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2 Systems Engineering and Operations BACKGROUND AND STATUS Major factors in space system costs are the launch and mission operations. Since the ultimate cost is determined at the time the system is designed, operations must be a major consideration during the initial systems design. The emerging small spacecraft industry has been supported to a significant degree by ARPA and BMDO and, to some degree, by the Small Explorer and the MST! programs. These agencies have largely abandoned the design, development, and systems engineering practices employed by producers of large spacecraft systems. The companies that develop small spacecraft systems are also creating new approaches to launch and mission operations that are simpler and much less costly per mission than their larger counterparts. Several companies and consortia are currently engaged in the design of new communications systems that employ low-Earth-orbit constellations of small, low-cost spacecraft, which will have graceful system degradation and shorter transmission delay than is achievable with geosynchronous orbits (Seitz, 1993a; Seitz and de Selding, 19931. Numerous agencies and companies are engaged in small spacecraft activities. Several examples are included in Table 2-~. Some of these programs are successfully demonstrating systems for tracking, telemetry, and mission data operations that employ, when appropriate, the latest standard commercial communications equipment, data processing equipment, and software, as well as substantial automation technology, to reduce cost while maximizing performance. It has been demonstrated that such systems can provide sophisticated services with high reliability at costs well below those achievable with the conventional approach, and they can do so in much shorter periods of time. It also has been demonstrated that a fundamental design philosophy for minimization of costs is to design, build, and operate the system with minimal personnel and only the absolutely necessary documentation. Broad application of these techniques in combination with new technology development programs can have a major impact on the cost and utility of future NASA and commercial space systems. 12
Systems Engineering and Operations TABLE 2-l Examples of Current Small Spacecraft and Launch Vehicle Activities 13 AGENCY/COMPANY NASA GSFC JPL BMDO/U.S. Air Force Phillips Lab oratory /IPL BMDO/Naval Research Laboratory (NRL)/NASA ARPA/Defense Systems Incorporated/ U.S. Air Force Orbital Sciences Corporation Lockheed/Motorola/Iridium Inc. Ellipsat Starsys Global Positioning, Inc. SMALL SPACECRAFT/LAUNCH VEHICLE ACTIVITY Small Explorer Program Mars Pathfinder Miniature Sensor Technology Integration Program (MSTI) Deep Space Program Science Experiment (Clementine) Microsats, DARPASAT Space Test Experiment Platform (STEP) Pegasus, Taurus, Orbcomm, Pegastar LEV- I, IRIDIUM Ellipso Starsys SMALL SPACECRAFT SYSTEMS ENGINEERING The initial phase of a program is very important in establishing the methods by which cost will be reduced. Decisions involving trade-offs among mission objectives, mission operation concepts, system and subsystem performance, life-cycle cost, schedule, risk, and reliability can have a large impact. These trades should be performed as the first step, before committing to a specific spacecraft configuration and design approach. By utilizing advanced technology on small spacecraft, increased capabilities can be achieved for a wide variety of missions, with only small reductions in performance relative to the performance of large systems. These trade-offs could result in substantially different system configurations. For example, several small comnlementarv spacecraft with specific capabilities could be used in combination to achieve the -or ~ ~ -~--~ -r - ~ - - - - - -- - - - - --- - -- ~ . . . . . . ~ . ~ . . . ~ . ~ _ . . . . . total mission objectives. Alternatively, a higher failure rate could be accepted by using new technology that has not yet been qualified by space flight but that offers a large advantage in cost, weight, or performance. A complete backup could be provided in case of failure, and the cost might still be lower. Since personnel costs associated with ground operations have been shown to be a major contributor to space system life-cycle costs, systems trade-offs may require the shifting of ground functions to the spacecraft for more autonomous, lower-cost space operations (Larson and Wertz, 1992~. In other cases, however, lower system costs may result from shifting functionality to Earth-based, yet automated, facilities. Furthermore, since many past failures
14 Technology for Small Spacecraft have resulted due to human error, technology that reduces the number of personnel can possibly reduce the risk of failure. Some key technologies that may play a role in determining these trade-offs are miniaturized digital electronics; built-in self testing; expert systems techniques; high-density, solid-state memory; on-board communications and data processing; autonomous GPS navigation, guidance, and spacecraft attitude control; and massively parallel computers employed in open system architectures, often using commercially available hardware and software. Another important trade-off concerns selection of the launch vehicle and the desirability of a spacecraft having compatibility with several different launch vehicles. The venous launch vehicle options that can be considered are (~) use of one of the existing or one of several soon-to-be-available small spacecraft launch vehicles; (2) use of a medium launch vehicle that can launch several small spacecraft at once; or (3) use of a medium or large launch system (e.g., the Space Shuttle) that can launch a small spacecraft in conjunction with other payloads. Currently, models and simulations of the trade-off process cover costs of the systems engineering, design, and production of the spacecraft with minimal consideration of the life-cycle costs, which frequently are a large part of the overall commitment. There is little published data on small spacecraft costs, so there is some probability of error. However, significant improvement in accuracy over current costing practice could be achieved with modeling that includes a database of recent small spacecraft costs. Several other factors not necessarily involving technology have a major impact on the cost of a small spacecraft program. A number of guidelines to reduce cost of small spacecraft are listed below: Use a design-to-cost philosophy, which permits achievement of most of the original objectives with resources available to the program. Use small, integrated product development teams for design, manufacture, test, launch operations, and Hight operations. Preferably, the engineers who design the system will also use the system. The result is simpler, easier-to-operate systems, such as the Microsats spacecraft. Keep outside oversight at an appropriately low level with emphasis on personal accountability of the individuals doing the work. Maintain close, well-coordinated relationships among users, operators, and funding sponsors that enable straightforward and rapid negotiation of key requirements. Compare the use of existing launch facilities and infrastructure versus the employment of small spacecraft launch facilities and innovative mission operation concepts and architectures. To the largest extent possible, use off-the-shelf hardware and software. This may require innovation to allow the use of technology that has not been flight qualified. For example, the Solar Anomalous and Magnetospheric Particle Explorer (S AMPEX) program was able to use a standard commercial microprocessor that was not radiation hardened by
Systems Engineering and Operations . placing it in a location that was protected from space radiation by other elements of the spacecraft. Provide as much on-board data storage and processing as possible, combined with data compression techniques, to minimize the frequency of ground-station interaction. A large memory also allows more commands to be installed for later execution and a programmable memory permits later alteration. SMALL SPACECRAFT LAUNCH OPERATIONS The cost of launch operations can be a major factor in total space system costs. High costs result when a large number of people and extended periods of time are required to prepare the launch vehicle and the spacecraft after reaching the launch site. The high cost of such systems requires a highly reliable launch. This demands extensive oversight and review activities, which place additional burdens on the launch crew. All launch operations are inhibited by several payload and operational constraints; for example, the early need of the payload for vehicle integration, inability to access the payload during the countdown, compliance with range rules and overflight restrictions, and extensive safely requirements associated with very energetic propellants and ordnance. Technologies, as discussed below, can be used to ameliorate several of these constraints and lower the cost of launch operations. Spacecraft/I,aunch Vehicle Checkout and Health Monitoring The task of ensuring that the space system is functioning properly is a large consumer of manpower and equipment. The ability to ship the flight vehicles directly from the factory to the launch site and to launch without further testing except to verify interfaces between the spacecraft and the launch vehicle would be optimal. This idea can be approached through the use of on-board health monitoring and, where economical, fault correction. The DoD agencies have made extensive use of built-in-test capability to simplify operations and reduce equipment and personnel requirements in the field for aircraft and missile systems. Under the National Launch System program, which was terminated, the U.S. Air Force sponsored architecture and instrumentation technologies to monitor vehicle and engine system health. Many of these developments could have application to small spacecraft and launch vehicles. In addition, NASA has ongoing technology efforts to evaluate architecture, instrumentation, and software for both vehicle and propulsion system health monitoring. NASA also currently sponsors a center of excellence at the University of Cincinnati for condition health monitoring. For those checkout requirements that demand extensive ground equipment, the number of people and the amount of equipment could be reduced by using a single set of checkout equipment located at the factory. The equipment could communicate by data link with the vehicle at the launch site. Data could be transmitted over commercially 15
16 Technology for Small Spacecraft available systems, utilizing, if necessary, data storage and reconstitution devices for overload conditions. This approach could reduce the number of people at the launch site who are often idle between launches. For example, the Radio Amateur Satellite Organization has successfully used personal computers to interface with its spacecraft during launch and reduce the personnel required. With the use of existing launch vehicles, if anomalies are detected during the launch process and a component or subsystem must be replaced, there is often the need to restart the countdown (or a major portion thereof). The result is long delays, missed opportunities, consternation, and cost increases. New launch vehicles and components should be developed that permit component or subsystem replacement without the need to restart the preparation process from the beginning, while still bearing in mind the requirements for pad and personnel safety. Spacecraft/Launch Vehicle Integration The time required to verify the spacecraft/launch vehicle interfaces during integration is a function of the complexity of the interfaces. This can be an especially complicated problem when using a launch vehicle that must accommodate numerous spacecraft configurations. Several contractors and government agencies are pursuing the development of standard spacecraft buses. This issue has been addressed to some extent in the Ariane program by providing a standard interface, which greatly simplifies the integration of very small spacecraft. However, since there is no coordination between various agencies and companies, existing launch vehicles must still accommodate several different spacecraft configurations. Standardization of components and system architecture offers an opportunity for time and cost savings. Standardization at the interface level, with the resultant reduction in interface negotiations, documentation integration, and checkout effort, could produce large cost savings. While this approach might require some degree of mission-specific cabling, the majority of the interfaces could be standardized. Range Safety Considerations One of the current unavoidable costs in launch operations is that of range safety tracking, which is done using a series of ground radars that track the launch vehicle's flight. A range safety officer monitors the trajectory ano initiates a destruct command if the launch vehicle displays performance that is outside of preset limits. Much ground equipment and many maintenance and operations personnel could be eliminated if a highly reliable and accurate on-board system for determination of trajectory were available. It is conceivable that GPS could be used to perform this function and transmit the trajectory information to the range safety officer if determined by range safety experts to be an acceptable alternative to the current practices. in. . , . ~, ^` .. .. . . . . . ...
Systems Engineering and Operations Spacecraft Accessibility and Safety Some space missions require access to the spacecraft late in the countdown procedure, for example, to enable insertion of life science experiment specimens or to repair a spacecraft component. The design of current systems does not permit access after the payload shroud is installed. Also, access to the pad is severely restricted on current systems by safety requirements, especially those associated with highly reactive propellants and ordnance devices. One possible solution to the shroud problem is to provide a means for installation of the shroud late in the countdown, but this would require development of attachment methods that are simple, safe, and verifiable. Another method is to provide access into the spacecraft through the shroud. Resolution of the ordnance problem is more difficult. Various methods have been proposed. One requires developing ordnance devices that would be inert until activated remotely. A possible concept would entail insertion late in the countdown using robotic devices. Another approach would be to use inert materials such as memory metals (e.g., Nitinol), which undergo a phase transformation upon heating, to sever structural connections. Significant costs for operation of current systems are the result of safety requirements associated with the very energetic and environmentally sensitive propellants used, including the high-energy solid rocket motors. Use of hybrid rockets) wouic} preclude the need for these extensive safety measures because of the improved operability offered by the inherent inertness of the propellant elements up to the time combustion is initiated at launch. The American Rocket Company, with other industry support, has carried out privately funcled development work in this area for several years. Their hybrid rocket motor has been test fired, but it is not yet flight qualified (Boyer, 19931. Additionally, there has been independent research and development work on hybrid propulsion by other industrial firms and the U.S. Air Force Academy. Recently, an industry and government consortium was formed for hybrid technology with support from NASA and DoD under the federal Technology Reinvestment Program (American Rocket Company, 1994; NASA, 1993b; U.S. Congress, 19931. Flight Programming Another major element of launch operations costs (and of flight operations costs) is the preparation of the flight programming software required for each individual mission and for each individual launch vehicle. A computer program for flight programming that would prepare the flight programming software for the launch upon insertion of several trajectory and launch vehicle parameters could reduce the time and cost required for this activity. The BMDO/McDonnell Douglas Single-Stage-to-Orbit project was working on the development of such a program prior to its cancellation ~ Hybrid rockets employ a liquid oxidizer with a solid, inert fuel. 17
18 Technology for Small Spacecraft (Palsulich and Raspet, 19931. At the time of this report, announcements indicate the single-stage-to-orbit technology efforts will be continued under the auspices of NASA (lannotta, 1994~. The previously mentioned MST} program also has as one of its objectives the demonstration of automation of the design of the control software and flight code software (Mattock et al., 19931. SMALL SPACECRAFT MISSION OPERATIONS Mission operations, which include the people, hardware, software, ground systems, and space assets necessary to conduct day-to-day activities, are a significant life- cycle cost driver for many space systems. In fact, recent procurements suggest that the cost of mission operations for longer, more complex missions can equal or exceed development cost. In the past, mission operators got involved too late in the project definition phase to have opportunities to reduce the life-cycle cost significantly. For small spacecraft missions, the mission operations concept and supporting space mission architecture must be addressed early in the program. In fact, if possible, the spacecraft should be developed by the team of spacecraft designers and the engineers and technicians who will operate and use it. Today NASA maintains and operates a number of facilities for transmitting and processing spacecraft data. These facilities, which represent the existing infrastructure for NASA operations, consist of . . ~· ~ · · ~ the Tracking and Data Relay Satellite System (TDRSS) network, which uses large geosynchronous satellites and a major Earth station in New Mexico (this network services most U.S. low Earth-orbiting spacecraft and the Space Shuttle); the Deep Space Network, maintained and operated by JPL for planetary and high Earth orbit missions; the Ground/Space Tracking and Data Network, which is made up of various smaller ground facilities for general tracking and data reception and retransmission; the Wallops Island ground station, which is used for the Small Explorer program; and a number of services maintained and operated by commercial and common carriers. The TDRSS, Deep Space Network, and Ground/Space Tracking and Data Network all offer some standardized communications interfaces. During the last decade, the developers and operators of low-cost, small Earth- orbiting spacecraft systems have avoided using the existing infrastructure. It was found to be complex, costly, and incompatible with the overall concepts of short development time and low-cost operations. However, dedicated receiving and tracking facilities on the ground are too costly if there is a mission requirement for real-time data, and reliance
Systems Engineering and Operations must be placed on space-borne systems such as TDRSS. To increase the usage of the TDRSS for small spacecraft support (particularly for real-time high-data-rate missions) or to permit high-data-rate transmission directly to the ground (with dedicates! or specialized ground antennas), several efforts are underway in private industry and in government to replace the costly, heavy transponders needed today. The private ventures seem to have reached the limit of corporate independent research and development funding and may need enhanced government support to take them from laboratory ventures to flight-qualif~ed status. The Principal companies involved are Motorola Cincinnati Electronics, and Stanford Electronics. Several NASA facilities (GSFC, JPL, and Wallops Island) are also interested in developing ways to increase TDRSS's use with small spacecraft. Another major cost element in mission operations is personnel. Mission operations is a labor-intensive activity. Most approaches to reducing its cost involve one or a combination of the following: . . distribution of ground control functions or portions of them to other areas (e.g., on-board orbit determination and controls, distributed processing of remote sensing and scientific data); standardization of interfaces and communications; automation of repetitive, labor-intensive functions; and reuse of existing software, hardware, and procedures. Distributed Functions An effective way to reduce mission operations costs is to reduce the number of functions required of the mission operations team. Application of currently available technology for on-board orbital position determination would enable the spacecraft to autonomously determine its orbit parameters and command the proper systems to maintain the desired orbit parameters, achieving autonomous station keeping. The MST} program has an objective to demonstrate this capability using an advanced star tracking system. An on-board GPS receiver could also provide the position information for most Earth-orbiting spacecraft. The distribution of payload data analysis also could relieve the mission operations team of a large workload. Payload data for remote sensing ant} scientific missions could be processed on-board and the processed data transmitted to the grounc} to reduce transmission load, and it could be distributed directly to locations where further processing could be done more cost effectively. The computing power to handle much of the processing load is readily available. The technical challenge is to develop a data ~ _ _ distribution system that gets the data from the spacecraft to the user's computers In the appropriate timeframe and medium. For example, the Radio Amateur Satellite Organization and the NASA Solar Mesosphere Explorer program both have ground stations that allow experimenters to receive data directly from the spacecraft. 19
20 Technology for Small Spacecraft Standardization Standardization of certain aspects of mission operations has the potential of reducing cost. However, imposition of numerous standards carries the risk of overly restricting the creativity of small spacecraft system design teams and requiring excessive documentation, which could conceivably result in increased cost. Mandatory standards should be chosen very selectively, but the availability of standards, which the design teams could choose to adapt, could have large potential for cost savings. The following are specific areas of standardization for consideration (Wall and ~better, 19911. Tracking aM orbit data formats require use of a common data structure for spacecraft tracking data and a common set of conventions for the models and coordinate systems used to process the tracking data by all agencies participating. Telecommunications characteristics require using common frequency bands; ground-timing stability criteria; and command, telemetry, and ranging bandwidths among and within all facilities and agencies participating. Sta~ard-format data units require use of a common data structure for transfer of data between any elements of the ground data system. Common time-code formats require all spacecraft and ground systems to use a common format for time and to select that format from a predetermined set of formats. On-board clocks would be limited to specific oscillator frequencies, formats, and characteristics. Packetized2 telecommar~s require all ground-prepared commands for transmission to a spacecraft to conform to a common data structure, including frame size and format. Packetized telemetry requires payload and housekeeping data on the spacecraft to conform to a common data structure. including frame size and format. Telemetry channel coding requires data coded on a spacecraft to select from a set of acceptable downlink coding algorithms. ~., Automation Automation of carefully selected tasks can reduce the cost of space mission operations. Typical goals of automation are to reduce life-cycle cost, enhance efficiency, and reduce the number and frequency of errors. The key is to automate the appropriate tasks in the spacecraft or on the ground. Candidates for automation are straightforward, 2 Packetized consolidated communications commands that can be accepted or rejected as a group.
Systems Engineering arid Operations repetitive tasks like command verification, trend analysis of spacecraft subsystems, fault detection, and even operations status briefings. Expert systems may even be useful to augment the efforts of people performing mission operations. Reuse of Software, Hardware, and Procedures Reusing software and procedures for mission operations, if done properly, can greatly reduce development cost. Many software routines and procedures are resident within the existing mission operations infrastructure, where they have been developed, tested, and used to conduct mission operations. A program can realize the greatest savings by reviewing existing software, hardware, and procedures early in the program and adopting acceptable items. Spacecraft developers and mission operations teams can then design other necessary software and procedures to be compatible with the existing resource. Goddard Space Flight Center, for example, has doubled the amount of software and procedures they reuse, from 40 percent to 82 percent (Boden and Larson, 19941. PRIORITIZED RECOMMENDATIONS In order to enhance engineering and operations of small spacecraft systems, the Pane! on Small Spacecraft Technology makes the following prioritized recommendations for NASA: I. Capabilities and design tools should be developed that facilitate improved up-front concept development for low-cost small spacecraft missions. These capabilities and tools should facilitate in-depth trades that result in improving the ability to estimate and in lowering overall life-cycle costs. Key trades include: . Tools that would be useful are 21 operational mission concepts; many small spacecraft versus larger, fully integrated systems; the degree of autonomy on the spacecraft and on the ground; the effect of launch strategy and vehicle selection; the degree of acceptable risk and approach to reliability; and dedicated versus shared mission operations facilities. data bases and cost estimating software that address life-cycle cost of small missions; and nationally available data bases for existing parts, components, and new technologies.
22 Technology for Small Spacecraft 2. Technologies and techniques should be developed that would reduce the required number of mission operations personnel. These techniques include: . autonomous orbit determination and correction; on-board data screening to reduce the amount of data to be transmitted to the ground; and communication systems for distribution of mission data clirectly from the spacecraft to the data users. 3. Technologies and practices required to enable a factory-to-launch sequence with minimum checkout at the launch site should be developed and demonstrated. These should utilize expert systems when appropriate, including, as a minimum, the following: on-board health monitoring and checkout and, where economical, fault correction, for both the launch vehicle ant! the spacecraft; techniques for remote system checkout; automated preparation of flight software for guidance and control of both the launch vehicle and spacecraft; a set of standard hardware interfaces for small launch vehicles and spacecraft; on-board launch trajectory determination for range safety tracking; spacecraft accessibility late in the countdown; and reduction of launch pad safety requirements through use of technologies such as hybrid propulsion and nonexplosive separation devices. 4. Data storage and transmission techniques should be developed that meet the needs unique to small spacecraft. These techniques should utilize: Tow-cost, miniaturized, high-capacity, reliable data storage devices efficient, high-data-rate transmission techniques; better forward error-correction codes; and efficient protocols for high-speed-data interactive transactions. ~, 5. Standardized communications interfaces for mission control functions should be developed. Areas for standardization include: tracking and orbit data formats; telecommunications characteristics; standard-format data units; time-code formats; packetized telecommands; packetized telemetry; and telemetry channel coding.