The last several years has seen an emphasis on the development of numerous complementary Positioning, Navigation, and Timing (PNT) approaches to provide resilience to current and emerging threats to the Global Positioning System (GPS). The integration of these approaches into new and existing systems has been challenging due to the diversity of Department of Defense (DoD) missions, platforms, and interfaces. Within PNT, there is growing interest to employ Modular Open System Approaches (MOSA) in development activities in order to address this challenge, thereby enabling faster technology refresh, cost savings and avoidance, and increased interoperability. Utilizing modular design principles and open standards enables PNT systems with architectural flexibility allowing new capabilities to be more rapidly integrated and deployed.

The Office of the Under Secretary of Defense (OUSD), Research and Engineering (R&E) has initiated an effort to develop MOSA implementations for PNT. The goal is to enable consistent acquisitions and interoperability across PNT programs by providing a common data standard for PNT systems. The data standard use the Defense Advanced Research Projects Agency (DARPA) interface control documents created for the All Source Position and Navigation (ASPN) program. Many companies and projects continue to implement and use ASPN, though some problems have arisen in the years since the last major ASPN update.