This primary source comes from the Records of the National Aeronautics and Space Administration.
Full Citation: Letter from Colonel Thomas P. Stafford to Dr. Robert R. Gilruth; 6/27/1969; AS-505 Apollo 10 1968-1969, 1968 - 1975; News Media Files, 1968 - 1975; Records of the National Aeronautics and Space Administration, Record Group 255; National Archives at Atlanta (RE-AT), Morrow, GA. [Online Version, https://www.docsteach.org/documents/document/letter-colonel-thomas-p-stafford-dr-robert-r-gilruth, May 15, 2024]