|TUPEX-4: Verification of an Extendable Boom System
|Merlin Barschke, M.Sc.
|Federal Ministry of Economics and Technology
Technische Universität Berlin is currently developing an extendable boom system for nanosatellite applications. The system is intended for gravity gradient attitude stabilization of small satellites. Furthermore, it can be used to perform scientific experiments and measurements outside the satellites sphere of influence. A prototype of the system was tested during the 23rd DLR parabolic flight campaign at NOVESPACE in Bordeaux, France in September 2013.
The extendable boom system is based on a thin-walled, slotted copper-beryllium tube that is wound onto a metallic spool. Inside the spool a failsafe brake inhibits rotation while not supplied with electrical power, such that the spool is free to rotate as soon as the brake is released. The rotation is driven by a spiral spring connected to the spool. By rotating the spool, the boom tube is unfolded and extended. A proximity sensor measures the angular movement of the spool to calculate the length of the boom during the extension process. As the desired length is reached, the extension is stopped by the brake. The boom control electronics are implemented in cold redundancy to increase reliability. An additional electronics board located at the tip of the boom carries MEMS accelerometers, MEMS gyroscopes and magnetometers to observe the extension process as well as the magnetic field without disturbances from satellite electronics.
The primary objective was to test the overall system under zero-gravity conditions. Besides the verification of the overall design, possible bending and torsional vibrations of the boom-tube were observed and recorded as a function of boom length, weight of tip-mass and extension speed. The secondary objective was to determine the optimal speed of extension for different combinations of boom length and tip-mass. Since the boom is not designed to withstand the bending loads which would be induced by the tip-mass and its own weight when extended on the ground, functional testing was only possible in a microgravity environment.