NeLS Research Center was formed in the end of 1997, and started the key technology developments of the low earth orbit constellation system for global multimedia mobile satellite communications service. For the NeLS constellation, 120 satellites with 1200 km of satellite altitude, was selected. For the satellite antenna developments, the digital beam forming technology was employed. In order to reduce the SSPA power consumption and to keep good linearity, novel pre-distortion type and distortion feedback type linearizer were developed. For the optical ISL system, de optical modem and optical tracking mechanism were developed. The optical DPSK/differential detection modem was evaluated. For the optical antenna mechanism, Coude type, the elbow type and the active universal joint type of optical antenna mechanism were developed. For the satellite network study, the satellite ATM network simulator was developed.