Communication spacecraft are widely used for communicating between earth stations, and are becoming more important for communications in regions of the world where other communication paths are not available. Ordinary geosynchronous spacecraft at their present state of development require expenditure of propellant in order to aid in maintaining their attitude andor station. When the propellant is exhausted, the utility of the spacecraft is ended, and a new spacecraft must be launched to take over the communication function. Thus, there is a substantial industry which engages in fabrication and launch of spacecraft, both for new communications functions, and to replace spacecraft which become inoperable.
The fabrication and launch of communication spacecraft has in the past been very costly, at least in part because each spacecraft was custom-designed and built for a particular use. Some attention has been directed to reducing cost in the fabrication of spacecraft by using common elements in spacecraft of a series of spacecraft. Thus, the dimensions of a spacecraft and of key portions thereof are increased in five-inch increments, as described in U.S. Pat. No. 5,344,104, issued Sep. 6, 1994 in the name of Homer et al., and common polygonal spacecraft shapes are described in U.S. Pat. No. 5,411,226, issued May 2, 1995 in the name of Jones et al. Aspects of each spacecraft which are unique to the particular mission which it is to serve have been more resistant to modularization. Thus, the attitude control and stationkeeping system must maintain the spacecraft in a particular attitude at a particular station, and must be adapted to that station. Similarly, the number of transponder channels, and their frequencies and power, tend to differ from one spacecraft to the next, and the configurations of the transmitters and channelizing arrangements differ correspondingly. The antenna footprint and operating frequencies also tend to differ from one spacecraft to the next, and antennas are ordinarily custom-designed. All these custom designs require the attention of skilled engineers, and fabrication of the custom design is expensive, and requires extensive testing, all of which increases the lead time.
Improved spacecraft are desired.