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 http://www.aip.org/fyi/2004/096.html).
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 http://www4.nationalacademies.org/news.nsf/isbn/0309095301?OpenDocument
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