Four-bar linkage hold down and release mechanical optimisation for the Athena X-IFU door entrance assembly Centre Spatial de Liège

Abstract

This master thesis presents the conceptual design of the hold-down and release mechanism (HDRM) of the DEA door cryo-mechanism of the XIFU instrument aboard the ATHENA space observatory. The HDRM is essential for preserving the cryostat integrity during launch by maintaining a vacuum-tight seal, thereby protecting the ultra-thin aluminium filter at the DEA entrance. This thesis focuses on the design and analysis of a four-bar linkage mechanism used as the HDRM.

First, preliminary calculations are performed to verify the vacuum-tight condition through static equilibrium and actuation force analysis. A parametric analytical model is then developed in Python to describe the kinematics and static equilibrium of the mechanism. A randomised parallel search over the design space is conducted on the CECI NIC5 high-performance computing cluster, exploring on the order of 10^18 parameter combinations. Two configurations are investigated: one parallel and one perpendicular to the door lever axis, yielding optimal force ratios of 8.88 and 7.41 respectively.

Preliminary analytical analyses confirm the mechanical feasibility of the concept, covering Hertz contact stress at pivot joints, pin shear stress, cryogenic thermal contraction, and shaft vibration frequencies. These results are complemented by three-dimensional finite element simulations performed in Siemens NX, demonstrating positive margins of safety in all components and natural frequencies well above the 140 Hz launch requirement.

Finally, a multi-criteria comparison is carried out to evaluate the two configurations. The analysis concludes with a slight advantage for the perpendicular configuration, although both remain viable candidates for further development.