Verification by analysis of a flown deployable truss: what the MODE ground-to-orbit frequency shift is not

Result

The stiffening prediction is one of three made with the flight data withheld. The other two: the suspension sway frequency, 0.284 Hz predicted against 0.28 Hz documented, and the preload trend across the three tested cable tensions, −2.34% predicted against −2.07% measured, with cable slack emerging unprompted at the lowest preload. Before any prediction, the rebuilt model was verified against an independently written solver to better than 0.5% and reproduced the 1993 analysis to within 0.8% without calibration.

The shift being explained is a softening between 1 g and 0 g of 1.4% in torsion, 0.8% in bending and 0.7% in shearing. Seven candidate mechanisms were tested, each as a stiffness perturbation with its gravity driver quantified from converged static states, and all seven are eliminated. Every quantity gravity does change substantially, such as longeron compression at 6.3%, drives bending instead of torsion. Damping is excluded separately, being two to three orders of magnitude too small to move the peak.