QEMU-Based Emulation-in-the-Loop for the Simulation of Small Satellite Flight Software

Hardware-in-the-loop testing is a popular, economi-cal way to test and validate flight software systems for small satellites compared to testing on flight hardware. Further cost savings can be achieved by replacing the hardware in these systems with functionally equivalent emulations (some-times termed “emulation-in-the-loop”). This work aims to better inform system-level small satellite flight software test design through a study of the tradeoffs between hardware-in-the-loop and emulation-in-the-loop systems. In this work, two systems are presented-one featuring hardware, the other featuring emulation-which are used to evaluate the advantages and disadvantages of a traditional hardware-in-the-loop testbed compared to an emulation-in-the-loop testbed. Two demon-strations are performed on these two testbeds: (1) a large-scale spacecraft cluster demonstration, which seeks to show how hardware and emulation perform at scale; and (2) an image processing demonstration, which seeks to show how hardware and emulation differ for more compute-intensive applications. The hardware-in-the-loop testbed is composed of an instance of NASA's core Flight System (cFS) running on the ARM Cortex-A9 processor of a Zynq-7020 System-on-Chip (SoC) interfaced with NASA Goddard's open-source 42 spacecraft simulator to create a closed-loop system. The emulation-in-the-loop testbed is identical but with the ARM processor emulated instead. Emulation-in-the-loop systems offer portability, cost savings, and improved scalability over hardware-in-the-loop systems but at the cost of system accuracy and increased complexity. In the case of flight software for small satellites, the inherent reduced accuracy of emulation-in-the-loop can prove acceptable in light of the significant cost savings, the reduction in depen-dence on hardware early in development, and the reduction of wear on hardware. In addition to the two emulation-based and hardware-based demonstrations, a comprehensive view of the benefits and drawbacks of QEMU-based emulation as a replacement for traditional hardware is presented for the case of in-the-loop simulation of flight software.