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Exploration of the Outer Heliosphere and the Local Interstellar Medium: A Workshop Report Appendixes

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Exploration of the Outer Heliosphere and the Local Interstellar Medium: A Workshop Report A Statement of Task Background The NRC Solar and Space Physics Survey Committee has just published, “The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics.” In addition, a NASA internal advisory committee has just completed a “Roadmap” for the Sun-Earth Connection, which is planning space missions as part of its Living With A Star and Solar-Terrestrial Probes programs. Richard Fisher, Director of NASA’s Sun-Earth Connection program, and prominent members of the solar and space physics community (e.g., Dr. Lennard Fisk, Professor and former NASA Associate Administrator for Space Science) are concerned that exploration of the outer heliosphere is the least thoroughly developed aspect of either strategy. The NASA Roadmap and NRC Decadal Survey emphasize that the baseline mission to explore the outer heliosphere—“Interstellar Probe”—is very exciting; however, its success requires significant technical developments, especially in the propulsion area. The recent NASA/OMB decision to seek funding for nuclear propulsion does not change the timetable for Interstellar Probe, but does indicate a higher probability that such a mission can be accomplished. In view of the long lead time to develop needed mission technologies, NASA is seeking a sampling of the current state of research in this field and the likely notable scientific questions that are likely to emerge over the next few years. Currently, the only NASA probes in the vicinity of this region are the Voyager spacecraft. Plan The Space Studies Board Committee on Solar and Space Physics will organize a workshop to explore issues related to NASA’s exploration of the outer heliosphere. Four areas will be targeted for special emphasis: The role of NASA’s Voyager 1 and 2 spacecraft. These missions should probably last another 15 years with V-1 reaching 140 astronomical units (AU). The magnetometer experiment should return to complete coverage after the spacecraft crosses the termination shock. One can regard the Voyagers as reasonably well instrumented for this portion of the mission. However, there are concerns regarding support from NASA Headquarters and the availability of continuing data coverage from the Deep Space Network of receivers.

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Exploration of the Outer Heliosphere and the Local Interstellar Medium: A Workshop Report Imaging the region of the termination shock and heliosheath. This capability is steadily increasing with several laboratories now working on experiments in this area. Imaging of energetic neutral atoms is a very promising area, with the technology probably outstripping theory at present. Such a mission could probably be accomplished within NASA’s MIDEX Program. For the interim period this might complement on-going Voyager activities well. Other remote observation possibilities include Lyman-alpha absorption and backscatter. Theoretical and modeling studies. Continuing studies are still needed in this area as illustrated by the numerous unsolved problems that Voyager and Ulysses continue to present. As in 2), above, theoretical studies lag observations substantially. Interstellar Probe. Mission technical requirements, payload, feasibility, etc., with a focus on propulsion issues/nuclear electric power. These areas will be explored in a 1.5-day workshop that would coincide with a regularly scheduled meeting of the committee. The results of the workshop will be published in a summary report that will be written by the committee; the report will not include recommendations. Schedule The committee will hold a 1.5 day workshop in late Spring/early Summer 2003. Writing and editing of the workshop report will be completed by December 31, 2003.