A copper or aluminum tube is cut and sealed in an ultrasonic tube sealer. A section of the tube is placed laterally in a V-shaped recess of a center member of a forming tool of an anvil of the ultrasonic tube sealer. The anvil and a horn tip are brought together with the center member received in a channel of a forming tool of the horn tip to cut the tube with the cut tube having cut ends on opposed sides of the center member. At least one of the cut ends is pinched together between the forming tool of the anvil and the forming tool of the ultrasonic horn tip and the ultrasonic horn is ultrasonically vibrated to ultrasonically weld the at least one cut end together to seal that cut end.

Tooling for an ultrasonic tube sealer includes an ultrasonic horn tip and an anvil. The ultrasonic horn tip and the anvil each have at least one forming tool. The forming tools have a configuration that form an end of a tube when it is sealed by the ultrasonic tube sealer to be rounded.

Aspects of the disclosure relate to manufacturing balloon envelopes for use in high-altitude mesh networks for packet-data communications. As an example, a gore portion may be placed on a table such that the gore portion overlies a groove within the table. A tendon may be placed on the gore portion and within the groove. A portion of tubing may be placed over the tendon. The tubing may have one or more surface openings. Restraining tape is applied over the one or more surface openings in the tubing. A constant force roller is applied to secure the tendon to the gore portion and to secure the tendon to the tubing. As an alternative or in addition to the surface openings, double-sided restraining tape may be placed between the tendon and the tubing. The tubing and restraining tape may prevent undesired lateral and longitudinal movement of the tendon during deployment.

Aspects of the disclosure relate to systems and techniques for inspecting seals for high altitude balloons. In one example, a system may include a reflective surface, a translucent material on the reflective surface, and a movable light source configured to move along the reflective surface and provide light to the reflective surface. The light is provided such that it is reflected from the reflective surface and through the translucent material in order to backlight a balloon envelope seal for inspection. A method for inspecting a balloon envelope seal may include placing balloon envelope material on a table, forming a seal between portions of the material, moving a light over the seal, shining light onto a reflective portion of the table below the seal to backlight the seal, and inspecting the seal using the backlighting of the seal.

Aspects of the disclosure relate to techniques for manufacturing a balloon envelope including a duct for high altitude balloons. In one example, a first sheet of material may be provided. A premade duct may be arranged at least partially on the first sheet of material. The duct may include a first substance on an internal surface. A second sheet of material may be arranged over at least a portion of the duct. A heat sealing device may be applied to the second sheet of material to heat seal the first sheet of material to the second sheet of material. The heat sealing device may be applied over at least a portion of the duct in order to seal external surfaces of the duct to each of the first and second sheets of material and form a balloon gore. The first substance may keep the duct from being sealed to itself.

Aspects of the disclosure relate to manufacturing a balloon envelope for use in a stratospheric balloon system. For instance, a stream of polyethylene mixture is extruded through an extruder in order to orient molecules of polymer chains of polyethylene and to provide an oriented film. The oriented film is passed through an electron beam and thereby crosslinking the polymer chains to provide a cross-linked film. The cross-linked film is heat sealed to form the balloon envelope.

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.