Assessment of Options for Extending the Life of the Hubble Space Telescope: Letter Report (2004)

The Hubble Space Telescope was originally launched aboard the space shuttle in 1990, with a designed mission lifetime of 15 years. Since then the telescope has been repaired or upgraded four times, each requiring a very complex, dedicated space shuttle mission and unique HST servicing support equipment. Over its lifetime, HST has been an unprecedented scientific success, having earning extraordinary scientific and public recognition for its contributions to all areas of astronomy. Prior to the accidental loss of the space shuttle Columbia and crew in February 2003 there had been plans for another shuttle servicing mission, designated SM-4, to replace aging spacecraft batteries and gyroscopes and to install two new science instruments on the telescope.

Following the Columbia accident, the Columbia Accident Investigation Board (CAIB) was created to determine the cause of the accident and to advise NASA about steps to prevent future accidents. In its August 2003 report, the CAIB noted the inherent risk in any form of human space flight, and it made 29 recommendations, 15 of which were required to be completed before the space shuttle could return to flight. The report made specific recommendations about on-orbit 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 advice about how to implement the CAIB recommendations and any other related actions. NASA Administrator Sean O’Keefe committed the agency to following all recommendations from both groups.

In mid-January 2004 Mr. O’Keefe announced that, as a consequence of safety considerations, NASA would reduce its shuttle manifest to only the 25 planned missions to the ISS. The decision was also made, on the basis of risk, to not pursue SM-4, but instead to investigate other options to extend the life of HST. Following that announcement Senator Barbara Mikulski asked O’Keefe to seek an independent opinion on whether the decision was, in fact, required to comply with the CAIB recommendations, and 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.”

O’Keefe subsequently asked the National Academies for the study.

NASA plans to continue operation of the HST until it can no longer support scientific investigationscurrently anticipated to occur in the 2007-2008 time frame. The telescope’s life may, in fact, be extended if NASA is successful in employing operational techniques to preserve battery and gyroscope functions. Meanwhile, NASA is investigating innovative ways to extend the science lifetime of the HST for as long as possible, including robotic servicing. Current plans are to safely de-orbit HST by means of a robotic spacecraft by approximately 2013.

The committee will conduct an independent assessment of options for extending the life of the Hubble Space Telescope. The study will address the following tasks:

1. Assess the viability of a space shuttle servicing mission that will satisfy all recommendations from the CAIB, as well as ones identified by NASA’s own Return-to-Flight activities. In making this assessment, compare the risks of a space shuttle servicing mission to HST with the risks of a shuttle mission to the ISS and, where there are differences, describe the extent to which those differences are significant. Estimate to the extent possible the time and resources needed to overcome any unique technical or safety issues associated with HST servicing that are required to meet the CAIB recommendations, as well as those from the Stafford-Covey team.

2. Survey other available engineering options, including both on-orbit robotic intervention and optimization of ground operations, that could extend the HST lifetime.

3. Assess the response of the spacecraft to likely component failures and the resulting impact on servicing feasibility, lost science, and the ability to safely dispose of HST at the end of its service life.

4. Based upon the results of the tasks above, provide a benefit/risk assessment of whether extension of HST service life, via (a) a shuttle serving mission if one is deemed viable under task #1 and/or (b) a robotic servicing mission if one is deemed viable under task #2, is worth the risks involved. The assessment should include consideration of the scientific gains from different options considered and of the scientific value of HST in the larger context of ground and space-based astronomy and science more broadly. Special attention should be paid to the practical implications of the limited time available for meaningful intervention robotically or via the shuttle.

The committee is not expected to make either organizational or budgetary recommendations, but it may need to consider cost as a factor in weighing the relative benefits of alternative approaches.

The committee will investigate the possibility of providing an interim report to NASA that addresses a portion of the items in the task statement in advance of delivering a full final report if such an approach is deemed feasible and able to provide early, credible answers to the questions being considered.