Power System for a Venus Aerobot

A range of concepts for long duration aerial missions,using high altitude balloons operating in the clouds of Venus,have been studied by NASA and JPL for the Planetary Scienceand Astrobiology Decadal Survey and for NASA’s competitiveNew Frontiers and Discovery programs. These concepts offer arich set of scientific opportunities in atmospheric chemistry,astrobiology, atmospheric dynamics, seismology and sub-cloudsurface imaging. The Venus aerobot would be sustained in flightby a variable-altitude balloon and carry a payload ofinstruments at altitudes between 52 and 62 km. The aerobotwould fly in the cloud layer containing sulfuric acid aerosols andbe subject to large temperature extremes as it traverses a rangeof altitudes and latitudes at different times of day.To achieve the desired lifetime on the order of one Venus day wehave defined a solar power system that would supply power overthe full altitude range while the aerobot is circumnavigating theplanet. We have initiated development of the requisitetechnology, including rechargeable batteries, solar arrays, anda peak power tracker for this challenging mission.We have fabricated triple-junction inverted metamorphic(IMM) solar cells optimized for power generation in the uniquespectrum of light expected at 51.5 km altitude and measured34.0 mW/cm2 power output at room temperature in initialtesting. We developed a coating to protect aerobot solar panelsfrom corrosion in sulfuric acid and demonstrated survivalwithout performance degradation after 96 hours in 96%aqueous sulfuric acid at room temperature. Initial performancedata were obtained on a peak power tracker showing 96%power conversion efficiency.We have developed specialized lithium-ion cells intended tooperate between -30 and 100oC and demonstrated 80% capacityretention after 90 cycles at 100% depth of discharge at 100 degC. These cells were incorporated into a 4s1p battery module andsuccessfully tested under expected flight-like random vibrationand thermal vacuum conditions.These results represent key steps in the process of developingthe power system technology needed to bring the Venus aerobotmission to fruition.