The countdown clock is officially rolling at Kennedy Space Center in Florida, where four astronauts are preparing to take off on the mission of a lifetime — circumnavigating the moon and returning humans to deep space for the first time in five decades.After nearly two months of tests and troubleshooting, NASA appears to be on the cusp of firing its 322-foot-tall (98-meter) Space Launch System rocket to orbit. The current target for takeoff is a two-hour launch window that opens at 6:24 p.m. ET on Wednesday.Rockets launch fairly frequently from the United States’ Space Coast, as the area surrounding NASA’s KSC facilities is called, but this mission is an obvious standout. NASA’s Reid Wiseman, Victor Glover, and Christina Koch along with Canadian Space Agency astronaut Jeremy Hansen will climb aboard the Orion spacecraft — which sits atop the Space Launch System rocket — and blast toward space, going from zero to 500 miles per hour (about 805 kilometers per hour) in just two seconds.AdvertisementAdvertisementWithin three and a half hours after liftoff, the Orion capsule will be fully separated from the rocket, and the astronauts will get a chance to manually pilot the spacecraft.Rocket launches are complex, hours-long affairs, but here are a few key moments to watch for and things to know.Tracking Ts and LsThe SLS rocket and Orion spacecraft sit on Launch Pad 39B as the countdown clock runs at the Kennedy Space Center on Monday. – Joe Raedle/Getty ImagesOne important note for those planning to follow …
