Interplanetary dust particle shielding capability of spacecraft multi-layer insulation

The Solar Probe Plus (SPP) spacecraft is expected to encounter unprecedented levels of interplanetary dust particle (IDP) exposure during its approximately 7-year journey. To assure mission success it is necessary to define the dust hypervelocity impact (HVI) protection levels provided by its Multi-Layer Insulation (MLI)/thermal blankets with a reliability that is on par with that available for metallic Whipple shields. Development of a new ballistic limit equation (BLE) in the 7-150 km/s HVI range for representative 2-wall Whipple shields in which spacecraft MLI is the bumper material impacted by fused silica dust, was necessitated and is presented. A baseline SPP configuration was adopted for analysis: 0.0176 cm-thk. Kapton bumper (monolithic and layered), 2.54 cm standoff and 0.0762 cm-thk. Ti-6Al-4V rear wall. With a solid Kapton bumper, the critical particle diameter for incipient spall, which is chosen to be the failure criterion for SPP, is found to be in the ~650-1100 μm range, with the largest and the smallest sizes corresponding to 30 km/s and 150 km/s HVI, respectively. When the bumper is layered in a manner similar to that found in actual blankets (140 μm spacing), the critical particle diameter is indicated to be in the ~450-600 μm range. The existing BLE with an equivalently thick Aluminum bumper is found to be in reasonable agreement with the computed results in the 30-150 km/s range but non-conservative by a factor of ~2x at 7 km/s. A limited analysis has also been performed to assess the effect of spacing between the Kapton layers - 140 μm versus 320 μm - in a blanket on critical particle size in the 30-150 km/s HVI range. Little change in the critical particle size is found, suggesting that the response of the blanket layers to high-velocity IDP may be similar to that of multi-shock shields.