• Civil Aviation
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KC-135 “Vomit Comet”

The KC-135 Stratotanker provides the core aerial refueling capability for the US Air Force and has excelled in this role for more than 60 years. This unique asset enhances the Air Force’s capability to accomplish its primary mission of global reach. It also provides aerial refueling support to Air Force, Navy, Marine Corps and allied nation aircraft. The KC-135 is also capable of transporting litter and ambulatory patients using patient support pallets during aeromedical evacuations.

Until 2004 the KC-135 was also used by NASA as a reduced-gravity aircraft to simulate conditions of weightlessness. In a typical flight, it traversed the Gulf of Mexico in a series of large parabolic arcs. Peaking at 32,000 feet, the plane then dived to 24,000 feet, its fuselage pitched down at 40 degrees. At the top of the parabola, passengers lost all sense of gravity and became weightless for a period of roughly 25 seconds. When the airplane came out of the dive and began its next ascent, the plane pitched upward at about 50 degrees and passengers on the craft were subjected to forces up to 1.8 times that of gravity. This climbing and diving was repeated thirty times in what might be described as the ultimate roller coaster ride. Flying on the KC-135 nauseated passengers so frequently, however, that the plane was nicknamed the “Vomit Comet”.

Flying parabolic trajectories

NASA Astronaut and award-winning author [CLICK HERE to check out his website) Clayton –“Astro Clay”– Anderson recalls on Quora;
‘Why yes, I have experienced zero gravity… multiple times. And the very first time —in 1981— it did make me sick.

‘I was a summer intern at NASA’s Johnson Space Center in Houston, Texas. NASA was seeking volunteers to participate in various science experiments related to astronauts, zero gravity, and something they called Space Adaptation Syndrome (SAS). Fresh out of college, I really had no idea what was going on, but flying on their vaunted “Vomit Comet” seemed like a really cool thing to do. And, after all, I wanted to (one day) become an astronaut.

‘Then, the vomit comet was a NASA KC-135 aircraft, modified to fly parabolic trajectories (big arcs) and flown by NASA Aircraft Operations Directorate (AOD) pilots.

‘We would pull about 2 g’s going up the arc and 2 g’s coming down (think rollercoaster!). For about 30 seconds in between, we would be weightless. Back then a typical flight consisted of about 44 parabolas. 40 were “normal,” producing the expected effect of weightlessness. The remaining four (2 each)… we were told… would be flown to simulate Lunar gravity (about 1/6 that of Earth) and Martian gravity (about 1/3 that of Earth).

NASA Astronaut recalls puking during reduced-gravity flight

‘My first flight occurred in the summer of 1981. Being part of a NASA experiment, I had several restrictions. I would be blindfolded, remain in my seat, and wear a neck brace (unless I blew chunks… then all bets were off). I was not allowed to take any medications pre-flight or in-flight. In addition, it was explained that John Denver the musician, was scheduled to fly with us, as was Life Magazine (they were to cover his participation). John never showed, but Life Magazine did and for one of their photographers, puking ensued on parabola 6 or 7.

‘I survived 33 parabolas that day before “discharging” into the provided white bag. A portion of that discharge crept up the side of my face (I was not astute at “… getting a proper seal”) as it occurred during the zero-g portion of a parabola. While the first two or three parabolas were invigorating, and absolutely amazing, I spent parabolas 4–32 trying to keep from barfing, having fully decided the remainder were totally unnecessary for this neophyte space wannabe. Once safely back on the ground, the pilots (jokingly?) asked who wanted to go get BBQ. I nearly lost it again. It would take a long afternoon nap in my one-bedroom apartment before I felt recovered enough to ingest anything into my body that wasn’t clear water.’

Anderson concludes;

‘I would go on to fly 167 days in outer space. And you know what? I didn’t puke once!’

Photo credit: NASA and MikeRun via Wikipedia