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), polar-orbiting 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 ¿ 10-2 rad2/sec, while ~1.5 ¿ 10-5 rad2/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.