Lichtgedanken 03

Rubrik 74 If you have a burning desire to float in zero gravity, there is no need to fly to the ISS, as you can experience this phenomenon on a parabolic flight. The European Space Agency (ESA) offers such flights in partnership with the German Aerospace Cen- ter (DLR), with a special airplane taking off from Bordeaux in France. Flights are carried out for the purposes of scientific research, but also for simple curiosity, as in some cases tourists can also book a flight. »Weightlessness starts very suddenly—there’s no transition phase,« says Prof. Markus Rettenmayr. You have to be careful, as spontaneous movements can quickly lead to violent collisi- ons, adds the scientist from the Otto Schott Institute of Mate- rial Research. If you are squatting on the floor of the aircraft when weightlessness starts and try to stand up in the usual way, you will bash your head against the ceiling. Not for no- thing are there four helpers and a doctor on board, and the ceiling of the plane is also padded. Rettenmayr took his first parabolic flight last summer, and it was probably also his last. Not because he did not enjoy it, but rather because other scientists working on the same research project would also like to have a go at zero gravity. During the flights, Rettenmayr and his team investigate how melted metal alloys resolidify in crystalline or vitreous form. The aim is to eliminate the influence of gravity as much as possible in this process. Highly sensitive measuring devices are used, which measure factors such as viscosity, thermal conductivity and solidification velocity. »These experiments will be exten- ded later on aboard the ISS,« says academic employee Robert Hanke. The parabolic flights are a necessary preparation for the experiments on the space station. The long-term goal is to obtain a model for the solidification behaviour of metal alloys that is as precise as possible. The plane used for the parabo- lic flights is the German Airbus A 310 that used to carry the German Chancellor. Where Angela Merkel and her entourage used to sit, there is now equipment to be used in a variety of experiments. There is also a system of belts and straps, so that weightless passengers do not completely lose control. Only in the rear of the plane are there still seats. »It’s like being seasick, but worse!« Before the flight, passengers take medication against mo- tion sickness. »It feels as if you’re seasick, but worse,« says Rettenmayr. Headaches, nausea and vomiting are common symptoms, which is why parabolic flight aircraft have been nicknamed »vomit comets«. After taking off from Bordeaux, you first fly out over the open sea and a quiet area is sought for the parabolic flights. The Airbus pilots then accelerate to 2 g—twice the acceleration of gravity—and pull the nose of the plane up to an angle of 50 degrees. After the climb, the engines are throttled and the plane follows the path of a tra- jectory parabola, during which passengers experience 22 sec- onds near absolute weightlessness. The plane then returns to the horizontal. The changes in gravity imply flying close to the aircraft’s technical limits, says Rettenmayr, adding: »This flying manoeuvre demands great skill.« It is no wonder that the crew consists of four former military pilots. One flight day involves around 30 parabolas, with a one-minute break after each period of weightlessness. The passengers enjoy floating around inside the aircraft. The physical discomfort of motion sickness is the price that must be paid. However: »One or two days later, everything is fine again!« Reaserch in Microgravity The materials scientist, Prof. Markus Rettenmayr (Photo above), experienced a microgravity parabolic flight last summer. He talks here about the fascina- tion of weightlessness and suffering in the cause of science. BY STEPHAN LAUDIEN Behind the Scenes Doctoral candidate Robert Hanke (seen here during a flight in 2016) remained earth- bound in Bordeaux on this occasion and provided the team with technical support.