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The Hubble Space Telescope (HST) was designed for periodic servicing by Space Shuttle astronauts. These servicing missions enable state-of-the-art upgrades to the Observatory’s scientific capabilities, engineering upgrades and refurbishments, and, when needed, repairs. Since its launch and deployment in 1990, there have been four space shuttle missions to service the HST. (A fifth is currently scheduled for March 2004) In each case, upon completion of a servicing mission and the astronauts’ release of the telescope, HST undergoes a period of intense and highly coordinated verification activities designed to commission the Observatory’s new capabilities and components for normal operations. The commissioning program following the 1990 deployment mission was known as OV/SV (orbital verification/science verification) while each of those following the subsequent Shuttle servicings has become known as servicing mission observatory verification, or SMOV. The 1990 OV/SV activities were hampered and greatly complicated by the problem of spherical aberration of the primary optics. The first servicing mission, SM1, in December 1993, is still remembered as the Hubble repair mission, having restored HST’s optics to within the original mission specifications. SMOV1 was important not only for confirming the optical fixes with spectacular early images, but also for demonstrating the effectiveness of “success-oriented” scheduling as a technique for orbital verification. The second servicing mission, SM2, in February 1997, greatly enhanced the scientific capabilities of HST but did so at the cost of greatly increased mechanical and operational complexity. The resulting SMOV2 program was accordingly the most complicated and ambitious till then and, as it turned out, the most responsive and resilient, as the newly installed instruments presented serious, unforeseen on-orbit problems. The third servicing mission, SM3a, carried out in December 1999, was essentially an emergency mission to replace failed gyros and the SMOV3a was correspondingly relatively simple. SM3b, scheduled for March 2002, will feature further significant scientific upgrades in the form of a new wide-field camera and the revival of the prematurely defunct infrared instrument. In addition to describing the highlights of these verification programs, this paper presents the general principles, guidelines, and lessons learned in the process of commissioning the HST Observatory.
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