What Happens When A Bug Rears Its Head At Mach Two?

While some may see amateur rocketry as little more than attaching fins to a motor and letting it fly, it is, in fact, rocket science. This fact became very clear to [BPS.space] when a parachute deployed on a rocket traveling at approximately Mach 1.8. 

The rocket design is rather simple — essentially just 3D printed fins glued onto a motor with a nose-cone for avionics. A single servo and trim tab provide a modicum of roll control, and a parachute is mounted in the nose along with a homing beacon for faster recovery. Seemingly, the only thing different about this flight is properly validated telemetry and GPS antennae.

After a final ground check of the telemetry and GPS signal quality, everything is ready for what seems like a routine launch. However, somewhere around Mach 1.8, the parachute prematurely deploys, ripping apart the Kevlar rope holding together the three rocket sections. Fortunately, the booster and avionics sections could be recovered from the desert.

But this begs the question, what could possibly have caused a parachute deployment at nearly twice the speed of sound?[BPS.space] had made a quick untested change to the flight control software, in an attempt to get more accurate speed data. By feeding into the flight controller barometric altitude changes during the decent stage, it should be able to more accurately estimate its position. However, direct static pressure readings at supersonic speeds are not an accurate way of measuring altitude. So, during the boost phase, the speed estimation function should only rely on accelerometer data.

However, a simple mistake in boolean logic resulted in the accelerometer velocity being passed into the velocity estimate function during the boost phase. This gave an erroneous velocity value below zero triggering the parachute deployment. Nevertheless, the test was successful in proving antenna choice resulted in poor telemetry and GPS readings on earlier launches.

If you want to see a far more successful [BPS.space] rocket launch, make sure to check out this self landing rocket next!