Space shuttle Endeavour roared into orbit carrying teacher-astronaut Barbara Morgan, who was finally fulfilling the dream of Christa McAuliffe and the rest of the fallen Challenger crew. Endeavour and its crew of seven rose from the seaside pad at 6:36 p.m. (2236 GMT) Wednesday, right on time, and pierced a solidly blue sky. They are expected to reach the international space station on Friday. Once Endeavour was safely past the 73-second mark of the flight, the moment when Challenger exploded shortly after the call "Go at throttle up," Mission Control exclaimed, "Morgan racing toward space on the wings of a legacy." Immediately after the shuttle reached orbit, Mission Control announced, "For Barbara Morgan and her crewmates, class is in session." Morgan was McAuliffe's backup for Challenger's doomed launch in 1986 and, even after two space shuttle disasters, never swayed in her dedication to NASA and the agency's on-and-off quest to send a schoolteacher into space. She rocketed away in the center seat of the cabin's lower compartment, the same seat that had been occupied by McAuliffe. McAuliffe's mother, Grace Corrigan, watched the launch on TV from her home in Massachusetts. "I'm very happy that it went up safely," she said. "We all send her our love," she added, her voice breaking.