ON A SULTRY AUGUST MORNING, we arrive at the Kennedy Space Center, in Cape Canaveral, Florida. When we meet for our preflight breakfast at the visitor complex, in addition to three Zero Gravity "coaches," a flight director, a flight attendant, and a staff photographer, there are 24 members of Mensa waiting to board. The brains have come from all over for the club's 60th anniversary, at Disney World.

Everyone is amped and jittery, making nervous small talk. (I divulge our mission to a Mensa lady wearing spectacles and a velour beret, who says, "Ewwww.") When we're issued our one-piece flight suits, I start getting nervous myself. With all these eggheads getting in the way, coital calisthenics could be a challenge.

A shuttle bus delivers our group to the tarmac. We enter the plane, walking

G-Force One climbs again, and this time Ashley throws her legs around my waist, clasping them tightly behind my back. Firmly entwined, I grab her head and pull it toward me, ramming my lips into hers like an overeager teenager. Technically, we kiss. But it's not pretty.

single file up clanky metal steps. Aside from five rows of seats in the rear, where we're told to sit during takeoff and landing, the plane is empty. The interior doesn't exactly ooze with romance: It's cavernous and cold, a long, hollow tube bathed in fluorescent light and padded with thick gym mats. One of our coaches, Matt Reyes, the 29-year-old director of technical operations for Zero Gravity, hands each of us a barf bag.

"Keep this handy," he commands.

Shortly after takeoff, our pilot slams the throttle and pulls the plane into a sharp 45-degree climb. In less than a minute, we zoom from 24,000 to 32,000 feet. He backs off the engines and we level out for a few seconds before teetering forward into a steep dive. For 30 seconds, at the apex of the parabola, everything inside the aircraft is weightless. It's cool, it's weird, it's pandemonium. Hyperventilating über-geeks are ping-ponging everywhere. Someone shouts, "Spin me! Spin me!"

G-Force One is climbing again for round two when I find Ashley amid a tangled heap of Mensa bodies. I grab her hand, ready to get down to business as the craft settles into its second apex. Unfortunately, our first kiss in zero gravity is a bust. It lasts only a split second—a grinding of noses, lips, and teeth—before I bounce off her like a slo-mo Super Ball thrown against a brick wall. During weightlessness, even a small amount of force triggers a ricochet effect: I somersault into the rear cabin while she cartwheels toward the cockpit.