 laser facility. Spherically symmetric, laser-driven, millimeter-scale x-ray sources of K-shell and L-shell emission from various mid-Z elements were designed for the 0-00 keV energy range of the NXS. The absolute spectral brightness was measured by two calibrated spectrometers. We compare the measured performance of the target design to radiation hydrodynamics simulations.  The calibration campaign of the National Ignition Facility X-raySpectrometer (NXS) was carried out at the O