In an example embodiment, a doser assembly includes a hopper assembly configured to receive plant material, a bracket assembly connected to the hopper assembly, and a roller in a hopper opening defined by the hopper assembly extending through the hopper assembly. An interior surface of the hopper assembly may define the hopper opening. The bracket assembly may include a shaft extending across a portion of the hopper opening. The roller may be in the portion of the hopper opening of the hopper assembly and may extend between a first part and a second part of the interior surface of the hopper assembly. The roller may be connected to the shaft and may be configured to rotate with rotation of the shaft.

Aspects of the disclosure relate to manufacturing a balloon envelope for use in a stratospheric balloon system using an improved double-bubble blown-film extrusion process with water quenching and electron beam processing. A stream of polyethylene mixture is extruded through an extruder to orient molecules of polymer chains and provide an oriented film. The oriented film is passed through an electron beam, crosslinking the polymer chains to produce a cross-linked film with enhanced mechanical properties. The cross-linked film is heat sealed to form the balloon envelope comprising multiple gores. The resulting balloon envelope exhibits superior characteristics including crystallinity greater than 50%, strength to weight ratio greater than 1 MPa/(dtg/cm.sup.3), thickness less than 1.5 mil, thermal emissivity less than 0.03 at 193K, and optical clarity greater than 95%. The manufacturing process may include water quenching to enhance optical clarity and dual electron beam treatment for uniform crosslinking throughout the film thickness.