Peter Diamandis’ ambitions have always been too big for the measly planet onto which he was born. The serial entrepreneur built his first dozen companies as technological launch pads for future space colonies. But in more recent years, the founder of the X Prize Foundation has become increasingly interested in helping humans live their healthiest, longest lives right here on Earth. He’s far from the first Silicon Valley futurist to welcome middle age with a pivot toward lifespan extension tech—Sergey Brin and Larry Page have Calico, Jeff Bezos and Peter Thiel have Unity Biotechnology—but he’s getting to be one of the most prolific.

Diamandis started with Human Longevity Inc, a biotechnology company he co-founded in 2014 with with genomics guru Craig Venter and stem cell pioneer Robert Hariri. While the secretive San Diego-based company has so far offered little more to the public than $25,000 “health intelligence assessments,” it has built up a wealth of patient information it’s now funneling into Diamandis’ latest venture. Today, he and Hariri announce Celularity, a $250 million company devoted to using stem cells to turn back the clock on aging. They’re calling it “augmented longevity.”

The catchphrase might be new, but the idea isn’t. In the ‘90s it was dubbed “gero-technology”; in the aughts, “regenerative medicine.” For the last two decades, dozens of companies have tried (and failed) to turn stem cells into a miracle cure for age-related decrepitude. To be sure, hundreds of clinics around the US will inject you with your own stem cells for a hefty fee to treat everything from a bum hip to failing vision. But the products these businesses are hawking aren’t scientifically proven or FDA-approved, and have occasionally led to disastrous results. Stem cells, it has turned out, are much harder to control than anyone realized.

So what makes Diamandis think things will be any different this time around? Well, for one he says, the world has changed. “This conversation around extending the healthy human lifespan is beginning to become mainstream,” he says. “There’s a realization that we can treat aging as a disease and a desire for people to spend money that way.” The FDA is different today too; thanks to the passing of the 21st Century Cures Act in December 2016, the agency has a congressional mandate to put regenerative cell therapies on the fast track. Those therapies of course, still need to pass scientific muster. And for that, Celularity is going to have to rely on Bob Hariri.

Diamandis met Hariri 12 years ago, on an airstrip in Las Cruces, New Mexico. The latter had had flown his Lear jet 2,000 miles for the weekend’s air show. The former was there to award the X Prize Cup’s cash prizes to that year’s civilian spaceflight stars. They started chatting about Charles Lindbergh, whose memoir inspired Diamandis to create the X Prize. But talk soon turned from rocket-powered planes to placentas.

In the ‘80s, when Hariri was a young neurosurgeon at Cornell University, he had an epiphany while looking at a first-trimester ultrasound of his oldest daughter. The placenta was developing so much faster than his peanut-sized progeny, he hypothesized it must be rich in the kinds of cells that give rise to all others: stem cells. And he turned out to be right. The placenta was indeed a stem cell factory. Up until then, stem cells used in medical research were taken from bone marrow, the umbilical cords of newborn babies, and aborted fetal tissue. That last one was the one stoking the flames of a fiercely raging ethics debate. Hariri saw in the placenta a way to get around that moral morass, and an economical one to boot—the temporary organ carries roughly 10 times the amount of stem cells that can be harvested from cord blood.