Elon Musk plans for SpaceX to launch its manned Mars mission sometime in 2024 and to arrive on the planet by 2025. If he and his team are successful, they will have reached a tremendous milestone. But it’s not the first milestone they need to hit; it’s actually the sixth.

(Disclaimer: Musk hasn’t specified whether he intends to have astronauts land on the planet or simply orbit it, but for our purposes, there is very little difference between those goals.)

SpaceX, founded by Musk with the express goal of enabling the colonization of Mars, certainly isn’t the only player eyeing the red planet. After all, NASA has an annual budget of about $20 million dedicated to getting astronauts to the fourth planet. But NASA has set a much more distant target deadline of 2040 to make the trip.

Can SpaceX realistically send people to Mars in less than a decade? The company has been on an incredible roll of success in the last few years, establishing its Falcon 9 rocket as a potentially reusable instrument, and demonstrating the viability of the Dragon capsule as an efficient mode of transporting supplies to and from space. But transporting humans to Mars is a different game than getting a couple tons of supplies to a space station in low-Earth orbit. That’s — in the broadest sense possible — why SpaceX probably won’t succeed.

But let’s be more specific about what Musk is going to have to accomplish first.

Send People to Space

One year ago, a SpaceX Falcon 9 rocket launched from Cape Canaveral carrying supplies for the International Space Station. A little over two minutes after takeoff, the whole thing blew up. The future of SpaceX was suddenly unclear.

The company bounced back and proved doubters wrong. Before the year was out, the company would conduct a successful vertical landing of its rocket after multiple failed attempts and then land the sucker three more times on a drone ship in the Atlantic Ocean.

That’s a pretty significant improvement. But there’s one thing still missing: a launch in which SpaceX actually sends human beings into space. After 26 Falcon 9 launches, SpaceX has not conducted a crewed test. And this presents a very obvious problem: If SpaceX can’t yet demonstrate the ability to put a human in space and bring them back, the company is in no position to suggest it is prepared to conduct crewed launches to low-Earth orbit, let alone Mars.

Send a Spacecraft to Mars (or the Moon)

SpaceX’s stated desire is to send its Dragon capsule to Mars in 2018. It won’t have anybody in it, but this is a critical first step to proving that the company is able to actually make it to the red planet. This kind of interplanetary test flight of the “Red Dragon” would actually be the first time someone has sent a spacecraft to Mars that had the potential of carrying human passengers — something that not even NASA has tried yet.

A Dragon capsule being shipped out of SpaceX HQ in Hawthorne, California, February 2015. SpaceX

Musk wants to take advantage of the fact that SpaceX is a private company that raises its own funding. It could just conduct Mars missions one after another, without having to move through the horrendously slow bureaucratic process that plagues NASA.

“The basic game plan is we’re going to send a mission to Mars with every Mars opportunity from 2018 onwards,” Musk told the audience at Code Conference 2016 earlier this month. “They occur approximately every 26 months. We’re establishing cargo flights to Mars that people can count on for cargo.”

While SpaceX can conduct multiple launches a year, or even a month if the company’s leaders so desired, it’s worth noting that NASA’s bureaucratic process in large is part of a rigorous system of checks and testing to ensure the safety of its astronauts. SpaceX, if not careful, will run into many more mission failures that could irrevocably shake the confidence the rest of the public has in the company and destroy the goodwill earned from the last year.

This brings us to the next issue at hand…

Improve Space Launch System

SpaceX is no stranger to failure — and in order to make commercial space travel affordable and sustainable, big risks have to be taken with the understanding of possible failure. Musk does not shy away from this — and it’s been to the company’s benefit so far. But last year’s accident reinforced the fact that SpaceX is a young company. Musk might be pretty comfortable with the notion of people dying on the way to pave the way for future Martian colonizations, but he’s going to find that a much tougher sell to others.

I don’t just mean making sure the public is on his side — I also mean that the other manufacturers SpaceX relies on for rocket and spacecraft parts may not want to do business with a guy who feels that brazen about the loss of human life.

How do you remedy this? Well, if you’re not going to change your rhetoric (and when you consider how well Donald Trump is doing these days, why bother?) then you have to simply have to make sure people don’t have a reason to think your missions to Mars will end in failure. Be better at launches and cut down on crashes. It’s that simple.

Solve the Cosmic Radiation Problem

Space radiation is perhaps the biggest issue at play, and it’s not quite clear if Musk has a good understanding of how it works and the extent to which it’s stopping us from sending astronauts to far off worlds. Cosmic rays still pose a very real threat to the health of humans traveling through space.

Earth's magnetic field protects us from space radiation. But beyond that, astronauts are potentially exposed to the full brunt of cosmic rays permeating the solar system. NASA

Outside of the protection of Earth’s magnetic field, cosmic rays run freely. And the longer you are exposed to them, the more damage incurs in your cells and tissue. Right now, NASA uses the aluminum casing of spacecraft to protect astronauts — that’s how we sent people to the moon and back — but a one-way trip to Mars would be on the scale of six months minimum.

NASA thinks of space radiation the same way private employers think about acceptable safety risks they can subject their employees to. The space agency will not send astronauts out to Mars if the risk of them developing cancer because of cosmic ray exposure is too high (for NASA, that’s a three percent excess lifetime risk).

SpaceX ought to operate under the same standard. If NASA itself hasn’t yet figured out how to develop a spacecraft or other interventions that can prevent the risk of cancer from going beyond this three percent threshold, it’s almost certain SpaceX hasn’t solved that problem either. For Musk and his colleagues to move forward and simply disregard the problem posed by cosmic rays would be insanely irresponsible.

Create a Spacecraft Capable of Making it There and Back

And perhaps that brings us to the final major obstacle at hand: developing a spacecraft that can take humans to Mars comfortably and bring them back under a finite amount of fuel and resources. Although the spacecraft in question, a variant of the Dragon 2 capsule affectionally nicknamed Red Dragon, is finally being built, it’s nowhere near a state where it can take people to Mars and back. It’s currently got the interior size of an SUV, although a future incarnation would ideally have much more space. Details are even more sparse about exactly what kind of propulsion it will use to move through space, how it will carry enough resources for human passengers.

Naturally, it’s in SpaceX’s best interest to keep mum on these bits of proprietary information, but so far, it’s unclear whether the company has a true plan for how it’s going to send humans to Mars within a decade.