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Mechanical and Thermal Design

Scope and Description

This topic page covers mechanical and thermal design of spacecraft hardware - from full spacecraft to subsystems and components. Beyond the specific functional and interfacing requirements, mechanical design of smallsat hardware is primarily driven by dynamic and static structural loading experienced during launch. Thermal design is primarily driven by component temperature ratings and worst-case hot/cold states of the spacecraft, which is, in turn, driven by thermal dissipation of electronics and the dynamic thermal radiation environment on-orbit. The relative simplicity and compact nature of small satellites results in particularly close coupling between mechanical and thermal design, both at the spacecraft and subsystem-levels.

Resources under this topic area are primarily book chapters on relevant space hardware design topics and CAD tools for mechanical design.

Best Practices and Lessons Learned

  • The ratios of mass and volume allotted to cubesats means that they are typically volume constrained, not mass constrained. So, when designing cubesat structures or subsystems, focus on volumetric efficiency and choose performance and mechanical integration flexibility/accessibility over mass efficiency.
  • Design for manufacturability from the start. Modern CAD tools make it easy for users to design exceptionally complex parts and assemblies. Beyond the basics of mechanical manufacturability (e.g. paying attention to tolerances and ensuring that internal corners in machined parts are filleted), maintain a continuous understanding of the manufacturing and assembly plans for the design. A 5% smaller assembly may not be worth the lead time, cost, and probability of workmanship flaws due to the resulting manufacturing complexities.
  • Maintain a library of reusable components. This will quickly deliver return on investment given the time-consuming process involved in creating or downloading/importing models for parts like fasteners, standard electronic packages, and connectors. Always try vendors for CAD files before creating your own models. If you have to request via email, push them to provide a whole product line at once so that you can avoid waiting for files in the future.
  • Integrate reduced-fidelity thermal and structural simulation and analysis into your workflows. This will reduce the likelihood of disruptive changes as the design matures.
  • Many thermal interface materials require sufficient compression to be effective, especially in the vacuum of space. Therefore, design these interfaces with bolt sizes, preload torques, surface finishes, and geometries/bolt patterns to ensure sufficient compression and meet thermal interface conductivity requirements (with margin).
  • Use thermal interface materials liberally at mechanical/thermal interfaces. This will - of course - improve thermal conductivity in general, but will also make the thermal properties of the system more consistent and predictable across ambient testing, vacuum testing, and on-orbit. The small-scale convective heat transfer present within the microscopic voids in metal-to-metal interfaces at ambient pressure (or before they have the time to fully vent under vacuum) will produce higher conductivity than you will see on-orbit or after significant time in a vacuum chamber.

Resources

Software Tool
Autodesk

This 3D CAD tool is comparable to Inventor and SolidWorks, but is cloud-based and takes a fundamentally ... different approach to system/assembly design. Fusion 360 is not as capable as these other tools at modeling of complex assemblies, but offers other advantages due to its cloud architecture and intuitive workflows.

White Paper
Ala Hijazi

Solid engineering graphics enable efficient technical communication among engineering teams. This resource ... provides background on different codes and standards for organizing drawings. It also supplies well-rounded summary of how to produce quality drawings. It covers topics like dimensioning, projection, and exploded and assembly views.

Book
George Sebestyen et al.

This book chapter, titled "Thermal Design" covers thermal design, analysis, and testing for LEO satellites. ... This includes background on the physics of heat transfer, thermal control hardware, and processes for thermal design, analysis, and testing. Note that this chapter is only 13 pages, and does not go into significant detail on any of the included topics.

Book
David Gilmore

This chapter titled "Mountings and Interfaces" is a comprehensive reference regarding the thermal design ... and analysis of interfaces for space applications. It includes design guidance, formulas for modeling thermal interfaces, surface roughness values for various production methods, and thermal interface material properties.

Standard
NASA

This NASA manual provides the minimum acceptable requirements for engineering drawings of flight hardware ... and ground support systems. From basic drawing definitions to unit details and cross-section diagrams, this document provides detailed information on what is required to completed engineering drawings of spacecraft based on GSFC standards.

Standard
ASME

This book from the American Society of Mechanical Engineers (ASME) discusses the standards applicable ... to the preparation and revision of engineering drawings, whether manual or computer-aided.

Software Tool
Dassault Systemes

This software tool can be used to model 3D objects directly in the context of its real-life behavior. ... The available modeling tools provide quality and performance insights in the early stages of the product development life-cycle. Systems engineers can easily develop models and leverage model-based systems engineering principles to design, simulate, and validate complex models. Compared to most other mechanical CAD tools, CATIA is exceptional at handling large, complex systems.

Software Tool
Dassault Systemes

This is a relatively easy to learn and powerful 3D CAD tool for mechanical design of components and assemblies. ... This tool is comparable to Autodesk Inventor. Optional SolidWorks Simulation capabilities can be integrated to provide relatively user-friendly thermal and structural analysis within the CAD design tool user interface.

Software Tool
Autodesk

This 3D CAD tool is relatively easy to learn and can be used for mechanical design, documentation, and ... product simulation and analysis. This tool is comparable to SolidWorks 3D CAD. Autodesk provides a suite of software tools that can be integrated for greater collaboration within an engineering team.

This annual state-of-the-art report from NASA provides an assessment of the current state of the smallsat ... industry, guidance, and best practices for all aspects of the smallsat development life-cycle. This section, titled "Thermal Control", primarily discusses passive and active thermal control systems, as well as new thermal control technologies that are in use on larger spacecraft and may be miniaturized for use on smallsats in the future.

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