The 135th and final flight of America’s space shuttle fleet landed safely at Kennedy Space Center early Thursday — ending the three-­­decade lifetime of a technologically remarkable and versatile spacecraft, the likes of which the world is unlikely to see for a very long time.

While hailing the successful landing and all those associated with it, NASA officials worked hard Thursday to convince the public that this was not the end of the nation’s space ambitions but, rather, a change of course.

At a news conference after the landing, the associate administrator for space operations, William H. Gerstenmaier, who has worked on the shuttle since the 1970s, said it was “time to move on and focus on the future.”

“Huge growth and huge improvements come from change,” he said. “We can’t afford to fly the space shuttle and [also] do other ambitious missions.”

Gerstenmaier said human space exploration and research will surely remain central to the agency’s mission. The international space station is complete and ready to begin long-delayed scientific work; plans are underway for commercial space companies to service it relatively soon. In addition, he said, NASA is working with Congress for the money and direction for building a heavy lift rocket to explore outer space.

NASA Administrator Charles Bolden set a similar tone shortly after touchdown — saying that the program was responsible for a long number of “firsts,” but also focusing on the frontiers that have yet to be conquered.

“Children who dream of being astronauts today may not fly on the space shuttle . . . but, one day, they may walk on Mars,” Bolden said. “The future belongs to us. And just like those who came before us, we have an obligation to set an ambitious course and take an inspired nation along for the journey.”

The shuttle Atlantis and its four crew members touched down in Florida at 5:56 a.m., shortly before sunrise, after a 13-day mission to the international space station, the space laboratory that could never have been built without the huge cargo-carrying capacity of the shuttle.

“After serving the world for over 30 years, the space shuttle’s earned its place in history. And it’s come to a final stop,” radioed commander Christopher Ferguson.

“Job well done, America,” said mission control.

Although the ballooning cost of the shuttle — now at about $1 billion per launch — and the two shuttle disasters have somewhat tarnished its image and legacy, its achievements are real. It is the only winged vehicle to orbit in space, it traveled at speeds of up to 17,500 mph and it withstood temperatures of as much as 3,000 degrees on reentry.

It was also used to launch the Hubble Space Telescope and other observatories and made five trips to the Hubble to repair and upgrade it. In addition, it made possible a level of international cooperation in space never seen before, especially between the United States and Russia.

At the mid-morning news conference, shuttle program director Mike Leinbach said the landing was very emotional, with “grown men and women crying on the runway.” Leinbach said there were tears of joy for the safe return of Atlantis and completion of the shuttle mission, but also tears of sadness, since the program was over and many people would be out of work.

Thousands of jobs will be lost as contractors for the shuttle program begin to lay off workers. Some companies have pledged to absorb the lost jobs and reassign the engineers, technicians and others who built and operated shuttle flights. But thousands will not be that lucky, starting with 1,500 at Kennedy Space Center who will be out the door Friday.

The United Space Alliance of Houston, which supplied workers for the mission, will ask employees to turn in their badges and fill out paperwork to finalize a “processing out” that’s been in the works for months. Each will receive a severance package, NASA officials said.

One who will be losing his job is Leonard Buffum, 44, an aerospace electronics technician who has worked on the mobile launch platform at Kennedy Space Center for 12 years. The safe completion of the final mission was a bittersweet moment for many of his co-workers, Buffum said in a telephone interview Thursday afternoon. “The mood was somber,” he said. “There were a lot of emotions flying around. The last shuttle comes in and then there’s nothing more.”

With no American spacecraft available to fly to the space station, it will now be restaffed using Russian Soyuz spaceships and resupplied by Russian and possibly European and Japanese capsules.

Signaling the urgency of the effort to return U.S. manned spacecraft to space, Gerstenmaier said Thursday that NASA and the company SpaceX are working “aggressively” to begin cargo delivery sooner than planned. He said the two have tentatively agreed to combine two planned test flights to the space station into one test flight later this year. If the tests are combined and succeed, the company’s Falcon 9 capsule could begin bringing cargo to the space station late this year.

Gerstenmaier said that realistically, however, the capability of private companies to fly astronauts (as opposed to cargo) to the space station won’t be in place until 2015 or 2016.

Atlantis left the space station Tuesday after delivering a year’s worth of supplies. The station, which took 12 years and 37 shuttle flights to build, is clearly the most enduring legacy of the shuttle program. Now formally designated as a national science laboratory and orbiting 250 miles above Earth, the station is just beginning to perform the science that was always planned for it.

One of the shuttle’s final missions was to deploy an eight-pound micro satellite, the last of 180 satellites and observatories large and small that took off from the shuttle. The spacecraft, first conceived in the late 1960s, was initially designed to be a launch pad for many more and larger vehicles, but that promise was never fulfilled.

The three remaining active shuttles will be decommissioned and put on display — Discovery at the Smithsonian’s Steven F. Udvar-Hazy Center museum outside Washington, Endeavour at the California Science Center Los Angeles and Atlantis at Kennedy Space Center. Two other shuttles, Challenger and Columbia, failed in 1986 and 2003, respectively, killing 14 astronauts.

Staff writers Lisa Rein and Steve Vogel contributed to this report.