Ultralight Balloon Systems for Exploring Uranus and Neptune

A report proposes ultralight balloon systems to carry a 10-kg payload, including scientific instruments for exploring the atmospheres of Uranus and Neptune. The system masses to be transported to those planets would be kept low by not transporting balloon-inflating gases. Each system would include an upper balloon about 4 m in diameter (0.5 kg) connected via a small port (about 0.25 m in diameter) to a lower balloon about 15 m in diameter (6.4 kg). Through an opening in the lower balloon, the balloons would become filled with low-molecular-weight atmospheric gas (which has little methane content) during initial descent through the upper atmosphere. At some point in the descent, the opening would be closed. Thereafter, the collected gas would provide buoyancy in the higher-molecular-weight atmosphere (methane content ≈2 percent) in the exploration altitude range below the methane-cloud tops, and the lower balloon (used for collection only) would be dropped. The altitude could be held constant or could be regulated by alternately venting gas and dropping ballast, as is done on balloons in the terrestrial atmosphere.