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In this section, you will find some longer blog posts about fun science adventures ☺️🙌🏼


Parabolic flight campaign - science meets zero gravity

Bordeaux, France
The alarm clock rings at 5 am, I brush my teeth and take a quick shower. I am heading down to the breakfast room, where I meet my colleagues from the German Aerospace Center (DLR). It's a weird breakfast because in a couple of hours I will do experiments in zero gravity on a parabolic flight, and I am not quite sure what to eat, or rather how much to eat...
I have been waiting for this day for a long time. I submitted my proposal 'Understanding the role of Si in Cu-Si metallic glass forming alloys' (we will get to the scientific details soon ☺️) roughly 4 months earlier and without the exceptional support of my colleagues (I must name Sonja, Mitja, and Fan 🧡🙏 ) the dream of being weightlessness would have been over quickly. But it worked out, my proposal got granted, the sample preparation and pre-tests were successful, and luckily the COVID numbers are not too high, so researchers are allowed on board the parabolic flight.

And this is how I ended up in Bordeaux and am just about to participate in the 39th DLR parabolic flight campaign. But what exactly is a parabolic flight? And why would you want to perform experiments in zero gravity?

Imagine, you hold a ball in one hand, throw it in the air, and catch it with your other hand. Well, you've just replicated a parabolic flight, where the ball begins its ballistic phase as it falls back to the ground. It's almost the same with the parabilic flight, only that you have an Airbus A310 with two engines instead of a ball and two hands. Or to say it in the words of Jean-François Clervoy, former astronaut, and chairman of Novespace, which is the hosting agency of our parabolic flight: “The principle of zero gravity flight is to throw the plane in the air and make it believe it is in a vacuum.” (Source: flightradar24). 
Protocol of one parabola: 20 seconds of hypergravity (1.8 g) are followed by 22 seconds of zero gravity, before you experience hypergravity for another 20 seconds.
Every parabola during the parabolic flight follows the same protocol, which you can see on the left: From steady flight (speed of 810 km/h and an attitude of 6000 m), the pilots raise the nose of the A310 to +50 degrees, which takes about 20 seconds. Within less than a minute the airplane climbs 1600 m and loses 150 km/h. During this time, everything inside the airplane experiences a hypergravity of 1.8 g. At a maximum slope of +50 degrees, the so-called injection occurs, meaning the pilots set the engines to idle, and weightlessness begins. During the next 22 seconds, the aircraft first reaches the highest point of the parabola (speed of 350 km/h and an attitude of 8500 m), before falling towards the earth with a maximum degree of -42 degrees. There, the pilots pull back the airplane for another 26 seconds (again hypergravity) before, finally enter a steady flight. 
That's how a parabolic flight works, but why do we do it? Why are we packing an Airbus A310 full of scientific equipment and flying with it up and down only for a few seconds of zero gravity? Well, even though the gravitational force is a very weak force, it is omnipresent on the ground, and therefore, it always influences scientific experiments. Sometimes scientists want to observe effects that are so small that they are, in a sense, superimposed by the gravitational force. In a parabolic flight, we and our experiments don't experience gravity, and in this way, we can make these effects observable. 

In addition to such experiments, a parabolic flight also hosts experiments that are designed for weightlessness, e.g., how to fuel spaceships in zero gravity or how certain muscles work when gravity is absent. Altogether, every parabolic flight campaign provides unique experimental conditions for measurements that contribute to future technologies, which are relevant for space but also for earth-bound applications. 
With this in mind, we can go back to the breakfast room in Bordeaux, where I managed to get some porridge and green tea (a combination, which is said to be quite beneficial, when you will be weightless in a few hours and your stomach doesn't know where top and bottom is...). After some casual small talk, it's time to head to the Novespace headquarter at the Bordeaux airport for final preparations.
Left: Novespace's AirZeroG A310 aircraft. Fun fact: This A310 was purchased by Novespace in 2014. Before that, it was used by the German government to transport the German Chancellor. Right: Stairway into the Airbus A310.
From the hotel, it is a 30-minute drive to Novespace, the company that owns and maintains the A310 and is the overall hosting agency of the parabolic flight. After registration, we directly enter the aircraft from the back. The inside of the A310 doesn't look like an aircraft at all. All experiments (in total 11) are set up in the front three-quarters, while the back holds regular seats, which are used for take-off and landing. In the scientific area, instead of windows, the walls as well as the floor and ceiling are covered with white paddings and guides, that keep free-floating scientists safe during zero gravity.

Our experiment has already been set up during the last few days by my colleagues from the DLR, so all we do for now is going through a final checklist. Since our setup is quite advanced, this takes a while. The electromagnetic levitator, high-voltage generator, vacuum pumps, infrared cameras, control computers, and a lot more components have to be checked. 
Excited me in the Airbus A310 (2 days before the flight day). Slowly, the aircraft fills up with the experimental setups of the various research groups.
So, what is my experiment actually about? Briefly, we are measuring the viscosity and surface tension of liquid metal alloys, which in my case are Cu-Si samples. In the experiment, the electrically conductive, approx. 6-8 mm large Cu-Si sample is positioned contactless by a high-frequency alternating magnetic field and melted via the induced eddy currents under an inert gas atmosphere. By means of the magnetic field, pulses can be induced in the sample, which makes the sample 'wobble' along the vertical axis. These 'wobbles' are recorded by cameras, and from the position, movement, and shape of the sample (as a function of time) we extract information about the viscosity and surface tension of our samples. 

Summarized, we levitate the sample in a magnetic field, heat and melt it via induced eddy currents, make it 'wobble' via pulses, and record these wobbles. All of this, we can also do on earth, but as mentioned earlier, gravity always impacts these measurements. Therefore, the experiments in zero gravity can be seen as benchmark measurements, where material properties are determined very, very precisely.
Working principle of an electromagnetic levitator in zero gravity. Credits for the poster go to the German Aerospace Center (DLR) - Institute for Material Physics in Space.
Mission patch and ID: you need both to enter the aircraft on flightday.
After working through the checklist, we exit the aircraft and head to the Novespace briefing room. We quickly go through the flight plan and slightly adjust the sample order and the respective measurement protocols. Then it's time to get dressed for the flight and we put on our super stylish blue flight overalls, including the parabolic flight campaign patch.

As a last step, everyone gets some medication against flying sickness, and then board the aircraft, take a seat in the seating area, and take-off for the 39th DLR parabolic flight campaign ✈️.

As soon as the seatbelt signs are turned off, we make our way to our experiments for final preparations. The first parabola usually happens shortly (20 - 25 minutes) after take-off and every second in zero gravity counts.
And then it's finally happening: my very first parabola. I am standing behind our setup and waiting for the countdown. 20, 10, 5, 3, 2, 1, pull-up! The pilots pull the aircraft to a maximum of 50 degrees with nose-up attitude. It sounds obvious, but everything started to feel heavier. It's only 1.8 times the earth gravity and in some rollercoasters, you experience 4 or even 5 g. But this is only for a fraction of a second. In a parabolic flight, there are solid 26 seconds of 1.8 g hypergravity and OMG this is heavy! My colleague Dirk turns around and smiles: "Have fun, nothing is like the first parabola!". True that. The pilots announce INJECTION and then we are weightless. I start to lift off from the ground, I am 'falling' forward, and my brain expects me to land safely on the ground, just like I landed the last 30 years ago. But not this time. I just keep on floating. My brain cannot handle it, my vision shortly turns upside down, there is literally no top and bottom anymore, I see some white flashes (probably while my brain tries to re-wire and process this new experience), and then everything is kind of normal. It's incredible how fast the human brain can adapt to such extraordinary environments. 

I am floating around in zero gravity, helping with the experiments, and then there is the countdown for the pull-out. After 22 seconds of zero gravity, there is again a hypergravity period of 20 seconds, before the aircraft returns to steady flight. 1 parabola down, 30 to go.

Below are some videos of the inside and outside of the A310 during a parabola, of me having fun in the free-floating area, and also of me failing miserably trying to do push-ups in hypergravity.
During the next parabolas, I am involved in the scientific experiments, then my samples are finished, and a colleague takes over. Now, I have time for some fun in zero gravity. There is a small free-floating area, where you can enjoy zero gravity with some rollovers and other gymnastic exercises. I tried to do a push-up in zero gravity but failed miserably... After the free-floating fun, I sit down in the seating area and watch the sky and the clouds falling from side to side during the parabola. One thing is for sure, I will probably not have a fear of flying so quickly anymore. I casually chat with other research groups about their experiments and results as I float around in the plane, always holding onto the guides so I don't drift off and crash into a scientific setup. 
Experimental plan for in total three flight-days with 31 parabolas each
And after roughly 3 hours, the last parabola is done. We sit down in the seating area, fasten our seatbelts, and wait for the landing. Back on the ground, we exit the aircraft, do a short group picture, and head for the control room. I am super exhausted (because of the meds and especially the hypergravity periods). After a short debriefing, where all the science groups report on how their experiments went and what can be improved for future flight days, it's time to drive back to the hotel. Slowly, I realize how addictive zero gravity is, and that I want to fly again as soon as possible. 



For more insight into parabolic flights, levitation techniques, and metal alloy research, feel free to drop a short message via Twitter or lucas.kreuzer@frm2.tum.de ☺️ 
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