The system design and characterization of a compact single-SDD (Silicon Drift Detector) module for X-ray and electron spectroscopy in a windowless, room-temperature, vacuum environment is presented. The module, characterized at room temperature with Iron-55 X-rays, demonstrated state-of-the-art performance: an energy resolution of 136 eV FWHM at 5.9 keV has been obtained with 1 µs filter peaking time, and its count-rate capability has been tested up to 4.2 Mcps with a 32 ns filter peaking time while maintaining an energy resolution of less than 200 eV FWHM at 5.9 keV.