Weightless research

The international space station iss is approaching its utilization phase

When on 31. October a soyuz capsule carried the three astronauts yuri gidzenko, sergei krikalev and william shepherd from the baikonur cosmodrome in kazakhstan to the international space station, a new phase in the history of the space base began: from now on there will be people here all the time, initially three, later six to seven (new space age). In addition to construction work, scientific research tasks will increasingly become the focus of their activities.

Weightless research

Initially, they will still be primarily concerned with the further expansion of the station. At the end of november, for example, an american space shuttle will bring a support structure, solar cell modules and heaters that have to be assembled. But gradually, in addition to the construction work, scientific research tasks will increasingly become the focus of their activities. At the latest when in january the american "destiny"-laboratory module docks and is equipped with experimental equipment a month later, the orbiting research laboratory can begin operations.

The uniqueness of such an orbital laboratory lies in the almost complete absence of gravity. This makes it possible to carry out investigations that cannot be carried out on earth, or only to a very limited extent. While other factors such as prere or temperature are relatively easy to control in terrestrial laboratories, the influence of gravity cannot be easily eliminated or regulated.

At the drop tower of the university of bremen, for example, weightlessness can be generated for just 4.7 seconds. A so-called parabolic flight with an airbus a300 takes about 20 to 30 seconds. And high-altitude rockets such as the german texus or the european maxus can expose payloads of several hundred kilograms to weightlessness for up to 13 minutes. Enough for some studies. Long-term studies, such as of biological processes, are dependent on the space station.

One focus of research interest is on so-called phase transitions, such as the solidification of a liquid or, conversely, the process of melting. On earth, the forces at work here are not readily apparent because they are superimposed by the dominant force of gravity: it causes, for example, that loose particles in a liquid gradually settle on the ground and gas bubbles drift upwards. To study such processes in detail, the international space station will gradually be equipped with several special furnaces.

Such research has already led to practical applications on earth. Under gravity conditions, for example, in a molten lead-aluminum alloy, the heavier lead sinks to the bottom, while the lighter aluminum forms a layer above it. In weightlessness, it was initially hoped, drops of the heavier material would have to be distributed homogeneously in the other metal even after cooling down. But during the first experiments in space, a clear separation occurred again: this time, a sphere was formed whose core was made of lead and whose mantle was made of aluminum. Further experiments showed that temperature differences during cooling were responsible for this effect.

Finally, after many years of study, it was possible to calculate the forces at work so precisely that they could be played off against gravity on earth and eventually led to improved alloys, which are now used to produce plain bearings for car engines. "The so-called ‘spaceframe’ between the window spar and the roof on the audi is also a product of space technology", says friedhelm claasen, responsible for iss utilization preparation at the german aerospace center (dlr) in bonn. "Based on microgravity experiments, we have learned, among other things, how to better control the directional solidification of aluminum."

Another research focus is the investigation of combustion processes. The complexity of the processes involved can be significantly reduced in microgravity. The researchers therefore hope that the experiments on the international space station will provide a deeper understanding of the mechanisms at work in combustion, which in turn could lead to cleaner and more efficient technologies, for example in aircraft engines.

Through periodic mission announcements, scientists around the world are invited to develop proposals for experiments to be conducted in the coming years with the equipment gradually installed on the space station. In particular, initiatives from industry are also desired. "Over the past two years, we have stepped up our efforts to target companies outside the aerospace industry", says claasen. Interest is still somewhat muted, but will certainly increase based on the recognized potential uses once the orbiting laboratories are fully established and operational, he said.

Another important aspect of the international space station, which is openly discussed in the united states, still leads a shadowy existence in germany: research in orbit also serves to prepare for long-term manned missions, for example to mars. According to claasen, the political climate in germany has not been favorable for such ideas in recent years. "But that is just beginning to change. What we used to think about only in silence is now being discussed more and more in public." ()

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