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FYI Number 158: December 14, 2004

NRC Panel Endorses Shuttle Servicing Mission to Hubble

"A shuttle astronaut servicing mission is the best option for extending the life of Hubble and preparing the observatory for eventual robotic de-orbiting.... Given the intrinsic value of a serviced Hubble, and the high likelihood of success for a shuttle servicing mission, the committee judges that such a mission is worth the risk." - Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope

A National Research Council panel evaluating the options for extending the scientific life of the Hubble Space Telescope (HST) finds that, in the time available, the likelihood of success of a proposed robotic servicing mission is "remote." The Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope reviewed NASA's plans for a proposed robotic servicing mission versus a manned servicing mission using the space shuttle, and warns that the "very aggressive" development schedule, as well as the required level of technological complexity, maturity, sophistication, and ability to adapt to unforeseen events, "make it unlikely that NASA will be able to extend the science life of HST through robotic servicing." It further concludes that a space shuttle servicing mission would be "highly likely to succeed," and could be flown "as early as the seventh flight after return to flight [of the shuttle fleet] without a critical operational impact" on the International Space Station (ISS).

The committee, composed of 21 experts from industry, academia and government, was asked to "conduct an independent assessment of options for extending the life" of the HST, including a benefit/risk assessment of whether servicing the Hubble, by a shuttle mission or other means, "is worth the risks involved." The committee submitted an interim report in July (see After a lengthy and comprehensive analysis, its final report is now in prepublication form. The report runs over 130 pages with appendices. Its eight chapters include background information on the Hubble, its past and future scientific impacts, projections of component failure, evaluations of robotic and shuttle servicing options, a benefit/risk assessment of the options, and final recommendations.

The Hubble is "the most powerful space astronomical facility ever built," says the report. It "provides wavelength coverage and capabilities that are unmatched by any other optical telescope currently operating or planned," and discoveries with the Hubble rank "among the most significant intellectual achievements of the space science program," the report continues. Given the growth in capabilities due to previous servicing missions and the potential for even greater scientific power with new scientific instruments, the committee finds the Hubble "a national asset well worth maintaining in operation."

According to the report, certain Hubble components are expected to fail in the coming years, leading to an anticipated termination of scientific operations in the 2007-2008 time frame if the telescope is not serviced. A space shuttle servicing mission, SM-4, was originally planned to replace aging components and install two new science instruments, but in the wake of the Columbia shuttle accident, NASA Administrator Sean O'Keefe announced that SM-4 would be cancelled for safety reasons. Upon expressions of concern by members of the science community, the public, Senator Barbara Mikulski (D-MD) and other Members of Congress, O'Keefe requested an analysis of servicing options from the National Research Council. At the same time, NASA went ahead with consideration of proposals for a robotic servicing mission.

The projected component failures, along with other strategic considerations, prompted the committee to urge NASA to conduct a servicing mission "as early as reasonably possible." The report notes that a robotic servicing mission, as currently envisioned by NASA, would require a 39-month development schedule. The committee finds that this schedule, combined with the anticipated failure of Hubble gyroscopes in mid to late 2007, would "result in a projected 29-month interruption of science operations." Additionally, consideration of past experiences and historical data led the committee to conclude that "the likelihood of successful development of the HST robotic servicing mission within the baseline 39-month schedule is remote." The committee also notes that the proposed robotic mission would not install all the upgrades planned for SM-4, and would have "minimal capacity for responding to and repairing unforeseen anomalies."

On the other hand, the committee expects "no interruption of science operations...for a realistically scheduled SM-4 shuttle mission." Based on the experience of previous shuttle servicing missions, the committee finds that the risk of failure "in the mission phase of a shuttle HST servicing mission is low." It also believes that NASA could meet the relevant Columbia Accident Investigation Board and Return-to-Flight requirements for a shuttle servicing mission, and it concludes that "the difference in risk of loss of the vehicle and crew between a single servicing mission to the Hubble and a single mission to ISS is extremely small." The committee "further believes that adding a shuttle flight for an HST SM-4 mission adds a percent or fraction more to the total risk of losing astronauts in the course of completing the already planned ISS program," and, "compared to the total cost of flying a shuttle flight, the resources required to overcome unique technical or safety issues involved in flying a shuttle mission to HST are small" and well within NASA's experience base.

The committee concludes that "the benefit/risk ratio for the human mission is high, and the benefit/risk ratio for the robotic mission is low." The committee makes three final recommendations:

1. "...NASA should commit to a servicing mission to the Hubble Space Telescope that accomplishes the objectives of the originally planned SM-4 mission."

2. "The committee recommends that NASA pursue a shuttle servicing mission to HST that would accomplish the above stated goal. Strong consideration should be given to flying this mission as early as possible after return to flight [of the shuttle fleet]."

3. "A robotic mission approach should be pursued solely to de-orbit Hubble after the period of extended science operations enabled by a shuttle astronaut servicing mission, thus allowing time for the appropriate development of the necessary robotic technology."

The entire report is not yet available, but a press release can be found at

Audrey T. Leath
Media and Government Relations Division
American Institute of Physics

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