Interstellar space is filled with a gas of highly energetic ions and electrons, the galactic cosmic rays. These mysterious particles move at nearly the speed of light; despite decades of research, their origin remains unknown. Measurements of the abundances of the heaviest elements in the galactic cosmic rays, made using the Trek detector onboard Mir, are in dramatic disagreement with the most widely-held ideas about the origin of the galactic cosmic rays. Building on the successful design of Trek, we plan to design and construct ECCO, a large array of BP-1 glass track-etch detectors which would be deployed on the International Space Station. ECCO, the Extremely Heavy Cosmic Ray Compsoition Observer, would have sufficient charge resolution and collecting power to accurately measure the abundances of the very rare actinides (Th, U, Pu, Cm) with respect to each other and with respect to the platinum-group elements. These abundance measurements will strongly distinguish between remaining models of GCR origin. Further, if, as many expect, the GCR nuclei are younger than approx 10 My, ECCO will measure for the first time the primary actinide nucleosynthetic yields, which are important but unknown parameters in calculations of the age of our galaxy using the actinides as clocks. ECCO would also carry out the most sensitive search to date in the GCRs for the long-sought superheavy elements. Elsewhere, we have described the scientific goals of ECCO; here we describe the mechanical design of ECCO and present options for EVA and EVR deployment on ISS.
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