Cooperative or networked navigation are terms used to describe an approach whereby members of a community (or network) exchange information to generate a navigation solution of higher quality than would have been possible if each had operated alone. There are many application in aerospace where cooperative navigation holds the promise of enabling new capabilities or enhancing existing ones. Examples capability enhancements in the operation of transport aircraft, small UAVs and CubeSat on deep-space missions are described. As will be shown, there are many technological and algorithmic challenges that must be addressed before networked navigation concepts become practical. One of the algorithmic challenges had to do with the design of suitable decentralized estimation algorithms. Challenges associated with decentralized estimation are discussed and solutions to deal with them are proposed. Flight tests results from community of small UAVs operating in a GNSS/GPS-denied environment is used to validate performance of the proposed algorithms.