The Future Of Mission-Driven Technology
By D.K. Sachdev
As the satellite industry works its way out of the recent downturn, the entire community watches with legitimate interest and some trepidation about any news of industry consolidation, ownership changes and merger & acquisition activities. The interest seems universal among satellite professionals worldwide.
While such changes will have a measurably positive impact on the future viability of this industry, we also should take note of the somewhat hidden but important role of advancing technologies almost across the board.
The manner in how new satellite technologies have been developed and harnessed has changed quite a bit over the years. Thus, the number of experimental satellites dedicated to the in-orbit qualification of specific technologies and for the validation of potential new applications has declined considerably, especially in the United States. Similarly, the substantial technology development funding that used to flow out of intergovernmental satellite operating organizations decreased substantially even before such organizations were privatized.
Fortunately, technological advances still are taking place. The advances are driven more often by specific missions and/or business sectors rather than by structured research and development programs. Thus, national and international space-research organizations continue to develop and to harness specific technologies needed for their ever-fascinating objectives. Military missions, particularly after the recent impressive display of what modern satellite systems can do, are introducing advanced technologies across the board, including some revolutionary IP-based system concepts that are part of what has been called the Global Information Grid (GIG). Commercial systems, despite their recent downturn, are not sitting still either. As this industry segment inexorably moves towards Direct-to-User (DTU) services, it is funding specific technologies for such systems. Examples principally include more capable DBS, and digital satellite radio, broadband and mobile systems.
A fascinating transition involving these mission- and business-driven technology initiatives has been taking place for the past several decades. That shift involves visible synergy between the end-to-end service objectives of quite a few military and commercial satellite systems. The military systems always have emphasized the need to access the front-line soldier, sailor or airman on the move, even when technological limitations made such access quite costly. In the last few years, however, the commercial systems are quite rapidly catching up with this universal ubiquity requirement, thanks to multiple technological advances coming together for a series of DTU systems. While in some respects the military requirements would remain unique, this growing commonality of the basic system objectives between the two groups of users is leading to several common technological objectives that are beneficial to all types of missions and businesses.
The following examples of major technologies feature applications for both commercial and military missions.
Large Deployable Reflectors
Military missions and advanced technology organizations like the Defense Advanced Research Projects Agency (DARPA) started sponsoring qualification of large deployable reflectors several decades ago at a stage when the commercial systems were by and large content with rigid reflectors (perhaps with some foldable flaps) that could fit in the launch vehicle shrouds. Today, a number of commercial systems, notably the DTU systems for broadband and mobile services, also are calling for large deployable reflectors. This trend is likely to continue, driven by the need to access small terminals via large numbers of spot beams to deliver ever increasing content.
For several decades, while frontline commercial antenna technology was emphasizing efficient frequency reuse, some of the military systems were emphasizing the ability for rapid in-orbit reconfigurability. That flexibility applies to pointing and the size of the spot on the ground. Commercial systems now are beginning to exploit similar technology. The new Spaceway satellite system, slated for launch next year, will use phase-array technology with the ability to create Ka-band pencil beams on demand at any point in its coverage area.
Digital Coding Techniques
As long as there have been digital links, they have recognized the benefits of coding in terms of higher capacity in a given bandwidth, lower error-rates, more efficient use of available power or all of the above. Satellite systems in particular, with their limited power, generally have been at the forefront in advancing and using newer coding schemes and techniques. Notable examples are transmissions from millions of miles away from deep-space missions as well as, nearer to home, high quality sound and video quality for satellite broadcast systems. Military systems, with their emphasis on direct user access from the very beginning, also have been at the forefront of this technology.
After decades of incremental advances in coding techniques, a quantum leap forward was taken in 1993 with the discovery of turbo codes that moved toward the theoretical limits of capacity predicted by Claude Shannon in 1948. A host of applications have begun to exploit such codes, including some previously formulated but not adequately recognized codes, for the entire spectrum of missions. Those missions include a new deep-space probe, named SMART-1, and 3G cellphones. Military systems with their high data-rate requirements to and from very small portable terminals will no doubt benefit from these advances.
Direct or cross-links between satellites in orbit have been a potential architectural tool for satellite systems from the very beginning. The basic technology was demonstrated for the military as early as in the 1960s. The first major publicly known application was for the NASA Tracking and Data Relay Network (TDRS) that provides inter-satellite links between geostationary nodes and a variety of low-Earth-orbit (LEO) missions, including the Shuttle, Hubble and many others.
The Iridium global system was the first major commercial system to use cross-links throughout the network. In addition, several other technology demonstration links have been successfully flown, establishing both microwave and optical technologies. The new Transformational Communication Architecture (TCA) of the U.S. military will be a major operational application of such cross-links in several satellite systems now under the design and planning phase. This architecture is likely to advance new commercial applications as well, and it should further integrate satellite-based systems with global IP networks.
For quite sometime, programmable semiconductor devices have been used during the design process of a typical radio receiver in order to optimize its performance before converting the design to its final hardware configuration, often in the form of Application Specific Integrated Circuits (ASICs). Typical recent examples are satellite radio receivers. While such design processes are quite efficient, they do not provide adequate flexibility to be able to change the basic system parameters once such devices are deployed in large numbers. Successive and even concurrent generations of military satellite systems often require dedicated receivers that are incompatible with each other.
Incompatible cellphone standards are another familiar example. On a broader scale, several recent studies have recognized that a much larger number of users could be accommodated in the current frequency bands if receivers with the flexibility to switch between bands and modulation techniques were widely available. In a limited way, we already are users of such flexibilities in our cordless phones and Wi-Fi networks. Military applications have taken a lead in this area, launching major efforts for a range of software- defined radios that can access multiple systems as needed. Once the power consumption and costs of such devices come within the affordable range, we can look forward to a host of such devices in the commercial systems as well.
In summary, satellite technology development is keeping pace with the evolving needs of the users. The synergy between military and commercial system objectives is beneficial in expanding the range of options to all prospective users. While it is conceivable that such mission-driven technology programs may leave some gaps in the range of technologies likely to be needed in the future, a benefit of this trend is that promising technologies will be developed to a much more mature level with less ambiguity about their costs and capabilities in future operations.
D.K. Sachdev is president of SpaceTel Consultancy of Vienna, Va. He can be reached at 703/757-5880 or by e-mail at firstname.lastname@example.org