  Venus is known for its extreme surface temperature and its sulfuric acid
clouds. But the cloud layers on Venus have similar temperature and pressure
conditions to those on the surface of Earth and are conjectured to be a
possible habitat for microscopic life forms. We propose a mission concept to
explore the clouds of Venus for up to 30 days to evaluate habitability and
search for signs of life. The baseline mission targets a 2026 launch
opportunity. A super-pressure variable float altitude balloon aerobot cycles
between the altitudes of 48 and 60 km, i.e., primarily traversing the lower,
middle, and part of the upper cloud layers. The instrument suite is carried by
a gondola design derived from the Pioneer Venus Large Probe pressure vessel.
The aerobot transmits data via an orbiter relay combined with a direct-to-Earth
link. The orbiter is captured into a 6-h retrograde orbit with a low, roughly
170-degree, inclination. The total mass of the orbiter and entry probe is
estimated to be 640 kg. An alternate concept for a constant float altitude
balloon is also discussed as a lower complexity option compared to the variable
float altitude version. The proposed mission would complement other planned
missions and could help elucidate the limits of habitability and the role of
unknown chemistry or possibly life itself in the Venus atmosphere.
