NASA wants to land a human crew on Mars in the 2030s. But to succeed with such an ambitious, expensive, long-timescale project, the agency needs a roadmap that inspires confidence that it really can send people to the Red Planet. Firouz Naderi, director of Solar System Exploration at NASA-JPL, has a budget-conscious idea: Let's land on Phobos first.

Of the two moons of Mars, Phobos is the larger one. Its proximity to Mars allows for a place to remotely control robotic rovers and landers in near real-time, without the minutes-long time delay inherent in sending instructions from Earth. In this way, a Phobos mission could test technologies for a big manned landing on the planet. It also provides a way to put boots on solid ground without extraordinary fuel requirements to return.

"Given that it is not going to break the bank and you can afford it, it seems almost intuitive to me that it would have advantages," Naderi says.

Phobos may be just the place if you want to arrive at Mars' doorstep without stepping inside.

Why Phobos

A Phobos landing won't be like a moon landing. At it's widest, Phobos is just 14 miles across. The Mars moon is mostly an oblong rock with a chunk taken out of it called the Stickney Crater. That site might prove an ideal location for landing.

A swift rotation means that Phobos orbits the planet every four hours. At just more than 3,200 miles above the surface of Mars, it also provides a great perch to study the surface of Mars from orbit and control robotic spacecraft below.

Phobos' smallness is a potential advantage for NASA. Attaching in orbit could be done with minimal fuel, and because a return mission wouldn't need to escape a planet-sized gravity well, a spacecraft departing Phobos would need a lot less fuel to launch than one leaving Mars. Taken together, these factors mean that Phobos may be just the place to shoot for if you want to arrive at Mars' doorstep without stepping inside.

We Need a Road Map

For all the talk of NASA's Journey to Mars, there is no real roadmap yet that outlines the exact steps that will take us there. It's because of a series of constraints in the way. Some are technological – the over-budget Space Launch System has to be ready to go, and the Orion capsule's testing timeline needs to be more concrete. Others are more political and predictable: Congress wants the agency to land on Mars without increasing the funding to do it.

Without that, and without a galvanizing "Kennedy moment" calling upon NASA to go to Mars, every move is a "stepping stone," but not one that necessarily leads us to the Red Planet.

"If you want to land early in the 2030s, the NASA budget needs to be spiked up three times what it is in human spaceflight," Naderi says. But barring that, "if that's all that you had, how do you mount a sustainable journey to Mars? Very quickly, it became apparent that you have to introduce complexity at Mars in stages."

So that's what he did. Naderi, Hoppy Price, and John Baker, and others at JPL put together their proposal in a paper called, A Minimal Architecture For Human Journeys to Mars. Simply put, it's a plan for making Mars work without much more money than NASA has now.

" The architecture needs to be executable and affordable, and that was a constraint on a technical design from the get-go," Naderi says. "If you really look at what it takes to put an architecture together, it is an art and it is a science about balancing various constraints. "

The plan includes no expensive flyby missions or keeping a craft in high orbit staring down at Mars. From the get-go, there are landings on solid bodies and experiments to perform, with each mission leading into the next. First you land on Phobos, then you land on Mars for a few weeks, paving the way for the final step: One year on Mars.

Decisions, Decisions

This is just a plan—it's not the NASA plan. And landing on Phobos is fraught with challenges. Phobos is a low-gravity body. A single jump could send an astronaut 12 stories high, and make her wait 12 minutes until landing. (Deimos, the other moon of Mars, is smaller and has even less gravity.) There are the kind of kinks that might be worked out in the Asteroid Redirect Mission—assuming that launches.

But the Phobos plan has some traction within the space community. The Planetary Society, a non-profit group that advocates for space exploration, published a report on Tuesday that outlines the benefits of a Phobos mission. Compared to other options, it's a low-cost, high-payload approach, serving as a proof of concept of Mars and a potential outpost for setting up future embankments. Of course, getting there wouldn't be so easy. NASA would need to launch multiple SLS missions and land 25 tons of gear on Mars. But it would all be in the name of figuring out if humans can survive on a planet so familiar and inviting yet so harsh, alien, and unforgiving at the same time.

"It would go a ways toward these astronauts interacting with their habitat in a way they'd have to on the surface of Mars," Naredi says.

Here's something to consider: If NASA chose this path to Mars, then little Phobos may be the first celestial object besides the Earth and the Moon that humans have ever set foot upon (unless we make it to an asteroid first). If an initial landing on Mars is untenable, then Phobos may just be the ticket. It'd be preferable to a 1,000-day roundtrip to glance at the planet and leave, anyhow.

"There's no advantage I see to going to Mars and just continue orbiting," Naderi says.

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