(AP) — NASA's Maven spacecraft entered orbit around Mars for an unprecedented study of the red planet's atmosphere following a 442 million-mile journey that began nearly a year ago. The robotic explorer successfully slipped into orbit around the red planet late Sunday night. [...] the real work begins for the $671 million mission, the first dedicated to studying the Martian upper atmosphere and the latest step in NASA's bid to send astronauts to Mars in the 2030s. Flight controllers in Colorado will spend the next six weeks adjusting Maven's altitude and checking its science instruments, and observing a comet streaking by at relatively close range. NASA launched Maven last November from Cape Canaveral, the 10th U.S.