[Progress in Astronautics and Rocketry] Space Power Systems Engineering Volume 16 || Low-Power Isotope Thermionic Development Program (SNAP-13) Presented at the Third Biennial Aerospace Power Systems Conference, Philadelphia, Pa., September 1-4, 1964 (not preprinted). Since 1962, this work was sponsored under Contract AT(30-1)-3060; earlier it was Task 5 of AT(30-3)-217.