We know how to get to Mars. We know how to land on Mars. Now comes the hard part: figuring out how to leave.
When NASA engineers look at Mars, they see a planet-sized Venus flytrap.
It lures us with the promise of scientific discovery—but the moment we land there, gravity and a harsh climate will conspire to keep us stuck on the surface.
And that’s not an option. If The Martian holds one lesson for real-life space exploration, it's that the public won't stand for spending billions of dollars only to leave astronauts stranded on another world. The most crucial part of any NASA plan for visiting the red planet, arguably, is getting off it.
The spacecraft that NASA would build to get the job done, the Mars Ascent Vehicle (MAV), represents a formidable engineering challenge. When fully loaded with fuel, it’s too heavy to launch from Earth and land safely on Mars.
Instead, the vehicle would need to be pre-assembled and sent to the red planet—years before the astronauts arrive—where it would make its own propellant by squeezing it out of the thin Martian atmosphere.
And after that? The MAV must be built tough enough to remain fully operational despite being pummeled by massive dust storms and punishing UV radiation. When the cramped vehicle does finally take off, it needs to sustain the astronauts for days, as they maneuver to rendezvous with the orbiting vessel that will finally take them home.
The Mars Ascent Vehicle will be a mission within a mission: a crewed spacecraft launched into orbit from the surface of an alien planet.
And there’s only one chance to get it right.
HAULING ALL OUR STUFF
A mission to Mars will be humankind’s first deep space caravan. As many as five separate spacecraft might be needed to ferry the astronauts and their cargo to the red planet.
There and Back AgainNASA engineers are faced with the daunting task of landing a Mars Ascent Vehicle (MAV) safely on the Red Planet, where it will manufacture its own fuel to bring the astronauts home.
Some of that cargo can be broken down into smaller components and then reassembled by the astronauts upon their arrival. Not so the MAV. “You don't want to be on Mars trying to bolt engines on, in your space suit, essentially wearing mittens in a dusty environment,” says Michelle Rucker, a system engineer at NASA’s Johnson Space Center.
In NASA-speak, that makes the MAV the “largest indivisible payload element” on the mission, weighing an estimated 18 tons. To date, the most massive object that we’ve sent to the Martian surface is the one-ton Curiosity rover.
Landing an object on Mars—especially one that that weighs several tons—is not as easy as landing it on Earth, where a capsule basically falls from the sky, relying on the atmosphere to reduce the speed of its descent.
On Mars, where the air is a hundredth the thickness of Earth’s, “there's just enough atmosphere to be a pain in the butt, but not enough to do anything useful for you,” says Rucker. Or, put another way, it will burn you up but it won’t do much to slow you down.
That’s why NASA is developing technology such as the Hypersonic Inflatable Aerodynamic Decelerator—a massive, cone-shaped inflatable heat shield that would also act as a braking system.
The shield would deploy upon entering the Martian atmosphere, slowing the lander from hypersonic to merely supersonic speeds. At that point, rocket engines would kick in for a controlled landing.
Here's the kind of math astronaut Mark Watney would do to make it work: The landing will burn up around five to seven tons of propellant. When it comes time to take off from the Martian surface, the MAV will need 33 tons of propellant to break free of the red planet’s gravity, push through its atmosphere, and safely ferry the astronauts and their scientific cargo into orbit, where they can rendezvous and dock with their Earth Return Vehicle.
And that's too much to send ahead. The propellant will need to be manufactured on Mars.
LIVING OFF THE LAND
If expeditions to the red planet are going to have any chance of succeeding, they’ll need to live off the land.
By making fuel on Mars, NASA can shave several tons off the initial payload mass. And, after the first mission is over, the equipment can be left on Mars to serve as nascent infrastructure for expanded facilities to process not only fuel, but also water and air for future explorers.
The engines of the MAV will be powered by methane and liquid oxygen. All the ingredients needed to make that fuel—carbon, hydrogen, and oxygen—can be found on the red planet, if you know where to look.
In theory, oxygen can be extracted from the Martian atmosphere, which is 95 percent carbon dioxide (CO2), and from liquid and frozen water (H20) buried beneath the surface. The leftover carbon and hydrogen would be combined to make liquid methane.
Drilling for water, however, would add an unwelcome element of uncertainty to an already difficult mission. Excavating and processing is a lot more complex than simply taking atmosphere from Mars. “The other problem with underground water propellant production is that it drives you to land where you're pretty sure there's water,” says Rucker. If you need to dig and “you land somewhere where it turns out you're on top of bedrock, then all bets are off,” she says.
If hydrogen won’t be extracted from Martian water, then Plan B would be to send a payload of hydrogen to Mars as seed stock for making methane. But, for an initial mission, that idea is also off the table. Although hydrogen isn’t heavy, it requires large tanks for storage that would take up a lot of precious space.
“We've got a lander design; it kind of has a flatbed deck on top,” says Tara Polsgrove, an aerospace engineer at NASA’s Marshall Space Flight Center. “Right now, the MAV is taking up most of the room on that deck. There's not a whole lot of room there for a hydrogen tank.”
NASA engineers could accommodate hydrogen tanks by making the MAV taller instead of wider. But, increasing the height of the spacecraft is a scenario they’d like to avoid. They’re concerned that if the vehicle is too tall, there’s a greater risk of it tipping over after landing.
And, Rucker says, a taller MAV could place a difficult physical burden on the astronauts. If one or more of them are incapacitated during the mission, then climbing a tall ladder is the last thing they’d want. Easy access needs to be a high priority.
As such, the current plan envisions sending an ascent vehicle fully loaded with liquid methane and equipped with a chemical plant that would manufacture liquid oxygen from the Martian atmosphere.
The process is expected to take one to two years. When the MAV’s tanks are full, the human crew will be sent to Mars, secure in the knowledge that they’ll have a gassed-up vehicle waiting to get them back into space.