CAPE CANAVERAL, Fla. – Space shuttle Endeavour roared into orbit Wednesday 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., 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 that Morgan was “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, now 55, was McAuliffe’s backup for Challenger’s doomed launch in 1986. Even after two space shuttle disasters, she 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.

More than half of NASA’s 114 Teacher-in-Space nominees in 1985 gathered at the launch site, along with hundreds of other educators.

Also on hand was the widow of Challenger commander Dick Scobee. She said earlier in the day that she would be praying and pacing at liftoff and would not relax until Morgan was safely back on Earth in two weeks.

The Challenger crew “would be so happy with Barbara Morgan,” June Scobee Rodgers said. “It’s important that the lessons will be taught because there’s a nation of people waiting, still, who remember where they were when we lost the Challenger and they remember a teacher was aboard.”

NASA Administrator Michael Griffin met Tuesday night with several members of the Challenger astronaut families who were in town for the launch – although not with the McAuliffe family.

After liftoff, Education Secretary Margaret Spellings sent congratulations from Washington and called Morgan “an inspiring example for our next generation of teachers, scientists, engineers, innovators and entrepreneurs.”

Midway through the flight, Morgan will speak with students in Idaho, where she taught elementary classes before moving to Houston in 1998 to train as a full-fledged astronaut, the first teacher to do so. If the mission is extended from 11 days to 14 days as planned, she will have a chance to answer questions from students in two other states.

But Morgan’s main responsibility in orbit will be to her commander, Navy Cmdr. Scott Kelly. She will help operate Endeavour’s robot arm and oversee the transfer of cargo from the shuttle to the station. The rest of the crew will be busy installing a huge square-shaped beam to the exterior of the station and replacing a broken gyroscope. Three and possibly four spacewalks are planned.

Late Wednesday, Morgan sounded all business from orbit, periodically updating Mission Control on the activation of the shuttle’s cargo-carrying module.

“There’s a lot of work, a lot of challenges in front of us, but I think this is a great way to start out,” NASA’s space operations chief, Bill Gerstenmaier, said after the shuttle reached orbit.

The space station is currently more than half finished. NASA plans to wrap up construction in 2010 when the shuttle program ends.

Endeavour’s astronauts also will use a 50-foot laser boom on the end of the robot arm to inspect the shuttle’s wings, nose and belly. The scan for damage from fuel-tank insulating foam and other debris from launch, or micrometeorites in space, has been standard procedure ever since Columbia’s catastrophic re-entry in 2003.

A preliminary check of launch video showed four or five small pieces of debris falling off the external fuel tank, but it occurred too late in the launch to pose any threat to the shuttle, NASA officials said.

NASA is hoping a successful flight will draw some attention away from the rash of embarrassments it has faced this year, most recently a NASA-commissioned medical panel’s report suggesting astronauts were intoxicated on launch day on at least two occasions.

Griffin said NASA is investigating the anonymous allegations. The space agency’s top safety official has gone back 10 years through every shuttle flight and can find no flight surgeon, astronaut or document hinting at launch day drinking by a crew member, he said.

No evidence has been found yet for astronaut drinking right before a Russian Soyuz flight, either, he said.

“This is not a credible scenario. They’re on TV. We just watched them having breakfast,” Griffin said early Wednesday afternoon, referring to the Endeavour astronauts.

“The charges seem uncredible, and it also seems uncredible that somebody would just make it up. That’s why it’s so puzzling and that’s why it’s serious and that’s why we will investigate.”

This is Endeavour’s first flight since 2002. The shuttle underwent a massive overhaul and was outfitted with complete satellite navigation, improved main engine monitoring equipment, and a new system for transferring power from the station to the shuttle. The extra power will allow the shuttle to remain docked at the space station longer than ever before.

Besides Morgan and commander Kelly, the crew also includes Marine Lt. Col. Charles Hobaugh, the copilot; Rick Mastracchio, Tracy Caldwell, Air Force Col. Alvin Drew and Canadian physician Dave Williams.