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Uhuru — first satellite dedicated to X-ray astronomy

1970 AD · Transmission: Global
AstronomyPhysicsInstrumentNorth American

Following the discovery of Sco X-1 in 1962, Riccardo Giacconi's group at American Science and Engineering (AS&E) faced a fundamental limitation: suborbital rockets provided only a few minutes of observation before falling back into the atmosphere. To systematically and prolongedly study the X-ray sky, Giacconi proposed to NASA the construction of a dedicated satellite in permanent orbit. The project was accepted after considerable debate, since it meant entrusting a large-scale program to a small private company rather than a university or major aerospace contractor. The satellite, named Uhuru ("freedom" in Swahili, in tribute to the country from which it was launched), lifted off on December 12, 1970 from the San Marco marine platform off the coast of Kenya, coinciding with the seventh anniversary of Kenyan independence. During its more than two years of operation (until March 1973), Uhuru carried out the first systematic survey of the entire X-ray sky, cataloging 339 sources — the so-called 4U catalog — and providing the first solid observational evidence of black holes in X-ray binary systems, including Cygnus X-1. Uhuru demonstrated that continuous orbital observation, not just single suborbital flights, was the necessary path to consolidating X-ray astronomy as a mature discipline, and laid the technical and conceptual groundwork for later space observatories, from the Einstein Observatory (1978) to Chandra and XMM-Newton.

InstitutionAmerican Science and Engineering, Inc. / NASA
Historical regionUnited States / Kenya (launch)
Primary sourceGiacconi, R., Kellogg, E., Gorenstein, P., Gursky, H. & Tananbaum, H. — "An X-Ray Scan of the Galactic Plane from UHURU" (The Astrophysical Journal Letters, 165, L27, 1971). DOI: 10.1086/180711
Secondary sourceNASA NSSDCA — Uhuru (SAS-A) Spacecraft Details; Smithsonian National Air and Space Museum — Satellite, Uhuru, Reconstructed Craft; Harvard-Smithsonian Center for Astrophysics — "Uhuru"; Riccardo Giacconi, 2002 Nobel Lecture (nobelprize.org)
Original languageEnglish
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