11. System Integration
11.3 Typical Requirements and Design Considerations
Requirements considering integration and testing fall under manufacturability (for fabrication), technical interfaces (for integration), modularity, and ease of access (for testing). Other than the technical interface requirements, many of these other -ility requirements are programmatic requirements that optimize for schedule, labor, and cost.
Fabrication
During the fabrication phase, manufacturability could refer to how simple a metal structure is to cut from a block of metal, affecting the number of capable vendors and the cost of the part, or how simple an electronics board is to manufacture at a boarding house, affecting schedule and cost.
Integration
Consistent and specific technical interfaces ensure smooth integration and expected functionality. Interface aspects include mechanical (e.g. bolt hole size and placement), electrical (e.g. voltage and current limits), and software (e.g. object structures). These interfaces are especially important when you are adopting someone else’s design, such as when you buy a component that you must interact with. The component comes with a set mechanical and electrical design; you did not get to design this interface but you had a hand in choosing what this interface would be. The component or subsystem should also come with an interface control document (ICD) or User Manual that tells you, the user, how to interact with the component/subsystem. A common ICD that all spacecraft teams will become accustomed to is their launch provider’s vehicle ICD or User Manual, like this LM-3A Manual.
Artemis Kit Specific
For the Artemis CubeSat Kit, interfaces within the satellite include but is not limited to:
- The bolt pattern on each board of the stack to mate with the four threaded roads
- Geometry and smoothness of structure rails to slide within a standard CubeSat deployer
- CubeSat Kit Header to align power, ground, and data pins between the boards
- Bolt standard to join structure pieces to each other
- Bolt pattern to mount solar panels to the structure look around the kit. Identify joints in which one component touches another component. That’s an interface. You’ll see there are a lot of places where two parts connect. Design interfaces take meticulous coordination between within and between subsystems. While you’re designing your spacecraft in the earlier project phases, communicate frequently with engineers and scientists who will be affected by your design decision, document your design interfaces explicitly, and try to make your interfaces as simple as possible (like using a standard bolt size across various interfaces).
Modularity and Ease of Access
During integration and testing, modularity and ease of access help the spacecraft team isolate problems. Modularity speaks to how “densely connected compartments within a system can be decoupled into separate communities or clusters which interact more among themselves rather than other communities” [ScienceDirect]. Modularity could manifest itself in a spacecraft where all the functionality of an entire subsystem is on a single board, as the Power Distribution Unit. If power is not correctly distributed to the other subsystems and we suspect the problem is in the PDU board, we can easily disintegrate the PDU board from the larger assembly to conduct further inspection and testing. Therein lies the beauty of modularity. Ease of access is a similar concept in which aspects of the design are readily available to de-integrate due to bolt placement of probe due to electrical pin placement. Ease of access could be creating/attaching a breakout board to a component specifically designed to allow a testing engineer to monitor signals, or routing electrical pins that carry important information to an easily accessible spot, like the outside of the CubeSat.
