Uhuru (Swahili: freedom) was the name given to the first in a series of three Explorer satellites developed for NASA to investigate X-ray and gamma-ray sources both inside and outside the Galaxy. It was launched in 1970 atop a Scout rocket from the Italian San Marcos platform off the coast of Kenya, on Kenya's Independence Day, December 12. It is also known as Small Astronomy Satellite 1, SAS 1, and Explorer 42.The main structure of the satellite, built by the Applied Physics Laboratory of The Johns Hopkins University, was a 143-kg (315-lb) aluminum cylindrical drum 61 cm (2 ft) in diameter and 61 cm (2 ft) high. Four panels of solar-energy cells hinged around the circumference of the cylinder provided 27 W of electrical power for the satellite. Star and Sun sensors permitted the locations of specific sources to be determined. Two X-ray detectors with mechanical collimators were located atop the drum. One covered a 1 deg-by-1 deg field-of-view for high resolution; the other a 10 deg-by-10 deg field-of-view for high sensitivity.Uhuru and its two subsequent (1972 and 1975) companionsÑExplorers 48 (SAS 2) and 53Ñwere all highly successful and laid the technological and scientific groundwork for later and more advanced satellites such as the High Energy Astronomical Observatory satellites. Uhuru produced data that led astronomers to argue the existence of superclusters of galaxies bound together by a hot but thin gas with a mass many times that of the galaxies themselves (see X-ray astronomy).