After half a century at the forefront of space exploration, NASA’s been hit by hard times. Last year, its groundbreaking and celebrated space-shuttle program was shuttered. The cosmos won’t see another American spacecraft for at least another decade, and that once dreamed of trip to Mars – not too long ago a serious interest of the U.S. government – isn’t even close to being a priority. Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, considers what the future of NASA is, and what could be done to reinvigorate the program in his book “Space Chronicles: Facing the Ultimate Frontier.”