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Usually, placozoa prefer warmer temperatures. For science, the simplest multicellular organisms in the world have made its way to northern Sweden – and from there into microgravity for a short time. On board the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) MAPHEUS 9 sounding rocket, the marine organisms successfully launched from the Esrange Space Center rocket launch area on 29 January 2022. Three other experiments from the fields of physics, materials research and manufacturing technology also enjoyed six minutes and 10 seconds in microgravity.

The 11.7-metre-long rocket, which had a launch mass of 1.7 tonnes, reached a maximum altitude of 254 kilometres in the almost 15 minutes between launch and landing. The payload with the scientific experiments followed a parabolic flight trajectory after separation of the rocket motors. It landed after being decelerated by a parachute and was successfully recovered by helicopter. The flight campaign was prepared and carried out by DLR's Mobile Rocket Base (MORABA), which also provided the recovery system, service module, cold gas control system, separation and ignition systems, telemetry station, launch pad and the rocket hardware.

GraviPlax – how does gravity shape the appearance of cells and organisms?

Despite their simple structure, placozoa – Trichoplax adhaerens – can distinguish between the directions up and down, which means they can perceive gravity. Around 450 specimens of these marine organisms, which are only 0.5 millimetres in size, were carried on board the MAPHEUS 9 rocket. The scientists were particularly interested in how microgravity affects the placozoa. "We are looking at the genetic responses of the organisms in microgravity. We are paying particular attention to the gene groups that are responsible for polarity, in other words, the structure of our cells in the body. Polarity is lost when cancer develops," summarises gravitational biologist Jens Hauslage from the DLR Institute of Aerospace Medicine. In the GraviPlax (Gravitation/Trichoplax) project, DLR is working closely with teams from the University of Veterinary Medicine Hannover (TiHo) and Australia's La Trobe University in Melbourne. The teams carry out the molecular biological analyses to precisely trace the effects on the cells. The tiny organisms have all the major gene groups that are necessary to study and better understand these fundamental mechanisms.

GRASCHA – how do granulates obtain their properties?

Granulates are granular solids such as powder, soil or gravel. Their physical properties are not that easy to understand. This is because they depend decisively on how tightly a granulate is piled up, or 'packed', and how compacted or compressed it is. In the GRASCHA (GRAnular Sound CHAracterization / GRAnulat SCHAll) experiment, spherical particles of glass with diameters of three to four millimetres serve as granules. With their help, the scientific team wants to test existing and new theories that explain the loss of mechanical stability of granulate packings. "We have the chance to fundamentally understand how granulates obtain their properties," explains DLR researcher Karsten Tell from the Institute of Materials Physics in Space. "Among other things, this is important in the field of geophysics. For example, if you want to understand why Earth's soil suddenly starts to slide sometimes. It consists of nothing but solid particles. Slight changes in their arrangement can cause the soil to no longer behave 'solidly', but more like a liquid." In addition to landslides, avalanches could also be better explained with this knowledge. The findings could also be interesting for the chemical and pharmaceutical industries. This is because powdery substances are often used there, and these need to be processed, conveyed and mixed as efficiently as possible. The same applies to sand and cement in the construction industry. The microgravity phase during the MAPHEUS 9 flight allowed the particles of the granulate to be arranged so loosely that they just barely made contact with each other. On Earth, this condition cannot be established due to gravity and hydrostatic pressure. At the slightest vibration, the granulate packing loses its stability in microgravity. It is precisely this process that interests the researchers the most. To investigate it, they measure the speed of sound and shear waves. This shows how quickly the shear modulus drops when the packing pressure is reduced.

MARS – 3D printing in microgravity using powders

For the third time, the MARS (Metal-based Additive Manufacturing for Research Space and Microgravity Applications) experiment set off on a short journey into space. The focus was to further explore 3D printing, especially with powdery substances, in microgravity conditions. The team from the DLR Institute of Materials Physics in Space had already produced a first workpiece made of metallic glass during the previous flights. Now the task was to further optimise the process. "The main challenge is to apply the powder evenly to the surface in a short time under microgravity or low gravity conditions," explains DLR researcher Mélanie Clozel. "With each flight of our experiment into microgravity, we have the opportunity to further develop our approaches, test them and thus increase our expertise." Metallic glass is characterised by its high strength and corrosion resistance. Both are important properties for use in space. In the future, 3D printing could also be used to manufacture components directly in space, for example on space stations. Regolith – powdered rock dust – could also be used on the surface of the Moon or Mars to manufacture components.

SOMEX – soft matter under the laser magnifier

The SOMEX (Soft Matter Experiments) experiment platform enables various experiments with soft matter in microgravity. It was also part of the MAPHEUS 9 flight campaign. Soft matter refers to a variety of materials that consist of two phases. They exist between the solid and liquid states of aggregation. These include, for example, gels and viscous liquids such as soap or paint, granulates, foams and biological and cell tissues. This time, the scientists used laser measurement techniques to observe two physical phenomena: With the help of artificial micro-swimmers, the researchers want to better understand the active motion of living organisms. This includes, for example, the formation of colonies of bacteria. They used tiny glass beads that floated in a solvent. These were coated with a material that absorbs light very strongly. When the glass beads are irradiated with a laser, they absorb the light or heat energy and move. In addition to the GRASCHA experiment, they also investigated granulates; the focus here was also on the question of how the individual particles of the granular matter move. In this way, new insights into the structure and dynamics of such systems can be gained experimentally and compared with theoretical models.

A detailed description of the experiments is available for download here.