Propulsion for the aircraft segment in unmanned aircraft systems (UAS) is provided not only by widely used propulsion technologies such as reciprocating piston engines and jet and prop turbine engines, but also by electric motors running off some combination of batteries, solar cells, and fuel cells. These disparate propulsion technologies pose a challenge to researchers and regulators in comparing systems, determining equivalent levels of safety, developing performance and safety requirements, etc. In the systems view of UAS propulsion presented here, the propulsion system is decomposed into five subsystems: (1) An energy source; (2) An energy transformer; (3) A powerplant; (4) A propulsion effecter; and (5) A control effecter. For example, a UAS employing an avgas fueled reciprocating piston engine would have petroleum distillates for its energy source, combustion as its energy transformer, the piston/crankshaft as its powerplant, a propeller as its propulsion effecter, and control of the flow of fuel, air, and electricity as its control effecter; a proton exchange membrane fuel cell driven UAS would have the hydrogen as its energy source, the fuel cell unit as its energy transformer, an electric motor as its powerplant, a propeller as its propulsion effecter, and control of applied voltage and current as its control effecter. The system framework is exploited in a technology survey of existing UAS propulsion systems that presents representative examples of the various propulsion technologies and compares the way in which the different generic subsystems are instantiated as the propulsion systems of various aircraft. The advantages and disadvantages of the propulsion technologies are discussed, as is the manner in which the systems framework facilitates comparison among different propulsion technologies and the way it may facilitate development of regulations appropriate for UAS. The ability of the framework to describe not only extant technologies, but also developing propulsion technologies such as fuel cells, micro jets, ultracapacitors, etc., is explained, and supported with key examples.

Engineers who become managers must acquire essential knowledge about management to be successful. Major aerospace projects are complex organizations with three or four levels of management, and often have over a hundred cost account managers. Management skills are critical to the planning and implementation of these projects, especially in today's cost-conscious world. Aerospace organizations must address the gaps between excellent engineering educations and excellent knowledge about engineering management if they hope to succeed with major aerospace projects. Essential engineering management knowledge includes how to: plan work, estimate cost, prepare schedules, manage performance under normal circumstances, manage performance under adverse circumstances, and handle people. While some engineering students learn about cost estimation in their university education, many do not. Few engineering students get significant training on the other management skills mentioned above. However, the best and brightest engineers often become cost account managers within several years after they graduate, and many of these move on to higher levels of management within several more years. Their management skills, or lack thereof, lead directly to the success or failure of complex aerospace projects. There are at least four approaches for developing engineering managers: (1) let them watch other managers perform on real jobs; (2) active mentoring; (3) self-directed study of books and journal articles on management; (4) formal training sponsored by the employer. Formal training is the foundation for sound development of engineering managers. All of the other approaches can be helpful, but are seriously undermined if formal training is absent or otherwise inadequate. Bad habits and inconsistent practices can be learned, until the organization gets itself into serious trouble. This paper describes successful practices at JPL in developing engineering managers through formal training. The author has been engaged in project and proposal work for over thirty years at JPL, and in formal training over the last ten years. Over the last decade he has addressed the needs of approximately 1,500 students.

NASA is planning to upgrade its network infrastructure to support missions for the 21st century. The first step is to increase the data rate provided to science missions to at least the 100 Mbps range. This is under way, using Ka-band 26 GHz, erecting an 18-meter antenna for the Lunar Reconnaissance Orbiter, and the planned upgrade of the Deep Space Network (DSN) 34-meter network to support the James Webb Space Telescope (JWST). The next step is the support of manned missions to the Moon and beyond. Establishing an outpost with several activities such as rovers, colonization, and observatories, is better achieved by using a network configuration rather than the current method of point-to-point. Another challenge associated with the Moon is communication coverage with the Earth. The Moon's South Pole, targeted for human habitat and exploration, is obscured from Earth view for half of the 28-day lunar cycle and requires the use of lunar relay satellites to provide coverage for the times when there is no direct view of the Earth. The future NASA and Constellation network architecture is described in the Space Communications Architecture Working Group (SCAWG) Report[l]. The Space Communications and Navigation (SCAN) Constellation Integration Project (SCIP) is responsible for coordinating Constellation requirements and has assigned the responsibility for implementing these requirements to the existing NASA communication providers: DSN, Space Network (SN), Ground Network (GN) and the NASA Integrated Services Network (NISN). The SCAWG Report provides a future architecture but does not provide implementation details. The architecture calls for a Netcentric system, using hundreds of 12-meter antennas, a ground antenna array, and a relay network around the Moon. The report did not use cost as a variable in determining the feasibility of this approach. As part of the SCIP Mission Concept Review and the second iteration of the Lunar Architecture Team (LAT), the focus is on cost, as well as communication coverage using operational scenarios. This approach maximizes use of existing assets and adds capability in small increments. This paper addresses architecture decisions such as the Radio Frequency (RF) signal and network (Netcentric) decisions that need to be made and the difficulty of implementing them into the existing Space Network and DSN. It discusses the evolution of the lunar system and describes its components: TDRSS, Earth-based ground stations, Lunar Relay, and surface systems.

Digital Mockups (Virtual Prototypes) significantly reduce risk and cost on large aerospace programs, but their accuracy hinges on the creation of 3D models of existing facilities, based on "as-built" field conditions instead of less-accurate design blueprints. Methods for creating as-built models vary from tedious hand-measurements, to photograph-rectification-survey techniques (collectively known as photogrammetry), to the evolving technology of terrestrial laser scanning. Lockheed Martin has proven through robust field testing that the accuracy of each technology is variable to specific applications. Therefore, we have developed a hybrid method that leverages the strengths of each technology, including edge recognition, targeting accuracy, and complex-surface collection. This hybridization has helped to identify key technical deficiencies in the current state-of- practice for as-built CAD modeling, such as automatic modeling and feature extraction. In addition, Lockheed Martin has refined a statistical evaluation technique to objectively measure the accuracy of the final model against the field conditions, regardless of the technology utilized. The advantages and disadvantages of each technology are presented here, as well as methodologies for effectively combining the technologies into a more-accurate and efficient hybrid process. This overall capability is crucial to Lockheed Martin for reducing reliance on physical prototypes, and optimizing project return on cost, schedule, and risk.

Over the past twenty years, the health monitoring community has vastly extended its capability to monitor systems for operational health. Studies on various systems have revealed means of deducing the health of their parts such as specific engine components, traction and control systems including vehicle monitoring, aircraft parts such as landing gear, and many more. In most cases, researchers mapped the signatures of known areas of concern and determined methods to detect these signatures as they occurred. In safety critical applications, the emphasis became development of early detection techniques for termination of operation of the system before severe loss occurred. Existing health monitoring systems include spacecraft monitoring systems, aircraft in-flight monitors, and ground vehicle monitors, each designed to identify and notify the vehicle operation team of existing or pending maintenance and safety issues as they develop. In some systems, such as Boeing aircraft, health monitors allow the vehicle to call ahead to a ground station while en-route to report upcoming necessary maintenance based on known issues. Through the years of development, while health monitor systems have grown more complex and capable, the method of creating these systems has remained somewhat simplistic throughout the industry, using bottom up approaches or ad-hoc implementation in the design of these systems. In this paper, we will discuss another approach. We discuss a top-down functional health monitor design approach. We show that alternate methods are incapable of determining a provably closed-form and tractable health monitor system, and that application of this technique can help eliminate important oversight that threatens the safety of a vehicle. The result of its application is a far safer vehicle through a methodical application of this approach that addresses the various sources of loss within the system.

High reliable reconfigurable applications today require system platforms that can easily and quickly detect and correct single event upsets. This capability, however, can be costly for FPGAs. This paper demonstrates a technique for detecting and repairing SEUs within the configuration memory of a Xilinx Virtex-4 FPGA using the ICAP interface. The internal configuration access port (ICAP) provides a port internal to the FPGA for configuring the FPGA device. An application note demonstrates how this port can be used for both error injection and scrubbing (L. Jones, 2007). We have extended this work to create a fault tolerant ICAP scrubber by triplicating the internal ICAP circuit using TMR and block memory scrubbing. This paper will describe the costs, benefits, and reliability of this fault-tolerant ICAP controller.

The calibration of radio antenna performance is a well understood process, especially for single large-diameter antennas. However, the measurement of efficiency, optimal focus, pointing corrections, system temperature, and other parameters as functions of observing frequency, antenna elevation and azimuth, temperature, and wind velocity can be time-consuming. For any future arrays consisting of very large numbers of small antennas, it will be necessary to minimize the time spent calibrating each antenna. This paper considers ways to speed up the calibration of antennas being added to an existing array by taking advantage of interferometer measurements and script-based automation.

This paper presents a direct method of analyzing the distortion effects of the power amplifier nonlinearity on the CDMA signal. In the analysis approach of the paper, the various user signals, which are composed of data-modulated Walsh codes, which are also modulated by various scrambling codes, are modeled as independent random sequences. These sequences are band limited, using square-root raised cosine filters and modulated by a carrier frequency before being input to the nonlinear power amplifier. In the analysis approach of the paper, the amplifier characteristics are approximated by a polynomial of sufficiently high degree such that over the range of input signal, the approximation error is negligible. For the region of amplifier operation of interest in this paper, terms of degree higher than forty may be needed compared to an earlier simplified analysis presented by the author wherein only cubic distortion terms have been considered. The expressions for both the output signal power and the output signal power-to-distortion power spectral density ratio are given in the form of a finite series with its coefficients being a function of the amplifier input power level, the number of codes, and the amplifier transfer characteristics. The paper also shows that the amplifier possesses a maximum capacity defined as the maximum total bit rate Rt that can be present at the amplifier input for a specified output signal power back-off and the required output bit energy to distortion power spectral density ratio (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0d</sub> ). Also for any given output back-off and user data rate, the (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0d</sub> ) ratio is a strong function of the number of codes M in the CDMA signal.

A challenge in scientific communities is that one member of the community will acquire new literature but the information never gets passed on to other interested colleagues within the community. We designed and are building a Web-based tool to overcome this challenge. This system is the Scientific Literature Exchange and Database System or SciExchange. SciExchange allows a scientist who reads an article, an online journal article or science news update, to log onto the SciExchange Web site and easily submit the article or link to the article to the database. Next, SciExchange automatically sends a notification email to the list of subscribing scientists who asked to be notified if articles on topics of interest to them were entered into the SciExchange database. The email contains a link to the article referred to. Its design, construction, planned uses, and implications for NASA's Goddard Space Flight Center (GSFC) are detailed in this paper.

During the 1970's through the early 1990's, NASA Langley Research Center (LaRC) conducted studies for the design and construction of large space structures in Low Earth Orbit (LEO). The Langley studies focused on the design and construction of erectable space structures. The construction studies evaluated assembly methods using astronauts with and without mechanized foot-restraints. Astronaut construction was shown to be very effective and efficient when the structure and the construction methods were developed in parallel. This paper presents an overview of the LaRC astronaut construction studies of erectable structures, including a database of assembly rates and lessons learned. In addition this paper presents potential applications of erectable structure assembly methods using EVA astronauts and a suggested integrated approach for construction of large space structures.