Non-Cooled Power System for Venus Lander

Abstract

The Planetary Science Decadal Survey of 2013-2022 stated that the exploration of Venus is of significant interest. Studying the seismic activity of the planet is of particular importance because the findings can be compared to the seismic activity of Earth. Further, the geological and atmospheric properties of Venus will shed light into the past and future of Earth. This paper presents a radioisotope power system (RPS) design for a small low-power Venus lander. The feasibility of the new power system is then compared to that of primary batteries. A requirement for the power source system is to avoid moving parts in order to not interfere with the primary objective of the mission -to collect data about the seismic activity of Venus using a seismometer. The target mission duration of the lander is 117 days, a significant leap from Venera 13, the longest-lived lander on the surface of Venus, which survived for 2 hours. One major assumption for this mission design is that the power source system will not provide cooling to the other components of the lander. This assumption is based on high-temperature electronics technology that will enable the electronics and components of the lander to operate at Venus surface temperature. For the proposed RPS, a customized General Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG) is designed and analyzed. The GPHS-RTG is chosen primarily because it has no moving parts and it is capable of operating for long duration missions on the order of years. This power system is modeled as a spherical structure for a fundamental thermal analysis. The total mass and electrical output of the system are calculated to be 24 kilograms and 26 Watts, respectively. An alternative design for a battery-based power system uses Sodium Sulfur batteries. To deliver a similar electrical output for 117 days, the battery mass is calculated to be 234 kilograms. Reducing mission duration or power required will reduce the required battery mass. Finally, the advantages and disadvantages of both power systems with regard to science return, risk, and cost are briefly compared. The design of the radioisotope power system is considerably riskier because it is novel and would require additional years of further refinement, manufacturing, safety analysis, and testing that the primary batteries do not need. However, the lifetime of the radioisotope power system makes its science return more promising.

Venus high temperature atmospheric dropsonde and extreme-environment seismometer (HADES)

“…The trade study for the power system of the lander compared a radioisotope power system (RPS) and primary sodium sulphur (NaS) batteries. The methodology and conclusions of this study are fully described in Salazar, et al (2014). 38 A customized General Purpose Heat Source -Radioisotope Thermal Generator (GPHS-RTG) is chosen for the RPS.…”

“…The methodology and conclusions of this study are fully described in Salazar, et al (2014). 38 A customized General Purpose Heat Source -Radioisotope Thermal Generator (GPHS-RTG) is chosen for the RPS. It consists of 2 GPHS blocks, microtherm insulation, 64 Silicon Germanium (SiGe) thermoelectrics, a titanium pressure vessel wall, pyrolytic graphite fins, and a gas management valve.…”