The original Challenger Technical Manual can be downloaded in two parts in Acrobat PDF.
The manual has 85 pages and is two files of 5.9Mbytes each. On a modem connection expect the download to take 30 - 60 minutes.
For constructors the Manual left a lot of puzzles and guesswork!
MANUAL
PART 1 - TEXT
MANUAL
PART 2 - DIAGRAMS & ILLUSTRATIONS