In-situ exploration of Venus is challenging due to its severe environment, which is benign (25^oC) at an altitude of 55 km, but rapidly becoming more hostile at lower altitudes. The temperature increases at ~7^oC/km to ~465°C, with the pressure reaching 90 bars at the surface.¹ These challenging conditions have limited in-situ exploration missions to high altitude balloons at 55 km (above the clouds) that lasted for 48 h, or even shorter duration surface missions that survived for two hours.^2,3 The high-altitude (55-65km) balloon missions are stymied by the opaqueness of the Venusian clouds, which underlines the need for more long-duration in-situ missions for a better understanding of the Venus atmosphere across the cloud layers and below, as recommended by the Venus science community, Venus Exploration Analysis Group (VEXAG).⁴ Long-duration variable-altitude balloons (VABs) extending below the clouds have gained particular interest. Durable VABs would allow i) long-term measurements across Venus clouds, ii) determination of chemical species and isotopes underneath the clouds, iii) transport to different longitudes on the planet and measure atmospheric flow patterns, especially with the altitude control, iv) probing the interior structure through close-range imaging, and v) investigation of the seismic activity from acoustic measurements at various altitudes.

For these missions, conventional power technologies are inadequate. For example, the performance of photovoltaics (PV) is hampered by the decreasing solar flux deeper in the clouds, the selective loss of short wavelength radiation, and the performance loss from the high temperatures.⁵ An energy storage system tolerant to high temperatures is needed to compensate for the reduced power generation of PVs at low altitudes, and to support nighttime operations for the VABs. In this paper, we will describe a novel ‘Venus Interior Probe using in-situ Power and Propulsion (VIP-INSPR) architecture we have been developing under NASA-NIAC (Novel Innovative and Advanced Concepts) program for sustained Venus atmospheric exploration. The probe concept utilizes: i) PV as a power source to the probe at high altitudes, and to electrolyze water carried from ground using regenerative solid oxide fuel/ electrolysis cell (SOEC), ii) Solid oxide fuel cell (SOFC)⁶ to provide power at low altitudes, iii) hydrogen storage bed for on-demand storage or release of hydrogen,⁷ iv) and a balloon filled with hydrogen and with hydrogen buoyancy-based altitude control system. Both H₂ and O₂ would be regenerated through electrolysis of the water produced in the fuel cell (a closed–system) at high altitudes.

Acknowledgments: This work presented here was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with National Aeronautics and Space Administration and supported NASA-NIAC.

References: 1) T. Basilevsky, J. W. Head, "The surface of Venus". Rep. Prog. Phys. 66, 1699 (2003); 2) R. Z. Sagdeev, et al., The VEGA Venus balloon experiment, Science, 231, 1407, 1986; 3) M. Wade, "Venera 1VA". Encyclopedia Astronautica. Retrieved 28 July 2010; 4) “Aerial Platforms For the Scientific Exploration of Venus”, The Venus Aerial Platforms Study Team Summary Report, August 2018; 5) G. A. Landis and T. Vo, "Photovoltaic Performance in the Venus Environment," 34th IEEE Photovoltaic Specialists Conference, Philadelphia PA, June 7-12, 2009; 6) A. B. Stambouli and E. Traversa, Renewable and Sustainable Energy Reviews, 6 (2002) 433-455, 7) G. Sandrock, S. Suda and L. Schlapbach, “Applications,” in Hydrogen in Intermetallic Compounds II, Topics in Appl. Phys. V. 67, Springer-Verlag 1992, ISBN 3-540-54668-5.