CrossTrac Engineering, in cooperation with its subcontractors Dr. Suneel Sheikh of ASTER Labs, Inc, and Mr. Paul Graven of Cateni, Inc., proposes to develop a next generation star tracker capable of measuring the attitude of a spacecraft with mill-arcsecond accuracy. This unprecedented improvement in star tracker accuracy is achieved by tracking a single, bright guide star in the deep ultraviolet to soft x-ray bands (1 eV to 10 keV) using a differential measurement of guide star offset angle. The overall field-of-view of the Milli-arcsecond X-ray Star Tracker (MXST) will be limited to a fraction of a degree square with the highest accuracies achieved when the guide star is aligned with the star tracker boresight. This allows a simple, differential measurement to be made of the guide star location relative to the spacecraft coordinate system. By observing guide stars at high energy (short wavelength), the compact star tracker can achieve diffraction limited performance of one milli-arcsecond in a small, compact package.