Contaminant Tolerant Scroll Vacuum Pump for Oxygen Production from Lunar Regolith

Summary

Part of my time at Air Squared was spent designing a scroll vacuum pump capable of handling vapors created in the process used to generate oxygen from lunar regolith (moon dust). In order to prevent these vapors from escaping into space and transfer them to a subsystem where they can be processed, a vacuum pump is needed. Some of the challenges included handling various harsh gases such as HF and HCl, as well as meeting flow and life requirements in such a harsh environment.

Details on the SBIR can be found here: https://sbir.nasa.gov/SBIR/abstracts/21/sbir/phase2/SBIR-21-2-Z12.01-1706.html

An article detailing the background of this project and a summary of the SBIR Phase 1 findings can be found in the LinkedIn post at the bottom of this page.

Skills Utilized:

Since I was the sole design engineer on this project, I performed every aspect of the design from conceptual design to drawing creation.

1. CONCEPTUAL DESIGN

   Once the scrolls were sized, I created a basic, conceptual design surrounding the scrolls that incorporated allowances for isolating the working fluid and integrating a motor.

2. DETAILED DESIGN

   Once a configuration had been settled upon, I went back over the design and reduced weight where I could while maintaining structural integrity, and I balanced the compressor with counterweights to offset the forces exerted on the housing by the orbiting scroll. I also integrated cooling allowances and made the interface with the compressor as simple as possible. I made sure the compressor was easy to assemble based on feedback from the technicians, and tried to keep machining costs down where possible by reducing the number of complex parts, expanding tolerances, and meeting with machinists to discuss ways to aid manufacturability.

3. BEARING CALCULATIONS

   Once the design was in a good spot, I sized bearings that would be able to take the load of the orbiting scroll for the amount of hours that this vacuum pump would see usage.

4. FASTENER CALCULATIONS

   I calculated yield/tensile strength, thread shear, and joint separation factors of safety, and in an iterative process, I calculated torques and selected a bolt size and material that would work well not only with the load that was being applied to it, but also with the thread shear limitations of the material it was being threaded into.

5. FEA

   I performed FEA on all components that would undergo significant load. For this project, I was mostly worried about deflection at certain points in the assembly, and my analysis was used to determine where parts needed to be stiffened and where weight could be saved.

6. FLOW SIMULATION

   I utilized Solidworks Flow Simulation to analyze the cooling channels and determine pressure drop and temperature rise across the channels.

7. GD&T

   I created all the drawings for every component on this assembly. This consisted of heavily utilizing GD&T, as I tried to maximize tolerances where possible while maintaining functionality of the parts. Position, perpendicularity, parallelism, profile, and max material callouts all have their place on assemblies like this that require precision machined components and smooth operation.

8. ASSEMBLY PROCEDURE

   From almost a year of working closely with the technicians on our team, I’ve learned to catch certain aspects of my design that will make their life difficult. An especially helpful way to find these errors is writing the assembly procedure that the techs will use to make the product. By creating this procedure, I am usually able to catch a few things such as wire clearances, assembly orientations, and tool allowances that would be easy to overlook otherwise.