Communication Satellites

Complex nonconstant envelope high-order digital modulation schemes used in modern communication satellites bring new requirements for the linearity and power efficiency of the on-board traveling-wave tubes (TWTs). As a result, a reassessment of typical TWT specifications is required. A digital system-level figure-of-merit, the total degradation, is proposed. It accounts for the characteristics of any coded signaling scheme, as well as

Optimal design and experimental verification of a magnetically actuated optical image stabilization system for cameras in mobile phones. ... OIS) is proposed, which is installed inside the limited inner space of a mobile phone. ... Photography, photographic instruments; xerography. ...

On ESA's large communication satellite OLYMPUS a set of three orthogonally arranged microaccelerometers is installed. The aim of this experiment is to characterize and observe the behavior of the different mechanisms in space and to get measurements of the vibration levels which are of relevance for the design of optical communication payloads. During the commissioning phase of the spacecraft in August and September 1989, a lot of data recordings were made. The measured acceleration spectra show a higher than expected amount of vibration in the frequency region above 100 Hz. The most disturbing vibration sources, solar array drive, thruster firing and waveguide switching, and the transmission through the spacecraft structure cannot be characterized precisely enough by on-ground measurements. This confirms that measurements in space are mandatory before flying an optical payload. In this paper the equipment on board OLYMPUS will be briefly described, followed by presentation of typical measured data. The main emphasis is on the discussion of the importance of the measured data for the design of optical payloads. The optimal tracking control loop transfer function for a transient will be presented for the first time.

: Since the end of the Cold War, the availability of new technologies and changes in the national security environment have raised the possibility of substantial new demand for military space systems. Trends in technology, military operations, politics, and economics highlight several possible trajectories for national security space policy. Decisionmakers in the United States and in Europe are preparing today to make key choices about military doctrine, resource investments, and the policy goals that leaders hope to achieve using military operations that rely on space assets. The wish-list for new space systems includes improved intelligence-gathering satellites, navigation satellites to enable precision strike against fixed and mobile targets, and communications satellites to allow decentralized forces to share access to information and coordinate operations in a complex environment. Both the U.S. and European governments may find it useful to cooperate on national security space ...

Several prediction methods for rain attenuation are evaluated using a common long-term data base (total 124 sets of measurements) for oblique propagation paths with frequencies of from 10 to 20 GHz, and an improved prediction method reflecting the evaluation results performed is proposed. The evaluation results indicate that CCIR methods give relatively high precision, although in this respect, there is

NASA is currently the only U.S. government agency developing advanced technology on behalf of the commercial communications satellite industry. The Agency's commercial communications program includes several activities which are either directly or indirectly related to the potential use of satellites within a broadband integrated services digital network (BISDN). Lewis Research Center's Space Electronics Division is actively pursuing a number of