Over 40 years have passed since any human has walked on the moon, and all of them were American.

Russia has some grand plans to change that as the US turns its attention to Mars.

Roscosmos, the Russian space agency, wants to set up a high-tech lunar base, complete with human habitats, science and tech labs, a launching and landing port for spacecraft, and even an astronomy observatory.

The moon and Roscosmos have a complicated past. During the Apollo-era space race, the former Soviet Union landed robotic rovers on the moon — but a series of rocket failures and explosions halted progress on any human-carrying missions. Eventually, Roscosmos decided its moon program wasn't worth the money and the risk and shut it down.

But now Roscosmos is reviving that program and sending a robotic spacecraft, called Luna 25, to the moon to do some scouting for a future lunar base. The agency has announced that it will land Luna 25 on the moon's south pole in 2024.

Engineers are already building the spacecraft, and the finished product will carry eight cameras to help it navigate, take pictures, and keep an eye on its drill tool as it digs into the lunar surface.

Here's a model of what the spacecraft will look like:

Roscosmos

The Luna 25 spacecraft will run its electronics using a battery fueled by a radioactive material called plutonium-238. As the plutonium-238 naturally decays it generates heat, and the battery converts the heat into electricity.

Plutonium-238 is pretty much impossible to turn into a nuclear weapon, according to the Environmental Protection Agency. It's also not the same kind of dangerous, skin-piercing radiation that humans have to worry about (unless it gets inside our lungs).

Lots of spacecraft are powered this way, but the world is quickly running out of Plutonium-238. Space agencies will need to come up with another fuel source soon — unless Russia has a secret reserve of the valuable stuff, or some way of making it.

Plutonium-238 glowing from its own heat. Department of Energy

Roscosmos isn't the only agency thinking about a return to the moon. The European Space Agency already announced plans for its own ambitious moon colony.

In contrast, the US has turned its attention from the moon to Mars. Some spaceflight experts and engineers have criticized the US for this. They argue that NASA should practice setting up a lunar base first, and then move on to the more difficult — and more dangerous — Martian base once its worked out all the kinks. (Buzz Aldrin has a plan that incorporates both a moon base and a Mars base.)

Others argue that a return to the moon would be like moving backwards for NASA: We need to test the limits of human ingenuity if we want to make progress as a species, they say. Getting to Mars is one way to do that.

"Let's just go [to Mars] — prove that it is doable, prove that it is feasible and then examine how you do it on a regular basis that's affordable," Harley Thronson, a senior scientist at NASA, told Space.com in 2013.

It's not clear which strategy — moon or Mars? — is best for the US space agency.

"I refer to them as the Martians and the Lunatics – the people who want to go to Mars, and the people who want to go back to the moon," Roger Launius, a senior space history curator at the Smithsonian, told Space.com in 2012. "No one side has the clear-cut answer. There are positives and negatives for both."