Extended Stroke and Miniaturized Reverse-Operation DTE Thermal Switches

This paper describes two advanced thermal switches under development at JPL that are offshoots of the recently flight-qualified 2500:1 reverse-operation differential thermal expansion (DTE) thermal switch (ROD-TSW). The first new device is the extended stroke ROD-TSW (or ES-ROD-TSW) while the second new device is the miniaturized ROD-TSW (or mini-ROD-TSW). ES-ROD-TSW development was funded by a NASA Center Innovation Fund (CIF) Advanced Concepts FY20 award to JPL, which is a joint project with NASA/MSFC, who was funded by their own FY20 NASA CIF award to participate in ES-ROD-TSW development. Mini-ROD-TSW development was funded by an internal JPL R&TD award in FY20. Each of these two new thermal switches employs multiple diametrically nested DTE stages in contrast to the original single-stage ROD-TSW. The ES-ROD-TSW employs two such stages as well as a novel negative CTE material known as Allvar and its main purpose is to extend the stroke of the ROD-TSW so that the gap when OFF is large enough (1 mm) for operation in non-vacuum planetary environments. The mini-ROD-TSW employs four such stages, and its main purpose is to miniaturize its size (2.54 cm envelope, 30 gram mass) for use in miniaturized lunar instruments and rovers. The ES-ROD-TSW was lab bench and TVAC tested at JPL and its ON/OFF ratio is 13000:1 based on a measured ON conductance of 6.89 W/K and a calculated OFF conductance of 0.00053 W/K. The measured OFF conductance of the ES-ROD-TSW of 0.003 W/K is likely erroneously high due to instrumentation limitations. The target performance for the mini-ROD-TSW was an ON conductance of 1.5 W/K and an OFF conductance of 0.0015 W/K, both of which were verified by analysis. Test verification of mini-ROD-TSW performance remains to be carried out. The paper will provide design and performance details of these two new advanced thermal switching devices.