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The first man to walk on the moon has blasted off at the Obama administration's stripped-down space plans, describing the president's proposals as "devastating." But supporters of the president's latest plan, which will be unveiled on Thursday, insist all systems are go for an accelerated rocket program that sets new goals for the American effort in outer space.

Moonwalk icon Neil Armstrong, in an open letter co-signed by Apollo Commanders James Lovell and Eugene Cernan, wrote on Tuesday that "The … decision to cancel the Constellation program, its Ares 1 and Ares V rockets, and the Orion spacecraft, is devastating.

"America's only path to low Earth orbit and the International Space Station will now be subject to an agreement with Russia to purchase space on their Soyuz (at a price of over 50 million dollars per seat with significant increases expected in the near future) until we have the capacity to provide transportation for ourselves. The availability of a commercial transport to orbit as envisioned in the President's proposal cannot be predicted with any certainty....

"It appears that we will have wasted our current $10-plus billion investment in Constellation," the former astronauts wrote.

In another letter, released on Monday, more than two dozen Apollo-era veterans called the plan a "misguided proposal that forces NASA out of human space operations for the foreseeable future."

The harsh criticism from the men and women celebrated for decades for having "The Right Stuff" has sharply raised interest in America's space program in advance of Obama's planned address on Thursday to top NASA officials at the Kennedy Space Center in Florida.

The president will announce a set of stepping-stone achievements that will take the United States farther into space, along a range of destinations including lunar orbit, so-called "Lagrange points" (prime destinations for permanent, orbiting fuel depots), near-Earth asteroids, the moons of Mars, and eventually Mars itself.

Whle Armstrong and others derided the elimination of Constellation, the planned replacement for the aging space shuttle, Obama will announce plans to salvage a portion of it: the Orion space capsule, which was intended to house astronauts during their travel to the International Space Station and on later missions to the Moon. It also was to be capable of docking at the Space Station for six months and returning crews to Earth.

"We wanted to take the best of what was available from Constellation," a NASA official told The Associated Press as part of a White House briefing.

Orion will serve temporarily to provide standby emergency escape capabilities for astronauts on the Space Station, addressing fears from some experts that U.S. astronauts on the space station would be held "hostage" to Russian interests.

"The U.S. has surrendered its advantage in space, conceding the high ground to others who are probably our enemies," Jane Orient, a science policy expert and professor at the University of Arizona, recently told FoxNews.com. "We are apparently leaving seven astronauts in space as hostages. Their loss would be a tragedy, but only a small part of the total disaster. It would symbolize the lack of respect that America has for its pioneers."

Obama hopes NASA will be able to launch the Orion vehicle within the next few years, creating an escape capability that will increase the safety of Americans on the Space Station, reduce U.S. dependence on foreign providers and simplify requirements for other commercial crew providers.

Famed astronaut Buzz Aldrin weighed in following the revelations of Obama's plans, strongly endorsing the president's new direction for NASA.

"The truth is, that we have already been to the moon -- some 40 years ago. A near-term focus on lowering the cost of access to space and on developing key, cutting-edge technologies to take us further, faster, is just what our nation needs to maintain its position as the leader in space exploration for the rest of this century," Aldrin said.

To address Armstrong's other major fear, that replacement for the Ares heavy lift vehicle is "likely to take substantially longer and be more expensive than we would hope," administration officials said NASA will speed up development of a larger "heavy-lift" rocket that would take cargo and crew away from Earth orbit to the moon, asteroids and other places.

The president on Thursday will announce his commitment to choosing a single heavy-lift rocket design by 2015 and then starting its construction, officials said. This shift means NASA would launch a heavy rocket years before it was supposed to under the old Constellation plan, the NASA official said.

But the new rocket will be different from the Apollo-like Ares V rocket that the Constellation plan would have used. Instead, it will incorporate newer concepts, such as refueling in orbit or using inflatable habitats, officials said.

Overall, the Obama program will mean 2,500 more Florida jobs than the old Bush program, a senior White House official said. In addition, the commercial space industry on Tuesday released a study that said the president's plan for private ships to fly astronauts to and from the space station would result in 11,800 jobs.