“When a stone hits a lake, it stops and then it sinks,” Boshuizen told reporters. “So we literally hit the atmosphere and stopped, and it was about 5Gs…I’ve never experienced that. I was trying to smile but my jaw was pushed back in my head.”

Private space companies have pledged for years to open up spaceflight to more people. But Americans are used to imagining astronauts as people in prime physical condition, siphoned out of competitive selection processes like those overseen by NASA. So is it really safe for just anyone, even a 90-year-old, to go to space?

At 2G, they feel like they weigh twice their body weight. At 5G, a 200-pound person feels like they weigh 1,000 pounds.

Donoviel pointed to three specific studies that saw people — with a broad range of ages, physical conditions and ailments — endure up to 6G.

For its part, Blue Origin does put some limitations on who can fly aboard New Shepard, its suborbital space tourism rocket, including an age requirement that tourists be 18 years or older, be between 5’0″ and 6’4″ and 110 pounds and 223 pounds, and be in good enough physical shape to climb seven flights of stairs in a minute and a half.

The stair climb is no joke: Blue Origin passengers must rapidly climb what’s called the gantry, a tower that allows the crew to access their capsule as the 60-foot-tall rocket sits on the launch pad, brimming with fuel and ready to blast off.

Shatner quipped about scaling the tower after his flight, saying “good lord, just getting up the bloody gantry.”

But Donoviel said she believes even little kids could potentially be blasted into outer space without concern on an otherwise safe rocket ride.

“I actually have no concerns about children flying,” she said. “As long as they’re big enough to fit in the seats…The same thing as going on a rollercoaster ride — you must be this tall to ride this ride.”

It should be noted that getting to — and especially returning from — space is not necessarily comfortable, though all of the Blue Origin passengers on Wednesday raved about their trip.

Spaceflight passengers often describe the moments of discomfort with nostalgic glee. After all, it can be a visceral reminder that you’re on a supersonic excursion to outer space.

And in Shatner’s case, it did appear to provide a transformational experience.

It’s not something a person can understand until “you’re up there and you see the black darkness, the ugliness,” he told CNN’s Kristin Fisher in a post-flight interview. “From our point of view, space is filled with mystery…but in that moment, it is blackness and death. In this moment down here, as we look down, [Earth] is life and nurturing. That’s what everybody needs to know.”

Physiological concerns aside, any future participant should keep in mind that spaceflight is inherently risky. Drumming up enough speed and power to defy gravity requires rockets to use powerful, controlled explosions and complex technology that always involves some uncertainties.