Mathematics – Logic
Scientific paper
Sep 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.524..121p&link_type=abstract
In: Proceedings of the 10th European Space Mechanisms and Tribology Symposium, 24-26 September 2003, San Sebastián, Spain. Compi
Mathematics
Logic
Holddown And Release Mechanisms
Scientific paper
Due to the launch vibration environment, the use of locking device is necessary for large or heavy mechanisms. This remark is true in particular for the inertial actuators like magnetic bearing reaction wheels. These actuators have a rotor that is in magnetic levitation without any contact with the stator. Locking device is mandatory to maintain the rotor during the launch vibrations. To avoid contact between rotor and stator during the functional phase, the link created by the locking device must be completely released. This article presents a pneumatic locking device with pyrotechnical sub-systems that have been realised by "ALCATEL Space Industries" for the reaction wheels development in the frame of a CNES satellites family. The first paragraph presents the wheel functioning and briefly describes the Electro-mechanical components of the reaction wheel. The second paragraph describes a device based on a metallic bellows ring. A nitrogen pressure in the ring allows pushing the rotor against the stator. The rotor release is obtained by drilling the system tubing with a pyrotechnic valve. The third point describes the qualification tests and the resulting data. Some functional tests are made in warm and cold case with the locking device in order to improve some mechanical characteristics including the locking effort generated and the leakage rate. Launch vibrations and thermal tests have been realised and the good functioning of the mechanism is proven. At the end of these tests, the qualification has been pronounced. The device is now implemented within the reaction wheel. This equipment should flight in 2004. The next paragraph presents the works realised under CNES Research and Technology contract. The objectives were the characterisation of metallic bellows and some technological studies to improve the knowledge of the mechanical and functional characteristics of these elements. The first study was to create a Finite Element model of a bellow in order to describe its behaviour when it is submitted to pressure loads. The resulting data were strengths and force versus displacement. In parallel some test have been realised to verify the adequacy of the model. The last part synthesises the advantages and the drawbacks of the mechanism and the lessons derived from the study.
da Costa Arlindo
Privat Michel
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