FWIW, the NASA Technical Reports Server is a good resource for technical docs from Apollo to Shuttle. Many of them have enough detail to implement the algorithm

FWIW, the NASA Technical Reports Server is a good resource for technical docs from Apollo to Shuttle. Many of them have enough detail to implement the algorithms. https://ntrs.nasa.gov/search?q=shuttle%20guidance https://ntrs.nasa.gov/search?q=shuttle%20guidance