Some NASA scientists had grand plans heading into AAP's establishment in 1968. But the program's budget as allocated by Congress severely constrained what might have been, Portree said.
Onward to Mars?
Another mission that never took off, but had been in the works for years, was a manned flyby of Mars using Apollo and AAP hardware. Slated for the mid-1970s, the quest's four-man crew would conduct telescopic observations and run experiments on themselves to learn about the health effects of prolonged weightlessness. The astronauts would arrive back at Earth about a year later. [Would Humans Born on Mars Grow Taller Than Earthlings?]
Other proposed journeys included dual-planet flybys of both Venus and Mars, as well as launching probes to collect samples for return to Earth.
With these proposals, "there was the idea of creating a bridge — a little bit like Gemini was for Apollo — for much more complex Mars landing missions in the 1980s," Portree told Life's Little Mysteries, a sister site to SPACE.com.
Events did not conspire to bring about such challenging expeditions then or since. According to Portree, Congress felt NASA needed to be punished after the tragic Apollo 1 fire that killed three astronauts in January 1967, and that led to budget cuts for future endeavors. The rising costs of the escalating conflict in Vietnam did not help NASA's budget either, and the new Nixon administration, elected in 1968, wanted to carve out its own space policy distinct from the Apollo years.
Were it not for these factors, Portree said, "I think the more ambitious Apollo and Apollo follow-ons would have happened."
Technological dividends at home
An expanded Apollo program might have produced more than a legacy of awe-inspiring planetary excursions. The Apollo as it actually existed also spawned loads of so-called spinoffs – commercialized technologies developed by NASA.
Famous examples include memory foam (as found in Tempur-Pedic mattresses), long-lasting freeze-dried food, Dustbuster hand vacuums and fabric roofs. Big leaps in computer technology also occurred, yielding faster processors, lower power consumption and smaller component sizes to name a few.
Had Apollo carried on, "maybe the computer boom would have happened sooner," Portree speculated. "Maybe we would have learned new things about medical problems people have on Earth because we were trying to solve them for astronauts bound for Mars."
The Apollo miracle
Of course, beyond NASA's preliminary sketches, the voyages an enduring Apollo program might have embarked on — and the technological advances they could have sparked — remain science fiction. Although it's unlikely that Apollo 30-something would have put mankind on Mars, such an alternative history does seem less far-fetched than Apollo 18 finding aliens on the Moon.
That the Apollo program actually succeeded is perhaps the greatest surprise of all, as no one has since set foot on the moon.
"It's a little tough to imagine how [Apollo] could have happened differently," said Portree, "but it's tough to imagine that we went in the first place."