consistently developed innovative procedures and techniques to bring about desired mission success when encountering unplanned for or unexpected contingencies on-orbit.

FINDING: The risk in the mission phase of a shuttle HST servicing mission is low.

COMPARISON OF THE RISKS AND THE BENEFITS OF SERVICING

As noted above, the Hubble Space Telescope provides unique capabilities for astronomical research. These capabilities will not be replaced by any existing or currently planned astronomy facility in space or on Earth. Hubble’s continuing and extraordinary impact on human understanding of the physical universe has been internationally recognized by scientists and the public alike.

Upgrading Hubble to address the predictable decline in HST component performance over time and thus ensure system reliability requires a timely and successful servicing mission in order to minimize further degradation and prevent a significant gap in science data return. Although it considered other options for extending the life of Hubble, the committee focused on two approaches: robotic servicing and shuttle astronaut servicing.

The need for timely servicing of Hubble imposes difficult requirements on the development of a robotic servicing mission. The very aggressive schedule, the complexity of the mission design, the current low level of technology maturity, and the inability of a robotic servicing mission to respond to unforeseen failures that may well occur on Hubble between now and a servicing mission make it unlikely that the science life of HST will be extended through robotic servicing.

A shuttle astronaut servicing mission is the best option for extending the life of Hubble and preparing the observatory for eventual robotic de-orbit by, for example, attaching targets to Hubble. The committee believes that a shuttle HST servicing mission could occur as early as the seventh shuttle mission following return to flight, at which point critical shuttle missions required for maintaining ISS will have been accomplished. All important systems needed to keep Hubble functioning well through 2011 were included in the original SM-4 shuttle servicing plan. Replacement of batteries and gyros and one FGS is deemed essential. Any spacecraft is subject to unanticipated failures, but if the repairs planned for the SM-4 mission are carried out promptly, there is every prospect that Hubble can operate effectively for another 4 to 5 years after servicing.

The committee finds that the difference between the risk faced by the crew of a single shuttle mission to ISS—already accepted by NASA and the nation—and the risk faced by the crew of a single shuttle servicing mission to HST, is very small. 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.

RECOMMENDATIONS

  1. The committee reiterates the recommendation from its interim report that 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.

  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.



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