Over the last 50 years, we’ve sent tons of cool spacecraft to Mars.

Flybys, orbiters, landers, rovers — it seems like we’ve done everything. Still, there is one kind of mission we haven’t done yet: No Mars mission has flown through the air — but that might change in just a few years.

Nothing’s final yet, but engineers are experimenting with the idea of including a drone, called the Mars Helicopter, on the upcoming Mars 2020 rover. Mars 2020 is NASA’s successor to Curiosity, and it’s expected to launch in — you guessed it — 2020. It has a similar design to Curiosity and will also study potentially habitable environments.

It will also select and package samples we could return to Earth on a future mission. Adding a helicopter could help this rover overcome one of Curiosity’s biggest problems: It just doesn’t go that far. Curiosity’s been on Mars for over five years, but in that time, it’s only driven about 17.5 kilometers — or an average of less than 10 meters per day.

Part of that is because the rover stops and studies things, but it’s also because driving a rover on another planet is pretty dang hard. Radio communication with Mars takes anywhere from 8 to 48 minutes round-trip, depending on where Earth and Mars are in their orbits, so mission controllers can’t just drive Curiosity Mario Kart style. It can steer itself across simple terrain like a self-driving car, but it still needs to stop every now and again to get input from Earth.

And there are some kinds of rocky or difficult terrain it just can’t handle. Picking Curiosity’s path isn’t always the easiest, either. To decide where it should go, engineers rely on pictures from the rover and from satellites in orbit — but Curiosity’s cameras can only see so far.

And the satellites have a top-down view, so they can’t always see the true shape of surface features. If Mars 2020 could launch a drone to scout out the area ahead, it could anticipate obstacles and identify the most interesting things to study. And someday, a Mars helicopter — or Marscopter — might even be able to explore places a rover couldn’t reach, like small channels or cliffs.

This all sounds like an amazing idea, but there’s a big problem: Mars is not a very good place to fly. Helicopters stay in the air because they experience lift, or more pressure underneath them than above them. And the more dense the air is, the more lift your helicopter can get, because there’s more air molecules for it to push against.

The problem is, Mars’ atmosphere is really thin — like, less than a 60th the density of Earth’s atmosphere at sea level — so it’s a lot harder to create lift. But good news: There’s less gravity so that’s one thing working in favor for us but it is not enough to counteract just the lack of molecules to push against. For this to work, engineers would have to give their Marscopter extra long rotor blades.

Basically, this would let the helicopter push against more air molecules at once, even if they’re spread farther apart. To carry just 1 kilogram across the Martian surface, the Mars Helicopter would need rotors more than a meter across, which is a lot bigger than your neighbor’s photography drone. And that doesn’t mean the drone could carry one kilogram of samples, either.

Everything, from the rotors to the flight computer to the solar panels, would need to add up to a kilogram of mass. But amazingly, getting airborne might actually be one of the easiest parts of a Mars helicopter. Remember that communications delay between Earth and Mars?

Well, unlike a rover, which can sit around and wait for instructions, once the Mars Helicopter is airborne - clock’s ticking. It would probably fly for 2 to 3 minutes and could cover up to half a kilometer of terrain — but since we wouldn’t be able to steer it in real-time, every second of that would have to be on autopilot. It would have to take off, judge the wind speed, fly in the right direction, take pictures, and find a safe place to land, all in 180 seconds or less.

That might seem like a ton of work, but it could come with a big payoff. NASA engineers estimate having a Mars Helicopter could help a rover like Mars 2020 travel three times farther than Curiosity in a day — and when you’re talking about multi-billion dollar missions, tripling efficiency is a pretty sweet deal. As a bonus, all those extra near-surface images would be really helpful for scientists studying Mars.

You’d get a mission that could study not only more targets, but better ones, and that’s a heck of a good thing for exploration. So far, NASA has already tested a prototype of the helicopter design, but they’ll need to do a lot more work before we’re ready to start zooming around. Since Mars 2020 is expected to launch in less than three years, hopefully we’ll be hearing more about it soon.

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