Attitude Control Simulations produce results

On November 24, 2022, students succeeded in running hardware-in-the-loop (HIL) simulations of the attitude control of MIST that match earlier software-in-the-loop (SIL) simulations (see figure above). The earlier simulations ran in a laptop where control code, sensors, actuators,and the orbital motion of the satellite, sun and magnetic field orientations are all run in software. These simulations first yielded results more than two years ago. The time scale is in seconds (from 0 to 30000 seconds about 8.3 hours). The vertical scale is pointing error from nadir in degrees. Deviations from nadir pointing occur at entry into eclipse. Attempts will now be made to adjust control parameters to reduce the size of these pointing error peaks.

Since then a test bench has been built up where the attitude control code runs in the onboard computer and sensors (analog sun sensors and magnetometer) and actuators (magnetic torquers) ars are simulated in hardware devices (Arduinos) that have identical electrical interfaces to the onboard computer as those in flight. The hardware-in-the-loop principle is shown schematically in the figure below which is dated 9 November 2017.

The box with a green rim is a laptop running the support code for orbital position, sun direction and earth albedo, magnetic field direction, satellite geometry, dynamic model of the attitude motion. The blue text shows previously developed code for the simulation of solar panel power generation by the student Gustav Pettersson. The black text shows code written for the HIL. The boxes marked mikro-C and D/A denote the sun sensor simulator.

The picture below shows the devices in the sketch above as they look in real life in the MIST integration laboratory. SSS=Sun sensor simulator, iMTQ sim.=Simulator of the iMTQ device made by ISISPACE: magnetometer and magnetic torquers, iOBC=the onboard computer flight model, “The Green Box” refers to the block with a green outline in the schematic description of the HIL setup..

Many students have worked on the preparations for the HIL simulations over the years, and their names appear in the table below. Some students have worked on various test subunits.

The student who has had as his task during 2022 to make the HIL simulation work is Mathias Dahlman. In this work he has of course had help from other students, but Mathias was the student that had to suffer the indignity of reporting, at every project meeting, that the HIL simulations still didn’t work. For enduring this ordeal he was given a toy medal by the MIST project manager at the 30 November 2022 project meeting (see picture below)!