Researchers in Finland are investigating the posibility of using a wind propelled landing craft for space exploration, utilizing composite materials.
The project being developed by Helsinki University of Technology is based on the Thistle-type locomotion first developed by the Jet Propulsion Laboratory (JPL). The JPL built and tested a 1.5 m inflatable ball that was driven by the wind in a similar manner as the russian thistle, known as “tumbleweed” in USA. The Martian Tumbleweed would travel at speeds up to 10 m/s in the 20 m/s wind of a typical Martian afternoon, with the ball expected to climb 20° slopes with ease.
This Finnish project, funded by ESA/ESTEC under the ARIADNA-program, focusses on new innovations to develop a robust and efficient locomotion system for use in space exploration.
The project is still in an early stage of development, although numerous tests have been conducted and a paper was recently presented at the ATRA conference for the ESA Ariadna program. The prototype, pictured here, was produced for functional testing, with the researchers now at the stage where questions are being raised over the kind of materials that need to be used.
The rover was constructed with 18 glass-fibre rods (8-mm in diameter, 1.5 m in length) which were low-cost and easily manipulated into a spherical shape. Initially, 9 rods would have sufficed in terms of structural strength, but the rolling became too unco-ordinated and the spherical shape was compromised during testing. The next stage of testing will address this issue by introducing carbon fibre rods which the researchers hope will add more rigidity and will benefir from being more lightweight.
Carbon fibre rods may provide similar strength with less mass, provided that sufficient flexibility is still available with carbon fibre. There is also the possibility that the rods will be manufactured into the shape of an arc before assembly.
The 1.3 m sphere is also made with a 32-mm glass fibre central rod with the sails made of nylon-fabric weights of 4.5 kg. The researchers add that the sails will probably be replaced with more lightweight space-qualified plastic material, like Mylar or Kapton foil.
The strength and rip-resistance of the material is also a major issue as the rover tumbles over the rocky surface of Mars.
The researchers state that the structure is very flexible, acting as a spring to ride over small obstacles and reducing impact upon collision of obstacles, adding that the glass-fibre rods provide “interesting elastic properties for the Thistle”.
Flexibility also introduces hysteresis into the structure, and the self-balancing capability of the device is reduced. Without active guidance the system tends to move in circular motions rather than moving forward. Increased stiffness of carbon-fibre rods would reduce the hysteresis and increase stability of this rover.
The project, made with martian conditions in mind, is to be tested in future space explorations, with the research being sponsored by ESA.
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