Effect of sensor sampling frequency (10-100 Hz) on Apogee estimation accuracy in a model rocket flight

Abstract

Student rocketeers like me are mostly excited about achieving the maximum altitude also referred to as Apogee for the model rocket launches. Finding low cost flight computers as alternatives to measure the Apogee got me interested and I embarked on this study to investigate how sensor sampling frequency affects the Apogee calculation. I built a custom flight computer using Adafruit Feather RP2040 Adalogger, a BMP388 barometer, and an LSM6DSO32 accelerometer and identified 10, 50 and 100 Hz as sampling frequencies to calculate the Apogee and bring out the impact of these sensor sampling frequencies on the Apogee estimation. I conducted a single flight of Estes Lil’ Spite on AeroTech G74W-4 motor and configured the custom flight computer to log the data at 100 Hz. The data samples for 50 Hz and 10 Hz were derived from data log by down sampling. The Apogee calculation was derived from both the barometer and accelerometer observations with Jolly Logic AltimeterTwo measurements as independent check. I started with a hypothesis that the higher sampling frequencies would improve the Apogee calculations significantly as I felt that the more readings, the better the Apogee estimate. However, to my surprise, I found that the barometer apogee calculations were barely impacted by the sampling frequencies as the ten 10 Hz estimates were within 0.3 m of the 100 Hz recordings. In case of accelerometer, while the average Apogee was not impacted by the sampling frequencies, the range of possible values grew from 12 m at 50 Hz to 66 m at 10 Hz and it also impacted peak acceleration as lower sampling rates gave lower peak. Hence I concluded that the lower sampling rates impacted the precision more than the accuracy. I deduced that 20-50 Hz sampling frequency should be sufficient for barometer Apogee while accelerometer needs 100 Hz sampling frequency for optimal results. I was glad to find that the barometer apogee reading at 100 Hz was within 1% of the AltimeterTwo reading.