BOX 2-1 Safety Office Top 10 Hazards (August 1996)
  1. Extremely hazardous extravehicular activity (EVA) may be required to jettison a damaged or partially deployed but jammed solar array.

  2. Software development for the ISS is behind schedule, resulting in an incomplete safety assessment for some systems.

  3. The Russian functional cargo block (FGB) docking probe motor is not two-fault tolerant.

  4. The structural interface between segments Z1 and P6 is net two-fault tolerant.

  5. The ISS has no continuous carbon monoxide monitoring system.

  6. The risk from meteoroids and debris is unacceptably high, primarily because of the inadequate shielding of the Russian modules.

  7. The Russian segment may be unable to survive depressurization and repressurization without experiencing critical equipment failures.

  8. Some features on the outside surface of the ISS would be hazardous to astronauts conducting EVAs.

  9. During deberthing operations, the Soyuz could potentially collide with the ISS photovoltaic arrays.

  10. The retraction mechanism for the KURs antenna on the FGB module is net two-fault tolerant, thereby creating a possible collision risk.

The ISS program created all AIT to be responsible for meteoroid and orbital debris risk management. The meteoroid and orbital debris AIT members are responsible for all aspects of the problem, including modeling the environment, calculating the likelihood that debris or meteoroids will penetrate modules, performing hypervelocity impact tests, and designing and evaluating shields. The meteoroid and orbital debris AIT reports to the mechanical subsystems AIT, which reports to the systems integration AIT, which, in turn, reports to the vehicle IPT. Figure 2-2 shows this chain of command.

The meteoroid and orbital debris AIT strategic plan for risk management is to shield against particles up to about 1 cm in diameter, to maneuver to avoid collisions with objects larger than about 10 cm in diameter that can be tracked by ground-based sensors, and to implement procedures to mitigate the damaging effects of impacts with objects between about 1 and 10 cm in diameter. These three methods are discussed in detail in chapter 4, chapter 5, and chapter 6. Figure 2-3 illustrates this overall approach to managing the risk from meteoroids and debris.

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