[Editor's Note: Viewpoint author Brand flew on Apollo-Soyuz and commanded three shuttle missions as a NASA astronaut.]

The U.S. currently leads the world in the human exploration of deep space, but the nation is on the verge of losing that distinction. It is approaching a tipping point. Apollo 17, the last lunar landing with humans, was 40 years ago. Transportation to Earth orbit is being turned over to the commercial sector, which is desirable. The exploration of deep space by humans is what is being dismantled.

Today, NASA is developing a heavy-lift launch system and the Orion manned spacecraft, but there are no credible destinations or goals for them. What will historians say about us 50 years from now?

In the 15th century, the Chinese had a large naval fleet that ranged far from home. But after exploring successfully, there was a change of policy, and government support for the fleet ended abruptly. A half-century later, European countries enjoyed the benefit of their own expeditions beginning with Columbus's voyages that opened the New World to European colonization. China had already withdrawn and missed the opportunity to have a stake in the Americas.

I am concerned that America's capability to explore outer space with humans—a capability that has taken decades to develop and apparently is taken for granted—will wither and die. We are looking at a human exploration generation gap. The Obama administration may think of it as “creative destruction” for the sake of enabling commercialization in Earth orbit, but in fact it is destruction of America's deep-space exploration capabilities.

These capabilities cannot quickly be rebuilt. Unless U.S. wakes up, the baton will pass to China or another country that is more motivated than America to lead the exploration of the Solar System in the 21st century. Does America still want to lead—or has America changed? Are we more risk-averse now? We are in the process of finding out.

Right now, America needs to kick-start its economy. Exploration preparations would contribute by stimulating invention, business and employment. Moreover, we would get stimulation of education at all levels and technology spinoffs into the U.S. economy, as was demonstrated by Apollo.

We must start by defining a deep-space destination, goals and a program. What should be the destination? Mars is a good place to start. Revisiting the Moon and visiting an asteroid with humans are not on the shortest path to Mars. The mission requirements are dissimilar. Besides, after learning how to send people to Mars, returning to the Moon or deflecting a threatening asteroid may prove easy.

What should we do to get started? I suggest the following: