Using the Trek ultraheavy galactic cosmic ray collector onboard Mir, we have measured the abundances of even-Z elements from _(76)Os through the actinides in the galactic cosmic rays, with a charge resolution of approx 0.45 e, roughly a hthree-fold improvement in resolution over pioneering measurements by HEAO, Ariel, and UHCRE onboard LDEF. Building on the sccessful design of trek, we plan to design and construct ECCO, a large array of BP-1 glass track-etch detectors which would be depolyed on the International Space Station. ECCO, the Extremely Heavy Cosmic ray Composition Observer, would have sufficient charge resolution and collecting power to accurately measure the abundances of the very rare actinides with resolution and collecting power to accurately measure the abundances of the very rare actinides with respect to each other and with rspect to the platinum-group. These abundance measurements will strongly distinguish between models of GCR origih. We are verifying a promising new detector concept, which would result in significant cost savings, and would have several technical advantages over previous detector configurations; also, we are testing an advanced gas-transfer hodoscope for ECCO. Finally, we are constructing mockup ECCO modules for flight testing in preparation for a launch in 2003 and supporting an accommodation and design study for ECCO at GSFC.
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