Since GPS does not meet all the different user segment requirements, there are several GPS Augmentation Systems which have been developed to aid the accuracy and integrity of GPS. These systems enhance GPS by providing differential corrections to the basic satellite measurements to properly equip users. These corrections are based on the systems' accurate knowledge of the geographic locations of a network of reference stations. The corrections are then transmitted to GPS users who apply the corrections to their received GPS signals, with all processing being done without the human needing to be in the loop. NASA currently contributes to two such networks: International GNSS Service (IGS) and the Global Differential GPS System (GDGPS). NASA is also investigating the use of its Tracking and Data Relay Satellite System (TDRSS) to disseminate GPS differential corrections, integrity information, and other data to space users such as space weather.