Flight Termination

                Team Weathered Warriors will be using a flight termination unit to ensure the flight of our weather balloon ends when we need it to. The primary cut down system for the flight is the balloon’s expansion as the altitude rises.  As altitude increases the air density will decrease, this will cause the balloon to expand in volume. Upon reaching our target altitude of 100,000 feet, the balloon will expand past its maximum volume and pop due to the pressure difference between the inside and outside of the balloon. If this system fails for any reason, we’ll be using a secondary flight termination unit. This is also in accordance with FAA regulations.

                The flight termination unit (FTU) that we’ve built and tested will use current running through a high resistance nichrome wire. The current will cause the wire to heat up dramatically. This nichrome wire will be wrapped around the kite string which connects the payload to the balloon. The heat will sever the kite string and the payload will fall back to Earth.

                To do this, we’ve employed a second arduino and a relay circuit. The arduino is programmed to send a current through a pin after a specific amount of time has passed. For this flight, the ascent time will be about 90 minutes.  To test this system we built a circuit which used a relay to light an LED with a 9 volt battery. After the secondary arduino had been powered for 10 seconds, the relay switch was flipped and the secondary was closed. This allowed the LED to light up using the relay circuit battery only. Once this had been tested, the LED was replaced with a small segment of nichrome wire. The relay circuit worked as anticipated and the 9 volt battery caused the wire to heat up to high enough temperature to melt the kite string we will be using in our flight.