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OVERVIEW The demonstrated capabilities of the Space Shuttle and rapid advancements in both ground- and space-based technology offer new opportunities for developing space systems for practical use. It soon may be possible, for example, to assemble large structures in space, to revisit and refurbish spacecraft, and to provide the large amounts of electric power in space that some uses would require. Large-scale integrated circuits offer new possibilities for control of spacecraft functions and for data handling that would be of great importance in certain applications. These and other capabilities may make it possible to carry out some activities in space at lower cost than before, and also to achieve objectives not previously considered realistic. In view of these capabilities and the anticipated national requirement for human presence in space on a long-term basis, the National Aeronautics and Space Administration (NASA) is studying the possibility of developing a manned space station and, in conjunction with the station, one or more unmanned space platforms. At NASA's request, the Space Applications Board (SAB) of the National Research Council conducted a study to determine the technical requirements that should be considered in the conceptual design of a space station and/or space platform so that, if developed, these spacecraft would have utility for practical applications. The SAB study, conducted in August l982, consisted of the deliberations of five user-oriented panels, one in each of the following areas: (l) earth's resources, (2) earth's environment, (3) ocean operations, (4) satellite communications, and (5) materials science and engineering. A sixth panel, Which dealt with system
design factors, helped examine areas of commonality among the requirements of the various applications. Each user-oriented panel was asked to consider what practical applications of space systems may be expected in their particular areas beginning about the year l990. The panels were asked also to identify technological progress that would need to be made and that should be emphasized in order for space systems with practical uses to have greater utility by the time a space station or space platform might be available. In addition, other issues of major importanceâe.g., the need for human presence in space, desired orbits of spacecraft, and major new devices that the various applications would requireâwere to be addressed. On l5 October l982, the Space Applications Board sent NASA an interim response based on the study. This formal report of the study consists of six chapters, one for each use area and one on system design. The following overview is a summary of the findings and recommendations of the six panels and some overall conclusions. The Earth's Resources Panel considered the application of remote sensing for assessing such resources as crops, forests and rangelands, minerals and petroleum, water, and land. Satellite remote sensing is a relatively new information source, providing a means to survey and inventory a wide array of earth resources. It provides a capability to monitor changes and, by predictive modeling, to provide a forecast for the future. Use of this new capability is still in its infancy, and much further study and development will be required for its full exploitation. A diversity of requirements for the several application areas were uncovered. However, some basic mission requirements seem to be common for virtually all applications. The most important of these are a space station, or an unmanned platform, in a low, near-polar, sun-synchronous orbit; a variety of sensors that can operate continuously and interactively; a data format that merges the outputs from a disparate set of sensors; timely delivery and archiving of data for the user communities; and a commitment to long-term continuity of data acquisition and distribution. Onboard data processing is important for almost all remotely sensed data streams, and a highly trained individual might be useful in the operation of the onboard processing system, although this might be accomplished by
ground control. A human presence would be most important during the research or exploratory phase of a new remote sensing program. Even in an operational phase, man's ability to identify transient phenomena, to monitor data quality, to adjust instruments rapidly, and to make in-situ decisions on data handling could prove useful. The Earth's Environment Panel addressed four broad applications of remote sensing: upper atmosphere research, global chemical cycles, weather, and climate. Several important roles for a space station were foreseen. First, it could permit use of many different sensors to make simultaneous observations of chemical species, with onboard processing and merging of the data. Second, a human presence could enable a frequent recalibration of instrumentation. In this respect, the station could play a valuable role in comparing data from onboard sensors with that obtained by other free-flying satellites. Other possibilities are the servicing of instruments, including the replenishment of cryogenic coolant and the periodic maintenance, repair, and replacement of sensor packages. Finally, a space station could facilitate the use of active sensor payloads, such as lidar or microwave sounders, which because of their large size and power requirements have been regarded as beyond the near-term capabilities of free-flying satellites. Most environmental observations would prefer a low, near-polar, sun-synchronous orbit. There are benefits and disadvantages associated with a human presence. On one hand, humans can contribute to the calibration and servicing of instruments. On the other hand, a number of potentially serious problems could develop, such as the impact of human presence on sensor pointing accuracy and stability, or the possibility of contamination in and around the vehicle. More study of the human role is required before a determination can be made. The Ocean Operations Panel looked at a wide variety of space applications, including coastal preservation, fisheries, oil and gas exploration, ocean pollution, sea ice monitoring, mineral extraction, and commercial shipping. There is a growing need for more and better data about the oceans. The needs are diverse, and are currently dispersed among many agencies, organizations, and individuals.
Only satellite-borne sensors can provide broad area data coverage of the world's oceans. Hence, more emphasis should be placed on collecting data and making it available to ocean users in a timely manner, on a daily basis for some users. Since data is required for regions that extend to the earth's poles, high-inclination orbits are desired for most applications. A low, near-polar, sun-synchronous orbit would fill most requirements. With regard to the benefits of a human presence, the Ocean Operations and the Earth's Environment panels came to the same general conclusion: there is no meaningful role for man in the acquisition of data. However, a manned space station could provide the capability for modification and repair of sensors and spacecraft in orbit. For example, the $l25 million Seasat oceanographic satellite probably could have been restored to operation if a means had been provided for its retrieval and repair. The Satellite Communications Panel surveyed projected communications services for the period from l990 to 2000 and concluded that a manned space station would offer little benefit during this period. In addition, communication satellites need to be located in synchronous, geostationary orbits. The launch capability provided by the Shuttle-Centaur combination is adequate for all requirements envisioned prior to the year 2000. However, some ancillary uses of a space station at low earth orbit were envisioned. The station might serve as a fuel depot and base of operations for assembling and launching satellites to synchronous orbit, with the possible benefit of reducing launch costs or allowing launch of heavier payloads. Also, use of a low-orbit station for conducting some communication experiments, such as the deployment and evaluation of very large antennas, is possible. The Materials Science and Engineering Panel envisioned a space station that would provide a laboratory staffed with technically trained operators. The materials community would make good use of a space station if it were to be developed. Several key requirements for a space station laboratory were identified. In addition to a low-gravity environment, materials processing requires a relatively large amount of electric power and needs facilities for
cooling hot materials in a controlled manner. The usefulness of a space station laboratory would depend, in large part, on the qualifications and experience of the technical staff manning the facility. The need for one or more trained scientists to perform the materials experiments is foreseen, with at least one experienced technician to maintain, repair, and modify the processing equipment. A space station could provide some important advantages over the current shuttle capability. Chief among these would be the much longer flight time and the possibility of less interference from firings of the attitude control thrusters. The ability to carry out weeks, or even months, of interactive materials experimentation in a space station would represent a great improvement over use of the Space Shuttle spacelab. The System Design Panel did not address a specific applications area; rather it focused on system design and integration issues that apply to the space station concept. Two novel concepts were identified for further study and analysis. One involves the use of real-time communication coupled with remote control to provide an operator on the earth's surface the capability to carry out complex operations within the space station. This real-time, closed-loop control is called telepresence, and is put forth as a complementary role to human presence for some space station operations. It features two new technologiesâwideband, high-data-rate telecommunications and computer-controlled robotics. Another concept is the development of a space service station, which would tend the in-orbit needs of unmanned satellites and space platforms. Functional capabilities would include repair, servicing, and replacement of expendables for various types of instruments and spacecraft. The System Design Panel recommended that NASA develop design rules for a number of important space station concepts, including system modularity, subsystem interfaces, and technology upgrading. Early definition of modular system architecture and subsystem interfaces would be very helpful in guiding industry's developmental work on a space station.
In summary, we find that most remote sensing applications require sensor payloads in a low, near-polar, sun-synchronous orbit. This suggests that the space station program should include a multifunctional sensor platform in a near polar orbit, with propulsion capability to accommodate mission-dependent orbit changes. The platform should include a variety of sensors to serve the many earth resource, meteorological, and ocean operations communities. We feel that if a space station is developed, its effective utilization will need significant resources beyond those required for the space station alone. There should be as much of a commitment to payload development as there is to the station itself. Therefore, it is essential that NASA consider not only the anticipated costs of developing the station, but also the envelope of total system costs, including payload development. Finally, we recommend that NASA give serious consideration to a novel system concept that we call telepresence. At a minimum, telepresence would provide an important complementary capability to the functions made possible by a human being in space. Rapid advances in space communications and robotics seems to offer great potential for real-time control of many space station or space platform operations by an operator on the ground.