In September, Elon Musk finally outlined his grand plan to bring humans to Mars in a presentation to the International Astronautical Congress in Guadalajara, Mexico. But the visionary still left a few big questions left unanswered. In a Reddit AMA on Sunday, the Space X CEO took some time out of his schedule to fill in the blanks for his hungry fans.

One user asked about the equipment and procedures that would be used to refuel the ship and if the ship would be able to function autonomously for the test flight. A futuristic propellant system is crucial to the company’s mission to create ships that can venture back and forth between Mars and Earth, creating an Interplanetary Transport System.

Musk responded that the company is “still far from figuring this out in detail” but that they have a roughly four-step plan to get a propellant plant up and running on Mars.

First, on the Dragon scouting missions, researchers will determine how to safely land and the best way to get the water necessary for the CH4/O2 Sabatier Reaction to keep the ship running.

The second spaceship will fly to Mars only with the equipment needed to build a materials facilities on the planet. The first crewed mission will be sent with enough equipment to build a rudimentary base and complete the propellant plant.

Musk said the company will then “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.”

As Redditors quickly realized this means that The Heart of Gold’s first manned crew, which according to a later comment will be around roughly 12 crew members, will be heading to Mars without a propellant factory up and running to get them back to Earth. Yes, it’s risky, but what else did you expect from a man trying to build a colony on Mars?

Musk told Redditors that he hopes to release mockups of the habitation section of the ITS “in a year or two.” Hopefully it’s comfy because Mars’ first colonists might be living there a while.

Here’s the full question from El-Psy-Kangaroo:

What equipment and procedures will be required for refueling operations on Mars? Will they be designed to function autonomously for the initial unmanned test flight?

Also, are there any plans to introduce a third variant of the ITS with just a large shuttle-like payload bay to allow for transporting bulkier cargo?

And here’s Musk’s answer:

We are still far from figuring this out in detail, but the current plan is:

1. 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.

2. Heart of Gold spaceship flies to Mars loaded only with equipment to build the propellant plant.

3. First crewed mission with equipment to build rudimentary base and complete the propellant plant.

4. 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.

Photos via Getty Images / Roberto Gonzalez, Getty Images / Kevork Djansezian