President Barack Obama's cancellation of NASA's plan to renew manned lunar missions, the completion of major assembly milestones on the International Space Station and the imminent termination of the shuttle flights form a nexus from which to view a previous space juncture that also had profound implications for the U.S. space program.

That is the decision by President Richard M. Nixon to approve the reusable space shuttle, at the same time terminating NASA planning for a post-Apollo manned Mars program that NASA says would have required in-orbit support by a far more massive space station than the 6-person 800,000 lb. ISS currently in operation.

In researching NASA/White House coordination of these critical post-Apollo decisions, Spaceflight Now uncovered planning documents that show NASA was seeking Nixon's approval of a gigantic 100-astronaut space station to support initial manned flights to Mars as early as 1985.

NASA's Mars mission support station in Earth Orbit would had had several multi-floor plans. This would be the 1975 configuration with 15 astronauts. It was to grow to 100 crew members by 1980. Credit: NASA/Marshall Space Flight Center

Planning for such an enormously expensive and complex station, that never came to be, shows how ambitious (and often naive) NASA has been in planning the return of astronauts to the Moon and the use of a massive Earth orbit station to configure their ships for Mars.

After 40 years of flawed NASA overtures to seven U.S. Presidents, and 21 sessions of Congress, it is now President Barack Obama's turn to judge the merits of a new manned lunar or Mars program that NASA hopes will recapture the magic of Apollo.

But as the late George M. Low, Apollo spacecraft program manager, said somberly at the time, "There never will be another Apollo."

The Obama Administration's NASA Fiscal 2011 budget is forcing the space agency to abandon antiquated "Apollo-era thinking" that in the view of White House officials has foiled manned planning for operations beyond low Earth orbit for 40 years. But unlike under Nixon years, the Obama White House is striving to make any new lunar and Mars decisions more relevant to overall national space technology needs as part of a well thought out Obama space policy.

The legacy of the 100-man station will remain, however, with the assembly significant space-based infrastructure in the form of propellant tank farms, etc., to fuel missions bound for the Moon and beyond.

Tradeoffs for an operational U.S. space station that would follow Apollo are well known. The fact that it was to grow from about 12 astronauts in 1975 to a crew complement of 100 astronauts to aid Mars mission departures has been lost to history for the last four decades.

NASA was seeking support for an Earth orbit space station far larger than the current ISS.

Multiple sections of the giant station were to be launched by uprated two-stage versions of the Saturn V moon rocket with third stages configured as a furnished station module.

The challenge of building and operating a 100-astronaut station by 1980 would have been magnitudes more expensive than building the current ISS that will essentially finish this week with STS-130, the 32nd shuttle mission to the ISS over the last 10 years.

Mars lander with crew heads for the surface as nuclear-powered Mars transfer stage orbits over Martian volcano Olympus Mons. Credit: Pat Rawlings/SAIC for NASA

The current International Space Station with a crew of just six already has a mass of nearly 800,000 lb., with structure that would nearly span the length of an American football field.

Compare that scale with solar array and other needs of a facility that would have housed in space as many people who live in a large apartment building, along with their work areas, whatever that was to be.

Robert Mayo, Nixon's budget director, was dumbfounded when saw the 100-man station request from NASA.

Historians say it was the shock of committing to such a large manned station just to support Mars missions starting about 1985 that led Nixon to focus exclusively on development of a reusable space shuttle as the main manned program that would follow Apollo.

According to aerospace historian L. Parker Temple, III, Mayo told Nixon that it was possible to move forward without significant near-term budget expansion that the station and Mars operations would require, but to do it would be to start development of the space shuttle before the big station, and hope the shuttle could later build and operate a station at much less cost.

"This clever inversion of the STG recommendations allowed the prospect of a [theoretically] cost-effective launch system and temporary or even permanent deferral of the space station," says Temple. He has analyzed Nixon's role for the U.S. Air Force Historical Foundation and its journal, Air Power History.

NASA documentation on the 100-man station show that concepts for smaller stations were being rejected as "too conservative" by NASA.

The role of the ISS in an Obama Administration return to the Moon has yet to be defined, as has any new manned Moon or Mars initiative since Obama cancelled Constellation.

The ISS will be vital to assessing life sciences issues related to long duration Mars round-trip missions and possibly the testing and deployment of inflatable habitats that could be used on the Moon or Mars.

NASA/Mars Human Reference Mission drawing depicts large ascent stage firing off frame of descent stage after the crew spent several weeks exploring the Martian surface. Credit: NASA

But the Obama administration is also providing several hundred million dollars in science funding to maintain utilization of the International Space Station (ISS) through at least 2020, and about $2 billion to upgrade the Kennedy Space Center for a wider range of launch operations. The Johnson Space Center nor Marshall Space Flight Center will fare as well as Kennedy, NASA managers say.

After killing Constellation, NASA's Apollo look-alike program, Obama is giving NASA and several "New Space" commercial ventures a second chance to define a human flight capability beyond Earth orbit and encompassing more than the Moon and Mars. If it wants, the Congress could theoretically reinstate elements of Constellation, and theoretically Obama could veto it.

It took 30 years of additional planning and setbacks between 1969 and 1999 before assembly of the ISS as a joint program between NASA, the Russians, Europeans, Japanese and Canadians could get fully underway. And it has taken another 10 years of shuttle operations to launch and assemble the ISS infrastructure.

The same serious flaws under Bush Administration planning for the Vision of Space Exploration also led to cancellation of the entire Constellation program by Obama, according to NASA managers and officials at the White House Office of Management and Budget.

Mars remains the ultimate destination, possibly also with a limited NASA manned lunar capability as well. But the White House is still weighing whether a new infrastructure could be developed to also enable astronauts to visit asteroids for Earth threat assessments and Lagrangian points for telescope servicing.

The Martian moon Phobos remains a possible destination for detailed Mars science and infrastructure demonstrations short of taking on a blazing hypersonic descent through the Martian atmosphere to reach the surface.

The previous two Bush administrations (father and son) both approved space policies that would return astronauts to the Moon as a stepping stone to Mars. President Reagan did as well, but the Congress in all three cases under funded all of the initiatives, leaving NASA with no major new manned flight programs as the ISS is completed, the shuttle phased out and Earth orbit transportation to the ISS to be handed to commercial operators -- if all goes well.