The German Aerospace Center's (Deutsches Zentrum für Luft- und Raumfahrt; DLR) mobile rocket base MORABA launched the MAPHEUS-5 high-altitude research rocket at 06:55 CEST on 30 June 2015, carrying four DLR experiments on board. The 12-metre-high, two-stage rocket took off from the Swedish Esrange Space Center and ascended to an altitude of 253 kilometres – taking only 74 seconds to reach a state of microgravity lasting over six minutes, which was used to conduct experiments from the fields of material physics and biology. Plants responded to the absence of Earth's gravity during this period, while 2500 steel balls with a diameter of 1.6 millimetres collided, metal samples were X-rayed and suspended metal balls were melted using a laser. Using a parachute, the rocket section carrying the test systems landed after approximately 15 minutes at about 70 kilometres north of the launch site, where it was recovered by helicopter. Now the data acquired is being analysed and interpreted in the laboratories.
Collision processes in a microgravity environment
The common feature of all three experiments by the DLR Institute of Materials Physics in Space is that the measurements require the absence of the disturbing force of gravity. In MEGraMA 2.0, the DLR scientists analyse how collision processes play out. To do this, eight magnets were initially used to excite 2500 small balls during the flight; exposed to weightlessness, the balls then distributed evenly throughout a Plexiglas box. Acquiring 165 images per second, a camera recorded – in three dimensions – how collisions cause the balls to lose speed and assume an ordered pattern. This procedure was repeated several times during the six-minute microgravity phase to acquire a number of different datasets. "We use this test to analyse how collisions occur among granulates," explains Florian Kargl, a researcher at the DLR Institute of Materials Physics in Space and Scientific Director of the three contributed experiments.
X-rays and melting suspended samples in flight
The DLR researchers melted a number of suspended samples in the electrostatic levitator (Gravity Impact on Liquid Drops – Electrostatic Levitation; GOLD-ESL), meaning that the drops did not touch the wall of the crucible. This was an entirely new experience for the researchers: "Until now, it had not been possible to operate and test this technology in a weightless environment over several minutes," says Kargl. "MAPHEUS-5 allowed us to demonstrate that this highly complex levitation technology not only works in the laboratory setting back on Earth, but that it functions equally well in a weightless environment." An electromagnetic levitator (EML) is already in use on the International Space Station (ISS); here, though, the low-level electromagnetic fields can influence the molten samples – even in microgravity. In future, the ESL – the next stage of development – may prevent even these influences.
The X-ray system X-RISE was used to conduct two experiments simultaneously; first, aluminium-copper samples with varying degrees of copper content were diffused in a shear cell held in a microgravity environment. During this experiment, a camera acquired one image per second to record the diffusion process in real time. Next, the material physicists from DLR analysed the formation of microstructures during the solidification of aluminium-germanium samples, using X-rays to document the sequence. The various metal samples were completely melted and maintained at a uniform temperature shortly before the rocket took off. The diffusion data recorded during the flight provides the scientists with insight they can use to make comparisons with identical experiments conducted on the ground, and to calibrate these experiments. The microgravity environment stops the liquid flow otherwise caused by Earth’s gravity. This data is then used to increase precision in the determination of material properties and to review and optimise existing solidification models.
Plants sense weightlessness
It takes plants only approximately 20 seconds to notice the absence of Earth's gravity. This causes them to lose the sense of which way is up and which way is down. Seeking to establish how plants respond to a state of weightlessness, scientists from the DLR Institute of Aerospace Medicine dispatched several thousand specimens of Arabidopsis thaliana – thale cress – into a microgravity environment on board the MAPHEUS-5 rocket. "Thale cress is easy to cultivate and has already been studied in detail. One could even call it the laboratory guinea pig among flowering plants," says DLR biologist Jens Hauslage: "It is a good model organism." Methanol was added to fix the plants in their current state as soon as the weightlessness came to an end. They were then removed from the rocket after their flight. The DLR researchers are now busy analysing the 'specimens', although some have been passed on to other research institutes. "This will provide us with the best possible overall impression of all changes of proteins, metabolism and the transcription of plant genes in a weightless environment." It is important to know how weightlessness affects the plants and their growth in the event that plants should be used as a source of food and for oxygen production in future missions.