Extended-range Variable Altitude Balloons for Venus atmospheric missions

In-situ exploration of Venus is challenging due to its severe environment, which is benign (∼25 °C and 1 bar) at an altitude of 55 km, but rapidly becomes hostile at lower altitudes. The temperature increases to ∼465 °C, and pressure reaches 90 bars at the surface. These conditions have limited in-situ missions to high altitude balloons at 55 km that survived only 48 h. High-altitude balloon missions are stymied by the opaqueness of the Venusian clouds and constant altitude. Long-duration, extended range variable-altitude balloons covering below the clouds could enhance the science capabilities of the missions by measuring chemical species, isotopes and atmospheric flow patterns in and underneath the clouds. A new energy storage system tolerant to the high temperatures at low altitudes is needed to support such a balloon. A novel variable altitude balloon architecture with an extended range of 55–20 km (VAB-X) was developed under the NASA Innovative and Advanced Concepts (NIAC) program and is described here. The architecture comprises a high-temperature tolerant balloon and photovoltaic array for providing spacecraft power, a reversible solid oxide fuel (SOFC) for low-altitude power and fuel regeneration, and reversible metal hydride (MH) for hydrogen storage. Hydrogen is used for the buoyancy and altitude control of the zero-pressure balloon and as fuel for SOFC. Water brought from Earth can replenish the hydrogen lost to leaks during the mission. Preliminary analyses reveal the efficacy of the architecture for long-term Venus exploration over 55-20 km altitude, with a high proportion (∼20%) of the total suspended mass (>20 kg) available for science payload.