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TWENTY Chandra: The Dream Comes True—Some Comments on the NASA Space Program— The Nobel Prize First Loves and Last Words 358 Chandra: The Dream Comes True After 36 years of proposals,work,cancellations,and restarts,on July 19,1999, the Chandra X-Ray Observatory was finally launched. The 1.2-m x-ray telescope was placed into a highly elliptical orbit with an apogee of 121,279 km and a perigee of 27,539 km—the kind of orbit I had advocated in my paper in Science in 1987.1 Its distance from Earth,one-third of the way to the moon, means that Chandra is outside the earth’s Van Allen Belts most of the time and can spend 55 hours out of its 64-hour orbit obtaining useful, continuous observations. It is the largest and heaviest payload ever carried by the shuttle. To put it in its orbit, an inertial upper stage was required as well as an engine carried on the spacecraft itself (Plate 29). The observatory has operated continuously for the past nine years without any serious degradation since its first light in 1999. Chandra’s director Harvey Tananbaum and its project scientist Martin Weiskopf did a magnificent job, together with the principal investigator teams and the working group, of providing scientific guidance. Engineers and managers at the Marshall Space Flight Center and at TRW have given us a great platform from which to do science.2 Chandra’s sensitivity and resolution met or exceeded all expectations (Plates 30–32).3 For me, the use of Chandra time, 500,000 sec of my own and, thanks to Harvey Tananbaum’s kindness,500,000 sec of director’s discretionary time, was a dream come true. I should note that attached to the discretionary time was the condition that the entire 106 sec of data would be made available to the entire community in less than a month from the last observation. Piero Rosati and I studied carefully how best to point our successive exposures , and we decided to always point to a single position in the sky. The different orientations of the spacecraft rotated the pitch with which we observed our field, but the point response function (which is a function of the distance from the telescope axis) remained the same for every source. Thus, we could distinguish between point and extended sources. We chose the position in the sky (right ascension 3 h 32 min 28 sec, declination –27 deg 48 min 30 sec; J 2000) as the one with the lowest intervening absorption. The sensitivity of the observatory in 106 sec was 5.5 × 10–17 erg/cm2 ⋅ sec in the soft x-ray band (from 0.5 to 2 keV) and 4.5 × 10–16 erg/cm2 ⋅ sec in the hard band (from 2 to 10 keV). Thus, in 40 years we had improved x-ray astronomy observations between one and ten billion times with respect to the first observation of Sco X-1,the same factor that measures the improvement from the naked eye to Hubble in the visible.I wonder sometimes how Tycho Brahe would have felt if he could have contributed to the development of Hubble and could have used it himself. After many years of helping others do their science, it was great to be able to stare at my own data and let them flow through my fingers, as if panning for gold. I have always believed that contemplating data and keeping one’s mind open to what nature is trying to tell us is the best way to discover the underlying phenomena, and just as it had occurred with Uhuru in the early 1970s and Einstein in the late 1970s,here was a chance to find something new by exploring a new region of discovery space.I must confess that I had at first approached the new data with a sort of arrogant conceit. After all, I knew perfectly well that I would find the XRB to be made of individual point sources. Although I did not exactly know what objects they would be, I thought that by extrapolation from the work done with Einstein and ROSAT, we could confidently say that most of the objects would be galaxies with active nuclei or quasars. This in fact turned out to be the case, but nature, as usual, was richer and more inventive than I could imagine. Sometimes I think that nature is out there working...

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