This is what it's like to feel zero G aboard NASA's 'Vomit Comet'
Way back in the early '90s, when I was a U.S. Navy lieutenant serving as the editor of Approach magazine (Naval Aviation's Safety review), I was invited by NASA astronaut Bill Shepherd to come down to Houston for a hands-on tour. Along with suiting up in full astronaut gear and flying the shuttle simulator in all regimes of flight, I had the opportunity to ride in NASA's "reduced gravity aircraft," better known as the "vomit comet" (because of its tendency to cause passengers to throw up during the zero-G missions).
In those days NASA used a couple of KC-135 Stratotankers as the Vomit Comets, which were big ol' beasts relative to the contract Airbus 300s and 727s they used later. We launched out of Ellington Field at headed over the Gulf of Mexico. There were about a dozen passengers in the compartment with me, mostly engineers who were testing exercise equipment for future use on the space station.
There was a crew chief who was charged with making sure nobody got hurt, and he explained during his safety brief that the main way to avoid injury was to make sure you had a hand on the padded floor during the transition from zero-G back to 1-G. He said that passengers had sprained ankles and wrists or twisted neck muscles by getting disoriented while weightless and hitting the deck in an awkward fashion once G came back on the airplane.
The pilot announced "starting the pull," which meant he was commencing a 1.8 G pull until the aircraft's nose was pointed 45 degrees up. At that point he pushed the nose forward until the aircraft was right at zero G and held it there until the aircraft was pointed 45 degrees nose down, which resulted in about 30 seconds of weightlessness. At that point he's start another 1.8 G pull back to 45 degrees nose up into another zero G pushover . . . over and over again. Each cycle was known as a "parabola," and a mission consisted of 40 of them – 20 headed eastbound and 20 headed back to the base, westbound.
My host Navy Captain Bill Shepherd, a SEAL by warfare specialty who later broke the record for days on the International Space Station, had done the Vomit Comet missions many times. He'd admitted before the mission that he'd become airsick every time and predicted he'd do so on that day's mission as well.
I was a Tomcat Radar Intercept Officer with more than 1,000 tactical jet hours under my belt at the time, so high-G flight was nothing new to me. In fact, the parabola profile seemed pretty mild compared to the way a fighter maneuvered during a dogfight. But the engineers weren't as experienced, and Capt. Shepherd instructed me to watch them as the flight went along.
"Everybody will do the first 10 parabolas very giddy," he said. "They'll flip around and laugh and high five each other."
The next ten parabolas would have fewer spins and less laughter, he predicted. The 10 after that would consist of people fighting the urge to throw up. And the last 10 would be a bunch of miserable people wishing the flight would end as they floated for 30 seconds at a time after getting sick.
And that's pretty much what happened. At some point in the flight everybody's joy wore off as their inner ears said "WTF?" with all the gyrating and weird sensations. Along with Capt. Shepherd the majority of those in the compartment got airsick, and about three-quarters of the way through the mission all of the engineers were so incapacitated that they were unable to test the fitness equipment. According to former Reduced Gravity Research Program director John Yaniec, anxiety contributes most to passengers' airsickness. The stress on their bodies creates a sense of panic and therefor causes the passenger to vomit.
The crew chief noticed that I seemed to be doing okay, so he asked if I would jump in and try out the reclined bicycle and the stepper. I did, and we were able to flag that the stepper had a tendency to stick on the down-stroke during zero G.
I'd experience zero G many times before that, but never for 30 seconds at a time. The sensation of being weightless for that long was very cool, relaxing even. Although those suffering airsickness among us certainly didn't feel the same way, before I knew it we'd done 40 parabolas and we were back on deck at Ellington Field.
My flight on the Vomit Comet was among the most memorable experiences of my 20-year Navy career, and I'm glad I got to do it before the "reduced gravity" program was cancelled in 2014, another casualty of NASA's dwindling budget.