Direct Data Distribution from Low-Earth Orbit

NASA Lewis Research Center (LeRC) is developing the space and ground segnumt technologies necessary to demonsUa_ a direct data distribution (D 3) system for use in space-to-ground communication links fzom spa_r_ in low-Earthorbit (LEO) to strategically located tracking ground terminals. The key space segment technologies include a K-band (19 GHz) MMICbased transmit phased array antem_ and a multichannel bandwidthand power-efficient digital encoder/modulator with an aggregate data rate of 622 Mb/s. Along with small (1.8 meter), low-cost tracking tenuinals on the ground, the D 3 system enables affordable distribution of data to the end user or archive facility through mterol_rability with commercial terrestrial telccommunic,_ionsnetworks. The D 3 system is applicable to both government and commercial science and communications spacccraR in LEO. The features and benefits of the D3 system concept are described. Starting with typical orbital characteristics, a set of baseline requirements for represmtative applications is developed, including requirements for onboard storage and tracking terminals,and sample link budgets are presented. Characteristics of tbe transmit array amenna and digital cacoder/modulator are described. The architecture and components of the tracking terminal arc described, including technologies for the next generation terminal. Candidate flights of opportunity for risk mitigation and space demonstration of the D 3 features are identified.