U.S. President Barack Obama championed NASA's space program Thursday, with an ambitious plan that aims to send astronauts to Mars within three decades.

Speaking at the Kennedy Space Center in Cape Canaveral, Fla., Obama said that exploring the universe is a priority for his administration.

"I believe that space exploration is not a luxury, and it's especially not an afterthought," he said. "I am 100 per cent committed to the mission of NASA and its future."

Obama's plan for NASA includes a $6-billion boost to the space agency's budget over the next five years. This cash injection comes as Obama's administration has instituted a discretionary spending freeze and tried to make cuts elsewhere in the budget.

Meanwhile, the life of the International Space Station will be extended "likely by more than five years," Obama said.

Private industry will figure prominently in the "next chapter" of NASA, as companies compete to design vehicles for space travel.

Obama also outlined the development of an advanced telescope to follow Hubble, and a plan to spend $3 billion to research a new heavy-lift rocket.

However, Obama's predictions rely on technology yet to be conceived, and many critics believe that shifting goals will deal the space program a life-threatening blow.

Still, Obama said he expects that by 2025, manned missions will travel beyond the moon into deep space.

"We'll start by sending astronauts to an asteroid for the first time in history," he said. "By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow."

"I expect to be around to see it," he said.

Obama's plan also includes scrapping the return-to-the-moon plan laid out by former president George W. Bush, moving instead to a more complicated system that combines public and private space flights that would go elsewhere in space.

The change in direction has been the target of criticism, but Obama shot back at his detractors Thursday.

"We've been there before," he said of the moon. "There's a lot more of space to explore."

Obama has been criticized for lacking a clear vision when it comes to the future of the U.S. space program. Thursday's announcement was designed as a way for the president to articulate his administration's ambitions.

"I think he said all the right things," said George Washington University space expert John Logsdon, who praised Obama's speech and his Mars goals.

"I don't know what more you could have asked for."

But Republican critics contend that once the shuttle program is ended, thousands of jobs will be lost.

"The president's new plans for NASA are flat-out irresponsible," said Sen. David Vitter.

"He has evidently decided ... that it's time for us to simply walk away from manned space exploration for the foreseeable future, with no clear timeline for returning or for achieving any of our goals for deep space exploration."

But Obama countered those complaints by saying the space program will generate about 10,000 jobs across the U.S. in the next few years.

He also unveiled a $40-million initiative to develop a plan for economic growth and job creation in Florida, to target job losses as the space shuttle program winds down.

With files from The Associated Press