Almost 50 years have passed since the United States last put a man on the Moon — or anywhere else outside of low-Earth orbit. As China builds an increasingly sophisticated space program, it is high time for America to get moving again.

On July 20, 1969, Neil Armstrong set foot on the Moon with his famous line: “One small step for man, one giant leap for mankind.” The United States declared victory in the Space Race, and then rubbed it in by dispatching several more Apollo missions carrying astronauts to the Moon until 1972.

NASA and the Space Task Group, appointed by President Richard Nixon to advise America’s next steps in space, pushed for the country to ride its momentum. They presented the administration with an ambitious plan calling for a manned expedition to Mars by 1986, at the latest. But, after having spent so much on Apollo, Nixon nixed it.

Perhaps 1986 was not the right time to go to Mars. But 2036 may be.

The Soviet Union gave up its program to send cosmonauts to the Moon in 1974, and to date no Russians have touched the lunar surface. They might seem to be enjoying the last laugh now — U.S. astronauts still rely on rides in Russian spacecraft to get to the International Space Station, seven years after the retirement of the space shuttle — but Russia’s space program is aging and under-funded, as evidenced by a hole recently discovered on a Soyuz spacecraft docked at the ISS.

China, however, is emerging as a serious rival in a gradually-unfolding 21st-century space race. As the world’s second-largest economy with high-tech aspirations, Beijing can afford an ambitious space program. Chinese astronauts have already been in low-Earth orbit, and the country plans to have a space station ready to launch by 2020.

By 2036, according to the deputy commander of China’s Manned Space Program, Beijing expects to land astronauts on the Moon. At that point, China will have caught up to the United States in human space exploration and will then be poised to overtake it.

Unless the United States takes action to keep its lead.

The question, of course, is: Why should we? Going to the Moon and Mars is expensive, and there is nothing there but dirt and rocks. We have problems enough at home that need our money and attention, the argument goes. Besides, we have robots to explore space for us: the Voyager I probe has already made it clean out of the solar system.

That all misses the point. Mars may indeed be mostly dirt and rocks; but somewhere out there are planets that are just as alive as Earth. Astronomers are now identifying such potentially habitable exoplanets (as planets outside of our solar system are known) at an ever-increasing rate.

Using robots to find those planets and scout them out before humans can get there is sound policy. But, eventually, humans will need to get there themselves.

Why? Because it’s there. Because, as Elon Musk and others have argued, humanity has a much better chance of surviving a catastrophic natural disaster, like the one that wiped out the dinosaurs, if we are a multiplanetary species.

Because, also, national might and prestige matter. If China explores the cosmos and exploits the resources of space while the United States sulks on Earth, America will lose power and influence here, and with it the ability to stand up to authoritarian bullying.

And if China settles new planets, it will impose its own system there. The future centers of human civilization will come into being under the thumb of tyranny, and not in the open hands of liberty. Imagine if Russia, and not Great Britain, had planted colonies here on American soil. What would we be today?

For these reasons, as Caspar Weinberger, then deputy director of the Office of Management and Budget and later secretary of defense, put it to Nixon in a memorandum urging completion of the Apollo missions, “America should be able to afford something besides increased welfare, programs to repair our cities, or Appalachian relief and the like.”

Not that those other things are unimportant. Human space exploration is a long-term investment, for the country and for humankind. As we disburse resources for the immediate concerns we must address at home, we ought also to put enough aside to shape our future.

We also cannot leave space exploration solely to entrepreneurs such as Musk, as enthusiastic as they are. Space is an expensive and risky prospect for businesses. They will need infrastructure, security and a predictable legal regime in order to turn a profit. Only government can provide those public goods and ensure that our laws and liberties accompany us into the stars.

Private firms have a role, though, and the U.S. government, through NASA, ought to work hand in hand with them to extend humanity’s reach into space, as government did with the railroad companies when the United States expanded west.

Habitable exoplanets are many light-years away, and we do not yet have the technology to send people to them. That is where Mars comes in. It and the moons of Jupiter and Saturn can serve as stepping stones on the way out of the solar system, and not only in the literal sense of placing supply and fuel depots there.

Expeditions to Mars and Jupiter will compel our engineers and scientists to find more effective solutions to problems of spaceflight, making our spacecraft faster, lighter, more fuel-efficient and better able to penetrate the atmosphere of other planets. Humanity will be better placed to reach out to distant stars after a Mars mission than before it.

The United States, then, ought to reinvigorate NASA. We ought to send forth robotic probes before us to other solar systems. And when China goes to the Moon in 2036, we ought to go to Mars.