If you’re looking for educational CubeSat analogue/mock satellite designs that can be built and used on the ground, these are among the best open resources:
- AMSAT CubeSat Simulator (CubeSatSim)
https://cubesatsim.org/
Open-source educational CubeSat simulator with complete hardware designs, PCB files, 3D-printable enclosure, software, telemetry and lesson plans. - MOSAIC Mock Satellite
https://www.mosaicsat.org/
An open-source modular mock satellite designed for teaching spacecraft systems engineering, with CAD files, electronics and software. - CubeSat Resources
https://cubesat-resources.space/
A comprehensive collection of CubeSat design guides, tutorials, CAD models, software and documentation from numerous projects. - OreSat Open-Source CubeSat Subsystems
https://www.oresat.org/technologies/cubesat-subsystems
Open hardware reference designs for CubeSat mechanical, electrical and software subsystems based on a real satellite programme. - VyomSat
https://www.vyomsat.com/
An educational open-source CubeSat/PocketQube platform based on the Raspberry Pi RP2350, intended for teaching satellite engineering.
For someone interested in building a realistic but ground-based CubeSat analogue, CubeSatSim (https://cubesatsim.org/) is probably the best starting point because it provides detailed build instructions and a complete working system.