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