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Introduction

BACKGROUND

The Hubble Space Telescope (HST) was launched aboard the space shuttle in 1990 and has operated continuously in orbit for the past 14 years. Over its lifetime, HST has been an unprecedented scientific success, having earned extraordinary scientific and public recognition for its contributions to all areas of astronomy. Hubble today is not the same telescope that was launched in 1990. A series of shuttle astronaut servicing missions, planned from the beginning of NASA’s Space Telescope project in the late 1970s, has by now replaced, repaired, or upgraded many of the key components constituting the original telescope. Three of the four servicing missions contributed major new instrument observing capabilities. New observing modes were provided, and the efficiency of existing ones was increased dramatically. As a result, Hubble now produces much more data per unit time than it did originally.

Prior to the loss of the space shuttle Columbia and its crew in February 2003, planning was underway for a fifth shuttle servicing mission, designated SM-4, that would replace aging spacecraft batteries, fine-guidance sensors, and gyroscopes and would install two new science instruments on the telescope.

But in its August 2003 report, the Columbia Accident Investigation Board (CAIB), created to determine the cause of the Columbia accident and to advise NASA about steps to prevent future accidents, noted the inherent risk in any form of human spaceflight and made 29 recommendations, 15 of which it regarded as requirements to be completed before the space shuttle could return to flight.1 The report made specific recommendations about on-orbit shuttle inspections and repairs, and it noted differences between future flights to the International Space Station (ISS), which could be used as a safe haven, and other possible destinations. NASA subsequently formed an internal committee, called the Stafford-Covey Return-to-Flight Committee, to provide oversight of the efforts to comply with the 15

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Columbia Accident Investigation Board, Report, Volume I, August, 2003. Available online at http://www.nasa.gov/columbia/home/CAIB_Vol1.html.



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Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report 1 Introduction BACKGROUND The Hubble Space Telescope (HST) was launched aboard the space shuttle in 1990 and has operated continuously in orbit for the past 14 years. Over its lifetime, HST has been an unprecedented scientific success, having earned extraordinary scientific and public recognition for its contributions to all areas of astronomy. Hubble today is not the same telescope that was launched in 1990. A series of shuttle astronaut servicing missions, planned from the beginning of NASA’s Space Telescope project in the late 1970s, has by now replaced, repaired, or upgraded many of the key components constituting the original telescope. Three of the four servicing missions contributed major new instrument observing capabilities. New observing modes were provided, and the efficiency of existing ones was increased dramatically. As a result, Hubble now produces much more data per unit time than it did originally. Prior to the loss of the space shuttle Columbia and its crew in February 2003, planning was underway for a fifth shuttle servicing mission, designated SM-4, that would replace aging spacecraft batteries, fine-guidance sensors, and gyroscopes and would install two new science instruments on the telescope. But in its August 2003 report, the Columbia Accident Investigation Board (CAIB), created to determine the cause of the Columbia accident and to advise NASA about steps to prevent future accidents, noted the inherent risk in any form of human spaceflight and made 29 recommendations, 15 of which it regarded as requirements to be completed before the space shuttle could return to flight.1 The report made specific recommendations about on-orbit shuttle inspections and repairs, and it noted differences between future flights to the International Space Station (ISS), which could be used as a safe haven, and other possible destinations. NASA subsequently formed an internal committee, called the Stafford-Covey Return-to-Flight Committee, to provide oversight of the efforts to comply with the 15 1   Columbia Accident Investigation Board, Report, Volume I, August, 2003. Available online at http://www.nasa.gov/columbia/home/CAIB_Vol1.html.

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Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report recommendations of the CAIB that must be implemented prior to returning to flight. NASA Administrator Sean O’Keefe committed the agency to following the CAIB recommendations. In mid-January 2004 O’Keefe announced that, as a consequence of safety considerations, NASA would reduce its shuttle manifest to only the 25 to 30 (the precise number of flights required is uncertain at this time) planned missions required to build the ISS. The decision was also made, on the basis of risk, to not pursue the Hubble Space Telescope SM-4, but instead to investigate other options for extending the life of HST. That announcement was followed by considerable expression of public concern in many media outlets about the future of Hubble, and astronomers and other scientists also raised many questions about the decision. Senator Barbara Mikulski (D-Maryland) asked O’Keefe to seek an independent opinion on whether the decision to cancel SM-4 was, in fact, required for compliance with the CAIB’s recommendations. In response, O’Keefe asked the CAIB chair, Adm. Harold Gehman, to review the matter. In his March 5, 2003, letter to Mikulski, Gehman said that “the Board is split on the merits of flying this mission.” He also indicated that “whether to fly another mission to the Hubble is one of the public policy debates this nation should have,” and he called for a “deep and rich study of the entire gain/risk equation (to) answer the question of whether an extension of the life of [HST] is worth the risks involved.” Subsequently the National Research Council was asked to perform such a study. To do so, it appointed the Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope. This final report, together with an interim report released in July 2004,2 represents the outcome of that effort. GOALS OF THIS STUDY The principal goal of this study is to assess options for extending the life of HST. The assessment considers issues of safety in the use of the space shuttle for servicing HST with an astronaut crew, the feasibility of robotic servicing approaches, the impacts of servicing options on HST’s scientific capability, and risk/benefit relationships between servicing options that are deemed acceptable. The specific tasks addressed in the course of the study are listed in Appendix A. During the development of the most recent decadal strategy for astronomy and astrophysics,3 it was assumed that the Hubble SM-4 mission, long considered an integral element of the U.S. space astronomy program, would be conducted at the time necessary to prevent the demise of the telescope and to enable Hubble’s ongoing operation for conducting astronomical research in the wavelength range covered by HST. The next major facility initiative in space astronomy given priority in the 2001 decadal strategy was the James Webb Space Telescope (JWST). The advisory panel convened by NASA in 2003 to advise it on the transition from HST to the JWST concurred with the decadal survey on the need for the SM-4 servicing mission and noted the work that had already been done, and was currently in progress, toward this servicing.4 The advisory panel recommended that a servicing mission SM-5 also be pursued, but only “in a peer-reviewed competition with other new space astrophysics proposals.” 2   See Appendix C, National Research Council, “Assessment of Options for Extending the Life of the Hubble Space Telescope,” letter from Louis J. Lanzerotti, chair of the Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope, to Sean O’Keefe, NASA administrator, July 13, 2004. Available online at http://books.nap.edu/html/Hubble_Space_Telescope/letter_report.pdf. 3   National Research Council, 2001, Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C. 4   HST-JWST Transition Panel, Report of the HST-JWST Transition Panel, August 14, 2003. Available online at http://www.nasa.gov/pdf/49151main_hst-jwst.pdf.

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Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report In keeping with the statement of task given to the committee, this report does not address, or support, any changes in priorities for astronomical research or facilities. The committee assumed that NASA, in order to strive for frontier achievements in astronomy and astrophysics, would follow the 2001 decadal survey’s advisory recommendations. If NASA concludes that it cannot move forward with portions of the decadal survey strategy, then NASA will have to carry out an examination of priorities for the research field. The committee does not endorse such a re-examination. The committee notes that if a re-examination should occur it would have to be conducted in a very timely and very expeditious fashion in order to ensure the continued operation and integrity of Hubble (see discussions in Chapter 4). REPORT ORGANIZATION AND DEVELOPMENT To address the various aspects of its task required that the committee engage in considerable analysis of a large volume of technical material and information provided in various briefings. Two key documents to which the committee referred frequently were the report of the Columbia Accident Investigation Board and a NASA document titled NASA’s Implementation Plan for Space Shuttle Return to Flight and Beyond.5 In addition, the committee had access to numerous additional reports and technical documents on topics ranging from the test data on Hubble battery recharging cycles to industry proposals for the development of robotic missions.6 The committee’s work also benefited from the input of many experts at NASA and in academia and industry, who gave extensive briefings (listed in Appendix B), and from information received from many other individuals who made themselves available by telephone and e-mail to answer specific questions posed by committee members. The committee’s analysis was limited by the dearth of data in some areas, such as the lack of a probabilistic risk assessment that took into account the differences in the safety risk of shuttle missions to ISS versus to Hubble, and the lack of detailed cost estimates for the SM-4 shuttle mission. A study by the Government Accountability Office (previously the General Accounting Office) being prepared for release in late 2004 assesses the costs of such a mission, and its findings are expected to be considered along with those of this committee when a decision is made regarding HST servicing. Those issues that involved the most data, or required the most complex analysis, are treated in separate chapters of this report: (1) the scientific benefits of servicing Hubble, in Chapter 3; (2) the servicing needs and operational status of Hubble, in Chapter 4; (3) the prospects for Hubble servicing via a robotic mission, in Chapter 5; (4) the prospects for Hubble servicing via a shuttle mission, in Chapter 6; and (5) a discussion of the various types of risks involved in servicing Hubble, in Chapter 7. Although robotic servicing and shuttle servicing were the options to which the committee devoted the most time and energy, other options for extending the life of Hubble were considered, and discussion of these is included where appropriate throughout the report. Each section of the report contains findings relevant to the task statement. The final conclusions and recommendations of the study, stated simply in Chapter 8, derive directly from the findings and analysis presented in the preceding chapters. 5   NASA, NASA’s Implementation Plan for Space Shuttle Return to Flight and Beyond, Volume 1, Revision 1, October 15, 2003. This and subsequent revisions (2.1, July 28, 2004; 2.2, August 27, 2004) are available online at www.nasa.gov/news/highlights/returntoflight.html. During the course of this study, this document underwent a number of revisions, each of which was supplied to the committee. 6   See, for example, Steven J. Gentz, NASA Engineering and Safety Center, “Technical Consultation of the Hubble Space Telescope (HST) Nickel Hydrogen (NiH2) Battery Charge Capacity Prediction,” RP-04-08, June 17, 2004, NASA.