alt Hacker NewsI didn't see an explanation of what strapdown meant in this context, so I dug one up:
"Traditional, stable-platform navigation systems commonly involve separate accelerators and fibers or laser-based gyroscopes, with all the components mechanically and rigidly mounted on a stable platform that is isolated from the moving vehicle. This leads to the drawbacks of large size, poor reliability, and high cost. In contrast, in strapdown navigation systems, the inertial sensors are fastened directly to the vehicle’s body, which means the sensors rotate together with the vehicle. "
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I wonder if you could dangle the star tracker below the drone on a long string, decoupling its attitude from the attitude of the drone. A kevlar or spectra string capable of supporting 100 grams would be 20μm in diameter; 3 meters of it would weigh a milligram, which is significantly less than gimbals. A small weight a couple of meters below the star tracker on a carbon-fiber-composite rod would seem to be able to stabilize its attitude further except in yaw.
Or in short, the sensors are strapped down to the platform being measured - like your phone’s sensors for example.