Although gravity is the weakest force in comparison to all other basic forces, it dominates our everyday life to a large extent. Because “gravity” is, besides inertia, a property of mass. And thus, gravity can normally be experienced more frequently and more clearly than e.g. electromagnetic force (e.g. in the form of an electromagnet).
While gravity ensures that we normally literally have both feet on the ground and make life on this planet possible, it sometimes proves to be very obstructive in both basic and applied research.
In order to carry out experiments under so-called micro-g conditions (usually succinct, but not completely correctly described as weightlessness), it would ideally have to be moved into space . For example, on the ISS or installed in a satellite in orbit. Understandably, these possibilities are very complex, expensive and, especially for pre-tests, completely oversized.
What possibilities do we have here on Earth?
Besides, less known alternatives like the High Altitute Ballooning (mostly known under the term “weather balloon” – latex balloons filled with helium or hydrogen, which can transport measuring equipment into high atmospheric layers and thus in principle already into space , ), parabolic flights  are of course an interesting variant. However, they are also connected with high expenditure and high costs, a repetition is not given for many experiments, at least in a temporally justifiable framework.
This is where the drop towers come into play:
With drop distances of up to 140 m and drop times of slightly more than 5 s ,  (almost 10 s with additional use of the catapult at the German ZARM ), drop towers offer a rather short time of weightlessness, more correctly expressed, microgravity. However, they are many times cheaper, offer the possibility to drop experiments several times in a row and thus generate a sufficient amount of data, and are generally associated with less effort.
Since the fall distance increases proportionally to the square of the fall time according to the equations of motion for free fall (for simplicity’s sake the friction is neglected here), one quickly reaches limits  with regard to longer fall times. While for a fall time of 2 s a distance of approx. 20 m is required, for 3 s it is already 44 m. A drop tower that can deliver a drop time of 10 s without catapult technology or similar would have to be about 490 m high (for comparison: the Empire State Building including antenna is 443 m high).
When does air friction play a role?
In addition to these obvious limitations, there is another reason why drop towers with a drop time of approx. 2 to 2.2 s are being built worldwide first and foremost: From approx. 1.8 – 2.0 s onwards, the influence of air friction becomes more and more apparent, so that already at a fall time of 3 s a considerable deviation in the velocities of fall occurs and thus a corresponding deterioration in the residual acceleration (expressed in multiples of g, e.g. 10 – 5 g) . For experiments under microgravity conditions, however, this residual acceleration must be as low as possible so that the corresponding drop tower can be a sensible alternative to non-earth-bound platforms.
Here, for example, it is possible to drop experiments in a vacuum and thus eliminate air friction or to use a so-called Dragshield technology  (an inner capsule with experiment falls freely in an outer capsule, which in turn is exposed to air friction). However, both variants are associated with considerable effort and sometimes high costs. For this reason, drop towers at smaller universities ,  , which are intended as an experiment platform for students or for simpler pre-tests, are usually designed for a drop time of approx. 2 seconds. The influence of air friction remains low, but good results can be achieved with good residual acceleration (usually 10 -4 to 10 -5 g ).
The drop tower of the GÖDE-Stiftung
The Waldaschaff drop tower will presumably have a height of approx. 30 m and thus – minus the distances for the dropping and collecting unit – deliver a drop time of approx. 1.8 – 2.0 seconds.
In contrast to other drop towers of this format, however, this is a vacuum drop tower, which should provide a residual acceleration of approx. 10 -5 to 10 -6 g as well as the possibility of absolute measurement of drop distance and drop time.
Experimental platform for universities and industry
After its completion, the drop tower will also be made available to other scientists and research institutions, but also to engineers from industry for their own experiments. Exact conditions of use and costs per dropping can, however, only be determined after completion (according to the current plan: mid to end 2020).
In order to find the best technology for a largely vibration-free ejection and to realize the braking unit , , which is conceived as an adapted form of the eddy current brake, an evaluation version on a reduced scale is currently being built. Once all the necessary elements of the drop tower have been developed and optimized, the 2 s drop tower will be built. However, construction is not expected to start before the beginning of 2020.
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