The talk was bold for a couple of reasons. First, the plan itself is ambitious -- Musk hopes to fly 1 million people to the red planet as a sort of "backup drive" for Earth at cost of $100,000 to $200,000 per person. Second, he delivered the presentation weeks after a SpaceX rocket blew up on a launchpad.
Now Musk has written a new paper that outlines the most recent version of his Mars vision.
Published in the June issue of the academic journal New Space, the article appears to be an edited summary of Musk's September talk. (A full transcript of that, along with Musk's slide deck, is available here.) In the text, Musk describes his argument for reusing rockets to reduce the cost of spaceflight thousandfold. The paper also includes descriptions of early designs of the enormous spacecraft he hopes to build.
Although the recent publication does not present too many new details, several important events have happened since Musk's original presentation.
For one, Musk further elaborated on his Mars plans in October during an Ask Me Anything session on Reddit. He outlined a four-stage process to inhabit Mars, explained how he'd create fuel and air on the planet, and disclosed his name for the main spaceship: Heart of Gold, a nod to the book "The Hitchhiker's Guide to the Galaxy."
In the speech, Musk also disclosed the existence of a giant fuel tank for his Mars spaceship. That colossal tank, made entirely out of carbon fiber, passed a big pressure test in November, according to Musk.
SpaceX is also ramping up hiring. It had 473 open positions in March and 487 as of this posting, and many are dedicated to the company's Mars-exploration efforts.
And Musk's company is gearing up to launch its biggest launch system ever: Falcon Heavy. In a tweet on June 8, the SpaceX CEO said the first super-heavy-lift rocket could take off as soon as September.
If all goes according to plan, the Falcon Heavy could whisk two paying customers around the moon in 2018.
This post originally appeared on Business Insider.