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46th Lunar and Planetary Science Conference (2015)
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AERODYNAMIC AND ENGINEERING DESIGN OF A 1.5 SECONDS HIGH QUALITY MIRCROGRAVITY DROP TOWER FACILITY. V. Belser1,2, J. Breuninger1, R. Laufer2,1, K. Boehm3,2, M. Dropmann2,1, G. Herdrich1,2, T. Hyde2 and H.-P. Röser1, 1Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, 70569
Stuttgart, Germany, Email: valentin@belser-weil.de, 2Center for Astrophysics, Space Physics and Engineering Research, Baylor University, One Bear Place #97310, Waco, TX 76798, 3Institute of Aerospace Engineering, Technical University of Dresden, Marschner Strasse 32, 01062 Dresden, Germany
Introduction: Microgravity is the condition of a
body in free fall with a lack of external forces acting
on it. It results in a stress and strain free state, in
which especially fluids show an altered behavior.
Studying this altered behavior can lead to a better
understanding on what effect gravity has on fluids.
Therefore conducting experiments under the condition of microgravity is promising for research in
space science, planetary science, biology, fluid mechanics, combustion and material science [1]. Microgravity experiment platforms range in experiment
size, duration and quality of microgravity. The latter
is the difference in acceleration of the platform to the
gravitational acceleration g and according to Boehm
in [2] it should reach 10-5 and 10-6 g in order to satisfy
the requirements of most microgravity experiments.
Common research platforms include orbital
spacecraft, airplanes undergoing parabolic flight maneuvers and drop towers. The last-mentioned offer
good quality of microgravity combined with adequate
payload masses and the advantage of virtually unlimited repeatability under same experiment conditions,
at a low cost.
In a collaboration between the Institute of Space
Systems (IRS) at the University of Stuttgart, a new
drop tower facility is currently under development at
the Center for Astrophysics, Space Physics and Engineering Research (CASPER) at Baylor University
(BU) with the design parameters of at least 1.5 seconds drop duration while providing a quality of at
least 10-5 g. So far this has only been achieved in vacuum drop tower facilities in which the capsule experiences virtually no IC: Inner capsule, OC: Outer capsule
aerodynamic
drag
during the drop (an
unwanted
external
force). Since this
design comes at high
costs, another common drop tower design concept, which
does not require an
evacuated drop shaft,
was chosen. In this
design a dual capsule
system (figure 1) is Fig. 1. Dual Capsule Design
used, in which the capsule containing the experiment
(inner capsule) is protected from aerodynamic drag
by dropping a drag shield (or outer capsule) in front
of it.
Feasibility study: In order to show the general
feasibility of this drop tower design concept, a practical small scale study was conducted [2] which proves
that the quality of microgravity could be achieved
with this design option, by implementing aerodynamic improvements for the shape and dimensions of both
capsule. Additionally initial tests provided valuable
information for the design.
Aerodynamic Optimization: Other drop tower
facilities featuring this design have so far not been
able to provide the required quality of microgravity at
drop durations of approximately 2 seconds [3].
Therefore, as a first step of the drop tower development process, the dual capsule design and drop shaft
had to be aerodynamically optimized. This was done
by optimizing the shape of the outer the capsule and
the exact dimensions of both capsules (figure 1) with
the aid of computational fluid dynamics (CFD) simulations (figure 2). The simulations demonstrated that
the quality of microgravity can be met with an optimized capsule design. The results were verified by
testing a scaled model in a wind tunnel and with an
experiment setup in which some forces experienced
during the drop could be measured without actually
dropping a full scale dual capsule system. Furthermore, the aerodynamic influence of the drop shaft
was studied leading to the concept design seen in
figure 3.
Fig. 2. CFD results of Different OC shapes
46th Lunar and Planetary Science Conference (2015)
2833.pdf
Deceleration Device: The deceleration device
has the function to decelerate both capsules from the
highest (impact) velocity to standstill. The research
by Breuninger in [3] shows two eligible design options for such a device. A study has been conducted
in order to evaluate the best design for the BU drop
tower under the consideration of the aspects costs,
safety, maintenance, reliability and operational functionality.
Release Mechanism: Beside the capsules it
selves another key component affecting the quality of
microgravity is the device for capsule release. Initial
disturbances caused by the release device were observed at other drop tower facilities [4], which shorten the drop time under the desired quality of at least
10-5 g. To keep the release low of initial disturbances
currently an investigation of possible design options
is ongoing.
References:
[1] H. Dittus (1991) Endeavour, Volume 15, Issue 2,
Pages 72-78. [2] K. Boehm (2013), Design of a 2Second Drop Tower Facility for Small Satellite Technology Demonstration and Microgravity Research,
9th IAA Symposium on Small Satellites for Earth
Observation, Berlin. [3] J. Breuninger (2014), Design
of a 1.5 Seconds High Quality Micro Gravity Drop
Tower Facility, Bachelor Thesis, University of
Stuttgart. [4] European Users Guide to Low Gravity
Platforms, Chapter 3, Pages 1-22, European Space
Agency.
Fig. 3. Concept of Drop Shaft Design