Winston Scott knows how hard it is to be an astronaut. He was one.In the 1990s, he spent 24 days in space over two missions. It was stressful, he said: He always had lots of work to do and only short trips to get it done.But as NASA prepares to start hiring new astronauts next month, he figures his successors will face a different kind of challenge. The space agency wants to send astronauts into space for longer and longer stretches, farther and farther from help — to an asteroid and, eventually, to Mars."You're up there for four months, and you're doing the same thing over and over again," said Scott, now an associate vice president at the Florida Institute of Technology. "You can't get out of a spaceship and go off someplace and take a vacation. You're stuck in the same environment."That will take a different kind of astronaut, Scott said. They'll still need to be talented pilots and scientists in immaculate health, but perhaps more than ever, they'll also need to be easy to work with, willing to spend long stretches in a cramped space away from family and the comforts of home.NASA hasn't searched for new astronauts in four years, and this is just the second time it has since President Barack Obama and the space agency outlined plans to go to Mars sometime in the 2030s. The search comes as interest in the red planet has heated up. The Martian was a box office hit last month, and NASA announced in September that it found evidence of flowing water on Mars.Anne Roemer, head of NASA's Astronaut Selection Office, said the space agency is looking to pick between eight and 14 "astronaut candidates." The basic requirements are simple enough: a bachelor's degree and three years' work experience are musts, but an advanced degree is helpful. A select few will be called to Houston for medical evaluations, aptitude tests and interviews that will winnow the field, and the final candidates will be announced in 2017.Last time, more than 6,000 people applied. Only eight made the cut.Roemer said preparing for long-term spaceflight was important to NASA before its Mars ambitions were announced, thanks to its work on the International Space Station. Astronauts these days go into space for four to six months at a time, compared to 10 to 14 days during the space shuttle era. Astronaut Scott Kelly is eight months into a yearlong trip to study the effects of living in space. A trip to Mars could take well over a year and a half.But it's not just about the time away. Future astronauts might have a chance to go somewhere no one has in decades: deep space, out past the safer confines of low-Earth orbit, which is where satellites and the space station encircle the planet.To actually get to Mars would require practice missions closer to home so that astronauts can figure out how to operate in a new environment farther from help. NASA said it wants to put astronauts on an asteroid in the 2020s, and some observers hope the United States might return to the moon. Those would be the first manned trips into deep space since the Apollo missions sent men to the moon decades ago, said Jason Davis, who writes about human spaceflight at the pro-exploration Planetary Society."We essentially need to relearn a lot of these techniques. And it's not just a matter of learning things that we've forgotten; it's practicing new techniques that we didn't do for Apollo," Davis said. A trip to Mars "is different by leaps and bounds than anything we've ever done before in human spaceflight." Then again, no one knows quite when a mission into deep space might lift off. NASA has made its goals clear, but it's less certain when they might be fulfilled. The agency has been criticized for not laying out a more specific time line, and meanwhile, its funding is controlled by Congress and its direction by the president, meaning plans could change. "Because of this political uncertainty, they, like all other astronaut classes, will be wondering if they really ever are going to fly in space or if there will even be a vehicle or program for them to fly," former astronaut Nicole Stott, a Clearwater native, said in an email. That uncertainty has been felt acutely in Florida, where thousands lost their jobs after the space shuttle program ended in 2011 and where NASA's new rocket, dubbed the Space Launch System, will one day take off. Astronauts have always faced the risk of not making it back home, but a return to deep space — to the moon, an asteroid or even Mars — would raise a question they haven't had to wrestle with in decades, said Ramon Lugo, director of the Florida Space Institute at the University of Central Florida. Does the benefit to humanity of going into uncharted territory outweigh the risk to an astronaut's life? It's a question that harkens back to the early days of the space program, when a mission to the moon was an out-there goal, not a decades-old memory. "I'm not sure that we've had to do necessarily that kind of calculus when we were selecting astronauts in the past," Lugo said.Contact Thad Moore at [email protected] Follow @thadmoore.