BOX 5.1
Principal Level-1 Requirements for HST

  1. Work every feasible operational option and implement where possible, to extend HST’s life without servicing.

  2. Provide propulsion capability to safely de-orbit HST at some point in the future.

  3. Do no harm to HST.

  4. Extend the current scientific program of HST as long as possible.

  5. Enhance scientific capabilities with new instruments(s).

  6. Provide options to accomplish various levels of the above, which include schedule, risk, and cost assessments.

a package on an expendable launch vehicle, rendezvous with HST, and perform autonomous proximity and docking operations to mate the two modules to HST. The GA and DR will be contained in the EM, as will the replacement spacecraft hardware with the exception of the spacecraft batteries. The DM will contain the de-orbit motor and the replacement set of spacecraft batteries. Once the robotic servicing operations have been completed, the EM containing the removed spacecraft and instrument hardware will separate from HST and de-orbit. At the time of this writing, although the HST project has performed the high-level up-front systems engineering to establish the baseline architecture, the detailed systems engineering and analysis to understand and define how these elements and the ground system will all operate together as a system remain to be accomplished.

The committee assessed both the program and the technical plans as presented by the project as well as the project’s assessment of the readiness of the technology needed to robotically extend the life of HST. The committee’s assessment is provided below.


This section provides an assessment of both the mission-level risks and the technology risks associated with robotic servicing of HST.

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. In Chapter 7 the different types of risks considered are defined and include health and safety risk, programmatic risk, and mission risk. Of course, technology risks are embedded in the programmatic risks. Mission risks are discussed below and qualitatively assessed in Chapter 7. Health and safety risks are discussed in Chapter 6, and programmatic risks are discussed in several places in the report, including Chapter 7. It is important to realize that the discussions of risk are abbreviated and qualitative and do not have the benefit of the full-scope risk assessment that was recently under development by NASA.

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