Aerial and Surface Mobility at Venus Enabled by Aerobots

In response to a recommendation in the Origins, Worlds, and Life 2023–2032 Planetary Science and Astrobiology Decadal Survey, VEXAG (the Venus Exploration Analysis Group, a community-based forum for advocating for Venus exploration within the United States and beyond) stood up a subcommittee to develop a new strategy for the exploration of Venus.

This new Exploration Strategy identified in situ surface and atmospheric science as the next natural step in Venus exploration, and aerobot technologies as one of the keys to this goal. The thick, CO₂-dominated Venus atmosphere easily permits lighter-than-air flight—from a simple, single-altitude balloon to more ambitious, fixed-wing aircraft. Indeed, the flights of two helium-filled, fixed-altitude Soviet VeGa balloons in 1985 for almost two Earth days at an altitude of ~54 km, where temperature and pressure conditions are similar to those a few kilometers above sea level on Earth, demonstrated the feasibility of lighter-than-air flight at Venus.

Recent work underway at JPL and its partners to develop long-duration aerobot flight technology is centered on a balloon-within-a-balloon architecture allowing an aerobot to traverse a nominal altitude range of 52–62 km. This balloon design would operate for 100 Earth days, a duration that could be substantially lengthened by replacing lost lifting gas with electrolysis-derived gas from the atmosphere. Here, we review concepts for extending the altitude range of future aerobots to above and below the clouds and to the near-surface region.

Extending the range of the balloon-within-a-balloon architecture to reach the cloud tops near 72 km altitude requires a much larger balloon to carry the same payload. Moreover, this balloon would be exposed to the full intensity of sunlight during the daytime, necessitating very strong material to maintain its integrity over multiple circumnavigations.

A more tractable solution for an initial investigation above the cloud tops would be a solar balloon or heliotrope flown as its own self-contained mission or even deployed from the mid-cloud aerobot. This heliotrope would be ram inflated as it descends, rising to the cloud tops as a hot atmosphere balloon and operating for approximately three days until being swept around the planet into the night side. Such balloons have been deployed under similar conditions in Earth’s atmosphere and could be implemented with today’s technology.

A balloon designed to operate below the cloud base, at ~47 km altitude where the ambient temperature is 100°C, could perform night-time, high-resolution imaging of the surface in the infrared. A variant of variable-altitude balloon technology that could operate in this environment is the mechanical compression balloon developed by Thin Red Line aerospace. This balloon has been tested at temperatures equivalent to those at 45 km at Venus (135°C), surviving undamaged.

Aerobots built for accessing the deep atmosphere, where the temperature exceeds 400°C and pressures approach 90 bars, can still exploit buoyancy to facilitate vertical movement. A concept for a fixed-altitude buoyant vehicle was developed by Geoffrey Landis and, in principle, could even serve as its own entry system. The sphere would be pressurized such that, under the operating conditions on Venus, it would float at a fixed altitude with its internal pressure exceeding the ambient environmental pressure. This design places the sphere under tension, avoiding the risk of buckling under the great pressure at and near the surface.

Changing altitude within ≤15 km of the surface requires substantial aerobot construction materials, but the concept of modifying buoyancy by changing flotation device volume still applies. A metallic bellows concept similar in design to the Thin Red Line mechanical compression balloon would be suitable for this use case, and would descend to the surface where wind speeds are low and rise up to utilize higher-altitude winds to move more rapidly around the planet.

Eventually, when coupled with high-temperature electronics technologies, variable-altitude aerobots taking advantage of, and designed to operate within, the dense (70 kg/m³) lower Venus atmosphere could accomplish the same science objectives as, say, wheeled rovers on Mars or the Dragonfly rotorcraft. Such a vehicle would be able to return images of the surface at different locations, perform in situ analyses of surface materials, and even acquire and store samples to be delivered to a long-lived aerial platform within the clouds or to Earth. The capabilities of a variable-altitude, flotation-based Venus rover would be enhanced by propulsion for controlled lateral motion, and could be sized to carry a substantial onboard suite of instruments.

Other than stationary landed assets, the future of in situ Venus exploration requires mobility. That mobility can be accomplished by aerial vehicles design to float at fixed or variable altitudes—up to and, ultimately, roving on the Venus surface. Crucially, the technologies needed to take the first steps in the exploration of Venus with aerobots are ready now.