| Popis: |
NASA Lewis Research Center (LeRC) is developing the space and ground segment technologies necessary to demonstrate a direct data distribution (D/sup 3/) system for use in space-to-ground communication links from spacecraft in low-Earth orbit (LEG) to strategically located tracking ground terminals. The key space segment technologies include a K-band (19 GHz) MMIC-based transmit phased array antenna, and a multichannel bandwidth- and power-efficient digital encoder/modulator with an aggregate data rate of 622 Mb/s. Along with small (1.8 meter), low-cost tracking terminals on the ground, the D/sup 3/ system enables affordable distribution of data to the end user or archive facility through interoperability with commercial terrestrial telecommunications networks. The D/sup 3/ system is applicable to both government and commercial science and communications spacecraft in LEO. The features and benefits of the D/sup 3/ system concept are described. Starting with typical orbital characteristics, a set of baseline requirements for representative applications is developed, including requirements for onboard storage and tracking terminals, and sample link budgets are presented. Characteristics of the transmit array antenna and digital encoder/modulator are described. The architecture and components of the tracking terminal are described, including technologies for the next generation terminal. Candidate flights of opportunity for risk mitigation and space demonstration of the D/sup 3/ features are identified. |
