Miniature space GPS receivers have been developed by means of automobile-navigation technology. We expanded the frequency sweep range in order to cover large Doppler shift on orbit. The GPS receiver was modified to output pseudorange data with accurate time tag. We tested the performance in low earth orbits by means of a GPS simulator. The range error caused by the receiver is measured to be 1 meter. The position accuracy is estimated to be less than 17 meters (rms) in the low earth orbits. This GPS receiver was on-boarded on INDEX satellite, which was launched in 2005. Gold start positioning was confirmed repeatedly to finish within 30 minutes on orbit. The orbit determination was performed to evaluate the random position error of GPS receiver by means of the residual error. The random error of GPS position is as large as 2 meter for PDDP=2 on orbit. These results on orbit are consistent with the simulation results in use of a GPS simulator.
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