Venus Variable Altitude Aerobot Prototype Development

This paper reports results from a sub-scale prototype development effort for a cloud-level Venus aerobot capable of controlling its altitude through buoyancy modulation via transfer of helium gas. This buoyant exploration platform utilizes a balloon-within-a-balloon architecture where the helium moves between the pressurized inside balloon and the unpressurized outside balloon to effect altitude changes. The ultimate Venus mission architecture includes solar panels to provide electrical power for the helium pump, valves, avionics and science instruments thereby enabling very long duration (weeks to months) flight. The current prototype is constructed from Venus-compatible materials. The 4 m outer balloon consists of a Teflon FEP film and polyimide film laminate material with a thin silver layer between the two films. The Teflon protects the balloon from the sulfuric acid aerosols in the clouds of Venus, the silver layer minimizes solar heating and serves as a helium permeability barrier, and the polyimide provides tensile strength. The 2 m diameter inner balloon is a fabric-based laminate that supports the pressurization necessary for control authority in the face of expected diurnal heating changes and possible sustained vertical winds. Results are reported from indoor inflation and float tests along with supporting coupon-level materials testing for mechanical, optical and permeability properties. Design trade study results place this prototype in the context of possible future full-scale Venus mission designs. Finally, physics-based simulation results also are presented to quantify the expected flight performance of the sub-scale prototype at Earth and the future full-scale aerobot at Venus.