As a teenage boy in the 1960s, I found the first moon landing enthralling. I remember watching it on our black-and-white television as the world marveled at America’s leadership in space. I also charted the Apollo missions in their entirety and built scale models to commemorate them.

The Apollo program taught us that our nation can conquer even the most enormous technological problems if we are willing to devote sufficient energy and resources to solving them. We now face many such challenges, from climate change to energy independence, which we need to tackle even as we long for a return to the moon. Space exploration promises to propel science forward in myriad ways.

The flight of Apollo 11, a triumph of human endeavor, persistence, and technology, was one of the greatest achievements in history. This summer, institutions around the world are turning their eyes skyward to commemorate the 50th anniversary of man’s first lunar landing. You know, it’s remarkable to think that 50 years ago, two air force pilots and a naval aviator blasted off from Launch Pad 39A at Cape Kennedy, with a rendezvous with history. On July 20, 1969, Neil Armstrong and Buzz Aldrin became the first people to reach the moon when their Apollo 11 lunar lander touched down in the Sea of Tranquility. Nearly a half a century has passed since then and America continues to lead in space.

It’s been almost 50 years since humans first set foot on the moon. Back in 1961, Alan Shepard became the first American in space and, only eight years later, Apollo 11 astronauts were the first humans to walk on another world. As we celebrate the 50th anniversary of that event, I note that probably more than half the people in the world today were not alive to witness the moon landings. They are the youngest and most vibrant members of our society, and they seem very interested in space travel, I am happy to say.

For fans of space exploration, the 50th anniversary of Apollo 11’s mission to the moon is a celebration mingled with melancholy. For all the promised “giant leap for mankind” the mission foretold, the prophesied future of moon bases and journeys to Mars and beyond is still science fiction. Nine Apollo missions were launched moonward, and six of them landed. The cultural memories of those missions remain as bright as a new penny – and the aging astronauts who flew the Apollo space modules retain a status that goes beyond iconic. The last of six moon landings was in 1972. Since then, no one has left low Earth orbit.

The failure of nations to continue sending humans into deep space after Apollo is inexcusable. This 50th anniversary of Apollo 11 is a time to think about embarking on another human space adventure, one that might make the ultimate statement about our nature. We can choose to do something that is just barely possible, a unique endeavor in a class by itself.

The failure of nations to continue sending humans into deep space after Apollo is inexcusable

US President Donald Trump directed NASA to go back to the moon with Space Policy Directive 1. The announcement no doubt delighted people who want to see us go back to the moon and establish an ongoing presence there. One of the strongest arguments in support of a “moon first” approach is that the moon can serve as a testbed for technologies that will help support human life on Mars. However, NASA officials face a major test of their agency’s effectiveness: Is this another empty promise from an administration feeling nostalgic about the triumph of Apollo and looking to make a splash while in office, or can NASA somehow pull off what would be an audacious mission just in time for the presidential election?

Vice President Mike Pence further articulated the need for NASA to make an urgent effort to return to the moon. Pence called for changes in the agency’s approach, reflecting frustration within the administration at repeated delays in the development of NASA’s giant rocket, the Space Launch System, and Orion, a capsule for taking astronauts to the moon. But an accelerated pace has not been evident in the Trump administration’s NASA budget requests to Congress, raising many questions about how it will be possible for the agency to accomplish this ambitious goal.

The problem for NASA is that none of this architecture has been built or is even under contract. And without a budget or assurances from Congress that the program would be funded, many fear that the White House is setting the agency up for yet another letdown. We need specifics, not rhetoric. Because rhetoric that is not backed up by a concrete plan and believable cost estimates is just hot air. And hot air may be helpful in ballooning, but it won’t get us back to the moon.

Over the years, critics have lambasted NASA for losing the boldness that defined it during its early days, dampened by a pair of space shuttle disasters that killed 14 astronauts. Actually, 50 years ago, NASA sent men to the moon, 400,000 kilometers away. Today, our astronauts go to the International Space Station, 400 kilometers away, by hitchhiking on Russian rockets at a cost of more than $80 million a seat. This is because NASA hasn’t had the ability to fly humans to space since the nation’s shuttle fleet was retired in 2011.

China, meanwhile, has emerged as a rival in space. Earlier this year, it became the first nation to land a spacecraft on the far side of the moon. It plans to send another uncrewed mission to the moon later this year. In the process, China has revealed its ambition to seize the lunar strategic high ground and become the world’s preeminent space-faring nation. The plans underscore China’s ambitions in space at a time when the United States is curtailing NASA’s budget and increasingly handing over the business of space exploration to commercial adventurers.

Today, Israel, India, Japan, and China have lunar exploration projects in development. The United States’ own plan is perhaps the most ambitious – to return Americans to the moon by 2024 and eventually use it as a staging point for human flight to Mars and beyond. NASA needs to set firm goals and stick with them to reduce the risk of cost overruns, to enable commercial and international partnerships, and ultimately to maintain its leadership role in space exploration.

Neil Armstrong and Buzz Aldrin took their first steps on the moon on July 20, 1969. Fifty years later, the moon continues to offer a logical gateway to the universe and a potential staging area for Mars exploration. NASA needs to develop a strategy for effectively leveraging both commercial and international partners to send humans on missions to the moon. Fortunately, we now seem to be closer to a consensus that it is time for humans to move beyond low-Earth orbit and that an important part of that evolution will involve people landing on the Moon and establishing a foundation for an eventual mission to Mars.