Audacious is an understatement if you’re looking to sum up SpaceX’s grand plan to make humans a multi-planetary species, introduced last week by CEO Elon Musk. The Interplanetary Transport System could get us to Mars and beyond, but it would be just as flawed to say its foolproof. There is a lot of work to do.

Musk described the ITS as sort of a Union Pacific railroad for space, but instead of California, it’ll take pioneers to Mars. He was enthusiastic about how the ITS is supposed to work, but a few things will get tricky, as he noted to those assembled at the International Astronautical Congress in Guadalajara, Mexico, on September 27.

Here are five big obstacles Musk and his team need to overcome.

5. Radiation: “Not too big of a deal.”

Musk is anything but shy about saying outlandish things, but cosmic radiation is nothing to mess with: “There’s going to be some risk of radiation,” he said. “But it’s not deadly.” He acknowledges a risk of developing cancer, but dismisses it as “relatively minor.” Anyone who played Oregon Trail knows that pioneers face all sorts of ways to die for which they are unprepared. It’s no different for space pioneers.

Without outlining the kind of shielding that will be used on the ship — named Heart of Gold after the one in Hitchhiker’s Guide to the Galaxy — or any other methods to mitigate radiation exposure, Musk threw out mentions of pointing the rear of the rocket towards the sun to maximize shielding, and developing artificial magnetic fields to deflect high-energy particles. The latter is called “active shielding, and such technology is, for now, “unproven.”

esa proba v space radiation
An illustration of how the ESA's Proba-V will detect space radiation

Cosmic radiation is a big deal, and it’s maybe the single largest reason NASA has not yet attempted a crewed mission to the red planet. Taxpayer-funded NASA can’t approve a mission that is unsafe past a certain threshold, while SpaceX, a private company, is unencumbered by those constraints. We haven’t found a type of shielding that provides enough protection that’s also light enough for Mars-bound spacecraft.

Moreover, to say the risk of cancer is “minor” is wrong. Consider that deep space radiation is probably killing former Apollo astronauts who went to the moon and back — people who spent less than two weeks in space. A mission to Mars would take about six months. Moreover, Musk wants to create the ITS in order to make a Mars colony possible a place where people will live and work long term. Even on the surface of Mars, astronauts will be exposed to much higher-than-normal amounts of radiation due to the lack of a robust magnetic field on Mars.

4. Money: “It is a bit tricky.”

Musk hopes that one day a trip to Mars will cost about $200,000 a person. Musk wants someone to be able to get to the red planet for basically the cost of selling their house. It’s about $10 billion to send just one person to Mars right now. He wants to slash expenses by 50,000 times.

elon musk rich
This guy is rich AF, and even HE can't finance his own trip to Mars.

He’s banking on developing four pillars for the ITS: full reusability, refilling spacecraft in orbit, producing propellant on Mars with endemic resources, and using the right kind of propellant to achieve maximum efficiency.

This gets Musk out to improve costs by a magnitude of 4.5 — or roughly 31,000 times. That still quite shy of the $200,000 goal, but it’s a start. Musk’s biggest aid might come from the simple fact that all technologies become less expensive as time goes if he’s sticking with the same basic design for the ITS for the long haul, the costs will eventually come down.

3. Energy/Water: “We think we can do with large solar panels.”

Part of Musk’s plan calls for generating spacecraft fuel on the surface of Mars itself, using resources already found on the planet. He and his team think they can achieve the production of methane using carbon dioxide in the atmosphere and water that’s already stored as water-ice.

The major hurdle there is that Mars propellant production will require an extraordinary amount of energy. Musk suggest bringing large, powerful solar panels to the planet in order to generate the necessary energy. It’s unclear how those panels will be brought to the planet, and if indeed they will be able to capture enough sunlight and turn it into electricity.

mars south pole ice water
Mars' south pole contains plenty of frozen water. Getting it and harvesting it for liquid water, however, is a much different story.

Musk will need an extraordinary amount of energy just to harvest water from the ice stores at the poles. This is not currently practical or sustainable. Neither is Musk’s idea to use atmospheric water to grow plants and crops, since there’s not much on Mars.

SpaceX has to hope that NASA finds an aquifer on Mars.

nasa deep space network
NASA's Deep Space Network is the only one of its kind in the world.

2. Deep-Space Communication

We already know the first few Red Dragon missions will rely on NASA for communicating with Earth. The company does not have the interplanetary infrastructure.

SpaceX could definitely have the necessary communications instruments built and launched by the time the ITS is ready to go, but Musk and his team have yet to reveal any details on that front.

mars astrobiology mars life
If we seed Mars with life, we have no idea what might happen.

1. Planetary Protection

The international protocols of planetary protection prevent any nation or party in the world from seeding other worlds with life from Earth.

Would building a colony on Mars populated by a million human beings violate this agreement? It’s unclear. What is more than likely is that the Martian landscape will change dramatically from human behavior. It’s inevitable that bacteria, plants, funguses, or other organisms will make it to Mars, and if they’re strong or virile enough, they might find a way to survive.

What would be the consequences? Nobody knows. And that’s precisely why NASA is so keen on avoiding such a scenario until we know more about what the Martian environment is like.

Photos via ESA, Getty Images / Rich Polk, NASA/JPL/MSSS, NASA, SpaceX

Neel is a science and tech journalist from New York City, reporting on everything from brain-eating amoebas to space lasers used to zap debris out of orbit, for places like Popular Science and WIRED. He's addicted to black coffee, old pinball machines, and terrible dive bars.