Venus Surface Solar Array

The Venus surface solar array is a power source capable of long lived operation on the surface of Venus. This technology could help bring in a new era in planetary science exploration, by enabling an increase of two orders of magnitude in the duration of Venus landed missions. NASA's roadmap for Venus exploration has identified long-lived landers as one of the key mission types for the next decade. Such missions will require a power source that can operate in the harsh Venus surface environment for an extended period. The environment includes high temperature, low solar irradiance, high pressure and high corrosion. State-of-art power sources such as radioisotope thermoelectric generators, primary batteries or solar arrays are not suitable for long duration Venus surface missions due to their poor performance in the relevant environment. Because of this, only short-duration Venus surface missions of a few hours have been implemented so far. The goal of the proposed effort is to develop a solar array that can operate in the Venus surface environment and provide power to a lander for a period of at least one solar day (two Earth months). In a prior HOTTech-sponsored effort, we established the technical feasibility of solar cells optimized for low irradiance, high temperature (LIHT) environments, and demonstrated their operation for up to 49 days at 465°C. The current proposed effort will build upon these results and mature the technology to the level where it can be infused into flight projects. We plan to advance the Venus surface solar array from TRL3 currently, to TRL5 upon completion of the project. In order to mature the technology, advancements are needed in two key areas. First, at the device level, a reproducible process must be developed for fabricating LIHT solar cells, and their operational capability needs to be extended to 60 days at 500°C. Second, the level of integration of the power source must be elevated from device to assembly, i.e. from the solar cell level to the solar array level. The Venus surface solar array will be a fully integrated assembly comprising solar cells, interconnects, mechanical structures, optical components and wire harnessing, and capable of directly interfacing with other assemblies in the power subsystem. Importantly, the array will be able to withstand the high-temperature, high-pressure and corrosive atmosphere, while protecting the solar cells from corrosion degradation. The objectives of this proposal are: 1) Optimize the LIHT cell fabrication processes to achieve ≥ 3.4% average population efficiency at a temperature of 500°C, under a red-shifted spectral irradiance of 89.4 W/m2; 2) Design and fabricate a ~10 cm x 10 cm solar panel test article, representative of one module of a full size, flight-like solar array, and capable of stable operation under Venus surface temperature, pressure and corrosion conditions; and 3) Demonstrate through test a ≥ 2 W/m2 power output at the array level under Venus-surface temperature and irradiance conditions, and ≤ 20% degradation after exposure to the relevant temperature, corrosion and pressure environments for a period of ≥ 60 days. The technical approach is summarized as follows: at the device level, the LIHT cell will be iteratively optimized through design, fabrication and test. In parallel, the design of the solar panel test article will be completed, and long-lead parts for its fabrication will be procured. In addition, the solar simulator test capability will be developed for Venus-surface irradiance, spectral and temperature conditions. Next, the solar panel test article will be assembled with LIHT solar cells of optimized design. Finally, survival and performance of the test article will be demonstrated in the relevant environment, by characterizing its electrical performance under Venus surface conditions in the solar simulator laboratory, both before and after environmental exposure for 60 days in the GEER test facility.

Developing Instrument or spacecraft technology to improve measurements for future planetary science missions

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