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Riccardo Giacconi and the origins of Chandra Program

Many people are aware that we have worked on Chandra (originally AXAF) for more than 20 years, tracing back to an unsolicited proposal submitted to NASA in 1976, by Riccardo Giacconi (PI), myself (Co-PI) and Paul Gorenstein, Rick Harnden, Pat Henry, Ed Kellogg, Steve Murray, Herb Schnopper, and Leon VanSpeybroeck - all Co-Is and all members of our team at the Harvard-Smithsonian Center for Astrophysics. Martin Weisskopf came on-board in 1977 at MSFC as the Project Scientist. What some readers may not know is that the "roots" for this mission trace all the way back to 1963.

Just one year after the discovery of the first extra-solar X-ray source, Sco X-1, and the all-sky X-ray background (see article in this Newsletter about award of 2002 Nobel Prize to Riccardo Giacconi for leading this effort), Riccardo and his team at American Science and Engineering described their ideas to NASA for a long-range program of X-ray observations over the next decade. This 1963 plan described an ongoing rocket program, instruments to be flown on the OSO-4 spacecraft, an Explorer to do an all-sky survey (later built and flown as the UHURU satellite), a small X-ray telescope on an OAO spacecraft, and a 4ft diameter, 30ft focal length, arcsec class grazing incidence telescope.

The diameter and focal length of this telescope described in 1963 are essentially identical to the Chandra parameters. The suggested collecting area in 1963 was 400 sq cm, with the concept for nesting the optics not yet in vogue. The advertised angular resolution was characterized as order of seconds of arc - no doubt ambitious for a mirror design which had never been built, and only a bit less precise than the resolution achieved with Chandra nearly 40 years later. With detections for just Sco X-1, the Crab, and a few other fainter sources plus the all-sky background, Riccardo and his group already anticipated using such a telescope 'for detailed study of the structure of galactic and extra-galactic sources'. I think it is fair to say that Chandra has fulfilled that vision.

'And now you know the rest of the story' - or at least some of it.

Harvey Tananbaum

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