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In this paper we revive an experiment carried out by NASA more than decade ago now called micro-GPS. Based on SDR, the GPS receiver is implemented in software and operates in different modes depending on the battery status, autonomous, assisted, and passive. In autonomous mode, the receiver performs all the standard tasks including acquisition, tracking, navigation data decoding, and positioning. In assisted mode a long term ephemeris is uploaded in memory by the ground station and the receiver works in snapshot mode, processing 20ms of data every epoch and going to sleep between measurements. In passive mode, the receiver just records snapshots of RF data every epoch and downloads them to the ground station when possible.