HESSI Modal Survey FEM Verification

Navcon Engineering was contracted to conduct the modal survey of the High Energy Solar Spectroscopic Imager (HESSI) spacecraft. The primary objective was to identify the damped natural frequencies, damping factors and mode shapes in the frequency band between 70 Hz. and 170 Hz. The test results were used to dynamicaly tune the finite element model. In addition to the modal survey, Navcon conducted linearity and transmissibility tests.

High Energy Solar Spectroscopic Imager (HESSI) spacecraft. HESSI's primary mission is to explore the basic physics of particle acceleration and explosive energy release in solar flares.

The test item, referred to as the HESSI Bare Structure, consisted of a base ring, primary support struts, secondary support struts, central cylinder, deck, imager support ring, solar array support struts and a solar array support ring.

The modal survey was conducted using a SIMO testing method. The data acquisition system included an HP35670A Dynamic Signal Analyzer, an HP3566A Dynamic Signal Analyzer, an APS Dynamics Model 113 long stroke electro-dynamic exciter and PCB instrumentation.

Sample mode shapes are shown below.