Design, manufactoring and testing of a ball-head support for thermal vacuum chamber applications.

Design, manufactoring and testing of a ball-head support for thermal vacuum chamber applications. The purpose of this paper is to explain the process of the realization of a MGSE for the new photogrammetry system that has been developed at the ESTEC Test Centre. This hardware, employed to measure the thermo-elastic deformations, has been recently successfully qualified for thermal vacuum operations. The eight cameras must be used in several thermal vacuum chambers, at ESTEC but not limited to. The MGSE most crucial component is the spherical joint, that will need to be still and fixed once inserted in the thermal vacuum chamber, in order to allow the test; but able to move and allow a change on the field of view of the camera once the test is completed, for several cycles of testing. For these reasons, the greater part of the paper focuses on the conception, design and testing of the parts that make up the spherical joint. The ball-head was not only designed but also manufactured and tested in a small vacuum chamber to qualify the product. Initially, a broad bibliographical research was carried out, concerning especially the choice of materials to use in such high friction-vacuum-cryogenic application, which proved itself to be unusual. Once the materials have been selected, a design was made by means of CATIA V5, and FEM analysis were run to ensure the consistency of performances, conducting an iterative process to obtain a prototype design ready to be manufactured and tested. The main requirements that lead the design are the necessity of having a small, light, easy to install tool, while minimizing maintenance activities and the capability of having consistent performances both in ambient and in cryogenic-vacuum environment (the MGSE has to operate under the following conditions: Temperature: 100 to 313 K, Relative Humidity: 40% to 60%, Pressure: 3e-7 mbar), taking into account the tribological aspects throughout in the process. The main difficulties lied in: the use of different materials, that had to be coupled to ensure the consistency of performances in vacuum chambers, while tolerances must not be excessively tight, in order to allow the mounting and dismounting of the assembly; the limited researches available on tribology for such high friction vacuum application, and on the difficulty of modelling the physical constraints in FEM analysis on CATIA V5. These difficulties have been faced by applying security factors and by means of a continuous bibliographical research. An extensive explanation of the design and test support was carried out in chapter 6, in order to justify the conceptual choices that were made in the process. In chapter 7, a description of the test was carried out, the results prove the design to be consistent and qualify the component for thermal vacuum chambers applications. Future works include the supervision of the manufacturing and mounting of the 8 ball-heads, as well as the preparation and finalisation of the design and the manufacturing of the remaining parts of the MGSE that haven’t been discussed in detail in this paper.