10. GEMS
Jean Swank, Tim Kallman & Keith Jahoda (GSFC)

As the Science Mission Directorate (SMD) announced at the June AAS meeting and the July Astrophysics Subcommittee meeting, they decided not to confirm the Gravity and Extreme Magnetism Small Explorer (GEMS). On Sept. 10, 2012, SMD directed the GEMS project to terminate the project and provide a close-out plan. This was provided and on Sept. 28, was accepted. The Instrument and Mission Preliminary Design Reviews held Feb. 21-24 were judged to be very successful by the review boards, with the conclusion: "Overall project meets or exceeds PDR success criteria; numerous subsystems well beyond PDR level". However, SMD and the review board solicit Cost Reviews from organizations external to NASA. These estimated that there was a 50% chance that completing GEMS would cost as much as 25% more than the real year cost agreed upon with SMD in Apr. 2011. This was the reason given for termination. An independent assessment was carried out at the request of the Congressional Subcommittee on Commerce, Justice, Science, and Related Agencies. This assessment agreed that SMD had enough information for their decision and Congress raised no objection to the termination. GEMS is closing out with the flight parts in hand for two polarimeters, plus subassemblies that could be assembled into a prototype detector to verify lifetime and performance. The design and performance were described in Hill et al. and Baumgartner et al. at the 2012 SPIE meeting 8443. Foils and housings for two flight mirrors will be put into storage ready for testing. The GEMS team hopes that a sensitive X-ray polarimeter will be flown in the near future.

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