CAPE CANAVERAL Imagine yourself, feet planted in the soil, staring into the night sky. Your eyes focus on one bright dot, a shining star. It seems brighter than most others. And it looks bluish.In all probability, you feel powerful emotions while looking at this distant star, because you know it is Earth. But standing with your boots in the Martian soil, the home planet doesn't look much different from all the other pinpricks of the Milky Way.This is the lonely viewpoint of a traveler to Mars.And it's just one glimpse into the mind-bending challenges that could make a journey to Mars psychologically and physically impossible.The first astronauts on Mars would be the most isolated humans in history. And this might not even be the hard part.Just getting to Mars would require humans to survive cosmic radiation and the bone-crippling environment of space. It would require people smart enough to operate a spacecraft and crazy enough to live in a tiny, weightless condo for much of a three-year journey — with roommates. The human brain and body may simply not be up to the task.In case you're wondering, there is a reason for bringing all this up, and it's not just to ponder whether last year's movie The Martian was remotely plausible.Now, sending humans to Mars is official U.S. policy.Says NASA administrator and former astronaut Charles Bolden, "We are closer today than ever before in human history to sending American astronauts to the red planet."• • •At the Kennedy Space Center on Florida's east coast, sending humans to Mars is not a dream, and it's not a theory. It's a construction project underway right now inside NASA's Vehicle Assembly Building, which once housed spacecraft that transported men to the moon.Picture this building, one of the largest on Earth. It covers 8 acres and stands taller than the Statue of Liberty. With all that room, you could take the volume of the entire Pentagon and slide it in there with space to spare.Inside this giant, man-made cavern, ironworkers are installing 10 huge platforms to support a new rocket called the Space Launch System, or SLS.The SLS rocket will be 384 feet tall, the largest ever built. The 10 platforms will envelop it, giving future workers easy access to all stages of the rocket as they stack it, connect it, check and re-check it. "Right now we're about 70 percent complete in the reconfiguration," said Jose Perez Morales, the program manager supervising the work for NASA. As he speaks, workers dangle from baskets 16 stories high. Sparks cascade from a welder's torch.Three miles away, on an oceanside launchpad that dates to the 1960s Apollo era, a different army of workers is laying 100,000 heat-resistant bricks in a flame trench designed to withstand the new rocket's blaze.The setting overlooking the Atlantic Ocean is an odd combination of tranquility, history and construction zone. Some here used to work on this very pad to launch space shuttles.Regina Spellman, the NASA official supervising this portion of the project, sometimes pauses and realizes that all this brick, all this concrete, all this rewiring and rethinking is designed for the specific purpose of getting astronauts to Mars."This will be their last view of the planet before they leave," she said. "This is the last air they're going to breathe. This is the last time their feet are going to be on the ground before they go to Mars. It's going to be right here."But wait.How can workers at Cape Canaveral prepare for a mission to Mars, considering that NASA killed the space program?Answer: NASA didn't kill the space program.It just seemed that way.• • •Some of us remember — and some of us learned in grade school — that the Soviet Union and the United States engaged in a space race. The Soviets got humans into space first. But at least in our history books, the race pretty much ended when American astronauts triumphantly landed on the moon nearly half a century ago.Many of those astronauts expected to see people land on Mars within the next decade. Instead, we spent a good 30 years circling Earth in space shuttles and building the remarkable International Space Station.Then under President George W. Bush, NASA announced it would stop flying space shuttles and begin a program called Constellation, which would take humans back to the moon and on to Mars. The incoming Obama administration declared this plan to be behind schedule and unrealistic. It killed the plan but promised to replace it with a rocket that would venture into "deep space."Reaction was blistering. One senator called the move "the death march for the future of U.S. human spaceflight." Another called it "a crippling blow."Call it bad public relations, but Obama and NASA never effectively battled that impression. The idea persists that NASA has given up on human space flight, even as its astronauts orbit Earth on the space station. But the outlines of a Mars mission are starting to take shape. NASA is developing the capabilities needed to send humans to an asteroid by 2025 and Mars in the 2030s, the agency declared last year. The mission would be timed so that Mars and Earth are close together in their orbits. The astronauts would board a space capsule called Orion, capable of carrying a crew of four on long flights. The giant SLS rocket would be ignited, and 3 … 2 … 1 …Under one scenario, astronauts would spend nine months flying to Mars, more than a year on Mars and nine months flying back.The process is still in its early stages, said John Logsdon, a professor emeritus at George Washington University and one of the nation's most prominent space policy experts. But the progress is significant."As (NASA) administrator Bolden said, we're closer now to putting boots on the surface of Mars than we ever have been, and I think that is correct, but that doesn't mean we're very close," Logsdon said. "But for the first time since the 1960s, we're building hardware, the primary purpose of which is deep space exploration."• • •Now imagine something else. This time you're in a spacecraft, floating. Your eyes are shut. But somehow you see flashes of light.Astronauts have noticed these weird flashes since the Apollo days. The theory is, they may be caused by cosmic rays that shoot throughout the universe and can pass right through the human body and even a spacecraft. These particles may somehow interact with the optic nerve to create the sensation of flashing lights.Are flashing lights going to prevent astronauts from landing on Mars? No. But they're one example of how radically different things get as soon as we start poking out of the security blanket of Earth's atmosphere.The emptiness of space is actually full of hazards.Cosmic radiation blasts out of stars, including our sun and supernovae. This radiation can cause cancer. It could shorten life-spans of astronauts. But how much radiation would astronauts encounter on a nine-month trip to Mars, and how dangerous would it be?"This is a very difficult question," said Dr. Andre Diedrich, a physician and research professor at the Vanderbilt University Center for Space Physiology and Medicine. "For deep space exploration, this is unknown." Most astronauts, like those aboard the International Space Station, have travelled in low Earth orbit, still somewhat protected by Earth's magnetic field.Another danger: Astronauts lose bone density in space, maybe half a percent per month, maybe 1 or 2 percent each month, maybe more. Multiply that by 18 to 24 months, which could be how long astronauts spend flying to Mars and back. An astronaut could wind up with the skeleton of your grandmother. "The risk is really big, because if you lose more than 30 percent of your bone strength, then your bones are weak and can break," Diedrich said.Astronauts could face many other physical hazards, such as loss of muscle density and hearing, "circadian desynchronization" and altered immune response.Then there are the psychological challenges. Depression is a concern. So is group cohesion — how can a small group of astronauts work together and not succumb to chaos?To help answer that question, University of South Florida psychology professor Wendy Bedwell flew to Hawaii last month to meet with six people as they exited the longest Martian space simulation conducted in the United States.In the NASA experiment, six scientists spent a year inside a dome that amounted to a pretend Martian habitat on the Mauna Loa volcano. The scientists could communicate to family members outside of the habitat only by email, each message with a time delay of several minutes, like they'd experience on Mars. They left the dome for occasional "spacewalks" in spacesuits, walking across reddish volcanic rocks similar to those of Mars.Bedwell interviewed all six as they ended their year-long commitment. She wants to know whether it's important for all members of a Mars team to be very compatible or whether it's okay to have smaller groups of two or three who are especially close but capable of banding together with the entire group for the success of the mission."How are we going to get a group of four to six people from various cultural backgrounds to live and work together in an isolated, confined, extreme environment for an extended period of time?" she said.She noted that "astronauts have constantly talked about the importance of being able to see Earth when in space. That's their connection to home. And what is it going to do to them when they can no longer see Earth, or Earth looks like a star in the sky?"• • •Of course there is a cheaper and safer alternative to all this: robots.Unmanned spacecraft from various countries have zipped across the solar system like heroes out of a pulp fiction novelette, peeking at the moons of Saturn, punching into a comet and cruising to Pluto. To get an idea of how sophisticated these robotic spacecraft can be, consider one that launched in September from Kennedy Space Center. OSIRIS-REx has an ambitious mission.It is designed to go to an asteroid named Bennu. It will orbit and map the asteroid, a job that would not be easy for a spacecraft with humans because Bennu is small and doesn't have much gravity. Astronauts standing on Bennu could launch themselves into space just by jumping.Next, OSIRIS-REx will approach the asteroid's surface, scoop up a sample of rocks and fly it back to Earth for study, like the moon rocks collected by human astronauts.Asteroids are thought to be early remnants of the solar system and may even help explain the origins of water — and life — on Earth. So this is not some obscure project that matters only to a handful of scientists."What was the solar system like shortly after it was formed 4½ billion years ago?" asked Ed Beshore of the University of Arizona, who is deputy principal investigator for OSIRIS-REx. "We believe the right place to go is to some of these primitive asteroids because they really are the unprocessed remainder of the building of the solar system."With missions like this one exploring the most fundamental questions, some think it makes more sense to scrap human space flight and pour all the focus into these "science missions."Interestingly, Beshore is not among them. "I think they both have their role," he said. Send space probes first, he says. Then follow up with astronauts.Others interviewed for this story agreed that wanting to send humans out to explore is simply part of being human. "In the simplest sense, it's about benefiting and improving life on Earth," said Nicole Passonno Stott, a retired astronaut who grew up in Clearwater and recently returned from Houston to the Tampa Bay area. Casey Dreier, director of space policy for the Planetary Society, said a healthy culture explores and challenges itself: "Are we peacefully reaching out, pushing out, challenging ourselves technologically, engineering-wise, scientifically, and daring to just say, 'What's out there, and can we do this?' Versus doing nothing, turning purely internally, looking at our little cellphones." It's not only NASA that's interested in going to Mars. The privately funded space sector — a term that would have been an oxymoron a couple of decades ago — is growing explosively. Elon Musk of the company Space X has said he'd like to send humans to Mars, possibly by 2025.Despite all the work underway at the Kennedy Space Center, despite the development of the SLS rocket and Orion space capsule, the future of a Mars mission is not clear. Neither major-party presidential candidate, Hillary Clinton nor Donald Trump, has laid out an extensive space program. Work on the Mars mission has begun, but it's not like it couldn't be stopped."It's clearly the decision of the next president whether we continue on this path," said John Logsdon, the George Washington University professor. "We're at the relatively early stages. So it is reversible."