invade a volume of space above the polar atmosphere that at times of solar storms often significantly overlaps the ISS orbit.

Flight directors will almost certainly be faced with flights impacted by high-latitude radiation. This finding directs attention to the issue of radiation risk management. The responsibilities at JSC in this area are well defined. The CSSP/CSTR review of current JSC flight rules shows, however, that radiation risk management would benefit by exploiting resources and capabilities that currently exist elsewhere. This report discusses the relevant resources and capabilities, addresses issues related to their application to radiation risk management, and makes recommendations aimed at reducing radiation risk. One main recommendation emerges from Chapter 1.

Recommendation 1: Because it denies access to valid information and thus unnecessarily restrains flight-director options, flight directors should not adhere rigidly to the (unofficial) real-time, on-site data rule.

Simply put, reducing the dose to astronauts from solar energetic particles during EVAs entails avoiding EVAs during orbits that penetrate the SPE zones when SPE particles are present. To implement an operational procedure for SPE-zone avoidance, the flight director must act on information on the size and shape of the zones and on the occurrence, intensity, and duration of the SPE. Information on SPE zone geometry and SPE start, strength, and length must be reliable enough to gain the flight director's confidence and timely enough to allow the flight director to act on it. The status of the resources (existing or in development) that are needed to acquire such information is reviewed in Chapters 3 and 4 and Appendix A.

One might draw an analogy to the influence of terrestrial weather in the execution of space missions. A flight director will routinely delay a launch or a landing because of a thunderstorm forecast based on nonlocal data. Forecasts of space weather based on nonlocal data could, likewise, help the flight director reduce the probability of radiation exposure to astronauts during EVAs. The principal difference in these two cases is that a terrestrial weather forecast has consequences for hardware, whereas a space-weather (radiation) forecast affects the rotation of astronauts and their health and future flight opportunities.

For Recommendation 1 to be successful, flight directors should acquire ownership of any flight rule that replaces the one whose removal is recommended. They should therefore work with SRAG to approve sources of nonlocal data and models that use these data to specify and forecast radiation levels at ISS. Radiation conditions at ISS should be inferred from nonlocal data until resources become available to augment the nonlocal data and models with real-time, on-site data and modeling.

One instance indicates that flight directors might be able to participate more in reducing radiation risk. SRAG proposed putting a radiation monitor in the shuttle bay to provide real-time, on-site radiation data on flights before Flight 8A, which will install a radiation monitor on the station. However, the proposal failed to receive flight director approval in time to implement it before Flight 8A. This delay guaranteed that, under current operating procedures, no change to flight or EVA schedules in response to a radiation situation is possible prior to Flight 8A. Timely action by the flight directors could have made it possible to respond to a radiation situation under current flight rules.

1.8 NOTES AND REFERENCES

1.  

The 1999 report on space weather of the National Security Space Architect finds that during the preceding 16 years at least 13 satellites suffered total mission failure attributable to space weather. There were more failures in which space weather was implicated, but the evidence was not definitive.

2.  

J.R. Letaw, R. Silberberg, and C.H. Tsao, "Galactic cosmic radiation doses to astronauts outside the magnetosphere," in Terrestrial Space Radiation and its Biological Effects, P.D. McCormack, C.E. Swenberg, and H. Bucker, eds., Plenum Press, New York, 1988; J.W. Wilson, F.A. Cucinotta, J.L. Shinn, L.C. Simonsen, R.R. Dubey, W.R. Jordan, T.D. Jones, C.K. Chang, and M.Y. Kim, "Shielding from solar particle event exposures in deep space," in Proceedings of Workshop on Impact of Solar Energetic Particle Events for Design of Human Missions, September 9-11, 1997, Center for Advanced Space Studies, Houston.



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