A Balloon With a Tether Could Explore Venus’ Surface

Venus is very variable. Its surface constantly changes from volcanic activity, and the difference between its lower and upper atmosphere is night and day, with a dramatic change in sulfuric acid concentration. So, designing a system that works for all parts of Venus is particularly challenging. NASA thinks they might be on to a new idea of how to do so and has funded Ben Hockman, a roboticist at the Jet Propulsion Laboratory, to work on a tethered atmospheric sensor attached to a balloon as part of the NASA Institute of Advanced Concepts Phase I program.

The project, known as the Tethered Observatory for Balloon-based Imaging and Atmospheric Sampling (TOBIAS—assumedly not after the Arrested Development character), is based on a simple principle. On Venus, a very distinct cloud layer, between 47 and 52 km in altitude, separates the relatively stable upper atmosphere similar to Earth’s, with a hellish surface that no probes have yet lasted longer than a few minutes on. 

TOBIAS would float a helium-filled balloon in the upper atmosphere, where conditions are Earth-like. Then it would release a “towbody” – a stand-alone sensing platform connected to the balloon by a tether. That tether is intended to be several kilometers long, allowing the towbody to pass through the hazardous cloud layer and, hopefully, take accurate, high-resolution images of Venus’ surface.

Several design decisions will be the focus of the Phase I NIAC grant. According to Dr. Hockman’s interview with Fraser, one of the most important aspects will be the tether design. The most significant force on the tether wouldn’t be from the towbody itself but from the wind shear. The wind conditions are different enough from where the balloon is located (50-60km altitude) to where the towbody is intended to reside (45km altitude) that the forces on the tether would be strong enough to rip it apart if it’s not designed correctly.

Also, the tether’s material is essential. Standard copper wire could potentially power the towbody, but it would be too heavy to survive the mission’s expected wind shear conditions. Optical fiber could prove a viable alternative, but there are some concerns about the amount of power that could be transmitted that way. According to Dr. Hockman, “People have put power over fiber before.”

Much of that power would go to a cooling system that would make the temperature in that part of the Venusian atmosphere manageable. Dr. Hockman suggests alternative power sources, like solar panels (which would be affected by the same cloud layer that obscures the surface) to wind turbines, which would do well because of the high energy available from the wind but might lead to stability issues with the towbody.

Ultimately, if they can get the cable, power, and communication systems on the towbody to work, it could provide atmospheric sensing, and more importantly, direct imaging of the surface of Venus, in a variety of wavelengths. Near-infrared images, which TOBIAS could supply, could help answer outstanding questions about the history of Venusian volcanism.

Dr. Hockman even speculates about the potential for a tethered impactor to land on the surface, grab a sample, and reel itself back up to the balloon. That concept was the subject of a previous year’s NIAC grant, though it’s unclear whether further progress has been made.

TOBIAS would benefit from additional information about the Venusian atmosphere from DaVinci and Veritas, which will also contain instruments to peer through to the surface, just not in the wavelengths that the towbody would enable. Data from those missions could inform the design of TOBIAS’s balloon and tether system, hopefully making it more likely to survive Venus’ extreme conditions.

The project still has a long way to go before it has to survive anything, though. NIAC grants, especially Phase I, are meant to encourage very early design studies, many of which are unlikely to receive further funding. But, if Dr. Hockman proves the idea more and receives a Phase II grant sometime in the next few years, a balloon tugging along some sensors might one day reach Venusian skies.

Learn More:
NASA / Ben Hockman – TOBIAS: Tethered Observatory for Balloon-based Imaging and Atmospheric Sampling
UT – A Balloon Mission That Could Explore Venus Indefinitely
UT – The Best Way to Learn About Venus Could Be With a Fleet of Balloons
UT – Is There Seismic Activity on Venus? Here’s How We Could Find Out

Lead Image:
Artist’s concept of TOBIAS
Credit – Ben Hockman / NASA

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