Elon Musk's plan to colonise Mars involves tunneling robots and a nod to Deep Thought

Some call him the Tony Stark of our generation; others consider him to be a raving mad man. Whatever else you might think off him though, Elon Musk certainly knows how to fire up everyone’s imagination.Taking to Reddit for his latest AMA session (Ask-Me-Anything), Musk revealed a little bit more about his plans to colonise Mars. The AMA session was a follow up to his previous speech on "Making humans a multiplanetary species." You can read a full summary of his original announcement here, or simply watch the video embedded below.He started the AMA, by summarising his entire plan for Mars as follows:

• “Send Dragon scouting missions, initially just to make sure we know how to land without adding a crater and then to figure out the best way to get water for the CH4/O2 Sabatier Reaction.
• Heart of Gold spaceship flies to Mars loaded only with equipment to build the propellant plant.
• First crewed mission with equipment to build rudimentary base and complete the propellant plant.
• Try to double the number of flights with each Earth-Mars orbital rendezvous, which is every 26 months, until the city can grow by itself.”

The CH4/O2 Sabatier reaction that he’s referring to is a high pressure and temperature chemical reaction that will produce water and methane from carbon dioxide and hydrogen gas. This will, theoretically, supply the fuel and water for a sustainable Mars colony as well as for the rockets.Musk describes the initial permanent habitations as geodesic domes of glass and carbon-fibre. Interestingly, Musk expects an army of tunnelling robots to build pressurised tunnel systems for industrial operations. The domes, he claims, will be used for habitation only.On the topic of reusable booster rockets, he claims that the Falcon 9 booster rockets should be capable of being used “indefinitely.” This, he says, is because of the lower densitiy of the fuel mixture in the Falcon 9 stage.An intrepid Redditor also noted that the ICT booster (Interplanetary Colonial Transport) uses, prophetically, 42 booster rockets.“It had to be 42 for important scientific and fictional reasons!” said Musk.All things considered, this was an interesting AMA by Musk, albeit a very technical one. There's a lot more information to be gleaned from the AMA, so be sure to go through it in its entirety, it's worth a read.