We report the first year's on-orbit performance results for the Galaxy Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter modified Ritchey-Chrétien telescope with a 1Њ .25 field of view, selectable imaging and objectivegrism spectroscopic modes, and an innovative optical system with a thin-film multilayer dichroic beam splitter that enables simultaneous imaging by a pair of photon-counting, microchannel-plate, delay-line readout detectors. Initial measurements demonstrate that GALEX is performing well, meeting its requirements for resolution, efficiency, astrometry, bandpass definition, and survey sensitivity.

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By leveraging the existing Model‐Based Systems Engineering (MBSE) infrastructure at JPL and adding a modest investment, the Europa Mission Concept Study made striking advances in mission concept capture and analysis. This effort has reaffirmed the importance of architecting and successfully harnessed the synergistic relationship of system modeling to mission architecting. It clearly demonstrated that MBSE can provide greater agility than traditional systems engineering methods. This paper will describe the successful application of MBSE in the dynamic environment of early mission formulation, the significant results produced and lessons learned in the process.

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit m AB~2 0-21) to an ultra-deep survey of 4 square degrees (limit m AB~2 6). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (m AB~2 0-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey. SCIENCE OVERVIEWThe primary goals of GALEX are to address these questions:Local Universe Investigation: What are the UV properties of local galaxies, and how do rest UV properties, measured at high redshift by HST and NGST in their search for galaxy origins relate to star formation rate (SFR), extinction, metallicity, and burst history? Star Formation History Investigation:What is the star formation and metal production history of galaxies over the redshift range 0

Abstract. In May 2012 the Europa study team delivered to NASA the final reports on three distinct concepts for exploring Europa on a limited budget. The depth and quality of these reports have been widely praised by independent reviewers as well as by our sponsor. The application of Model Based Systems Engineering (MBSE) techniques is credited with enabling the team to study three quite different mission concepts for the resources normally sufficient to study only one or two. The Europa MBSE infusion itself has been awarded the NASA Systems Engineering Excellence Award in 2012. The Europa team is now preparing for its Mission Concept Review and has reaffirmed and strengthened the MBSE application. Significant new capabilities have been completed, most importantly the Powered Equipment List (PEL) and the computation of scenario-based power and energy margins. This paper provides an update on the continued successful application of MBSE in the dynamic environment of early mission formulation, the significant new results produced and several additional lessons learned in the process.