From 1956-1975, the Smithsonian Astrophysical Observatory's Moonwatch program issued ephemerides for artificial satellites and collected observations from amateur astronomers.
1959 Nov 30: Letter from Leon Campbell to R.V. Ramsay
1959 Dec 14: Letter from J.E. Kennedy to Leon Campbell
1960 Mar 9: Letter from Marie Fidler to G. Bakos
1959 Nov 30: Letter from Leon Campbell to I.K. Williamson
1959 Dec 3: Letter from Leon Campbell to J.E. Kennedy
1960 Mar 1: Letter from G. Bakos to J.E. Kennedy
1959 Sep 1: Letter from J.E. Kennedy to G. Bakos
