How do you create lunar gravity in a plane? A veteran zero-G pilot explains

BORDEAUX, FRANCE - Parabolic flight pilots are a rare breed. There are only eight of them in Europe capable of sharing the aircraft's controls during these nerve-wracking series of up-and-down maneuvers that create brief spells of weightlessness and reduced gravity conditions. These aviators include the cream of the crop of Europe's military and test pilots and even one active astronaut. Probably the most experienced of these magnificent eight is Eric Delesalle, the head pilot at Bordeaux-based company Novespace, a spin-off from French space agency CNES and Europe's only provider of parabolic flights for scientific, and sometimes entertainment purposes. 

I got to chat with Delesalle inside the cockpit of Novespace Air Zero G Airbus A310 as he was preparing for the first of three flights in a scientific campaign conducted in the last week of April that I had arrived in Bordeaux to report on. To start with, he made parabolic flight sound rather simple. But don't get fooled: These flights are so challenging that there must be four of these ultra-skilled pilots onboard each flight, making sure that the plane follows an ultra-precise trajectory as it climbs at a 50-degree angle, than falls down more than 8,200 feet (2,500 meters) before regaining a steady course. All of that takes place within a span of less than one and a half minutes, over and over again. 

So read on if you want to learn what makes the difference between weightlessness and lunar gravity in a parabolic flight, and why modern aircraft are absolutely unfit for such extreme flying.

Related: Watch an astronaut test a 'lunar wheelbarrow' in moon-like gravity for 1st time (exclusive video)

Space.com: Can you tell me what's going to happen tomorrow? Where are we going to fly and what are we going to do?

Eric Delesalle: Tomorrow we will fly near the Atlantic coast from Bordeaux, there is not too much traffic at the altitude that we will be flying in, between flight level 200 and 300 [20,000 to 30,000 feet or 6,000 to 9,000 m]. So it is quite comfortable and if we need more space, we will go a little farther toward Brittany over the Atlantic and we will fly between Bordeaux and Brittany.

Space.com: We will be flying flights that simulate lunar and Martian gravity. Is that true?

Delesalle: It will not be a simulation, it will be real apparent gravity that we have on the moon or Mars. 

Space.com: How do you do that?

Delesalle: We will fly this aircraft in such a way that the aircraft is falling down, but not too much, to keep just the level of gravity that we need. That is 0.16 G for moon gravity or 0.38 for Mars.

Space.com: What makes the difference between a parabola that gives you lunar gravity, or Martian gravity or no gravity at all? 

Delesalle: It's just a matter of how much we push on the stick. I will begin with zero gravity, that is the most simple. We are trying to have the zero gravity phases as long as possible. So, if I give you a ball and ask you to throw it in a way that it stays in the air as long as possible, you will throw it up. And then, from the time that you release the ball, it will begin to fall even if it's still climbing at the beginning. Then we have zero gravity conditions. 

For 0.16 G [lunar gravity], we push so that the plane would pull up first and then when it reaches a certain attitude, we push on the stick so that the aircraft would do this [Delesalle's hand follows an arc with a toy aircraft. Check our video above to see Delesalle's demonstration] as if it was falling in a vacuum. To keep it lunar, it will be a little less sharp [than for zero G] and for Martian even less, we will just push a little less to keep some gravity.

Eric Delesalle

Eric Delesalle is a French former military and test pilot and pioneer of parabolic flying in Europe. He's been flying parabolic flights simulating weightlessness and reduced gravity since 1996 when he served as a test pilot on Novespace first Zero G aircraft, an Airbus A300B. 

In his role as a Novespace chief pilot, Delesalle also ran the entire 2014 test campaign of the company's current Airbus A310 that had previously been used to fly the former German Chancellor Angela Merkel

Delesalle also runs the test department of regional aircraft manufacturer ATR where he is involved in the development and certification of new aircraft. 

Space.com: How difficult is it to pilot such flights?

Delesalle: We are all trained, we think a lot about the maneuver with the manufacturer of the aircraft, with the authorities. We made a flight test campaign to make sure that we have safety margins and the best compromise between the duration of the maneuver and safety.

Space.com: You are making it sound very easy, but I have actually heard that there will be four pilots on board the flight tomorrow, and I am quite certain that there were only two on that EasyJet flight that I arrived on from London. So that's twice as many pilots compared to a regular flight. Why is that?

Delesalle: We fly this aircraft in a very unusual way. In a normal aircraft, flying for an airline, there are two pilots and they share the four activities we perform during a flight: We fly the aircraft, we have to navigate, we have to speak with air control and we have to monitor the systems. These are the four tasks of the pilots and we share them. But normally, there is only one pilot flying the aircraft and having his hands on the controls. With this maneuver, the difficulty is to be very accurate. So we share the three axes of the aircraft between three pilots. One is flying the pitch that is making the zero G or the moon or the Martian gravity, and we use this kind of thing [an implement that attaches to the control wheel like and additional set of handlebars that doesn't allow sideways motion, check out our video to see Delesalle's demonstration) and we plug it into the radio and from now on, this pilot can only act on the pitch. You see, I cannot control roll with this. 

And during that time, the other pilot will use some very technical equipment [he removes the implement and instead slides what looks like two fabric bracelets onto each of the handles of the steering wheel and then shows how he controls the roll by gently tugging on these fabric bands on either side of the wheel], so that these two pilots are flying the aircraft at the same time. And the third pilot is acting on the throttle because as soon as everybody is flying in weightlessness in the cabin, if you have a little acceleration lateral or longitudinal, we would find everybody in the cockpit or in the aft toilets and we don't want that. 

Space.com: So that's three pilots, what about the fourth one?

Delesalle: And the fourth pilot is a spare one because all these tasks are quite difficult to do. It's a very demanding activity because we are trying to be very accurate. We fly completely manually and we even disconnect some of the devices that help pilots in regular flights. So we are taking turns and one is always relaxing in the cabin and speaking with the experimenters to see how it goes. 

Space.com: How does one become a parabolic flight pilot? Can any pilot do that?

Delesalle: We were all at the beginning experimental pilots, either test pilots or military pilots. We do extra training on a simulator at first and then in flight to train this specific maneuver. 

Space.com: How many people in Europe can do that?

Delesalle: There are eight of us in Europe. [Among these magnificent eight is European astronaut Thomas Pesquet, who was actually one of the four pilots on this reporter's flight]

Space.com: Let's talk about the aircraft. Is there anything special about an aircraft that can fly such flights? I know that this aircraft in the past used to transport the former German Chancellor Angela Merkel, but she probably didn't fly parabolic, so what makes this aircraft different?

Delesalle: When we were working on the qualification of this aircraft for parabolic flights, it still had all the fittings of Angela's era inside: Her office, her bedroom, the dining room. It was really funny. But the aircraft is very standard. Despite the extreme trajectory that we fly, we stay within the flight envelope, we never exceed the speed or any other factor. It's just a maneuver that is unusual and so the maintenance program is adapted to such flights. But the aircraft and all its systems are very standard. The cabin is different because we have a large free experimental area [the interior of the aircraft is essentially empty padded space with only forty seats left at the back behind a mesh partition. Even toilets have been removed.]

Space.com: I know this is an aircraft that is a little older. Why are you not using a modern plane?

Delesalle: In this aircraft, we have mechanical links to the controls, that means that the pilot is acting on the controls. But the next generation is the fly-by-wire aircraft and in this type of an aircraft, such as the Airbus A320 or Boeing 737, you send an order to the computer taking into account the altitude, speed and so on, and then the computer is acting on the controls. And then you can fit some protection into the system and if the pilot is making some action that is not considered appropriate, the computer filters that command out and doesn't allow it to go to the controls. But we are doing some very special maneuvers deliberately, such as going up at a 50 degree angle of pitch. But in an Airbus A320, you are limited to 30 degrees and you can pull as much as you want on the stick but the aircraft will never exceed 30 degrees. So we are working now with Airbus for the future because in the future we will have a flyby wire aircraft and it will have some special modifications that would allow us to do what we need to do. 

Space.com: You said we are going to fly above the Atlantic Ocean, there is a lot of aviation traffic around the U.K. and France. What do other aircraft pilots think when they see you doing these nose dives?

Delesalle: We are flying at a lower flight altitude, between flight level 2.00 and 3.00 [20,000 to 30,000 feet/6,100 to 9,100 meters] and that means that there are maybe some lighter aircraft below us but the liners going to the U.S. are already above. So we are nearly alone at this altitude. But the problem is that when you climb, there is a special equipment called the TCAS, for traffic collision and avoidance system, which is receiving the radar position of the other aircraft and if it computes that there might be a conflict, it triggers an alert and because when we are flying such steep climbs, the system doesn't know that we will dive soon, and if there is a liner coming at the higher altitude, the system computes that if we continue climbing like that, there will be a problem, so it triggers the alert. So we have to switch off this special equipment to avoid these alerts. 

But we are in constant contact with an aircraft controller from the Ministry of Defense and using the same procedures as test aircraft. So this controller is speaking with his colleagues, making sure that there isn't anybody coming in the area and not descending into our area. 

It's amazing to be flying these maneuvers because it's all manual and today, everything is automatic in aeronautics. So we are all very happy to fly this aircraft. It's always very interesting and we are trying to do all we can to be accurate and to provide the best service to our customers. We are a very good team.

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