Solar arrays (radiated or non-radiated) and other technologies are candidate materials for projects in JPL. Some of the projects need to qualify these potential technologies to cryogenic extreme temperatures (from 133 to 50 K or lower). Those technologies need to survive for more than 120 thermal cycles in a thermal vacuum environment to meet three times mission life of the ECM project per JPL design principles. There is not any published thermal cycling qualification data for solar arrays in vacuum to those of cryogenic temperatures. Therefore, an experimental assessment study was undertaken on behalf of the JPL pre-project office for the proposed Europa Clipper mission.
One can do thermal cycling to temperatures of 50 to 133 K using liquid helium. This process is exorbitantly expensive. For example, a liquid helium Dewar costs ≈$2,000 (at the time of this reporting) and will last for less than two hours or so. Furthermore, this is not a technically controllable qualification test process to 133 and 50 K. Therefore, a vacuum setup was used along with a cryostat to qualify the potential technologies to cryogenic extreme low temperatures.
This is a closed loop system in which helium gas is not lost, and resulted in a ≈35 K lowest temperature level for a given test coupon size studied. These temperatures are lower than what was intended to qualify the solar array technologies. The system successfully completed the qualification of solar array technologies down to 50 K.
A very high vacuum system was used to avoid the condensation of water at the temperatures required to qualify the SA technologies. Liquid helium was avoided for this qualification test. A specially built test fixture was used to attach a test coupon, and a LabView program was developed to conduct the tests autonomously. A closed loop system was used to interface with the test coupon to cool it to desired cryogenic temperatures. There was no change in the electrical continuity of the solar array test coupons as a result of 122 thermal cycles performed from 50 to 133 K, so it can be concluded that the test coupons remained intact after exposure to thermal cycling.
The solar array test coupons were successfully validated in vacuum. This is the first time the qualification of large solar array panel coupon [6 × 5 × 1.5 in. (≈15 × 13 × 4 cm)] was validated to those cryogenic temperatures.
This work was done by Rajeshuni Ramesham, Stephen F. Dawson, Antonio Ulloa-Severino, Timothy A. McCann, and Michael J. Errico of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49655
This Brief includes a Technical Support Package (TSP).
Thermal Cycle Qualification of Radiated Solar Arrays for 50 to 133 K Temperatures in Vacuum
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Overview
The document discusses the thermal cycle qualification of radiated solar arrays designed for the Europa Clipper Mission (ECM), which will operate in extreme temperature conditions ranging from approximately 50 K to 133 K. The research, conducted by Rajeshuni Ramesham, Stephen F. Dawson, and Antonio Ulloa-Severino at NASA's Jet Propulsion Laboratory, addresses the challenges of assessing the reliability of solar array materials at cryogenic temperatures, particularly since there is limited knowledge of their properties at such low temperatures.
To investigate the materials' performance, two specialized instruments were developed: a Thermo-Mechanical Analyzer (TMA) with a Three Point Bend Probe (TPBP) module, and a Dilatometer. The TMA measures Young's modulus (e-modulus) at cryogenic temperatures, while the Dilatometer assesses the Coefficient of Thermal Expansion (CTE). These measurements are crucial for evaluating the reliability of materials and processes intended for cryogenic applications, including the solar arrays for the ECM.
The document outlines a thermal cycling qualification process that simulates the conditions the solar arrays will face during the mission. The researchers successfully completed thermal cycling tests down to 50 K, achieving a significant milestone as this was the first time such qualifications were accomplished for solar array structures with solar cells. The testing involved cycling through 120 thermal cycles, which is three times the expected mission life, thereby meeting the Jet Propulsion Laboratory's design principles.
The research highlights the importance of understanding material properties at cryogenic temperatures, as the solar panels will experience extreme conditions during the mission, including Jovian eclipse scenarios. The findings from this study will contribute to the development of reliable solar array technologies for future space missions, ensuring that they can withstand the harsh environments encountered in space.
Overall, the document emphasizes the innovative approaches taken to qualify solar array materials for extreme temperatures, showcasing the advancements in aerospace technology and the commitment to ensuring mission success for the ECM. The results are expected to have broader implications for various technological, scientific, and commercial applications beyond the specific mission.
