The design intent of this part is for insertion into a high altitude balloon, of which is filled with helium, that will effectively seal off the balloon from leak during filling and flight. The material is 6061-T6 Aluminum. It is a space-grade aluminum which is commonly used for aerospace applications.
The Balloon Plug is machined on a lathe primarily however it does require a small amount of mill machining to complete the holes.
Picture 1: Turning the Balloon Plug
To complete the grooves, which accommodate the fastening zip ties, a picking method is utilized. The picking method includes fastening a blade parallel to the part on the lathe and proceeding to push directly into the surface. To ensure cutting instead of work hardening the blade was positioned slightly under the 180-degree angle from the radius of the plug. The depth of the grooves are 0.110 inches. The width is different for the center (y-axis) groove because it will accommodate the size of an aluminum clamp. This aluminum clamp does not exist yet because the style commonly used does not fit our needs. HABv3 will feature the aluminum clamp.
Picture #1: Solidworks 3D Model of the Balloon Plug
The balloon plug has an internal ¼” NPTF tap on the bottom of the hole. A quick disconnect valve is fastened to the balloon this way and allows quick and easy access to the helium hose that will direct the flow of the helium from the tank through the valve and into the balloon. After the filling is complete the hose is disconnected by a quick longitudinal movement of the valve switch that controls the allowance of flow. The balloon is then ready for launch. The plug simplifies the preflight setup process, reducing stress on launch day and reducing filling time.
The balloon plug will be fitted with sensors to record the pressure and temperature of the balloon. The wires for these sensors are fed through a hole passing vertically through the balloon plug. Both ends of the balloon plug are epoxied the night before launch and left to dry with the wires overnight.
The weight of this plug is 170 grams out of the 2721-gram payload weight limit placed on us by the Federal Aviation Administration. However, since the primary objective of the High Altitude Balloon team is to test CubeSat features in space-like conditions, all components must be able to survive altitudes of up to 100,000 feet (30480 meters). We may switch to 7075-T6 aluminum to optimize plug mass even further. Its properties are a good step up from 6061-T6 and would be a welcome improvement, but its cost and availability are problems.