Glove Mechanisms Developed, Specifications Defined, and Challenges Addressed

During the period of October 29, 2022 to November 12, 2022, Team JAMS has been hard at work developing three detailed concepts to address the current issues involved with the use of krypton tape in the NASA LSG’s glove and sleeve assembly. These concepts all serve the same function but use different methods of fastening to secure the nitrile glove to the hypalon sleeve. Aside from the development of the concepts, the team has also addressed challenges regarding methods of validating the vacuum seal of the device.

To begin with the concepts developed by the team, the first concept involves the use of a spool device and band to secure the nitrile glove and hypalon sleeve to the wrist of the user. This concept has been drawn out in a CAD file with proper dimensioning and sports a free spool mechanism to ensure the efficient and safe removal of the device in the event of an evacuation. A tension adjustment scroll wheel allows the user to set the device to a desired tension that will combat displacement of the glove during use, addressing another important design specification. The device implements the use of a compression spring to shift the device between free spool and its tension settings. As for hardware, proper screw fasteners, springs, and bands have been chosen for the device based on size constraints and needs and will be sourced from Amazon.com if the team decides to select this concept. Lastly, two springs have been chosen to be tested on the device with two calculated push button forces of 4.61 lb and 1.57 lb. The spring offering the most tactile feel for the device will be selected.

The second concept is based on a belt and latch system, with the latch tightening the belt surrounding the wrist, effectively creating a seal between the hypalon sleeve and nitrile glove by applying external pressure. The latch will work on a two pin system, with a central bar and a longer pulling bar. The central bar is attached to the base with a pin, held in by screws, and will be used to engage and disengage the system, which when pulled to the side, will become engaged pulling the pulling bar along with it. The pulling bar will be attached to the central bar with the second pin and has a hook that will pull on the belt hole and tighten it around the sleeve and glove. Because the belt and latch is meant to rest around the wrist, the dimensional goal is 2.25 inches long, 1.25 inches wide, and 0.5 inches thick, as this size will not take up a considerable amount of space and get in the way of operations in the LSG. The specific dimensions for the moving parts are undetermined as of right now, as there is no guarantee that parts of such a small scale will be able to be produced accurately and perform for multiple use cycles with little signs of wear. The material choice for this concept will be neoprene for the belt, and machined aluminum for the latch system. Given the size of the latch system, it may be difficult to source machining services that will be able to provide a product accurate to the desired concept, which may require compensation of size or production method.

The third concept is intended to integrate into the sleeve and improve on the technology used in the MSG, including an iris which seals the system with a plastic ring. This adjustable iris mechanism will use notches and grooves to adjust the tension on the gloves, reducing the need for small mechanical components that may potentially break off and interfere with the workspace. The LSG uses magnetically attachable hardware on the ferrous surfaces of the workspace, so the lack of metallic mechanical components provides a beneficial alternative. The device would be attached to the sleeves permanently using aquaseal urethane adhesive, the same adhesive used on the MSG. The device would be fabricated out of makroblend plastic to comply with the heat and chemical hazards of the LSG environment. Lastly, the iris of the device would be constructed of a nitrile ring or glove as an intermediate material to prevent damage to the more expensive hypalon sleeves. The internal diameter minimum is 150 millimeters, allowing the user to easily slide out of the iris mechanism.

Maintaining an airtight vacuum seal is one of the main goals of this project and in order to analyze this seal the team needs to calculate the leak rate using the pressure differential and the geometric specifications of the design. According to NASA’s vacuum design criteria the leak rate approximation can be calculated using the following formula,

L ≅ 0.7*F*D*P*Q*(1-S)^2

where L is the approximate leak rate of the seal, F is the permeability rate of the gas through the elastomer at the anticipated temperature, D is the inner diameter of the O-ring, P is the pressure differential across the seal, Q is the factor depending on the percent compression, and S is the percent compression on the O-ring cross section (Source: https://llis.nasa.gov/lesson/674). Through this formula, the leak rate can be calculated which will help to determine whether the vacuum seal is safe and effective. Furthermore, the team plans on discussing further analysis processes and options with Dr. Farah Hammami who has quite the experience in testing and analyzing different engineering concepts.

From November 12, 2022 to November 26, 2022, Team JAMS plans on independently developing a list of in depth pros and cons of each concept. This list will be used to ultimately select the best design to move forward with. After having a design chosen, the team will conduct design analysis on the device to ensure the device meets all design specifications. This analysis includes calculating for the leak rate or airflow of the device when placed in the vacuum environment of the LSG. This analysis will also include radial pressure measurements to ensure the device is within constraints. Specifications such as volume and mass will be accounted for and estimated using the materials planned to be used in the manufacturing of the device. A 3D CAD of the device will be finalized to be presented in the design review presentation along with a design matrix.