lunar rover
“NASA’s 2nd Generation Multi-Mission Space Exploration Vehicle (MMSEV) Nose-Cone Design Optimization”
Abstract
To maximize the number of destinations explored and minimize the number of systems developed, NASA designed a flexible platform that could satisfy multiple demands despite the changing political climate. The Multi-Mission Space Exploration Vehicle (MMSEV) is a modular system primarily comprised of a pressurized cabin that can be configured with mission-specific augments for in-space and surface exploration. The common cabin can be configured with a suit-port, windowed nosecone, and a chassis with wheels to serve as a rover with expedited EVA capabilities for 14 days to 28 days on the lunar or Martian surface. However, the prototype 2B glass nosecone for the MMSEV pressurized rover had issues with visibility and foot clearance during the 2009 Desert Research and Technology Studies (DRATS), due to its dome-like geometry. A redesign is due but human factors designers and structural engineers have two different approaches to design. Therefore, a cohesive design process will be demonstrated in this paper. The 2B glass nosecone will be the benchmark case for thorough comparison with potential design iterations. Primary design considerations investigated in this paper include minimal mass, maximum visibility, and structural integrity. Minimal mass refers to the bias of the rocket equation toward structures with the lowest weight in materials. Maximum visibility is the overall percentage of fenestration in relation to areas that crew members focus most on. Structural integrity is measured by the normal displacement, Von Mises, stiffness factor, and stress lines. Based on all the information presented, both bottom-up and top-down strategies for design considerations are necessary to design the MMSEV rover nosecone. From the bottom-up, the nosecone should be examined through several finite element analyses (FEA) to deduce structural design elements. These elements include corrugation, thickening, and areas of restriction due to stress concentration. Human factors such as visibility should be designed with a top-down mentality to make informed design decisions on aperture placement relative to the stress lines from the FEA.
Advisor: Sawako Kaijima
Team:
Francisco Jung
Maharshi Bhattacharya
Building on the existing prototype of NASA's 2nd Generation MMSEV, we worked towards identifying a balance between maximum visibility and corresponding minimum mass increment. We used computational tools such as C#, Grasshopper and Millipede on Rhino and Solidworks.
Francisco had previously worked on related projects during his time at NASA and as part of the coursework, which involved the design and resolution of a structural problem, we teamed up due to our common interests. Francisco brings to the team the knowledge base required to identify the problem. I assisted with computational work, analysis and devised models to test our hypothesis.
The final deliverable of the project was a paper that detailed our findings.
FEA Analysis Matrix.
Left: Schematic view of window construction in the US Lab Destiny on ISS; Right: Nadir window installed on the Lab (image credit: NASA)
The scope of this research was limited to the nosecone section of the pressurized rover. The glass nosecone is a shared component of the rover, ascent vehicle, and hopper platform. Design iterations have been done through fabrication of these different platforms for human-in-the-loop testing. The most current glass nosecone reflects the design for the ascent vehicle. Through the evolution of the glass nosecone, the geometry morphed to accommodate multiple requirements for different platforms. An optimal pressurized cabin from an engineering standpoint entails a symmetric, dome-like shell like SEV 2B, however when human factors are taken into account the optimal shell requires sharper filleted corners as we modified for SEV 3A.
SEV 3A mitigates foot collision with a more accommodating geometry for a slight structural trade-off. However, this form factor has never been tested with windows. Therefore, a structural analysis of the existing 2B glass nosecone was done as a benchmark case for potential windowed design iterations with the 3A form factor to meet or exceed. Design requirements and trade-offs considered are:
minimal mass,
maximum visibility; people have an approximate 60-degree angle of undistorted vision that extends as an imaginary cone from their eyes forward. Outside of the 60-degree angle, objects begin to blur. (view sectors image)
structural integrity.
Spacecraft window assemblies consist of 4 layers of fused silica for debris, redundancy, pressure, and scratch. Therefore windows should be conservatively placed for mass efficiency. Furthermore, only flat panes of glass or acrylic can be used in the design. Curved glass or acrylic induce visibility issues and added mass due to structural implications for positive pressure on a convex plane.