Between 1968 and 1972, 24 humans went and orbited the Moon. Of those Apollo astronauts, 12 of them stepped foot on the Moon. Since then, not a single human has ventured beyond low-Earth orbit. And for all the amazing work and research astronauts have done in the intervening decades, the question remains: Why didn’t humans push further when they had already come so far? Why, a half-century later, are we still not appreciably closer to our next great milestone, a trip to Mars?

That’s the question Star Trek: Voyager star Robert Picardo posed while moderating a Sunday panel of NASA scientists at the Star Trek: Mission New York Event. He asked Jeffrey Sheehy, the senior technology officer of NASA’s Space Technology Mission Directorate, whether it would have been possible to immediately follow up the Apollo missions with a trip to Mars. Sheehy’s answer was unequivocal.

“Fifty years on, should we have been able to go to Mars? Yeah, we could have gone to Mars,” Sheehy replied. “We could have mounted a mission to put someone in the Mars vicinity or a couple people in the Mars vicinity with the technologies and extensions of the technologies we had in the ‘70s.”

But just because we could have reached Mars back then doesn’t mean it would have been a good idea to do so, according to Sheehy. The issue is that a Mars mission has different parts. While reaching Mars was doable using 1970s-era tech, actually staying on our planetary neighbor long enough to justify the mission has only recently become possible.

“So once we get to Mars, we’ve got to leave them on Mars for a while.”

“You can’t come and go just anytime you want because of the energy expenditures required and the propulsion capabilities that would be needed,” Sheehy said. As he pointed out, it takes about 180 days each way to travel to Mars, and such trips are only possible when the two planets are properly aligned. And six months of travel in the weightlessness of space poses its own, often overlooked challenges. Sheehy pointed to the experiences of fellow panelist Kjell Lindgren, who spent 141 days on the International Space Station.

“Kjell was telling me when he got back from the space station after being up there for five, six months, the way the body adjusts to being in gravity again is such that when we put people on Mars they’re not going to be able to operate at full capability right away,” Sheehy continued. “They’re going to have to readjust for a while. So once we get to Mars, we’ve got to leave them on Mars for a while, and so to really set up shop on Mars takes technology capabilities that we’ve been developing over the last few decades.”

Sheehy ended his answer on an optimistic note, saying the kinds of advances in propulsion, power, and life support capabilities — not to mention the potential to extract resources from the Martian landscape itself — have all been developed in the last few decades and make a worthwhile mission to Mars a genuine possibility.

“It’s really technology that drives exploration,” he said. “And so that’s why this is the right time to start mounting a plan to go to Mars.”

Indeed, that’s NASA’s plan: Their Journey to Mars program calls for landing astronauts on an asteroid by 2025 and a trip to Mars by the 2030s.

Photos via NASA