In contrast to the early utilisation phase of the International Space Station (ISS), the scope of research is set to be expanded significantly over the coming years. In addition to experiments in the field of gravitational biology, scientists from Germany are increasingly working on projects relating to radiation and astrobiology. New devices within the European Columbus module and on its external platforms offer excellent opportunities for such studies.
In space medicine, the primary area of focus is the study of how the human body adapts to changed gravity conditions and life in isolation. These investigations and the radiation and astrobiology projects will make an important contribution to our understanding of the fundamental processes of life and to improving living conditions on Earth. At the same time, they also assist preparations for future long-term astronaut missions to the Moon or other exploration targets.
Gravitational biology – orientation of plants in space
Gravity has played a key role in the development of all organisms since evolution began. Therefore, researchers have been investigating the question of how organisms perceive and deal with gravity for a long time. For example, how do plants know which way is 'up' or 'down', and how do roots and sprouts manage to grow in the 'right' direction?
Scientists have already been able to uncover many secrets of nature with the help of experiments conducted in space. They have discovered how specialised plant cells react to a change in the direction of gravity via the displacement of cellular particles. Such studies have also revealed the part played by the cytoskeleton and the various messenger substances. At the level of genes and proteins, they have identified important signalling pathways and adaptations.
However, the exact processes involved in the individual steps, from the perception of gravity to the plant's response, are not yet fully understood. This is where Columbus experiments come in, for example in the Biolab facility, which investigates this question using modern molecular biological methods.
Radiation and astrobiology – life away from Earth
The strength and nature of radiation in space varies greatly. For this reason, further measurements are also planned for the future in order to assess the radiation risk more accurately. Making use of its many years of expertise in this field, the DLR Institute of Aerospace Medicine, in cooperation with national and international partners, will continue these measurements inside and outside the ISS over the coming years.
Almost more important than the dosimetric determination of the strength and composition of the radiation is analysis of its biological effects. The ‘Matroshka’ mannequin, a highly developed simulator of the human upper body and all its organs, has already provided some promising results for such analyses. Equipped with thousands of sensors, 'Helga' and 'Zohar', two additional simulators shaped like the female upper body, will occupy the seats on the first Orion mission and collect data on radiation exposure in space.
Exposure facilities on external ISS platforms are particularly productive for astrobiologists. In addition to conducting dosimetric radiation measurements, they expose various organisms and organic molecules to the extreme environmental conditions of space in these facilities, allowing their ability to survive or change to be examined. This is used to research the origin, evolution and spread of life and thus to answer the question of how life might have once come to Earth.
Human physiology – understanding changes to the human body
In the field of space medicine, the German ISS experiments over the coming years will focus on a comprehensive understanding of changes in the human body. Adopting the view of integrative physiology, where the whole person is considered as the interplay of their various systems and organs, scientists take into account the interactions between the brain, the system of bones and muscles, circulation, metabolism, the immune system and hormonal regulation.
A new approach that looks promising for the future involves the investigation of organoids and cell constructs. Researchers can conduct a variety of investigations on these organ-like tissues in a way that would not be possible with astronauts. The aim of the experiments is to understand the mechanisms of physical changes and then develop suitable countermeasures that not only benefit astronauts, but also people on Earth.
Physics and materials science
The ISS research activities in the fields of physics and materials science are set to be expanded over the coming years to encompass new areas such as quantum physics and new possibilities such as the in-situ processing of materials. New experiments for investigating granular matter and flows in planetary atmospheres will be initiated. In some disciplines, the focus is being placed on new, in many cases exploration-related issues, such as fire safety in combustion research.
As before, in addition to the relevance of such issues in space research, the terrestrial benefits are always considered. Miniaturised quantum sensors are also of interest on Earth (for example in geodesy or in shipping), as are improvements in the prevention or early detection of fires and in the optimisation of industrial materials.
Materials research – new prospects for metals and cement
About 90 percent of metallic and semiconducting materials originate from metallurgical melting processes. In order to optimise existing technologies or develop new ones, researchers work with computer simulations in addition to practical experiments. The aim of this is to reduce energy- and time-consuming preliminary tests. In microgravity conditions, disruptive forces in a melt, such as buoyancy and the deposition of components of different densities, are eliminated. These are decisive advantages for clarifying the interrelationship between solidification conditions, material structure and the resulting properties. For this purpose, experiments are conducted in the Materials Science Laboratory (MSL), with the solidified samples being brought back to Earth for evaluation.
Recently, experiments have also been taking place in the Microgravity Science Glovebox (MSG), in which transparent, organic materials – referred to as transparent alloys – are used instead of metals. Their melting and solidification behaviour is comparable to that of metal alloys and can be observed directly as they are processed. In this case, there is no need to transport the samples back to Earth. Matthias Maurer will use the MSG to analyse a sample contributed by German scientists during his ‘Cosmic Kiss’ mission. In parallel, a new facility called XRF is currently being developed for the ISS, with which metallic melting and solidification experiments can also be monitored in-situ for the first time using X-ray diagnostics.
Another aim of the materials science experiments is to measure the thermo-physical properties of reactive metal melts, such as conductivity or viscosity, using container-free processing to achieve far greater precision than would be possible under the influence of gravity on Earth. The Electromagnetic Levitator (EML) system is used for this. A third series of samples was recently produced for the EML and will now be processed on board the ISS. A fourth sample series has already been selected and plans are under way for a further upgrade to the EML system.
The curing of cement mixes will also be studied during the 'Cosmic Kiss' mission. The aim of the MASON/Concrete Hardening experiment is to investigate the hardening of concrete in microgravity for the first time. Sedimentation and convection cannot occur under these conditions. Special containers make it possible to mix sand, cement, water and aggregates without abrasive cement dust or the liquid cement mixture escaping.
The physical processes relevant for curing will be identified by making comparisons with samples that were cured under Earth gravity. It is hoped that this will pave the way for the optimisation of the manufacturing process on Earth in terms of material properties and manufacturing-related carbon dioxide emissions. In addition, the findings will also prove important for future exploration activities, including the building of structures on the surface of the Moon.
Combustion research – flames in microgravity
In addition to the optimisation of ignition processes, the topic of fire safety has moved into the focus of research in recent years. Large international projects such as Saffire and FLARE have German involvement and focus on this new area of interest. A new international standard is to be developed for the flammability of materials under microgravity conditions, as previous standards were formulated solely on the basis of gravitational forces on Earth. The impact of the surface structure of materials on the propagation of flame fronts will also be investigated. The first experiments as part of the Japanese FLARE project, which is housed in the Kibo module, are planned for the end of 2021. Some trials will also be conducted in Germany.
Fundamental physics – quanta, plasmas and planetary dust
Quantum physics first made an appearance on the ISS in 2018, in the form of NASA's Cold Atom Laboratory (CAL). Significantly more precise experiments are possible with quantum experiments performed on the Space Station, as ensembles of ultra-cold atoms (Bose-Einstein condensates) last much longer under microgravity than on Earth. The experiments serve to verify scientists' physical view of the world, as well as providing vital impetus for advancing the degree of maturity of quantum technologies for space applications, including in the fields of navigation (optical clocks, inertial sensors) and Earth observation (gravitational field measurements).
The German researchers who have attracted international attention with the success of the QUANTUS and MAIUS experiments are also involved in CAL. At the same time, work is currently under way on the Bose Einstein Condensate and Cold Atom Laboratory (BECCAL) experiment, which is part of a German-American cooperation and is to be brought to the ISS as the successor to CAL in 2025/26.
Research on complex plasmas and plasma crystals is set to continue after the phase-out of the PK-4 facility, as numerous questions relating to fundamental physical research still remain unanswered, including matters of phase transition and the theoretical description of turbulence. Discussions are currently taking place on the COMplex PlAsma faCiliTy (COMPACT), a successor to PK-4. COMPACT would be an international cooperation under German-American leadership.
A third strand to the fundamental physics research being conducted on board the ISS is laboratory astrophysics, which focuses on the formation of planets. To this day, the first steps from the smallest dust particles to larger accumulations of material, which attract each other through gravity and ultimately lead to the formation of larger bodies such as Earth, are still not well understood. Experiments such as LAPLACE, in which the dynamics of dust agglomeration is simulated in microgravity, are intended to change this. As an international experiment under German leadership, LAPLACE will uncover the secrets of planet formation from summer 2022.