EDAC events during the LADEE mission

Abstract

The purpose of the Lunar Atmosphere Dust Environment Explorer (LADEE) mission was to measure the density, composition and time variability of the lunar dust environment. The spacecraft was designed with modular common structural components that could be connected together to form the spacecraft. Spacecraft components were largely chosen from “off-the-shelf” sensors, actuators and avionics. The flight software was also designed using a layered modular approach leveraging model-based design concepts. High-level spacecraft control modules were autocoded from Simulink and integrated with reused executive and services modules and a small number of new hand-coded elements such as the software to control memory scrub hardware. The successful mission launched Sept 6, 2013 and was de-orbited and impacted the moon's surface on April 18, 2014. The spacecraft had 3 primary science instruments, the Lunar Dust Experiment, Neutral Mass Spectrometer, and the Ultra Violet Spectrometer. The mission also had a Laser Communications payload that set a record download rate of 622 MPS from the moon orbit. Over the course of the mission, LADEE had to tolerate a varying space radiation environment during a period of relative solar maximum and multiple passes through the Earth's Van Allen Radiation Belt. In order to mitigate this challenging environment, the Integrated Avionics Unit (IAU) chosen for the mission (a Broadreach Engineering RAD-750) implemented memory scrub in hardware. Software developed for the mission initialized and controlled the Error Detection and Correction (EDAC) circuitry and categorized and reported on errors that occurred during flight. The payloads, sensors and actuators each had varying degrees of tolerance to space radiation events, and events on these pieces of hardware were also tracked. This paper discusses the avionics and software for resilience to radiation events, and characterized the types of events during the course of LADEE's mission.