Teflon ® FEP (fluorinated ethylene propylene) surfaces on the Hubble Space Telescope (HST) have experienced significant degradation in mechanical properties during nearly ten years of exposure in the low Earth orbit environment. This paper describes results of mechanical properties testing of Teflon ® FEP materials exposed on HST for 9.7 years between launch and the third servicing mission (SM3A) and for 2.8 years between the second servicing mission (SM2) and SM3A. The results of tensile testing, bend testing and microscopic examination of crack morphology are described. The effects of post-retrieval heating and air compared with vacuum storage on the mechanical properties of the FEP surfaces are described as they significantly affect the interpretation of the results regarding the durability of FEP on HST. This paper provides comparisons of the properties of FEP surfaces retrieved during SM3A to previously reported results for FEP materials retrieved during the first servicing mission (SM1) and SM2. The environmental exposure conditions for the HST exposed materials are also described.
During the March 2002 Servicing Mission by Space Shuttle (STS 109), the Hubble Space Telescope (HST) was refurbished with two new solar arrays that now provide all of its power. These arrays were built with viscoelastic/titanium dampers, integral to the supporting masts, which reduce the interaction of the wing bending modes with the Telescope. Damping of over 3% of critical was achieved. 1 Figure 1. HST with Solar Array 3 (SA3) on orbit and SA3 finite element model showing damper locationTo assess the damper's ability to maintain nominal performance over the 10-year on-orbit design goal, material specimens were subjected to an accelerated life test. The test matrix consisted of scheduled events to expose the specimens to pre-determined combinations of temperatures, frequencies, displacement levels, and numbers of cycles. These exposure events were designed to replicate the life environment of the damper from fabrication through testing to launch and life on-orbit. To determine whether material degradation occurred during the exposure sequence, material performance was evaluated before and after the accelerated aging with complex stiffness measurements. Based on comparison of pre-and post-life-cycle measurements, the material is expected to maintain nominal performance through end of life on-orbit. Recent telemetry from the Telescope indicates that the dampers are performing as intended.Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/22/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx * The SA3 arrays are not rigid in the traditional mechanical sense, as the primary modes of these arrays are around 1 Hz. But SA3 is considered rigid compared to SA2; the primary modes of SA2 were about 0.l Hz.
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