US Patent 9346531 Balloon gas release flight termination system

A control system for terminating flight of a balloon having a balloon envelope is provided. The control system includes a shuttle that has one or more cutting blades. The cutting blades are configured to cut open the balloon envelope. A tubular track is attached to a section of the balloon envelope. This tubular track has a guiding portion arranged to receive and guide the shuttle along the track. The control system includes a type of releasable ballast attached to the shuttle. When the ballast is released, the ballast is configured to move the shuttle along the tubular track in order to cause at least one of the cutting blades to cut open a portion of the balloon envelope. This allows lift gas to escape from the balloon envelope.