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The "Spectroscopy of Plasma Evolution from Astrophysical Radiation" (SPEAR, also known as the "FarUltraviolet Imaging Spectrograph") instruments, flown aboard the STSAT-1 satellite mission, have provided the first large-area spectral mapping of the cosmic far-ultraviolet (FUV; 900-1750 ) background. We describe the A mission and its science motivation, the mission data and their processing, and the effects of mission performance on the science data. We present the first map of the cosmic FUV background (1360-1710 ) over most of the A sky as an example of the mission results. These SPEAR data reveal diffuse radiation from warm and hot (10 4 -10 6 K) plasma, molecular hydrogen fluorescence, and dust-scattered starlight. They allow for an unprecedented characterization of the spectral emission from a variety of environments, including the general interstellar medium (ISM), molecular clouds, supernova remnants, and superbubbles.

[1] Energy spectra of electron microbursts in the energy range 170-360 keV have been measured in the outer radiation zone by the low-altitude (680 km), polarorbiting Korean satellite STSAT-1. These electrons are the lower energy population of relativistic microbursts. Our observations show microburst energy spectra of precipitated electrons inside the loss cone (precipitated) have higher e-folding energies during disturbed times than quiet times. The loss cone at these energies is empty except when microbursts abruptly appear and fill the loss cone in less than 50 msec. This fast pitch angle diffusion requires diffusion coefficients larger than $3.5 Â 10 À2 rad 2 /sec, while $1.5 Â 10 À5 rad 2 /sec was proposed by a wave particle interaction theory. The source of microbursts remains unknown as our observations are not adequately explained by wave and particle resonant interaction models.

To prepare for a Korean lunar orbiter mission, a precise lunar orbit propagator; Yonsei precise lunar orbit propagator (YSPLOP) is developed. In the propagator, accelerations due to the Moon's non-spherical gravity, the point masses of the Earth, Moon, Sun, Mars, Jupiter and also, solar radiation pressures can be included. The developed propagator's performance is validated and propagation errors between YSPOLP and STK/Astrogator are found to have about maximum 4-m, in along-track direction during 30 days (Earth's time) of propagation. Also, it is found that the lifetime of a lunar polar orbiter is strongly affected by the different degrees and orders of the lunar gravity model, by a third body's gravitational attractions (especially the Earth), and by the different orbital inclinations. The reliable lifetime of circular lunar polar orbiter at about 100 km altitude is estimated to have about 160 days (Earth's time). However, to estimate the reasonable lifetime of circular lunar polar orbiter at about 100 km altitude, it is strongly recommended to consider at least 50 × 50 degrees and orders of the lunar gravity field. The results provided in this paper are expected to make further progress in the design fields of Korea's lunar orbiter missions.

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