"I support the encouragement of the newcomers toward their goal of lower cost access to space," Armstrong said. "But having cut my teeth in rockets more than 50 years ago, I am not confident."
US analysts, however, say the country's space program had no choice but to change, given new global realities.
"The world evolves, humanity evolves, our capabilities evolve. And the future of space exploration, therefore, must also evolve," said Jeff Foust, an aerospace consultant and the editor of TheSpaceReview.com.
For one thing, flights into low-Earth orbit are now considered routine, and privatizing them allows the space agency to focus its efforts on more cutting edge missions, according the Foust.
But there are no footsteps on Mars, and many other hopes that were dreamed of when Armstrong and Apollo 11 crewmates Buzz Aldrin and Michael Collins helped mankind make its "giant leap" in 1969 are still unrealized.
Foust said the succeed-at-any-cost mentality that drove the Apollo program to get the first person on the moon cannot be replicated. That program "was the result of the particular geopolitical factors, that Cold War atmosphere," Foust explained.