KEY TECHNICAL ISSUES AND FINDINGS

New Paradigms for Satellite Design, Prototyping and Manufacturing

Clearly, satellite manufacturing is at a crossroads. The traditional pattern of highly specialized, customized satellites, designed and built a few at a time, is changing. More emphasis is placed now on the use of common buses and the use of CAD tools to customize the communications payload.

We are experiencing a move towards new mass produced systems. In this case many satellites are produced at once in an assembly line environment. Integration and testing is highly automated. The extent and nature of testing will be greatly reduced after prototyping and initial production is accomplished. The essence of this new systems design and mass production manufacture is represented by the Globalstar, Teledesic, and Iridium constellations. If this approach proves successful it will be widely emulated in future years. It is believed that such techniques can reduce the cost of satellites by a factor of two to four. There are clear signs that Korean, European and Japanese manufacturers are attuned to this new production approach and have already learned a good deal from direct participation in the Iridium and Globalstar projects in this regard.

Although such innovations started with U.S. firms, others are already actively learning and applying this approach. Clearly it is to be used with the 64 satellite Skybridge system (Sativod) of Alcatel.

New High Powered Platforms

One of the key technical trends in response to the deployment of LEO and MEO satellites has been the design of large aperture GEO systems with very high power systems. Power sub-systems in commercial satellites five years ago produced no more than 7 kw; now for systems such as Agrani, Thuraya and ACeS, power levels have jumped to 8 to 12 kw. Designers have begun to discuss large flexible or "floppy" (i.e., non-rigid) solar arrays generating 50 to 60 kw (see trends discussed in Figure 1.3). At the same time, intensive efforts are underway to improve solar cell performance (gallium arsenide/germanium, multi-junction cells), with promise of solar cell efficiencies above 30%. Work continues on solar radiation concentrators, for example in Project VIOLET.

There are parallel efforts to improve battery (i.e., lithium ion) and fuel cell technology in order to produce higher and higher powered satellites. Even nuclear power has been discussed by some longer range satellite planners.

Critical Future Technologies

A survey of world satellite telecommunications technologies has shown that dozens of key long-term technologies are needed for the 21st century. Critical technologies for future satellite communications systems are:

In addition, experimental satellites are perhaps needed that can be used to test out new technology that cannot easily be tested on the ground. At the systems level, the future of satellites could also be impacted by high altitude, long endurance platforms which would operate from 65,000 to over 100,000 feet, such as airships and loitering aircraft. Such systems could be used to substitute for satellite communications in regional applications or could be used in conjunction with satellites as a system capacity multiplier over populated areas. Most of the technology required for these systems has been developed under U.S. defense funding but is spreading to other countries such as Canada, Germany, Italy and the U.K.

Strategic Planning for Future Technology Development

A balanced perspective is needed as to the appropriate future direction of NASA's satellite communications program. What might be very useful would be the counterpart of the Japanese Vision 21 strategic plan, which is a broad roadmap to the future. This plan, which was independently developed by industry and policy officials, establishes information and telecommunications goals for the future of Japan and tries to see where gaps, overlaps and opportunities for the future may lie in terms of applications, services and technology.

A white paper on satellite technology could perhaps be developed by a coalition of representatives derived from NASA, industry and academia. Such a white paper could indicate a new consensus with regard to the 21st century role of satellite communications vis-a-vis The global information infrastructure (GII). Such a paper would be extremely helpful not only to the aerospace and telecommunications industry, but the U.S. government as well. This document would simply indicate, after extensive national collaborative input: (a) the technologies, systems, and services which it is believed that industry can develop on its own; (b) the technologies, systems, and services where it is believed that collaborative government/industry/university or even international collaborative projects are appropriate and needed (this should logically be reviewed and vetted by industry and university representatives); and (c) the technologies, systems, and services which the government will undertake to fill special niches with respect to public social needs and/or emergency services. No such clear roadmap currently exists for the United States.

Based on the findings of this study, a clearly defined and focused program in pre-competitive satellite communications technologies would seem highly desirable in the technology areas listed above.


Published: December 1998; WTEC Hyper-Librarian