For many people human beings walking on Mars, much less building permanent colonies there, is still science fiction. Elon Musk is not one of those people.

In a 2007 interview with Wired magazine Musk said “The ultimate objective is to make humanity a multiplanet species. Thirty years from now, there’ll be a base on the moon and on Mars, and people will be going back and forth on SpaceX rockets.”

In 2015 it appears that Musk has not moved off of that timeline at all. In a Reddit AMA (short for Ask Me Anything) on January 5 the CEO and Chief Technical Officer of Space X indicated that he plans to unveil plans for the Mars Colonial Transporter before the end of the year.

“The Mars transport system will be a completely new architecture. Am hoping to present that towards the end of this year. Good thing we didn’t do it sooner, as we have learned a huge amount from Falcon and Dragon,” said Musk.

The Mars Colonial Transporter (MCT) is being designed as an interplanetary spacecraft capable of carrying 100 people at a time to and from Mars. During the Reddit AMA, Musk said that the goal is to carry 100 metric tons, or 220,500 pounds, of payload to the Martian surface.

By comparison the average payload of a space shuttle was 53,000 pounds. The record payload for a spacecraft is held by Saturn V at 260,000 pounds. That spacecraft also holds records for being the world’s most powerful, tallest and heaviest rocket. Saturn V however, only had to reach low-Earth orbit.

The MCT would have to travel the 140 million miles to Mars. Unless Musk has new propulsion systems planned the trip would take at least six months. If the spacecraft is, in fact, carrying 100 people it will have to be large enough that the passengers are not literally stacked on top of one another during the trip.

There are serious concerns about the psychological impact of long term space travel. Some have suggested that the mental challenges may be greater than the technological ones. These include likely feelings of isolation and boredom, personality conflicts with people living in close quarters for an extended period and the knowledge that Earth is very far away and unable to send help in a timely manner.

“If you have a fire you have to deal with it yourselves. You can’t evacuate anyone if they develop issues … You’re really isolated,” said Nick Kanas, a psychiatrist and professor emeritus at the University of California, San Francisco (UCSF) to National Geographic in 2013.

The MCT will not only have to be fast and powerful, it will have to be large enough to help passengers overcome these psychological issues.

Space X is certainly not the only organization with its eyes on Mars. Mars One is a not-for profit organizations that plans to establish a Mars colony, a few settlers at a time, starting in 2024. It is not immediately clear, however, how realistic Mars One’s plans are given that they do not appear to have the technology of Space X. Although NASA isn’t talking about colonies at this point, the space agency is interested in the human exploration of the Red Planet. The European Space Agency (ESA) and the China National Space Administration (CNSA) are also discussing Mars missions.

While human colonies on Mars may still be science fiction there appears to be a race heating up to make it science fact and, at the moment, Elon Musk and Space X appear to be in the lead.