Abstract
Microgravity experiments are essential for research in space science,
biology, fluid mechanics, combustion, and material sciences. One way to
conduct microgravity experiments on Earth is by using drop tower
facilities. These facilities combine a high quality of microgravity,
adequate payload masses and have the advantage of virtually unlimited
repeatability under same experimental conditions, at a low cost.
In a collaboration between the Institute of Space Systems (IRS) at the
University of Stuttgart and Baylor University (BU) in Waco, Texas, a new
drop tower is currently under development at the Center for
Astrophysics, Space Physics and Engineering Research (CASPER). The
design parameters of the drop tower ask for at least 1.5 sin free fall
duration while providing a quality of at least 10(-5) g. Previously,
this quality has only been achieved in vacuum drop tower facilities
where the capsule experiences virtually zero aerodynamic drag during its
free fall. Since this design comes at high costs, a different drop tower
design concept, which does not require an evacuated drop shaft, was
chosen. It features a dual-capsule system in which the experiment
capsule is shielded from aerodynamic forces by surrounding it with a
drag shield during the drop. As no other dual-capsule drop tower has
been able to achieve a quality as good as or better than 10-5 g previous
work optimized the design with an aerodynamic perspective by using
computational fluid dynamics (CFD) simulations to determine the ideal
shape and size of the outer capsule and to specify the aerodynamically
crucial dimensions for the overall system. Experiments later
demonstrated that the required quality of microgravity can be met with
the proposed design.
The main focus of this paper is the mechanical realization of the
capsule as well as the development and layout of the surrounding
components, such as the release mechanism, the deceleration device and
the drop shaft. Because the drop tower facility is a complex system with
many interdependencies between all of the components, several
engineering challenges had to be addressed. For example, initial
disturbances that are caused by the release mechanism are a common issue
that arises at drop tower facilities. These vibrations may decrease the
quality of microgravity during the initial segment of free fall. Because
this would reduce the free fall time experiencing high quality
microgravity, a mechanism has been developed to provide a soft release.
Challenges and proposed solutions for all components are highlighted in
this paper.
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