Veteran astronauts Neil Armstrong, Eugene Cernan and James Lovell have signed an open letter urging Barack Obama to reconsider the "devastating" cancellation of the Constellation programme.
In the letter, obtained by NBC, the trio of Apollo commanders insist that in order to avoid "a long downhill slide to mediocrity", the US must maintain its own lifting capability - in the form of the Ares I and V.
They warn that without these "the 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".
They add that "the availability of a commercial transport to orbit as envisioned in the President’s proposal cannot be predicted with any certainty, but is likely to take substantially longer and be more expensive than we would hope".
They insist: "For The United States, the leading space faring nation for nearly half a century, to be without carriage to low Earth orbit and with no human exploration capability to go beyond Earth orbit for an indeterminate time into the future, destines our nation to become one of second or even third rate stature."
Obama canned Constellation earlier this year, effectively putting a return to the Moon on indefinite hold in favour of developing "building blocks" for future space exploration. The US's immediate low Earth orbit needs have been placed in the hands of privateers such as Elon Musk and his Falcon 9.
Here's what Armstrong, Cernan and Lovell think of their country's space prospects, reproduced in full:
The United States entered into the challenge of space exploration under President Eisenhower’s first term, however, it was the Soviet Union who excelled in those early years. Under the bold vision of Presidents Kennedy, Johnson, and Nixon, and with the overwhelming approval of the American people, we rapidly closed the gap in the final third; of the 20th century, and became the world leader in space exploration.
America’s space accomplishments earned the respect and admiration of the world. Science probes were unlocking the secrets of the cosmos; space technology was providing instantaneous worldwide communication; orbital sentinels were helping man understand the vagaries of nature. Above all else, the people around the world were inspired by the human exploration of space and the expanding of man’s frontier. It suggested that what had been thought to be impossible was now within reach. Students were inspired to prepare themselves to be a part of this new age. No government program in modern history has been so effective in motivating the young to do “what has never been done before.”
World leadership in space was not achieved easily. In the first half-century of the space age, our country made a significant financial investment, thousands of Americans dedicated themselves to the effort, and some gave their lives to achieve the dream of a nation. In the latter part of the first half century of the space age, Americans and their international partners focused primarily on exploiting the near frontiers of space with the Space Shuttle and the International Space Station.