March 10, 2016 6:43 AM EST

In the wake of Scott Kelly’s safe and healthy return to Earth on March 2 after spending nearly a year aboard the International Space Station, NASA has said (and said and said) that this mission brings humanity a big step closer to a crewed landing on Mars. There’s some truth to that–but the next steps are complicated.

The human body does not react well to prolonged exposure to zero gravity and would break down in all manner of ways over the 2½ years a round-trip mission to Mars would take. Studying the extent of that damage–to the heart, the eyes, the muscles, the bones, the immune system and more–in a one-year, close-to-home mission can help scientists develop ways to reduce, if not eliminate, the harm. And with Kelly’s identical twin–retired astronaut Mark Kelly–serving as a control subject this past year and in the follow-up work to come, the results are likely to be especially robust.

But NASA has not just sold the value of the Kelly mission; it has oversold it, making it seem as if that were a final box that needed ticking before an expedition to the Red Planet could set sail. That’s not quite the case. The space agency’s Mars program still needs–in no particular order–a rocket, a crew vehicle, a budget, a target date, a firm schedule and a political commitment from Washington. And a single year-in-space mission simply cannot yield all the answers on the biomedical front.

It’s not overstating things to say that while NASA’s unmanned program has been thriving for decades–with the flyby of Pluto last summer only the latest in a string of deep-space triumphs–the business of exploring space with human crews has been adrift since the long-ago days of the moon landings. It would be wrong to think a trip to Mars is beyond us. But it would also be wrong to conclude that we’re ready to blast off.

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NEXT STOP MARS? NOT SO FAST

There are many problems to solve before humanity can cast off for the Red Planet. Some are biological, some technological, and some, alas, political. Here are three of the toughest. The good news: we checked all these boxes during the Apollo lunar program. The bad news: this time around, the science is harder and the politics uglier.

MORE LONG FLIGHTS

The International Space Station has perhaps a decade of life left, and NASA is considering as many as 10 one-year missions like Kelly’s. For this, diversity will be important. Kelly is a 50-something man who has flown four missions. A woman or a rookie or a younger astronaut (or even an older one) might react to a year in space in an entirely different way. Scientists must know how the human body in general fares, not just one type of body.

FIND YOUR FOCUS

For most of the Obama Administration, Mars has been a secondary goal for human exploration. First came an asteroid redirect mission (ARM), which involved sending a robot ship to find a small asteroid, push it to near lunar space and then send astronauts there. Why? That’s never been clear. Bet on the next President to scrap ARM and instead focus resources on Mars. That, at least, is a clear objective.

STAY THE COURSE

The moon program spanned 11 years, six Congresses and three Presidents. While there were fights over funding, there was bipartisan accord on the goal. That kind of comity will have to be repeated–and exceeded–if we’re going to reach Mars. Even the rosiest scenarios don’t envision a Martian expedition taking place before the early 2030s, which would require Washington follow-through for a daunting 15 years or more.

This appears in the March 21, 2016 issue of TIME.

Write to Jeffrey Kluger at jeffrey.kluger@time.com.

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