“Welcome back, Discovery,” Stephen N. Frick, a NASA astronaut communicating with the shuttle from mission control in Houston, said to the shuttle commander, Col. Steven W. Lindsey of the Air Force, after the shuttle had come to a halt.
Colonel Lindsey replied, “This was a great mission, a really great mission.”
The Discovery’s successful return nonetheless marks the beginning of the end of the shuttle program, which President Bush has ordered to be shut down by 2010.
In that time, the National Aeronautics and Space Administration is to perform 16 more shuttle missions to complete the International Space Station, the half-built orbiting laboratory that was the Discovery’s destination in this flight. The agency will then embark on the president’s stated goal of returning to the Moon in a new generation of space vehicles.
The morale boost of a successful flight after the loss of the shuttle Columbia in 2003 and a frustrating first test flight last year was evident in the beaming smiles of the crew and NASA officials — even Michael D. Griffin, the self-described emotionless engineer who is the space agency’s administrator.
N. Wayne Hale Jr., the shuttle program manager, said at a news conference at mission control in Houston, “The shuttle is back.”
Still, questions remain about whether the program has solved the safety problems that have plagued it over the years — problems that NASA officials pledged to pursue.
NASA managers said that the success of this mission reinforced their view that they could step up the tempo of launchings, with the shuttle Atlantis returning to space as early as Aug. 28 and the mission after that beginning in mid-December.
Mr. Griffin cautioned at a news conference here at the Kennedy Space Center, “We’re not going to get overconfident.” Engineers and analysts will pore over the data from this flight in the coming weeks and months, he said, to better understand issues like foam debris from the shuttle’s external tank before launching the next mission.
The amount of foam shed in the Discovery’s July 4 liftoff — the problem that doomed the Columbia and continued to plague last year’s return-to-flight mission — posed no threat to the shuttle, with the biggest piece weighing less than two ounces.
But a member of the independent board that investigated the Columbia disaster said the risks of shuttle flight were still very real.
“This shows that with appropriate care and vigilance, the odds of operating the shuttle with acceptable risk are good,” said the board member, John M. Logsdon, the director of the Space Policy Institute at George Washington University. But he added: “It doesn’t mean the shuttle is safe. The shuttle will remain a very risky vehicle to be operated with extreme care.”
The crew took thousands of pounds of supplies to the half-finished space station, performed three spacewalks in which they repaired broken equipment to allow the resumption of construction on future shuttle flights, and tested possible repair techniques.
They also carried up a new crew member, Thomas Reiter, a German astronaut from the European Space Agency. Mr. Reiter remained behind aboard the space station, bringing its crew to three for the first time since the Columbia disaster.
The crew was led by Colonel Lindsey, who was making his fourth trip to space and his second as a commander. The pilot, Cmdr. Mark E. Kelly of the Navy, was on his second shuttle mission. The two spacewalkers were Piers J. Sellers of England and Michael E. Fossum. The flight engineer, Cmdr. Lisa M. Nowak of the Navy, operated the robot arm during the spacewalks, along with Stephanie D. Wilson, who also supervised the transfer of tons of cargo between the two craft.
Despite the astronauts’ grueling schedule, there was time to both laugh and marvel. At a news conference here on Monday, Colonel Lindsey recalled that Commander Nowak’s ponytail, which acquired a will of its own in zero gravity, had gotten stuck on a strip of Velcro in the mid-deck of the shuttle.
Colonel Lindsey said he and the pilot, Commander Kelly, had had a view on the way home that was even more spectacular than usual.
