A satellite-navigation system comprises an observer platform for collecting signal observations from orbiting navigation satellites. A server platform provides a simplified navigation-satellite constellation almanac, ephemeris, differential correction, and client services. A navigation platform passes information between the observer and server platforms and provides for autonomous position solution computations for a limited time after a periodic call for an aiding data from the server platform. A measurement platform included in the server platform makes static observations of a navigation-satellite constellation and that builds a database of measurement errors and satellite data messages. An aiding data with light-weight models is provided by the server platform to the observer platform to eliminate all data storage of almanac and ephemeris, and to permit only fixed-point integer arithmetic to be used to solve for user position at the navigation platform.