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    POEMS Project

    This describes the POEMS instrument, as it was proposed in January of 1993 for a SMEX mission by a team led by Paul Evenson at the University of Delaware.

Scientific Justification:

Precise measurements of the cosmic positron-electron ratio, as a function of energy and time, are required to conquer one of the final frontiers in cosmic-ray research. Although the total positron plus electron spectrum is relatively well measured, the ratio of positrons to electrons is not well determined either from measurements or from theoretical arguments. The time variations and energy dependence of this ratio hold the key to answering many basic questions concerning the origin, acceleration, and interstellar propagation of galactic cosmic rays, the interaction of cosmic rays with the solar wind (solar modulation), and the acceleration of energetic particles in solar flares, in the solar wind, and at the outer boundaries of the heliosphere. To address these questions we propose a Small Explorer mission centered around a modified version of the POsitron Electron Magnetic Spectrometer (POEMS) originally selected for the EOS Polar Platform. POEMS will make fundamental contributions to the field of high energy particle astrophysics. Particle astrophysics research was cited as important for understanding violent events in the galaxy by the Astronomy Survey Committee ("Field Report"). Position-electron measurements specifically were recommended by the NASA Cosmic Ray Program Working Group (CRPWG) in 1982 and reaffirmed in its 1985 update.

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POEMS was selected for flight on the first EOS polar platform and successfully completed a Phase B definition study. In 1992 the CRPWG and the CHMOWG noted the de-selection of POEMS from EOS for budgetary reasons as one of the major problems facing the field. Subsequently the Space Physics Division commissioned a study (conducted by Ball Aerospace) of the possibility of implementing POEMS as defined for EOS on a free-flying spacecraft in low Earth orbit. The study concluded that this was completely feasible, but would require the use of a Taurus booster, the mass of the detector being somewhat beyond the capability of a Pegasus. In this proposal we demonstrate that relaxed magnetic cleanliness requirements allow a design that meets all scientific requirements with a major reduction in mass that puts POEMS well within the scope of a Small Explorer.

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Scientific Goals (SMEX)

We propose to make precise measurements of the energy spectra of cosmic electrons and positrons from 20 MeV to 2 GeV, and total electrons from 300 keV to 10 GeV, - with a time resolution of approximately one month - for a minimum of one year beginning in 1998. In addition we will make other measurements necessary for the interpretation of the primary data. Extension of the mission beyond one year would provide important additional data on time-dependent aspects of our investigation.

In addition to the Magnet Spectrometer (MS), the SMEX payload includes a second cosmic ray sensor, the Energy Extention Sensor (EES), will provide information on the electron spectrum below 20 MeV and on the particle environment at the spacecraft needed for interpretation of the primary data. 

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Payload Team Organization (SMEX-93)

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Page created and updated by Jacques L'Heureux
Last modified: August 6, 2003