Responding to the requirement of ESA's Human Space Flight Directorate in charge of ISS management to predict the impact of the novel FlyWheel Exercise Machine (FWED) on the structure of an enclosed human habitat flying in space, a calculation of the transmitted disturbances and loads from the payload interfaces through the Columbus structure was commended to TEC-MS in order to assure the safety of the crew on board the ISS during the use of the fitness machine.
Launched on the 7th February 2008 with Space Shuttle Atlantis on mission STS-122, and mounted on the International Space Station inside the Columbus laboratory, FWED is a training/fitness device for astronauts based on a patented yoyo effect, which, in contrast to other fitness devices, works independently of gravity.
The results of this activity validates ESA capability to analyse the multibody dynamics of coupled large space systems: the simulations of a complex space system was compared against independent software packages and verified with real test data (both on ground and in orbit), demonstrating the validity of the simulations predictions.
Spectrum of the accelerometer data during ATV docking
(Minus Eighty Degree Laboratory Freezer) is a cold storage unit that maintains experiment samples at low temperatures throughout a mission. MELFI will support a wide range of life science experiments by preserving biological samples collected on board ISS for later return and analysis.
The cooling system of MELFI is based on the Reverse Brayton Thermodynamic Cycle which uses nitrogen gas as a working fluid. This system was chosen for its power efficiency at the desired operating temperatures. The Brayton Machine utilizes a compression wheel and expansion wheel on the same shaft supported by a gas bearings system. The Brayton Machine can rotate at speeds up to 96,000 rpm depending on the cooling requirements.
The rotor of the Brayton Machine is supported by 2 radial and 1 axial gas bearings that are sensitive to external loads that occur during activities on board ISS, such as EVA, crew exercises, docking of support vehicles (STS, Progress), ATV thruster firings, etc.
A concern was raised that high accelerations could damage the Brayton Machine by clearance loss and subsequent interference in the gas bearings due to excessive loads. As a result, the Brayton Machine was turned off during these events, which is causing wear on the machine and impacting the cooling of science samples.
An analysis was performed to assess the impact of ISS events onto the clearance of the gas bearings of the Brayton Machine. Data of existing events recorded by the SAMS and MAMS accelerometer service on board ISS was used to generate excitation functions.
Model of Brayton machine
A model was set up that is representative in terms of mass and inertia properties of the Brayton Machine rotor, its rotational speed, and the radial and axial stiffness of the gas bearings.
Using the on board recorded accelerometer data of selected events, the change in bearing clearance was computed. This allows assessing whether or not events generating high accelerations would damage the Brayton Machine.
In addition, a sensitivity analysis was performed to assess whether or not and to what extend variations in the mechanical properties of the Brayton Machine, manufacturing and assembly tolerances, the running speed of the rotor and worst case environmental conditions will affect the analysis results and the variations in the bearing clearance. It was found, that none of the analyzed ISS events, no credible tolerance variation would significantly reduce the bearing clearance or even causes interference. As a result, the practice of shutting down the Brayton Machine during load generating events was discontinued.
Last update: 18 January 2011