NASA's Low Level Airship for Venus

In 2012 NASA commissioned a study of a low level airship for the exploration of the surface of Venus. The airship powered by a radioactive heat source would have enabled large areas of Venus's surface to be explored with much greater efficiency than a conventional rover like Curiosity and one airship could have the same return as all the rovers sent to Mars to date.. Abstact of Paper "The feasibility of a Stirling engine powered airship for the near surface exploration of Venus wasevaluated. The heat source for the Stirling engine was limited to 10 general purpose heat source (GPHS)blocks. The baseline airship utilized hydrogen as the lifting gas and the electronics and payload wereenclosed in a cooled insulated pressure vessel to maintain the internal temperature at 320 K and 1 Barpressure. The propulsion system consisted of an electric motor driving a propeller. An analysis was set upto size the airship that could operate near the Venus surface based on the available thermal power. Theatmospheric conditions on Venus were modeled and used in the analysis. The analysis was an iterativeprocess between sizing the airship to carry a specified payload and the power required to operate theelectronics, payload and cooling system as well as provide power to the propulsion system to overcomethe drag on the airship. A baseline configuration was determined that could meet the power requirementsand operate near the Venus surface. From this baseline design additional trades were made to see howother factors affected the design such as the internal temperature of the payload chamber and the flightaltitude. In addition other lifting methods were evaluated such as an evacuated chamber, heatedatmospheric gas and augmented heated lifting gas. However none of these methods proved viable." Follow the link to see the paper