Impacts of Low-Power Requirements on the LEMS HMS Design

Spacecraft designs often require optimizations for low power. When low power is required, design options become limited. The Lunar Environment Monitoring Station (LEMS) exemplifies how requirements for low power can have ramifications across a system, even impacting Field Programmable Gate Array (FPGA) design. LEMS is a standalone instrument suite concept with a number of sensors that collect geophysical measurements on the surface of the moon. It has completed Technology Readiness Level (TRL) 6 qualification. Continuous operation on the surface of the moon imposes great challenges, not least of which is power management. Owing to its slow rotation, lunar nighttime and daytimes lasts several weeks, and many science sensors have high power consumption. It is challenging to design a system that can operate during hot temperatures of the daytime and survive the long periods of the frigid nighttime. In fact, the challenge is such that missions that would attempt long duration operations on the moon are exceedingly rare. To complete its science missions, LEMS seeks to survive and operate on the moon for years. To solve the challenge of power management, LEMS utilizes a combination of techniques. A high-efficiency battery sustains operations through the lunar night while LEMS alternates between periods of being “awake” and in “hibernation.” The subsystem of LEMS that handles this switching of states is the Hibernation Management System (HMS). The HMS powers on and off the more power-hungry subsystems, such as the mass spectrometer, command and data handling, and radio, at scheduled intervals. The HMS itself is required to be very low power, which was paramount in the design decisions made for the HMS printed circuit board (PCB) and even in the FPGA’s internal hardware description language (HDL) code.