In less than a week, SpaceX’s CEO Elon Musk will finally explain how he plans to colonize Mars within the next few decades. It’s a goal that he has adamantly championed for years, though he hasn’t given many specifics about it. That will change on September 27th, when Musk is expected to talk about the vehicles and technologies needed to bring people to the Red Planet, and then build a long-term settlement there.

Musk has been very vocal about his desire to put people on Mars

For many, the lecture is long overdue. Musk has been very vocal about his desire to put people on Mars, arguing that it’s necessary for human survival. "I think there is a strong humanitarian argument for making life multi-planetary in order to safeguard the existence of humanity in the event that something catastrophic were to happen," Elon told Aeon Magazine in 2014.

The announcement comes at an awkward time for SpaceX, though. The company recently suffered a major failure after one of its Falcon 9 rockets exploded on the launch pad in Cape Canaveral, Florida. SpaceX is now grounded from spaceflight as it tries to figure out what caused the accident, but the explosion hasn’t changed Musk’s plans to talk about his vision for Mars next week, the company told The Verge.

Musk has been vague about his Mars colonization architecture so far, though the internet rumor mill has been busy. Here’s what we know about Musk’s vision and what he may or may not reveal at the International Astronautical Congress (IAC) in Guadalajara, Mexico. "I think it's gonna seem pretty crazy, no matter what," Musk told GQ in December.

What we kind of know

The Interplanetary Transport System, formally known as the Mars Colonial Transporter

Musk’s Mars plan hinges on two major elements: a monster rocket booster and a giant spaceship capable of carrying cargo and people to the Martian surface. The booster is supposed to launch the spaceship from Earth, and then the spaceship will continue the journey to Mars, according to Musk.

These two vehicles have often been referred to as the Mars Colonial Transporter, or MCT, though last week Musk jettisoned the name. Now dubbed the "Interplanetary Transport System," Musk believes the vehicles will be capable of going "well beyond Mars."

Turns out MCT can go well beyond Mars, so will need a new name… — Elon Musk (@elonmusk) September 17, 2016

We don’t know much about these vehicles. But Musk has given us a few details over the years — all of which, of course, are subject to change.

BFR

The monster rocket that SpaceX wants to build has been codenamed the BFR, an acronym for Big Fucking Rocket. It’s a nod to the video game Doom, which had a giant gun called the BFG. The booster will have to launch a spaceship filled with 100 tons of "useful payload" to the Martian surface, Musk explained in a Reddit AMA in January 2015. That will be way more cargo than anyone has ever delivered to Mars at one time. So — as you likely guessed from the name — the rocket’s got to be massive, either similar in size, or bigger, than the Saturn V rocket that sent astronauts to the Moon. "The scale of everything is going to have to grow exponentially," Bobby Braun, an associate professor of space technology at the Georgia Institute of Technology, tells to The Verge. "To get a two-story house all the way to Mars, you’re going to need a very large rocket."

An artistic rendering of the Falcon Heavy, which is supposed to fly next year. The BFR will likely be a lot bigger and only have a single core. (SpaceX)

We don’t know too many details about what the BFR will look like, but Musk has indicated that the vehicle will consist of a single massive rocket core. And the BFR will most likely be reusable — just like SpaceX’s Falcon 9. How will such a massive vehicle be built, and how much will it cost? We don’t know.

BFS

The BFR mostly serves the purpose of carrying a giant ship — codenamed BFS, for Big Fucking Spaceship — into space. This will be the main ride for passengers traveling to the Martian colony. But the structure of the vehicle and how it will operate is not yet known. Some have wondered if the BFS will spin to create artificial gravity for passengers, to minimize their muscle and bone density loss. And there has been speculation about how it will shield astronauts from deep-space radiation and solar flares.

But there’s another big concern, too: how will the BFS land on Mars? That will be tricky because Mars’ thin air provides less cushion to slow down incoming spacecraft, since its atmosphere is 1/100th the density of Earth’s. So large pieces of cargo run the risk of gathering too much speed en route to the surface, and slamming into it. This problem isn’t limited to SpaceX; NASA only knows how to land around 1 ton of cargo intact on Mars for now. (The Curiosity rover used a combination of parachutes and a sky crane to land.) But Musk will need to land up to 100 tons of people and cargo carried over by the BFS — about 100 times the weight of Curiosity.

Musk has said he hopes to launch the first BFS filled with passengers in 2024

SpaceX won’t be relying on NASA’s methods to land its cargo, though. Instead, it will likely figure out a way of using rocket engines to lower a vehicle down to a planet’s surface, according to Braun. This is called supersonic retro propulsion, and SpaceX has used it to land its Falcon 9 rockets after launch. The company will likely scale up the technique for its Mars spaceship. However, it’s not clear if the entire BFS will be capable of landing on Mars, or if only a portion of it will ferry crew and cargo to the Martian surface.

Musk has said multiple times that he hopes to launch the first BFS filled with passengers in 2024. That’s a short deadline for a company that hasn’t launched even one person into space yet.

Raptor engine

A key component of both the BFR and the BFS will be the Raptor — a giant new engine that SpaceX has been developing since 2009. The Raptor will be capable of about 500,000 pounds of thrust at liftoff, according to Musk, making it about as powerful as the Space Shuttle’s main engines. It will also use liquid methane for fuel, unlike the kerosene-based Merlin engines used to power the Falcon 9 rockets. It’s possible that the choice to switch fuels is due to the fact that methane can be made on Mars, using subsurface ice and carbon dioxide from the atmosphere, according to Braun. That means that the Raptor engines could be "refueled" with materials on the Red Planet.

A component for the Raptor rocket engine undergoing testing at NASA's Stennis Space Center. (NASA)

A whole bunch of these Raptor engines — it’s unclear how many — are supposed to power the BFR, as well as the BFS, according to Musk. SpaceX has already made some significant headway on the engine’s development. The first full-scale Raptor was shipped to SpaceX’s McGregor testing facility in Texas earlier this year, and Musk tweeted images on Monday of the engine being fired up for the first time. "SpaceX propulsion just achieved first firing of the Raptor interplanetary transport engine," he wrote, before offering a few specific details about the engine. Musk said he would share more specifications during his talk in Mexico.

Cargo Routes

Much of the hardware needed for a Martian settlement will have to be sent over before people arrive. And once the colonists eventually get there, they’ll still need food and supplies coming from Earth — plus plenty of replacement parts in case equipment breaks or malfunctions.

Musk’s solution is a series of Red Dragon missions, which were announced earlier this year. In 2018, SpaceX plans to launch a version of its Dragon cargo capsule to Mars, to see if the vehicle can deliver supplies to the planet’s surface. The capsule will launch on top of the Falcon Heavy, the heavy-lift rocket SpaceX plans to fly for the first time next year. And once the Dragon reaches the Red Planet, it will use supersonic retro propulsion to land.

SpaceX plans to keep sending these Red Dragons to Mars every 26 months — when Earth and Mars are closest to one another on their orbits. The idea is to establish a reliable cargo route to Mars. These Red Dragon "shipments" will bring supplies and replacement parts to the Martian colonists.

What we don’t really know at all

Propellant

There’s been a lot of speculation as to how the BFS will have enough fuel to get to Mars. Launching such a massive vehicle into space will probably use up a lot of fuel, meaning the spaceship will probably need to a refuel before it goes to the Red Planet. Additional rockets may have to bring propellant to the BFS, Braun suggests. "So you send up the structure and the bones of the spaceship," he says, "and then you send up basically freighters that are full of propellant, transfer that into the ship, and then it’s off to Mars."

Returning to Earth

Unlike the Mars One project — which supposedly promises a one-way trip to Mars — Musk’s plan will allow people to return to Earth. "You want to bring the spaceship back," Musk said at the MIT Aeronautics and Astronautics Centennial Symposium in 2014. "These spaceships are expensive, okay, they're hard to build. You can't just leave them there. So whether or not people want to come back or not is kind of — like they can jump on if they want, but we need the spaceship back."

"You want to bring the spaceship back."

But exactly how the spaceship will return to Earth is still unknown — and no vehicle has ever returned to Earth from the Martian surface before. That’s because launching from Mars is considered an incredible feat; it involves landing a vehicle with engines and enough fuel that can take off from Mars and make it back to Earth. But if Musk is able to refuel his vehicle’s engines on Mars, it may be capable of launching and returning to Earth.

Habitat and keeping people alive

Musk has said very little about where exactly people are going to live on Mars. Colonists will need a life-support system to create breathable air, a way to clean and recycle water, and a way to feed themselves. Most experts agree that Martian settlers will eventually have to live off the land in some way.

"Providing enough food, water, and air is the number one requirement, and most people that have looked at it agree it’s very hard to do that for a long mission, unless you make these things on Mars," Chris McKay, a planetary scientist at NASA Ames Research Center, tells The Verge. "Maybe the first few years you can bring your own food, but eventually you’ll have to grow your own food."

Inflatable space habitats manufactured by Bigelow Aerospace. It's unclear what types of habitats SpaceX will use for its Mars mission. (Bigelow Aerospace)

No one has ever tried doing any of these things on Mars — and there are a lot of challenges when it comes to supplying colonists with food. For instance, the soil on Mars is thought to contain salts known as perchlorates, which are toxic for humans. So if crops are going to be grown on Mars, they either need to be grown in soil from Earth or the Martian soil must be somehow cleaned. "It’s a difficult problem and no one has solved it," says McKay.

All of these elements could wreak havoc on the human body

Radiation levels on Mars are also higher than on Earth, the environment is a lot colder, and there’s about one-third the gravity. All of these elements could wreak havoc on the human body if not properly accounted for. But Braun says it’s possible we may not hear about solutions to these problems next week.

"SpaceX is a space transportation company, at least the way I think of them," says Braun. "I think that what you’re likely to hear is mostly a discussion of the space transportation architecture. I would assume they’re going to partner with others on a lot of those technologies required to keep humans safe."

Cost, who’s going to go, and more...

There are many other aspects of a Mars mission that need to be addressed, such as the types of people who will go and how the trip will be funded. And there could be even more challenges that crop up along the way. That's because a Mars mission will be a massive undertaking, requiring a ton of engineering and problem solving that crosses multiple disciplines. "I think it’s extremely difficult," Charles Miller, the president of NexGen Space LLC, a space consulting firm, tells The Verge. "I think it’s a very audacious goal worth dedicating your life to, and I share his belief in creating a second branch of human society. But it’s extremely difficult, and I kind of feel sorry for those who think it’s a lot easier than it is."

We don’t really know which details Musk will reveal at the IAC. He could go into the minutiae of each leg of the trip, or he could just give an overall outline of the architecture. We’ll only know once Musk talks, and fortunately for those not going to Guadalajara, the whole thing will be streamed live. You can watch the stream here on The Verge along with our coverage, starting at 8AM ET on Tuesday.

SpaceX trip to Mars simulation