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5 HST Robotic Servicing Assessment
Pages 56-73

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From page 56...
... The baseline HST robotic servicing mission program as presented to the committee by the HST project has a development schedule of approximately 39 months. The spacecraft and instrument hardware that the project has baselined to be installed by robotic servicing are essentially those items that were developed for SM-4.
From page 57...
... Mission Description and Risks The robotic servicing mission has a number of phases that involve relatively independent technical challenges and relatively independent risks, an assessment of which is provided below. It should be noted that risks are discussed in several different parts of this report.
From page 58...
... spaceflights suggests that the probability of failure should be estimated at around 5 percent. Regardless of the launch vehicle, if the failure occurs with the HST payload on board, the entire servicing mission is lost and cannot be attempted again.
From page 59...
... The biggest potential problems concern the inability of the near-field sensor suite to acquire HST; any limits on the fine-guidance control could preclude the ability of the HRV to fly in close formation with HST and could even result in a collision of the two vehicles. The technologies for near-field sensors and for matching vehicle rates for robotic missions have yet to be demonstrated in flight.
From page 60...
... , but given its timing (late 2006) the opportunity for feedback and incorporation of lessons learned into the HST robotic servicing mission may not occur.
From page 61...
... Thermal and Illumination Constraints The tasks in many of the past servicing missions occasionally were made more challenging because of the limitations imposed on allowable intrusion of sunlight on HST or by the HST thermal environment. While the assumption for robotic servicing is that there will be no such constraints because there are no time limitations for any specific task, consideration nevertheless will have to be given to realworld limitations imposed by HST orientation on each step of each operation.
From page 62...
... The axial bay doors are much larger than the servicing bay doors and can therefore be balkier. The particular axial doors that the first shuttle servicing mission crew had difficulty with are not candidates for the robotic mission.
From page 63...
... FINDING: The technology required for the proposed HST robotic servicing mission involves a level of complexity, sophistication, and maturity that requires significant development, integration, and demonstration to reach flight readiness and has inherent risks that are inconsistent with the need to service Hubble as soon as possible.
From page 64...
... The robotic missions planned by other agencies before or at approximately the same time as the HRSDM will include specific technology demonstrations and evaluations of several aspects of the technology challenges faced in an HST robotic mission, but these demonstrations will provide only limited, if any, opportunity to incorporate lessons learned. The individual hardware elements (GA, DR, and DM)
From page 65...
... This attachment will be required should NASA conclude after the planned mid-2005 critical design review that robotic servicing of HST is not a feasible option and that the original shuttle-based servicing mission should be pursued. The risk in attaching a robotic de-orbit module could be significantly reduced if astronauts would install appropriate hardware (such as targets, fiduciaries, and precision latches)
From page 66...
... FINDING: The control algorithms and software for lidar- and camera-based control of the grapple arm are mission-critical technologies that have not been flight-tested. Robotic Operations The servicing mission includes the installation of batteries, the gyroscopes, and the WFC3 package, and the COSTAR/COS change out.
From page 67...
... Application of the full breadth of NASA technical expertise is vital to this project, yet as of this writing the committee has seen no evidence that this support has been provided by either the Johnson Space Center or the Jet Propulsion Laboratory, which are organizations with directly applicable mission operations and robotic technology expertise. FINDING: The Goddard Space Flight Center HST project has a long history of HST shuttle servicing experience but has little experience with autonomous rendezvous and docking or robotic technology development, or with the operations required for the baseline HST robotic servicing mission.
From page 68...
... A robotic mission of this complexity requires a significant amount of up-front systems engineering and trade studies based on thorough analyses and simulations just to arrive at a starting point for the system design. This level of design definition is normally done before commitment to hardware procurements, especially for a mission as technically complex5 as the HST robotic servicing mission.
From page 69...
... report prepared for NASA, as presented to the committee.7 The committee concurs with the findings of both of these groups that there is no precedent for a 39-month development schedule for a mission as complex as the baseline HST robotic servicing mission. In fact, the committee agrees with the Aerospace Corporation findings, which suggest that a successful mission of this level of complexity would require a nominal development time of the order of 65 months.
From page 70...
... Normal Schedule Complexity There Robotic 1 + robotic Ejection Aerospace 1.6308x outcome. HST HST Module Module 0.675 0.9 with and as = 22.898e 2 = R Ejection y 0.8 complex HST Module complexity comparison as in 0.7 varying mission shown of a for 0.6 Index missions alternatives schedule 0.5 satellite De-orbit for HST Module 0.4 servicing Complexity development Complexity robotic schedules of 0.3 39-month 0.2 Telescope determined Missions development of successful Function be Space a as Successful Failed Impaired To Study Cancelled 0.1 for Hubble database 0 96 84 72 60 48 36 24 12 0 5.1 precedent Schedule 144 132 120 108 historical (months)
From page 71...
... Nor is it clear that the end-to-end mission scenarios can be replicated in ground testing to validate the operations plans, which in turn requires that the program development plan build quality into all elements of the program at the subsystem and component level. The committee was shown a laboratory demonstration of the elements of the HST servicing mission at GSFC.
From page 72...
... However, in general the robotic mission will of necessity be rigid in its design and in its ability to cope with unplanned anomalies such as those that have been encountered during each of the four previous shuttle servicing missions. CONCLUSION: The very aggressive schedule for development of a viable robotic servicing mission, the commitment to development of individual elements with incomplete systems engineering, the complexity of the mission design, the current low level of technology maturity, the magnitude of the risk-reduction efforts required, and the inability of a robotic servicing mission to respond to unforeseen failures that may well occur on Hubble between now and the mission, together make it unlikely that NASA will be able to extend the science life of HST through robotic servicing.
From page 73...
... HST ROBOTIC SERVICING ASSESSMENT 73 A more detailed discussion of the comparative risk between a robotic servicing mission and a shuttle mission to HST is presented in Chapter 7. FINDING: Many of the concerns raised by the committee regarding the risk of attempting to robotically service the Hubble Space Telescope could be mitigated for future programs through planning for robotic servicing in the initial spacecraft design.


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