First Iteration Communications Circuit for a Long-Lived In-situ Solar System Explorer (LLISSE)

Abstract

The first iteration communication system circuitry for the Venus Long-Lived In-situ Solar System Explorer (LLISSE) lander was developed using NASA Glenn Research Center SiC JFET technology. The atmosphere of Venus is a harsh environment that experiences temperatures upward of 460 °C, pressures of 1344 psi, and a dense, corrosive atmosphere composed of CO2, N2, SO2, HF, HCl, CO, OCS, H2S, and H2O making Venus a challenging environment for electronics. Previous missions to Venus have lasted for less than two hours, but LLISSE is being planned and developed to survive 60 Earth days. The communications circuit was designed in Keysight Advance Design Systems (ADS), using three stages of differential amplifiers with the bias circuit designed to be turned on and off for On-Off Keying (OOK) modulation. Buffer amplifiers are integrated into the circuit to facilitate testing. Based on JFET SiC technology developed at NASA Glenn Research Center, it's designed to operate at 5 MHz at room temperature, and 2 MHz at 460 °C. OOK gives the advantage of low power consumption and is ideal for the low frequency transmission. The SiC JFET has been shown to survive 60 days in a simulated Venusian environment. The circuits are tested in the laboratory on a high temperature probe station. The die is mounted and wirebonded on an alumina carrier for probing. Two output ports provide positive and negatively swinging signals to supply a balanced signal to the antenna; the input ports are for bias and a control signal that will come from a digital output of the sensors. The oscillation frequency, output power, phase noise, and data rate are measured as a function of temperature. The output power and phase noise are shown as a function of frequency. The output voltage is measured as a function of time at room temperature and Venus temperature for different bit rates. As a result, this paper demonstrates the first SiC-based communication circuit designed to operate on a long-lived Venus lander.