Savannah: Have you ever seen that old footage of Apollo astronauts hopping and skipping around on the lunar surface? Like, it looks so fun. But two years before Neil Armstrong made one small step, Surveyor 6 used its tiny rockets to perform the very first hop on the Moon; technically, it was the first rocket launch on a world that isn't the Earth, and over the decades, that little hop still serves as inspiration for ways to explore the Solar System.

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NASA scientists are pretty smart, so before they sent any of their fellow humans to the Moon, they figured it might be better to send some robots first: let them get the lay of the land, make sure the technology could handle the lunar environment, and that the soil wasn't so fluffy and brittle an astronaut would be swallowed up by the ground beneath them. You know, important stuff like that.

This was the job of the Surveyor Program, and if it sounds a little familiar, we covered the first Surveyor probe over on SciShow Space. But it wasn't Surveyor 1 that got to hop on the Moon; it was the second-to-last probe in the series, Surveyor 6.

After getting pushed into space by an Atlas Centaur rocket and a few days of coasting, Surveyor 6 landed on the lunar surface on November 10, 1967; so, a little over a year before any humans went around the Moon and and back, let alone landed on it. And for about two weeks, the robot checked off items on it's mission to-do list: It took photos, analyzed the lunar surface, measured the Moon's magnetic properties, it even performed an erosion test by basically blow-torching the surface with its rocket engines. And now I'm thinking about what lunar crème brûlée would taste like.

Surveyor 6 was tasked with analyzing the mechanical properties of the lunar soil, like how much weight it could support. And in order to do so, the researchers wanted to look at the footprints the prob made when it landed, which meant it had to move. But the surveyor probes weren't rovers; they were built to survive a landing on the Moon and then stay there - so, NASA made it hop.

After about a week on the Moon, scientists reactivated three of its liquid propellant engines. Now, these are a lot smaller than the image that might come to mind when you hear the phrase "rocket engines." They're called "Vernier engines" or "Vernier thrusters," and they're usually used for fine directional adjustments, like when you're trying to lower a falling probe onto the Moon's surface and don't want it to come in too fast, or perhaps - even more annoyingly - tip over. They're not meant for getting into space, but the Moon's gravity is so low, they were enough for Surveyor 6 to do a little hop. These rocket engines fired for 2.5 seconds and after a total hang time of about six seconds, the probe landed about 2.5 meters from where it started, which doesn't sound like much, but it's enough to make Surveyor 6 the first rocket to launch from non-Earth ground.

But hold on a second: Before we go around handing out awards, are we sure Surveyor 6 counts as a rocket? Fundamentally, a rocket is anything that can provide its own thrust by shooting stuff from inside of it outside of it. And thanks to Newton's third law, the rocket moves in the opposite direction that the stuff is getting shot out. Since all that propulsive oomph is coming from an internal source, it lets rockets operate in a vacuum, like the one you find in interplanetary space and on the surface of the Moon. Meanwhile, objects that can only propel themselves by interacting with the air around them, like through the use of jet engines or propeller blades, don't count as rockets. I'm sorry, Ingenuity. You are still awesome in your own way.

So, Surveyor 6, with its tiny Vernier engines, does count as a rocket, even if it doesn't look anything like the Atlas Centaur that got it off of the Earth in the first place. Thanks to its award-winning hop, Surveyor 6 got pictures of robot footprints, and scientists were able to combine the two vantage points to create stereo images of the lunar surface. But not only did this mission help us better understand the world Apollo astronauts were set to visit, it inspired even more rocket hopping.

For example, scientists have proposed designing hopping landers for low-cost, long distance missions to targets like Pluto or Neptune's moon Triton. A lander that hops between points of interest, rather than a rover with lots of breakable wheels, could be a lot cheaper in terms of R&D, and less risky to send to these far-flug worlds. There's also a steam-powered probe in development, called "Sparrow," which is being designed for missions to icy moons, like Europa and Enceladus. It's nice to see NASA finally entering its steampunk phase. Sparrow would be joined on the surface by a lander that would stay in place and mine the moon for water-ice. The probe could then boil the water and use the power of steam to hop across a variety of extraterrestrial surfaces, some of which might not be navigable otherwise.

But steam isn't the only new technique in the works. Because of a lot of the targets for these hopping missions are low-gravity worlds, some scientists have proposed the "jump and wait" method. It's basically what it says in the tin: launch a craft straight up and wait for the ground to rotate below it. When the craft comes back down, it will land in a totally new spot, practically no navigation necessary.

So one day, Surveyor 6 may become the predecessor of a whole new fleet of hopping, rocket-powered robots. And while it was never designed to try and leave the Moon, Surveyor 6's off-world launch also preceded every return mission. After all, all of the Apollo astronauts did make it back home. And over the decades, we've had multiple uncrewed missions land on not just the Moon but even an asteroid, and return samples to Earth for some hands-on investigation.

So, here's to Surveyor 6. I like to imagine that after a job well done, someone told that little probe, "That was one small hop for a rocket, one giant leap for rocket-kind." And then someone overheard and said, "Hey, Neil, I've got an idea."

Thanks for watching this episode of SciShow. This month, we're celebrating NASA's adorable hopping robot by immortalizing it in pin form. If you'd like to own your very own Surveyor 6 pin, you can fire up your own proverbial Vernier engines and hop on over to complexly.store.

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