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The AMSAT OSCAR-40 (AO-40) spacecraft occupies a highly elliptical orbit (HEO) to support amateur radio experiments. An interesting aspect of the mission is the attempted use of GPS for navigation and attitude determination in HEO. Previous experiences with GPS tracking in such orbits have demonstrated the ability to acquire GPS signals, but very little data were produced for navigation and orbit determination studies. The AO-40 spacecraft, flying two Trimble Advanced Navigation Sensor (TANS) Vector GPS receivers for signal reception at apogee and at perigee, is the first to demonstrate autonomous tracking of GPS signals from within a H E 0 with no interaction from ground controllers. Moreover, over 1 1 weeks of total operations as of June 2002, the receiver has returned a continuous stream of code phase, Doppler, and carrier phase measurements useful for studying GPS signal characteristics and performing post-processed orbit determination studies in HEO. This paper presents the initial efforts to generate AO-40 navigation solutions from pseudorange data reconstructed from the TANS Vector code phase, as well as to generate a precise orbit solution for the AO-40 spacecraft using a batch filter.

This paper describes the formation of a partnership between two competing technologies with very different approaches to the problem of enhanced formation flying (EFF) on the New Millennium Program (NMP) Earth Orbiter (EO)-l mission. This includes a brief description of the two approaches that were independently proposed by the Goddard Space Flight Center (GSFC)/Stanford University and JPL teams. The actual mission combines these two approaches within a single autonomous control architecture called AutoCon™. The software is designed so that a control mode switch can be set by the ground flight operations team to invoke either EFF algorithm. The advantage of this approach is that both EFF technologies can be incorporated onboard EO-1 within the AutoCon™ framework. In addition, the details of each proposed algorithm need not be divulged provided that the algorithms conform to the specifications of AutoCon™. Forming a partnership between two competing technologies represents a significant programmatic challenge. This paper discusses the programmatic issues and several of the technologies that have been developed to perform the EFF mission. In the process, several recommendations are provided that should streamline similar partnerships on future NMP missions.