Japan has been investigating the use of an airship system that will function as a stratospheric platform (SPF) for applications such as environmental monitoring, communications and broadcasting. If pseudolites were mounted on the platforms, their GPS-like signals would be stable augmentations that would improve the accuracy, availability, and integrity of GPS-based positioning systems because the airship network would cover all of Japan. The accuracy of the pseudolite positions would be a limiting factor for such a service since the pseudolite ‘ephemeris error’ is more serious than GPS due to the lower height of the platform. In this paper, a conceptual design of the SPF-based augmentation system is first introduced. Then some schemes for estimating the pseudolite position are described.