MULTIAXIS RANDOM VIBRATION TEST - A NEW VERIFICATION APPROACH FOR SPACE INSTRUMENT

The first ever known simultaneous multi-axis random vibration test campaign on a space telescope was conducted successfully through a collaboration between ESA/ESTEC and Leonardo S.p.A. on a tri-axial shaker at the MechVib laboratory of University of Ferrara. A preliminary overview on the test campaign has been already presented as Part I in previous ECSSMET conference. The topic of this paper, Part II, is a more indepth assessment on the comparison with FEM prediction. Moreover, the understanding of test measurements to provide an evaluation of the analyses performed against single axis specifications and in compliance with the multi-axis environment is presented in this paper. A proposal to develop test specifications for multi-axis vibration testing and on how to develop the adaptation of single-axis requirements to cover the multiaxis environment, as well as the methodology to define a possible notching approach in the multi-axis environment is also discussed. The need for this work arises from the fact that, for space payloads or subassemblies, the current qualification standard, to demonstrate the unit random vibration compliance with the level imposed at unit’s interface by the spacecraft acoustic environment, is to test on shaker where three single-axis excitations are performed separately in order to cover the three orthogonal axes response. However, the interface driven random load from the spacecraft is acting simultaneously in a multi-axis way. The single axis qualification approach is justified under the assumption that the crossaxis response of the unit is covered by a separate monoaxial testing. This is true provided that there is sufficient margin in the single axis qualification levels covering the multi-axis response, verifiable only during system testing but it often happens when the flight unit has been already installed, at spacecraft level. The Structural Thermal Model of JANUS (Jovis, Amorum ac Natorum Undique Scrutator) has been selected for this activity due to its structural behaviour, which shows important crossacceleration response with respect to mono-axial testing. This payload is a telescope whose Flight Model was installed on JUICE (JUpiter ICy moons Explorer) spacecraft, an ESA (European Space Agency) mission to Jupiter’s icy moons, launched with an Ariane 5 rocket on 14th Apr 2023 from the Europe's Spaceport in French Guiana. The extensive test campaigns addressed and the available measurements both for payload and satellite, made this payload an ideal candidate for this study.