This week six astronauts aboard space shuttle Endeavour are knocking its last mission to the International Space Station (ISS) out of the park. In July, Atlantis's final flight will bring down the curtain on NASA's 30-year shuttle program. However, when Atlantis's crew calls "wheels stop, Houston!" for the final time, many Americans will be startled to find that the nation has no replacement rocket that can launch astronauts to the ISS, 220 miles up. Fifty years ago tomorrow, John F. Kennedy committed the nation to reaching the moon within a decade. But soon we'll be unable to reach the space station we largely built and paid for without help.

Until roughly 2015, when American companies hope to produce a commercial rocket and spacecraft that can carry NASA's crews safely and economically, astronauts will be renting rides on the Russian Soyuz vehicle (at $55 million per seat and climbing). The fact that presidents and congresses have seen this gap coming and failed to close it is a significant gamble, and not just because it's unclear whether commercial spaceflight will be ready to deliver crews by the 2015 target. NASA has no backup: If the new space startups can't make a profit on flying astronauts and other customers to orbit, they will hang up the out-of-business sign and walk away. We'd be forced to buy Russian seats indefinitely while starting an expensive crash program to regain access to the ISS.

Once we find a way to reach the station, we face another gap—one of vision. Between now and 2020, the Obama administration proposes nothing more ambitious for the nation in space than operating the ISS in low Earth orbit, where we have been mired since 1972. The president's single mention last year of a 2025 mission to a nearby asteroid has not led to firm NASA program plans, realistic milestones or funding. This space-policy muddle is already having serious negative effects. NASA is letting go thousands of skilled engineers, technicians and scientists who made the shuttle a success and built the space station. As they scatter to other industries, the nation loses an irreplaceable resource. Congress stepped in and directed NASA to build a rocket and deep spacecraft, but senators and representatives are not paid to do rocket science. Only the president can propose and execute a coherent policy for space exploration.

To fill this vacuum in space policy, the president should chart a vigorous, well-funded exploration path that finally returns American explorers to deep space, with the twin goals of scientific exploration and the creation of a commercial, space-based economy. Astronauts should lead the way out of Earth orbit by 2020, using a new heavy-lift booster and deep-space craft that will serve the nation for at least the next two decades. Commercial competition can help to create an innovative design, but this is a job for NASA. To see a project of such scale realized, the government will have to fund it.

After tests in lunar orbit, astronauts should embark on a series of voyages to nearby asteroids that are rich in water and other resources. Robot explorers like the Lunar Reconnaissance Orbiter have already found water near the lunar poles, and ground-based telescopes, along with recovered meteorites, tell us that some nearby asteroids harbor minerals comprising as much as 20 percent water. Asteroids are also rich in iron, nickel, rare platinum group metals, and industrial catalysts. Following up discoveries by robot prospectors, astronauts could tap these space natural resources and demonstrate methods to produce water, structural materials and energy to fuel off-Earth industries.

NASA's mission will not just grow our economy, but also invigorate scientific discovery: The experience and resources derived from asteroids and our moon will lay the foundation for eventual expeditions to the moons and surface of Mars. And it could even lead to the technologies that will protect our society from the threat of a future asteroid impact. This pursuit will drive technological innovation for decades, spurring our high-tech economy and, like President Kennedy's declaration, inspiring new generations of young scientists, engineers and explorers.

Can we afford it? We'd be foolish not to invest in space. During Apollo, spurred by the Cold War, we spent nearly 5 percent of the annual federal budget on space, winning the space race and sparking a technological revolution. But NASA's budget has been shrinking for two decades; today, it is just over half a percent of annual spending. The Augustine Committee in 2009 recommended that we commit to a human spaceflight program "worthy of a great nation," estimating NASA would need only an additional $3 billion above the current $19 billion annually to launch America on voyages into deep space. That would still be less than 0.6 percent of the federal budget, an affordable investment to open this frontier and ensure our technological leadership in the 21st century.

As we debate America's future in space, we should look for leaders who will build on the shuttle's success, set ambitious goals and commit the resources to achieve them. Great nations are exploring nations. America's explorer-entrepreneurs are just waiting for the word "go!"

Tom Jones is a planetary scientist, veteran astronaut, speaker and author. He flew on four space shuttle missions and helped build the International Space Station. His website is Email:

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