Development of a Re-Configurable Infrasonic sensor array board for Planetary Exploration Applications

One of NASA’s priorities is to investigate the internal structure of Venus by measuring the signatures of seismic activity. Seismic activity has never been measured at Venus because the high surface temperature and pressure severely limit the lifetime of current state-of-the-art electronic components and conventional approaches to monitoring seismic activity. However, seismic activity generates low-frequency pressure waves known as infrasound. Given the high atmospheric density on Venus, ground motion couples with the atmosphere 60 times better than on Earth. These waves may be detected directly from balloons floating in the Earth-like temperature and pressure at ~50–60 km altitude on Venus. Infrasound originating from seismic events has been successfully detected using barometers deployed on high-altitude balloons on Earth. This paper will focus on our development of a miniaturized infrasound sensor assembly that can be arrayed for operation on a balloon or multi-balloon platforms. The primary capability that we are seeking is the accurate sensing of the infrasonic pressure levels. However, we are also looking to determine directional dependencies via sound localization techniques with vector infrasound or time of arrival differences on a large array baseline. The developed infrasonic sensors array will have a detection limit approaching 0.005 Pa over a bandwidth of 0.05 to 10 Hz. This sensitivity will allow detecting quakes having a magnitude ~5 at a distance of 1000 km. In order to enable and enhance this technology for planetary exploration, we are basing our design on a lightweight low power flex circuit that allows for data acquisition and control of a variety of infrasonic sensors including piezoresistive pressure sensors, resonance pressure sensors. Also, the instrument assembly includes a rigidly fixed and flex circuit tethered lightweight BNO055 Inertial Measurement Units (IMU) for differential acceleration corrections and vector infrasonic sensing. The current design is controlled via an ESP32-PICO microcontroller with an external Analog to Digital Converter ADC and has a serial CP2102 (USB to UART bridge) for programming the microcontroller and data access. In our final application we will program directly via contact pads and transmit data via a serial bus or a wireless adaptor. For a multi-balloon measurement scenario, we are investigating the use of LoRa or other extended range low power communications options. This paper will focus on our flex board designs and novel resonance, vector infrasound sensor designs, and the initial testing of these array elements. These tests will be done in an infrasonic testbed that we developed at JPL to quantify and compare our system with state-of-the-art infrasonic sensors developed for Earth applications. Although primarily designed for Venus applications these sensor arrays have the potential for exploration on other planetary bodies with atmospheres for monitoring fluctuations in atmospheric pressure caused by other physical processes that move atmospheric gas including volcanoes, thunder, ocean waves, wind and bolide entry.