Assessment of Options for Extending the Life of the Hubble Space Telescope Final Report (2005) / Chapter Skim
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7 Benefit/Risk Assessment of Hubble Space Telescope Servicing Options
7 Benefit/Risk Assessment of Hubble Space Telescope Servicing Options
Pages 92-108
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From page 92... ...
Nevertheless, the committee was able to assess the benefit/risk for alternative servicing options, based on qualitative risk assessments, and qualitative consideration of the specific scientific benefits expected as a result of the different servicing options. Benefit/risk comparisons were made for a human HST servicing mission and for a robotic servicing mission.
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From page 93... ...
Furthermore, the risk assessment procedures for NASA programs and projects do not require risk assessments for non-human-related missions. As a result of not having a risk assessment for either the shuttle or the robotic HST servicing missions for its review and analysis, the committee performed its own qualitative assessment of the risks of the two HST servicing options based on briefings, meetings with NASA and contractor personnel, and selected references.
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From page 94... ...
Since this section is focused on mission risk (or the probability of success of a servicing mission) , there is no assessment here of risk during reentry for either servicing option.
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From page 95... ...
Abort rendezvous Low/High Low Low Loss of radar High/Low Low Low Capture, grapple, RMS failure Low/High Low Low Mitigation mating alternatives available. RMS degradation Medium/Low Low Low Workarounds available for degraded performance.
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From page 96... ...
HST instrument obstruction Assumes partial loss compartments of mission. Inability to Low/Medium Low Low Assumes partial loss remove hardware of mission.
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From page 97... ...
Misalignment/ Low/Medium Low Medium binding of instrument during removal from HST Misalignment/ Medium/Medium Medium Medium Does not consider binding of instrument getting instrument during stuck, preventing insertion into HST safe closeout. Exceeding of Low/Low Low Low thermal limits/ attitude constraints continued
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From page 98... ...
aNot considered for robotic servicing mission due to assumption that re-boost will not be planned. bNot required for a robotic servicing mission.
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From page 99... ...
Hardware High/High High High Proximity development operations problems sensor technology immature. Multivehicle High/Medium Medium Medium systems engineering ground test failures Ground test Medium/Medium Medium Medium Systems architecture software not ready currently immature.
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From page 100... ...
Removal and Loss of control of Low/Low Low Low installation of connector hardware Dexterous robotic Medium/High High High system arm failure Vision system Medium/Medium Medium Low camera fails Failure of robotic Medium/Medium Medium Medium system to grapple/ release tool Failure of tool Medium/Medium Medium Low Two examples of tool failures on two of four HST servicing missions. Loss of servicing Medium/Low Low Low tool
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From page 101... ...
Contamination of Medium/High Medium Medium Hubble arrays, control surfaces, etc. Close and Latch failure High/Medium High Medium Assumes partial loss Secure All of mission.
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From page 102... ...
For example, a giant asteroid striking Earth would have catastrophic or possibly even existential consequences, but the extremely low frequency of its occurrence makes the risk of such an event low. Uncertainty In the absence of a quantitative expression of the risk, such as a frequency of occurrence parameter embedded in a probability distribution, a judgment of how uncertainty contributes to risk significance is based on an assessment of the quality of the supporting evidence.
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From page 103... ...
5NASA, 2004, "Hubble Space Telescope Robotic Servicing Mission Project," Hubble Space Telescope Review Team Report, July 26, NASA Independent Program Assessment Office, Washington, D.C.
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From page 104... ...
In addition, there is strong supporting evidence that mission risk is high when successful system development and testing of the robotic servicing option must be done in the short time now available. FINDING: Although a quantitative mission risk assessment does not exist for either a human or a robotic servicing mission to the Hubble Space Telescope, the committee's qualitative evaluations lead it to conclude that the human servicing mission poses a low risk to mission success.
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From page 105... ...
2. The conclusion in Chapter 6 that the safety risk for a single mission to the Hubble Space Telescope is comparable to the safety risk for a mission to the International Space Station.
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From page 106... ...
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 mission to respond to unforeseen failures that may well occur on Hubble between now and the mission make it highly unlikely that the science life of HST will be extended through robotic servicing.
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From page 107... ...
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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