Constellation of spacecraft, and broadcasting method using said constellation

Abstract

In general, a constellation of spacecraft is used to broadcast to a particular region with high angles of view in order to reduce blockage or shadowing. A constellation of a plurality of spacecraft is placed in 24-hour orbits having inclination of about 550, eccentricity of about 0.32, semi-major axis of about 42,000 km, longitude of the ascending node of about 43° East, argument of perigee of about 270°, and longitude of the ground track at maximum latitude of about 7° East. The preferred number of spacecraft ranges from three to six. In a particular application of Digital Audio Broadcast to Europe in some embodiments, the most populous cities are provided with service from no more than about 10° from vertical, and broadcast takes place when the spacecraft are above at least 35° North latitude. The broadcast power is reduced during those portions of the orbit in which the ground track lies in the Southern hemisphere. (146)

Description

[0001] This application claims the priority of Provisional application 60 / 356,775 filed Feb. 15, 2002.FIELD OF THE INVENTION [0002] This invention relates to spacecraft constellations for broadcast communication purposes, and more specifically to spacecraft constellations which are particularly suited to broadcast service to particular portions of a heavenly body. BACKGROUND OF THE INVENTION [0003] Space-based Digital Audio Broadcast (DAB) systems provide a new type of service for distribution of CD-quality radio broadcast to mobile users such as automobiles and trucks. A salient property of Digital Audio Broadcast service is that it can be provided over a large geographic area when delivered from an overhead satellite. [0004] Several digital Audio Broadcast systems are in use to provide service to the continental United States (CONUS). The service operated by XM Radio uses two geosynchronous-orbit spacecraft. Ideally, the DAB transmitter is located directly overhead of all mobile u...

AI Technical Summary

Problems solved by technology

A disadvantage of the use of geosynchronous spacecraft is that the required orbit is such that for northern latitude coverage, the elevation angle of the spacecraft as seen from potential users may be less than 60°, where the elevation angle is measured from the horizon.

Thus, the XM Radio system has a potential for significant signal loss or shadowing, corresponding to loss of service, for at least some users or subscribers in northern latitudes.

This can be corrected by the use of terrestrial repeaters, but such repeaters undesirably increase the cost and complexity of the system.

When applied to DAB service for Europe, the high orbit inclination of 64.3° results in poor elevation angle performance to users in central and southern Europe.

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