As of 2021 there are few fully open source satellites (OSSI-1, UPSat, FossaSat-1, Oresat, some more?) and numerous student groups building and documenting rockets. These projects are intended to be open source from the beginning to the end (design, production, operations etc.).
However, I wonder what are the most open source historical spaceflight missions (manned, unmanned, orbital, interplanetary...) that was not originally intended to be open source and during time, documentation was either released or leaked, software open-sourced, patents expired etc. and considerable amount of information was revealed. Probably every mission has some degree of open-source usually publishing photos of the spacecraft (outer structure known) but I am interested in where the most information is available.
The open source consists of both open source hardware and open source software. Let us try to evaluate the level of open source telling that HW is 50% and SW is 50%. Like this, a fully open sourced hardware and half open sourced software mission would rate 75% overall. The subsystems should be evaluated on a importance scale, if a mission has 5 critical subsystems (power, thermal, navigation, comms, etc.) then each should roughly have a score of 20%.
For example, how much "open source" are the Apollo lunar missions now? Was significant amount of information revealed throughout history, maybe unclassified because space race (or cold war) ended etc? What about Mercury, Gemini etc? Space Shuttle? ISS? Some Russian mission? We could probably divide the answers to missions including/excluding the launch systems since that usually has legal restrictions (ITAR etc.) preventing it from being published.