The 100-meter-tall Ares 1-X rocket was rolled out to the launch pad Tuesday morning at NASA's Kennedy Space Center in Florida. The rocket, targeted to launch October 27, is a test vehicle for Ares 1, which would carry astronauts to orbit via the Constellation program, the next-generation spaceflight system designed to replace the space shuttle and expected to come online around 2015.

But the future of Constellation, and of Ares 1 specifically, is hardly secure. An independent panel convened by the Obama administration to review NASA's plans for human spaceflight is expected to deliver its full assessment Thursday, but a summary version released in September deemed NASA to be "on an unsustainable trajectory." The Review of U.S. Human Space Flight Plans Committee estimated that Constellation won't send astronauts into orbit before 2017, two years later than is commonly projected.

What is more, the International Space Station, only now nearing completion, is at risk of being deorbited in 2016 on NASA's current budget. If the space agency chose to keep the station flying until 2020 without a budget boost from Congress, one way to recoup the cost, the committee noted, would be to scrap Ares 1 altogether and rely on commercial firms to launch astronauts into orbit.