mars right now that could cause problems for terraforming later on if they find an easier way to do it. And it gets in the way of scientific investigation - can't study Mars as it is now, if there are people who are busily trying to turn it into something else - e.g. things like the dry ice geysers, and especially the search for life and present day life on Mars - if it exists, what it is like etc
See my Trouble With Terraforming Mars
As far as I know he hasn't published or talked in any detail about such ideas. Or about life support for that matter for the human crew for missions to Mars, or dealing with problems of zero g or artificial gravity etc. He's a rocket person, focusing on the issue of how to send large amounts of mass from Earth to Mars. I suppose he probably thinks the other problems will sort themselves out once you've worked out how to send lots of mass there.
But - I don't think he has detailed ideas at all for what happens next. If he has, he hasn't shared them publicly as far as I know. The Mars Society think that it is possible, but they think in terms of a thousand year project to get to the point of air breathers and vegetation, and several thousand years after that to get to the point of an oxygen rich atmosphere (Chris McKay thinks 100,000 years), which they think is eventually possible, of course maintained using mirrors and greenhouse gases to keep the planet warm. An atmosphere breathable by humans would have at most 1% CO2, because CO2 is poisonous to us, it's not just lack of oxygen that kills when you have too much CO2 in the atmosphere - you can die of CO2 poisoning with plenty of oxygen.
So then - a breathable atmosphere has at most 1% CO2, with the rest oxygen and some buffer gas, perhaps nitrogen though whether Mars has enough nitrogen is again dubious and would require extracting it from nitrate rocks. So it would be much less warming than a pure CO2 atmosphere so you would need to step up the greenhouse gas production or use more space mirrors at that point.
As you can see, the science fiction ideas of the Mars Trilogy involve a fair bit of poetic license,speeding up the Mars Society ideas from 1000s of years to a few generations and ignoring a fair number of technical difficulties. As is of course very common in Sci-fi. In the interests of a good story.
About the Author
