25SMOI A Modernized Cutdown/Letdown Mechanism for Mobile Balloon Launches.

Mobile balloon launches at NOAA’s National Severe Storms Laboratory are vital for upper air data sources and in situ observations. Instruments such as the Electric Field Meter and the Particle Size, Imaging and Velocity probe are attached to balloons to investigate the local electric field and microphysical properties in storms where direct observations are sparse. In order to constrain the distance flown by the package, as well as limit potential damage sustained to sensors, a cutdown mechanism releases the instrument package from the balloon. Prior models used a superheated nichrome wire on a commanded circuit which melted a monofilament line, ultimately releasing the package. This led to some instances of cutdown failure when the line did not melt properly, the wire did not heat up properly, or the timer triggered early. The package also features an automatic letdown system to increase the distance between the sensor package and balloon once in flight to reduce the influence of the balloon on the measurements. Previous iterations used a variety of different mechanisms including mechanical spools and motor driven versions. While previous letdown iterations each had advantages, there were numerous failure modes such as binding or breaking of the line due to tensional forces applied during unspooling, partial unwinding and not triggering. The package was due for a modern mechanical upgrade to decrease the likelihood of errors within flight. Presented here is a prototype redesign which features a hook and latch mechanism which, when actuated, releases the instrument train. The hook and latch mechanism has proven to consistently sustain high stress loads typical of balloon launches while also being easier to reassemble for subsequent uses. The new design changes and capabilities will be demonstrated.