The CIA claims the Soviets were working from a rejected Shuttle design provided as part of an engineering misinformation campaign: https://www.cia.gov/library/

The CIA claims the Soviets were working from a rejected Shuttle design provided as part of an engineering misinformation campaign: https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/studies/96unclass/farewell.htm https://www.cia.gov/library/center-for-the-study-of-intellig...