Posey's Moonshot

Things that Surprised Me About Working in Zero Gravity

Brien has taken plenty of parabolic flights aboard the "vomit comet" by now, but there were plenty of things he was unprepared for when he first started his spaceflight training.

• By Brien Posey
• 04/30/2021

By far the best part of training to go to space has been the opportunity to spend a lot of time working in zero gravity.

The only way to create true zero gravity conditions on earth is through parabolic flight, which involves flying large, vertical arcs aboard an aircraft that is affectionately known as the "vomit comet." The downhill portion of the parabola (arc) is flown so you are descending at the same speed as gravity, effectively canceling out gravity's effect. The result is that everyone and everything onboard the airplane is weightless.

Even though the basic concept of parabolic flight is really simple, there are several things about parabolic flight that really surprised me, especially early on.

What Happens to Liquids
For example, I had never really stopped to think about the effect of zero gravity on the aircraft itself. As I said, everything in the aircraft becomes weightless during parabolic flight. That includes things like the aircraft's fuel and oil.

When liquids are weightless, they take on a spherical shape. Free-floating water, for example, looks a lot like a bubble. Just imagine what happens to the fuel inside the aircraft's fuel tanks. It presumably turns into a free-floating mass rather than collecting at the bottom of the fuel tank as it normally would.

Even though I don't know all of the specifics, I have been told that the jet in which I have done most of my parabolic flights had to be extensively modified to cope with these types of effects. In fact, during parabolic flights, we take a short break after every six parabolas so the pilots can do something with the aircraft's oil (I don't know the specifics, just that the task is required when the airplane is used for parabolic flight).

Windows: Avoid Them
Another thing that really surprised me about working in zero gravity is the weird things that can happen when you look out the windows. Most of the microgravity work that I have done has been on two different aircraft. One of those is a Boeing 727 that is used for space tourist flights (which give the average person a chance to see what it is like to be weightless) and for NASA research flights. That aircraft does not have any windows except on the emergency exit doors and in the cockpit, which you can't see from the passenger area. Takeoffs and landings feel a bit weird because you can't see outside, but someone told me early on that the windows had been covered to make zero gravity easier to tolerate.

I didn't think much more about the aircraft windows until I started doing a lot of parabolic flights aboard a Falcon 20. As you have probably already guessed, the Falcon 20's windows are not covered. The first time I did a parabolic flight on the Falcon 20, someone told me to avoid looking out the windows during the parabolas because it can make you sick. Despite the warning, I took a chance and looked out the window during a parabola. Looking out the window didn't make me sick, but I was amazed by just how steep the climb was. We weren't going straight up, but the climb was far steeper than I ever would have imagined.

The Falcon 20 does not have a cockpit door separating the pilots from the rest of the crew. During one of my more recent parabolic flights, I happened to catch a view out of the aircraft's front windows while we were weightless. What I saw was astounding: We were plunging nose-first toward the ground. Believe me when I say it was one of those sights you never, ever want to see while in an airplane. Of course, I was weightless and had no sensation of falling. I also knew the pilots were in complete control of the aircraft and this type of descent was perfectly normal. Nonetheless, the view out the front window was unsettling.

Upside Down Might Be Right Side Up
There is another effect related to looking out the window that is a lot harder to explain. It actually took me a while to figure out what was going on. In fact, this effect is so strange that I thought there was something wrong with me until I started talking to some of the other crew members and realized they experience the same thing.

The Falcon 20's seating is configured based on whatever it is we are trying to accomplish on the flight. The operational requirements usually result in most of the seats facing backward. The first time I ever flew in a rear-facing seat on a parabolic flight, it was an awful experience (and yes, it did make me sick). Each time we became weightless, I had the sensation that I was hanging upside down, dangling by my seatbelt.

I have taken aerobatic flying lessons and done inverted flight plenty of times, but this was different. When you fly inverted, you roll the aircraft into an inverted position. However, on this particular parabolic flight, the sensation of being upside down was instantaneous. There was no roll to transition into the feeling of being upside down because I wasn't actually upside down. In reality, I was weightless; I just didn't feel as though I was weightless. Every time the gravity went away, I immediately felt like I was upside down. When the gravity would come back at the end of the parabola, I instantly felt like I was right side up. All of the back and forth made me really sick.

It actually took several flights and multiple discussions with other crew members for me to figure out what was going on. Remember what I said about being warned not to look out the window? During the uphill portion of the parabola, I would usually stare at the back of the seat in front of me. Head movements and eye movements during a high G climb can provoke motion sickness, so I tend to stare at a fixed spot to avoid getting sick. Even though I was looking at a fixed point inside of the aircraft, my peripheral vision was picking up on the horizon outside the windows. When we would go over the top of the parabola, my brain would flip everything, making it seem as though I were upside down. This happened to some of the other crew members, as well. To fix the problem, I just made sure to either close my eyes or look elsewhere so I could not see the horizon.

You're Weightless More Often than You Think
One more thing that really surprised me about being weightless was how familiar the feeling was, even during my very first parabola. The feeling was completely natural, even though I was experiencing sustained zero gravity for the first time.

The reason why zero gravity felt so familiar was because there are things we do in everyday life that give us a tiny taste of what it is like to be weightless. Consider the experience of swinging on a swing set in a park. During each swing, there is a point at which you reach your highest point and then start to come back down. When you reach this point, there is a split second during which you are neither going up nor coming back down. At that point you are effectively weightless. There are also amusement park rides that can give you a second or two of weightlessness.

Despite any feelings of familiarity or challenges with motion sickness, I feel extremely fortunate to have spent so much time working in zero gravity. Parabolic flight truly is an amazing experience, and it is something that I never get tired of. If you ever have the opportunity to try out one of the parabolic flights offered to tourists, I highly recommend it. Being weightless is an experience that you will never forget.