Thermal-Mechanical Stability of a Large Spacecraft Structure within a Jovian Orbit

Pointing stability of spacecraft payloads is a vital part of ensuring high quality science return. This is especially true for fly-by missions that rely on precise pointing knowledge and control among a suite of elements to provide appropriate co-alignment between both optical and in-situ instruments. The Europa Clipper mission plans to execute over 45 fly-bys of Jupiter's moon Europa. To do this, the spacecraft will be put into highly elliptical orbits around Jupiter. Throughout each orbit, the Clipper spacecraft will experience a variety of thermal environments near 5 AU. It will be commanded to operate in a wide range of power cycles, experience cold soaks of up to nine hours in eclipse, then immediately be impacted by direct solar flux, and ultimately pass within 25km of Europa's icy surface. The most stressing duration for the spacecraft from a distortion perspective will be within +/-48 hours of closest approach to the Europan surface, due to the increased power demand from the instruments on the Nadir-pointed deck, as well as the electronic boxes in the Avionics Vault. Despite the structural distortions due to evolving thermal environments and demanding power schedules, the spacecraft is expected to maintain adequate pointing of its instruments throughout the orbit, especially during the fly-by, where the majority of science is captured. The objective of this work is to identify the driving thermal scenarios and analyze the Spacecraft-level thermal-mechanical distortions. The Europa Clipper Mechanical and Thermal teams have analyzed the thermal gradients of the Clipper spacecraft throughout an entire orbit of Jupiter. This transient analysis included appropriate power profiles, spacecraft attitudes and external albedo loads of orbit E41 of the 17F12v2 mission schedule. A thermal model (TM) of the spacecraft was linked to the NASTRAN structural finite element model (FEM). Thirty strategic points along the orbit were selected to map thermal gradients from the TM to the FEM and assess distortion of the structures. This integrated modeling and analysis effort provided confidence in the mechanical system design of the Europa Clipper spacecraft. Sensitive areas were then highlighted, which led to design modifications, aimed to provide thermal-mechanical stability robustness moving forward. This paper will discuss the modeling and analysis approach, results, design improvements, and lessons learned.