Design of the elastic suspension for a new concept accelerometer for space applications: LIG-A-CUBE mission

This thesis investigates the design possibilities for the mechanical elastic suspension of the test mass of the new concept LIG-A accelerometer, on board the space mission LIG-A-CUBE, developed with the INRiM research institute. The space mission goal is to demonstrate the feasibility of laser interferometry as a technology for acceleration readings. This new concept of accelerometers for space applications grant better accuracy performance than any existing technology. To achieve such low noise outputs, the accelerometer requires a mechanical suspension of the test mass with a main resonance frequency less than 1 Hz and 6 degrees of freedom of motion. In order to achieve this goals two design solution are considered: the use of a machined helical spring or a multiple sheets elastic suspension. The study is carried out using FEM modelling with Nastran static and modal analyses, with confirmation from empirical data through experimentations. Of particular interest are the numerical studies of the different design parameters and the development of an original analytical-numerical method for the rotation centre determination of the suspension that could find applications outside of this context. Three final design solution are proposed, all for a Beryllium-Copper test mass (in brackets the respective first resonance frequency): “Helical-C” (0.42 Hz) exploits the use of a Titanium Beta machined helical spring; “Model-2S” (0.26 Hz) and “Model-3S” (0.19 Hz) are made with two and three sheets of Beryllium-Copper alloy respectively. From static analyses, a limit displacement box is established, in order to avoid mechanical interference and to exclude structural failure. This work acts as a starting base for future prototype tests of the proposed designs to investigate criticalities such as the construction feasibility of the helical spring and the thermal noise resulting from the complex assembly of the multiple sheets suspensions.