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1 Introduction THE TASK The National Research Council's Aeronautics and Space Engineering Board established the Pane! on Small Spacecraft Technology to review the National Aeronautics and Space Administration's (NASA) plans for a new small spacecraft technology development program; review NASA's current technology program and priorities for relevance to small spacecraft, launch vehicles for small spacecraft, and small spacecraft ground operations; examine small spacecraft technology programs of other government agencies; assess technology efforts in industry that are relevant to small spacecraft, launch vehicles, and ground operations; and identify technology gaps and overlaps and prioritize areas in which greater investments are likely to have high payoff, considering the current and projected budgets, the NASA mission statement (see Appendix A), and the needs of industries that utilize space. Small spacecraft are variously defined within the aerospace industry as weighing less than 1,000 pounds, as weighing less than 1,000 kilograms, or as allowing the selection of a smaller launch vehicle. NASA uses the terms miniature spacecraft or micro-spacecraj! to imply the reduction of mass, volume, and components to allow downsizing by one or more launch vehicle classes over current practice (Hanks, 1993~. However, for consistency in this report, small spacecraft will be defined as those weighing approximately 600 kilograms or less. 6

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Introduction BACKGROUND AND STATUS In the past, NASA has focused a large percentage of its resources on the large manned system programs: Apollo, Space Shuttle, and Space Station. These types of programs not only have long duration and very expensive engineering and manufacturing phases, but commit NASA to very high operational costs extending over a period of ten to twenty years. Also, many of NASA's unmanned space programs such as the Tracking and Data Relay Satellite System, Viking, and the large observatories (High Energy Astronomy Observatory, Gamma Ray Observatory, and Hubble Space Telescope) cost hundreds of millions to billions of dollars during development and manufacture, and up to hundreds of millions of dollars in yearly operations costs. The national importance and visibility of these programs resulted in an environment in which the consequences of failure were so severe that any degree of technological risk to improve performance or reduce cost was unacceptable. It also brought about a large bureaucracy that included numerous levels of oversight review. in an effort to reverse this trend, NASA has indicated its intent to emphasize the use of small spacecraft to conduct the majority of its future space science and applications missions (Goiclin, 19931. This approach is intended to result in a space program with more frequent flights at markedly lower cost per flight. It is anticipated that such a program will engender a more aggressive approach to the application of advanced technology in its flight programs because of the higher tolerance for risk that will result from the much lower cost for each flight. NASA believes that this approach will also enable much shorter times from program initiation to flight (two to three years total), with the resultant greater versatility, improved responsiveness to mission requirements, and enhanced efficiency. Another stated objective is to develop technology and transfer it to industry, both in the aerospace and nonaerospace sectors, in order to enhance national competitiveness and stimulate the creation of jobs for Americans. The high cost of NASA's large space programs has resulted in minimal spending for advanced technology research and development, since most of the funds available to NASA have been spent in support of the large programs. As a consequence, much of the technology required to carry out future small spacecraft missions economically is not available from the NASA technology program. Fortunately, the Department of Defense (DoD), several of its agencies, and numerous industrial firms have had active small spacecraft technology development programs in the past, and the results of these efforts are now available for use by NASA. However, expenditures for national defense have been severely curtailed in recent years, and additional cutbacks are projected for the future. The United States is facing increasing international competition in the commercial space areas of communications, remote sensing, and in the launch vehicle market (Mintz, 1994; NRC, 1992; Pelton et al., 19921. If NASA is going to provide the leadership for itself and the commercial sector, it must maintain an evolving, long-term, continuous technology program specifically aimed at enabling future, highly demanding space missions at a reasonable cost. 7

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8 Technology for Small Spacecraft Space Systems Costs The overriding factor inhibiting access to space is cost. The cost drivers are the development and construction of the spacecraft, the mission sensors, the launch vehicle, launch and mission operations, and extensive testing and reviews to lower the perceived risk to an acceptable level. Advanced technology that has been sufficiently developed by NASA, other government agencies, and industry to permit incorporation in NASA small spacecraft can contribute to the reduction in cost for each of these elements and is addressed in this report. An effective way to lower launch costs is to reduce the weight of the spacecraft, including the mission payload sensors. For most spacecraft, the principal weight drivers are (~) electrical power systems, (2) propulsion and propellant systems, (3) structures, and (4) guidance and control systems. Payload instruments also can contribute significantly to the overall spacecraft weight (Auclair, et al., 1993; Davis, 1993; Larson and Wertz, 19921. Although not directly a technology issue, it is worth noting that the cost of developing and constructing the spacecraft can be influenced markedly by the customer and contractor program management implementation. NASA, DoD, and industry have demonstrated with recent small spacecraft technology development programs that simplified technical requirements, coupled with a design-to-cost approach and closely integrated engineering, operational, and manufacturing development activity, can reduce the cost of space missions. Such programs include the Small Explorer spacecraft program; the Miniature Sensor Technology Integration (MSTI) program; and the Microsats program.1 The panel believes these techniques can be successfully extended to future small spacecraft programs. Small Spacecraft Applications Technology has progressed so rapidly, particularly in the electronics arena, that much can be accomplished now with the use of integrated circuits, high-capacity computers, and small devices with large memory capability. In adclition, there have been impressive advances in miniaturized instruments, lightweight materials and structures, high-output and small power sources, and accurate position determination through use of the Global Positioning System (GPS). These technologies, combined with the changes in the approach to systems engineering, management, and operations processes, can ~ The Small Explorer program for science missions is sponsored by NASA's Goddard Space Flight Center (GSFC); the MST} program is sponsored by the Ballistic Missile Defense Organization (BMDO), the U.S. Air Force Phillips Laboratory, and the let Propulsion Laboratory (IPL) to test miniature sensor technology; and the Microsals program is sponsored by the Advanced Research Projects Agency (ARPA) to provide improvements to small spacecraft communications technology.

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Introduction permit small spacecraft to be far more efficient and cost effective, as well as to accomplish missions with much greater capability than previously believed possible. Using currently available technology augmented by a vigorous technology development program, the pane! believes that: . . . . For many missions, a small spacecraft can be used to achieve the mission requirements with capability approaching that of today's large spacecraft. The Small Explorer program is an example of a program that uses a small spacecraft to achieve significant scientific objectives. For many of the more demanding missions, small spacecraft can achieve a significant percentage of the mission objectives at much lower cost. The Mars Pathfinder program (formerly called the Mars Environmental Survey (MESUR)/Pathfinder program) is an example of a current effort to apply this philosophy to the unmanned exploration of Mars. It is likely that some missions requiring simultaneous measurements by multiple sensors can be accomplished with constellations of small spacecraft. Some missions that require larger, more complex spacecraft can be accomplished at significantly lower cost through application of technologies developed for small spacecraft. Not all small spacecraft missions are both faster and less expensive than large spacecraft, since technology research and development for miniaturization is costly. The pane} further recognizes that the use of multiple spacecraft in constellations may not be less expensive than large spacecraft. However, the use of small spacecraft in constellations distributes the risk among several spacecraft and launch vehicles rather than concentrating all the risk with one large spacecraft. This distribution of risk should result in a less costly systems engineering approach. Because of the lower cost to build and launch a small spacecraft replacement, the use of such constellations can enable a much more economical replacement of an instrument that fails on orbit than if it were one of several on a large spacecraft. A more detailed description of current and potential small spacecraft applications is given in Appendix B. Current Small Spacecraft Programs Although NASA's combined investments in large science missions (Voyager, Hubble, Galileo) are greater than its total investment in the more numerous small spacecraft missions, small spacecraft have served a long-standing role in NASA missions that predates the current enthusiasm for small spacecraft. Numerous space physics and astrophysics missions have been completed through the Explorer and Small Explorer programs, and JPL has participated in a number of DoD small spacecraft programs that sensed to advance component technology in several key areas. 9

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10 Terrestrial Probes. Technology for Small Spacecrap in order to transition from large, one-of-a-kind spacecraft to smaller spacecraft, NASA has initiated several programs. For example, the NASA Office of Space Science has initiated the Discovery program, which consists of a series of science missions that are intended to proceed from development to flight in three years or less at a development cost of less than $150 million each (FY 1992 dollars). The first mission, known as the Near Earth Asteroid Rendezvous, led by the Johns Hopkins University's Applied Physics Laboratory, is scheduled for launch in February 1996 (Leery, 19931. JPL is the leac' center on the Mars Pathfinder mission, the second Discovery mission, which is also projected for launch in 1996. JPL also has proposed the Pluto Fast Flyby mission. The goal is to launch two small spacecraft of less than 140 kilograms each on a direct trajectory to Pluto by 2001 (Staehie et al., 1993~. in addition, NASA has proposed the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission, which includes a system of probes to study little-known aspects of the Earth's upper atmosphere. TIMED is to be the first of the Office of Space Science's series of small spacecraft missions, known as the Solar in support of the emphasis on small spacecraft, the Spacecraft and Remote Sensing Division was created within the Office of Advanced Concepts and Technology (OACT) at NASA Headquarters. This division is responsible for the development of technology to reduce the cost and launch weight of spacecraft through miniaturized components, advanced instrumentation, operations technology, and sensors integrated into advanced design concepts. The Spacecraft and Remote Sensing Division is currently working with the Office of Space Science to develop and infuse advanced technology into three scientific small spacecraft missions: (~) the proposer! TIMED mission, (2) Mars Pathfinder, and (3) the proposed Pluto Fast Flyby mission (NASA/OACT, 19931. In addition to the technology infusion activities, OACT's Spacecraft and Remote Sensing Division has established a Small Spacecraft Technology Initiative. This program will demonstrate a new approach to technology integration. Two technology demonstration flights are planned within three years; each is designed to envelop a range of mission requirements and develop standard hardware and software interfaces for various applications. A Request for Proposal for the Small Spacecraft Technology Initiative was released February 28, 1994, with award dates scheduled for the second quarter of 1994. Programmatic and budget details of the Small Spacecraft Technology Initiative and current NASA programs are discussed further in Appendices C and D. The rate of progress of this initiative is in question, since it received less than one-half of NASA's requested budget for fiscal year 1994. As noted previously, DoD and its agencies have active small spacecraft programs. Appendix D gives a summary of those activities. In addition, a new small spacecraft industry is emerging, based to a large extent on past and current government programs. A listing of some commercial programs is given in Chapter 6 of this report.

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Introduction 11 APPROACH The Panel on Small Spacecraft Technology was established in late 1992 and met in January, April, May, June, September, and December, 1993. At the first three meetings, the entire panel heard over 32 briefings by representatives from many government agencies and industry and from other experts on small spacecraft technology issues. In addition, the pane! formed subpanels in several technical areas: (1) power and propulsion; (2) automation, robotics, and artificial intelligence; (3) materials and structures; (4) communications, guidance and control; (5) sensors; (6) launch vehicles; and (7) ground operations, infrastructure, and cost analysis. The subpanels conducted 23 site visits to various aerospace companies, NASA centers, and government laboratories. Appendix E lists the industry and government participants in this study. The panel membership is listed in the front of this report. At the June meeting, the panel met and discussed each subpanel's preliminary findings and recommendations. In December, the panel met to discuss and prioritize the overall findings and recommendations. In September and November of 1993, and January 1994, a writing team composed of several panel members met to work on the draft report. The data obtained by the panel during its meetings and site visits form the basis for this report. Detailed information on key, enabling technologies for small spacecraft are discussed in the venous chapters of the report along with specific findings ant! recommendations. Overall findings and prioritized recommendations on small spacecraft technology and NASA's small spacecraft program are noted in the last chapter of this report.