The 1965-16D satellite, the seventh satellite of the SOLRAD series, was launched from Wallops Island on January 11, 1965. This NRL satellite was spherical and, when measurements were obtained, it rotated around the spin axis at the speed of 1-2 turns per second. The satellite was not spin-stabilized, and two suitably designed photocells gave the necessary information about the solar aspect angle, i.e., the angle between the equatorial plane and the direction from the sun to the satellite. This satellite was instrumented to detect the solar X-ray emission and telemetered daily at Arcetri. As the other SOLRAD satellites, this satellite was equipped with ionization chambers and GM counters sensitive to the soft X-ray radiation, located on the equatorial plane of the satellite. The gradual absorption of the radiation as the satellite passed into and out of the shadow of the earth was used to measure the atmospheric density between 120 and 200 km. The bands used for such measurements were the 44-60, 8-14, and 8-12 A bands. For additional information, see M. Landini, D. Russo, and G. L. Tagliaferri, Space Res. VII, v. 2, p. 1281, 1967; M. Landini, D. Russo, and G. L. Tagliaferri, Icarus, v. 6, p. 236, 1967.