On April 29th, the space shuttle Endeavor will launch into orbit for its final mission as the world looks on.

Tucson’s tragic Jan. 8 shooting has turned the mission into a symbol of hope and a source of expectation, a drama that has hinged on deeply emotional cliffhangers—whether mission commander Mark Kelly would be willing to fly as his wife, Congresswoman Gabrielle Giffords, recovered from a gunshot wound to the head; whether she would be allowed to attend the launch and see her husband lift off; whether the public would catch a glimpse of her there.

Listen to Scott Kelly, Mark Kelly's twin brother and a fellow astronaut, discuss his brother's most recent mission:

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When Endeavor blasts off at 12:47 p.m., Giffords will be there, kept out of sight as is traditional for astronaut families. President Barack Obama and his family will also attend, along with a congressional contingent and hundreds of thousands of onlookers.

If all goes well, the 20-year-old spacecraft will lift off into clear Florida skies, reaching its orbit within minutes.

Three days later, it will rendezvous with the International Space Station, where it will deliver a $2 billion particle detector and a slew of spare parts, and then return to earth, having logged more than 100 million miles since it first joined the shuttle fleet.

It will not fly again. But the story won’t end there.

endeavour-port

Photo: NASA

Space shuttle Endeavour glistens in the sun on Launch Pad 39A at NASA's Kennedy Space Center in Florida.

The end of the NASA shuttle program will leave a void that has scientists, astronauts and other members of the aerospace community—many of whom are based in southern Arizona—wondering what comes next.

“This is the end of American independent access to space,” says Mark Sykes, director and CEO of the Planetary Science Institute, a Tucson-based nonprofit research institute focused on solar system exploration.

PSI and other southern Arizona-based aerospace companies, such as Paragon Space Development Corporation, have a lot at stake in a space program now left with significantly fewer resources at its disposal.

From here on out, says Sykes, American space exploration could involve “purchasing rides on the rockets of other countries,” unless the nation’s leaders can agree on a path for spaceflight’s future—and its funding.

“There are a lot of arguments over the plan for afterwards,” says Sykes, “but they all boil down to ‘who should get the money?’”

NASA hasn’t had to answer that question before. But delays in the planned Orion mission and the cancellation of NASA’s Constellation spaceflight program last year marked a profound shift in the agency’s approach.

“This is a game-changer,” says Michael Drake, director of the University of Arizona Lunar and Planetary Lab. “This is the transition from a Lewis and Clark-style expedition, where the government ran the exploration, to the railroad era, where the federal government put money into private companies that then did the exploring.”

Aided by NASA contracts, longtime government contractors like Lockheed Martin and recent startups like SpaceX are now charged with developing the future of American spaceflight.

Drake is excited by the prospect. He hopes the rise of a private spaceflight industry will spur interest in space careers among Americans, whose presence in math- and science-heavy fields has steadily declined since the Space Race.

He also hopes market forces will drive down the cost of spaceflight, giving way to safe and less expensive ways of getting cargo and humans into space, and perhaps to space tourism and other longer-term human developments in space.

“People like you or me will one day catch flights into space,” he says. “I think we’re at the start of that era.”

Sykes is less optimistic about the capabilities of commercial space companies, at least for the near future. None of the companies has yet managed to launch beyond low-earth orbit. Human exploration of the solar system will require a concerted, communal effort, says Sykes.

Regardless of who gets the money, says Drake, the drive to explore won’t go away.

“We’re not going to withdraw from space,” he says. “There’s a huge public support for human exploration in space. I think the question is how to move forward.”