TLS, one page, 8 x 11, University of Cincinnati letterhead, August 23, 1979. Armstrong responds to an inquiry related to Apollo 11. In full: “The Apollo navigation combined inertial and earth-based radar systems. The attached summary [not present] will give you the general idea. All good wishes.” An excerpt from “Flight Control of the Apollo Lunar-Landing Mission,” a paper presented by NASA to the Eighth International Symposium on Space Technology and Science in Tokyo, Japan on August 25, 1969 sheds light on the letter: “During the rendezvous in lunar orbit, the relative navigation of the LM [lunar module] to the command and service module (CSM) is performed on board. The relative motion between the Duo spacecraft is more accurately determined by the rendezvous radar in the LM and by the very-high-frequency ranging and optical tracking complement in the CSM than can be determined by ground-based radar at the lunar distance.... Earth-based radar data obtained after acquisition and prior to the powered descent are used to evaluate the execution of the DOI [descent orbit insertion] maneuver.... Altitude differences between the inertial system and the landing radar are also displayed to the flight controllers....” In fine condition, with intersecting mailing folds, one through a single letter of signature. JSA/Scott Cornish Auction LOA and RRAuction COA.
