Systems that are formed by massively distributed mobile resources, such as satellite constellations, often provide mission-critical functions. However, many existing quality-of-service (QoS) management concepts cannot be applied to those systems in a traditional way, due to the continuously changing readiness-to-serve of their mobile resources. In this paper, we describe a case study that investigates a method called "opportunity-adaptive QoS enhancement (OAQ)." Driven by an application-oriented QoS objective, the method focuses on a solution that permits a structurally degraded constellation to deliver signal-position-determination (geolocation) results with the best possible quality. More specifically, the OAQ algorithm enables iterative geolocation accuracy improvement by letting neighboring satellites coordinate, and by progressively expanding the scale of this coordination in the window of a dynamically determined opportunity. For effectiveness demonstration, we de.ne a QoS measure and solve it analytically. The results show that the OAQ approach significantly enhances a constellation?s ability to deliver service with the quality at the high end of a QoS spectrum, even in presence of structural degradation.