In Phase II, XNAV performance will be enhanced through the development of single photon processing algorithms, which utilize all available photon time data to improve the accuracy of XNAV. A detailed model of the XNAV system, including single photon techniques will be implemented in Orbit Determination Toolbox (ODTBX), increasing its functionality and providing a valuable mission design tool. ODTBX will be further refined by enhancements to detector and source models, including addition of new pulsars as their properties are better determined (including low flux sources). Time transfer and barycenter correction effects will be added. XNAV measurement types will include additional absolute range measurement types and range rate measurements. Functions developed for ODTBX will provide support for XNAV and XTIM studies including: enhanced dynamic functions and linearized process models for inclusion of clock and other bias states; and performance prediction for the single photon processing approaches. The team will work with NRL, JHU/APL, and NASA GSFC, focusing on sources and detectors to develop improved models, and assessing timing accuracy. This work will further validate the utility of XNAV for NASA, and develop and test relevant new technology to provide a rapid path to full flight software development should opportunity arise.