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NASA NTRS1991

The NASA/National Space Science Data Center trapped radiation environment model program, 1964 - 1991

The major effort that NASA, initially with the help of the United States Air Force (USAF), carried out for 27 years to synthesize the experimental and theoretical results of space research related to energetic charged particles into a quantitative description of the terrestrial trapped radiation environment in the form of model environments is detailed. The effort is called the Trapped Radiation Environment Modeling Program (TREMP). In chapter 2 the historical background leading to the establishment of this program is given. Also, the purpose of this modeling program as established by the founders of the program is discussed. This is followed in chapter 3 by the philosophy and approach that was applied in this program throughout its lifetime. As will be seen, this philosophy led to the continuation of the program long after it would have expired. The highlights of the accomplishments are presented in chapter 4. A view to future possible efforts in this arena is given in chapter 5, mainly to pass on to future workers the differences that are perceived from these many years of experience. Chapter 6 is an appendix that details the chronology of the development of TREMP. Finally, the references, which document the work accomplished over these years, are presented in chapter 7.

Vette, James I.↗

NASA NTRS1992

Role of automation in the ACRV operations

The Assured Crew Return Vehicle (ACRV) will provide the Space Station Freedom with contingency means of return to earth (1) of one disabled crew member during medical emergencies, (2) of all crew members in case of accidents or failures of SSF systems, and (3) in case of interruption of the Space Shuttle flights. A wide range of vehicle configurations and system approaches are currently under study. The Program requirements focus on minimizing life cycle costs by ensuring simple operations, built-in reliability and maintainability. The ACRV philosophy of embedded operations is based on maximum use of existing facilities, resources and processes, while minimizing the interfaces and impacts to the Space Shuttle and Freedom programs. A preliminary integrated operations concept based on this philosophy and covering the ground, flight, mission support, and landing and recovery operations has been produced. To implement the ACRV operations concept, the underlying approach has been to rely on vehicle autonomy and automation, to the extent possible. Candidate functions and processes which may benefit from current or near-term automation and robotics technologies are identified. These include, but are not limited to, built-in automated ground tests and checkouts; use of the Freedom and the Orbiter remote manipulator systems, for ACRV berthing; automated passive monitoring and performance trend analysis, and periodic active checkouts during dormant periods. The major ACRV operations concept issues as they relate to the use of automation are discussed.

Sepahban, S. F.↗

NASA NTRS1992

Soviet space nuclear reactor incidents - Perception versus reality

Since the Soviet Union reportedly began flying nuclear power sources in 1965 it has had four publicly known accidents involving space reactors, two publicly known accidents involving radioisotope power sources and one close call with a space reactor (Cosmos 1900). The reactor accidents, particularly Cosmos 954 and Cosmos 1402, indicated that the Soviets had adopted burnup as their reentry philosophy which is consistent with the U.S. philosophy from the 1960s and 1970s. While quantitative risk analyses have shown that the Soviet accidents have not posed a serious risk to the world's population, concerns still remain about Soviet space nuclear safety practices.

Bennett, Gary L.↗

NASA NTRS1993

Transputer based control system for MTLRS

The Modular Transportable Laser Ranging Systems (MTLRS-1 and MTLRS-2) have been designed in the early eighties and have been in operation very successfully since 1984. The original design of the electronic control system was based on the philosophy of parallel processing, but these ideas could at that time only be implemented to a very limited extent. This present system utilizes two MOTOROLA 6800 8-bit processors slaved to a HP A-600 micro-computer. These processors support the telescope tracking system and the data-acquisition/formatting, respectively. Nevertheless, the overall design still is largely hardware oriented. Because the system is now some nine years old, aging of components increases the risk of malfunctioning and some components or units are outdated and not available anymore. The control system for MTLRS is now being re-designed completely, based on the original philosophy of parallel processing, making use of contemporary advanced electronics and processor technology. The new design aims at the requirements for Satellite Laser Ranging (SLR) in the nineties, making use of the extensive operational experience obtained with the two transportable systems.

Vermaat, Erik↗

NASA NTRS1993

VMPLOT: A versatile analysis tool for mission operations

VMPLOT is a versatile analysis tool designed by the Magellan Spacecraft Team to graphically display engineering data used to support mission operations. While there is nothing revolutionary or innovative about graphical data analysis tools, VMPLOT has some distinguishing features that set it apart from other custom or commercially available software packages. These features include the ability to utilize time in a Universal Time Coordinated (UTC) or Spacecraft Clock (SCLK) format as an enumerated data type, the ability to automatically scale both axes based on the data to be displayed (including time), the ability to combine data from different files, and the ability to utilize the program either interactively or in batch mode, thereby enhancing automation. Another important feature of VMPLOT not visible to the user is the software engineering philosophies utilized. A layered approach was used to isolate program functionality to different layers. This was done to increase program portability to different platforms and to ease maintenance and enhancements due to changing requirements. The functionality of the unique features of VMPLOT as well as highlighting the algorithms that make these features possible are described. The software engineering philosophies used in the creation of the software tool are also summarized.

Bucher, Allen W.↗

NASA NTRS1994

Undersea applications of dexterous robotics

The revolution and application of dexterous robotics in the undersea energy production industry and how this mature technology has affected planned SSF dexterous robotic tasks are examined. Undersea telerobotics, or Remotely Operated Vehicles (ROV's), have evolved in design and use since the mid-1970s. Originally developed to replace commercial divers for both planned and unplanned tasks, they are now most commonly used to perform planned robotic tasks in all phases of assembly, inspection, and maintenance of undersea structures and installations. To accomplish these tasks, the worksites, the tasks themselves, and the tools are now engineered with both the telerobot's and the diver's capabilities in mind. In many cases, this planning has permitted a reduction in telerobot system complexity and cost. The philosophies and design practices that have resulted in the successful incorporation of telerobotics into the highly competitive and cost conscious offshore production industry have been largely ignored in the space community. Cases where these philosophies have been adopted or may be successfully adopted in the near future are explored.

Gittleman, Mark M.↗

NASA NTRS1994

Continual improvement: A bibliography with indexes, 1992-1993

This bibliography lists 606 references to reports and journal articles entered into the NASA Scientific and Technical Information Database during 1992 to 1993. Topics cover the philosophy and history of Continual Improvement (CI), basic approaches and strategies for implementation, and lessons learned from public and private sector models. Entries are arranged according to the following categories: Leadership for Quality, Information and Analysis, Strategic Planning for CI, Human Resources Utilization, Management of Process Quality, Supplier Quality, Assessing Results, Customer Focus and Satisfaction, TQM Tools and Philosophies, and Applications. Indexes include subject, personal author, corporate source, contract number, report number, and accession number.

Source record↗

NASA NTRS1994

Mission operations management

Redefining the approach and philosophy that operations management uses to define, develop, and implement space missions will be a central element in achieving high efficiency mission operations for the future. The goal of a cost effective space operations program cannot be realized if the attitudes and methodologies we currently employ to plan, develop, and manage space missions do not change. A management philosophy that is in synch with the environment in terms of budget, technology, and science objectives must be developed. Changing our basic perception of mission operations will require a shift in the way we view the mission. This requires a transition from current practices of viewing the mission as a unique end product, to a 'mission development concept' built on the visualization of the end-to-end mission. To achieve this change we must define realistic mission success criteria and develop pragmatic approaches to achieve our goals. Custom mission development for all but the largest and most unique programs is not practical in the current budget environment, and we simply do not have the resources to implement all of our planned science programs. We need to shift our management focus to allow us the opportunity make use of methodologies and approaches which are based on common building blocks that can be utilized in the space, ground, and mission unique segments of all missions.

Rocco, David A.↗

NASA NTRS1994

On the use of the systems approach to certify advanced aviation technologies

The field of human factors is as varied and diverse as the human subject itself. But one of its most important applications is the facilitation of safety and efficiency in a particular working environment through the implementation of paradigms known about humans and their working relationship with machines and systems. During the period since World War II (which is often viewed as the birth of Human Factors) no area has been the subject of more human factors research than aviation. And in no time during that epoch is the influence of human factors more important, nor more imperative than it is today. As technology driven designs have been finding their way into the national airspace system (NAS), there has been growing concern within the aviation industry itself, the Federal Aviation Administration (FAA), and the general public for a means by which to certify complex systems and the advanced aviation technologies that will be responsible for transporting, directing, and maintaining our airborne travel. While it is widely agreed human factors certification is desirable, the philosophy that will underlie the approach is debatable. There are, in general, two different approaches to certification: (1) the top-down or systems approach; and, (2) the bottom-up or monadical approach. The top-down approach is characterized by the underlying assumption that certification can be best achieved by looking at the system as a whole, understanding its objectives and operating environment, then examining the constituent parts. In an aircraft cockpit, this would be accomplished by first examining what the aircraft is supposed to be (e.g., fighter, general aviation, passenger), identifying its operating environment (IFR, VMC, combat, etc.) and looking at the entire working system which includes the hardware, software, liveware and their interactions; then, evaluative measures can be applied to the subsystems (e.g., individual instruments, CRT displays, controls). The bottom-up approach is founded on the philosophy that the whole can be best served by first examining it constituent elements. This approach would perform the above certification completely antithetically, by looking at the individual parts and certifying good human factors applications to those parts under the basic assumption that the whole is equal to the sum of its parts.

Wise, Mark A.↗

NASA NTRS1995

Artificial neural network application for space station power system fault diagnosis

This study presents a methodology for fault diagnosis using a Two-Stage Artificial Neural Network Clustering Algorithm. Previously, SPICE models of a 5-bus DC power distribution system with assumed constant output power during contingencies from the DDCU were used to evaluate the ANN's fault diagnosis capabilities. This on-going study uses EMTP models of the components (distribution lines, SPDU, TPDU, loads) and power sources (DDCU) of Space Station Alpha's electrical Power Distribution System as a basis for the ANN fault diagnostic tool. The results from the two studies are contrasted. In the event of a major fault, ground controllers need the ability to identify the type of fault, isolate the fault to the orbital replaceable unit level and provide the necessary information for the power management expert system to optimally determine a degraded-mode load schedule. To accomplish these goals, the electrical power distribution system's architecture can be subdivided into three major classes: DC-DC converter to loads, DC Switching Unit (DCSU) to Main bus Switching Unit (MBSU), and Power Sources to DCSU. Each class which has its own electrical characteristics and operations, requires a unique fault analysis philosophy. This study identifies these philosophies as Riddles 1, 2 and 3 respectively. The results of the on-going study addresses Riddle-1. It is concluded in this study that the combination of the EMTP models of the DDCU, distribution cables and electrical loads yields a more accurate model of the behavior and in addition yielded more accurate fault diagnosis using ANN versus the results obtained with the SPICE models.

Momoh, James A.↗

NASA NTRS1995

An overview of engineering concepts and current design algorithms for probabilistic structural analysis

The article begins by examining the fundamentals of traditional deterministic design philosophy. The initial section outlines the concepts of failure criteria and limit state functions two traditional notions that are embedded in deterministic design philosophy. This is followed by a discussion regarding safety factors (a possible limit state function) and the common utilization of statistical concepts in deterministic engineering design approaches. Next the fundamental aspects of a probabilistic failure analysis are explored and it is shown that deterministic design concepts mentioned in the initial portion of the article are embedded in probabilistic design methods. For components fabricated from ceramic materials (and other similarly brittle materials) the probabilistic design approach yields the widely used Weibull analysis after suitable assumptions are incorporated. The authors point out that Weibull analysis provides the rare instance where closed form solutions are available for a probabilistic failure analysis. Since numerical methods are usually required to evaluate component reliabilities, a section on Monte Carlo methods is included to introduce the concept. The article concludes with a presentation of the technical aspects that support the numerical method known as fast probability integration (FPI). This includes a discussion of the Hasofer-Lind and Rackwitz-Fiessler approximations.

Duffy, S. F.↗

NASA NTRS1995

Ascent Guidance Comparisons

This paper contains results from ascent guidance studies conducted at the NASA Marshall Space Flight Center. The studies include investigation of different guidance schemes for a variety of potential launch vehicles. Criteria of a successful ascent guidance scheme are low operations cost, satisfaction of load indicator constraints, and maximization of performance. Results show that open-loop designs as a function of altitude or velocity are preferable to designs that are functions of time. Optimized open-loop trajectories can increase performance while maintaining load indicators within limits. Closed-loop atmospheric schemes that involve linear tangent steering or feedback of velocity terms for trajectory modification did not yield any improvement. Early release of vacuum closed-loop guidance, including use during solid rocket booster operation, yields some improvements. Evaluation of a closed-loop optimization scheme for flying through the atmosphere shows no advantages over open-loop optimization. Dispersion study results for several potential guidance schemes and launch vehicles are included in the paper and are not a discriminator between guidance schemes. The primary cost driver is mission operations philosophy, not choice of guidance scheme. More autonomous guidance schemes can help in movement towards a philosophy that would reduce operations costs.

Hanson, John M.↗

NASA NTRS1998

SLR2000: a microlaser-based single photoelectron satellite laser ranging system

SLR2000 is an autonomous and eyesafe satellite laser ranging (SLR) station with an expected single shot range precision of about one centimeter and a normal point (time-averaged) precision better than 3 mm. The system wil provide continuous 24 hour tracking coverage for a constellation of over twenty artificial satellites. Replication costs are expected to be roughly an order of magnitude less than current operational systems, and the system will be about 75% less expensive to operate and maintain relative to manned systems. Computer simulations have predicted a daylight tracking capability to GPS and lower satellites with telescope apertures of 40 cm and have demonstrated the ability of our current autotracking algorithm to extract mean signal strengths below .001 photoelectrons per pulse from daytime background noise. The dominant cost driver in present SLR systems is the onsite and central infrastructure manpower required to operate the system, to service and maintain the complex subsystems, and to ensure that the transmitted laser beam is not a hazard to onsite personnel or to overflying aircraft. To keep development, fabrication, and maintenance costs at a minimum, we adopted the following design philosophies: (1) use off the shelf commercial components wherever possible; this allows rapid component replacement and "outsourcing" of engineering support; (2) use smaller telescopes (less than 50 cm) since this constrains the cost, size, and weight of the telescope and tracking mount; and (3) for low maintenance and failsafe reliability, choose simple versus complex technical approaches and, where possible, use passive techniques and components rather than active ones. Adherence to these philosophies has led to the SLR2000 design described here.

Degnan, John J.↗

NASA NTRS1998

Human Mars Missions: Cost Driven Architecture Assessments

This report investigates various methods of reducing the cost in space transportation systems for human Mars missions. The reference mission for this task is a mission currently under study at NASA. called the Mars Design Reference Mission, characterized by In-Situ propellant production at Mars. This study mainly consists of comparative evaluations to the reference mission with a view to selecting strategies that would reduce the cost of the Mars program as a whole. One of the objectives is to understand the implications of certain Mars architectures, mission modes, vehicle configurations, and potentials for vehicle reusability. The evaluations start with year 2011-2014 conjunction missions which were characterized by their abort-to-the-surface mission abort philosophy. Variations within this mission architecture, as well as outside the set to other architectures (not predicated on an abort to surface philosophy) were evaluated. Specific emphasis has been placed on identifying and assessing overall mission risk. Impacts that Mars mission vehicles might place upon the Space Station, if it were to be used as an assembly or operations base, were also discussed. Because of the short duration of this study only on a few propulsion elements were addressed (nuclear thermal, cryogenic oxygen-hydrogen, cryogenic oxygen-methane, and aerocapture). Primary ground rules and assumptions were taken from NASA material used in Marshall Space Flight Center's own assessment done in 1997.

Interplanetary Mission↗

NASA NTRS1998

X-33 Attitude Control System Design for Ascent, Transition, and Entry Flight Regimes

The Vehicle Control Systems Team at Marshall Space Flight Center, Systems Dynamics Laboratory, Guidance and Control Systems Division is designing under a cooperative agreement with Lockheed Martin Skunkworks, the Ascent, Transition, and Entry flight attitude control system for the X-33 experimental vehicle. Ascent flight control begins at liftoff and ends at linear aerospike main engine cutoff (NECO) while Transition and Entry flight control begins at MECO and concludes at the terminal area energy management (TAEM) interface. TAEM occurs at approximately Mach 3.0. This task includes not only the design of the vehicle attitude control systems but also the development of requirements for attitude control system components and subsystems. The X-33 attitude control system design is challenged by a short design cycle, the design environment (Mach 0 to about Mach 15), and the X-33 incremental test philosophy. The X-33 design-to-launch cycle of less than 3 years requires a concurrent design approach while the test philosophy requires design adaptation to vehicle variations that are a function of Mach number and mission profile. The flight attitude control system must deal with the mixing of aerosurfaces, reaction control thrusters, and linear aerospike engine control effectors and handle parasitic effects such as vehicle flexibility and propellant sloshing from the uniquely shaped propellant tanks. The attitude control system design is, as usual, closely linked to many other subsystems and must deal with constraints and requirements from these subsystems.

Hall, Charles E.↗

NASA NTRS1999

X-33 Attitude Control Using the XRS-2200 Linear Aerospike Engine

The Vehicle Control Systems Team at Marshall Space Flight Center, Structures and Dynamics Laboratory, Guidance and Control Systems Division is designing, under a cooperative agreement with Lockheed Martin Skunkworks, the Ascent, Transition, and Entry flight attitude control systems for the X-33 experimental vehicle. Test flights, while suborbital, will achieve sufficient altitudes and Mach numbers to test Single Stage To Orbit, Reusable Launch Vehicle technologies. Ascent flight control phase, the focus of this paper, begins at liftoff and ends at linear aerospike main engine cutoff (MECO). The X-33 attitude control system design is confronted by a myriad of design challenges: a short design cycle, the X-33 incremental test philosophy, the concurrent design philosophy chosen for the X-33 program, and the fact that the attitude control system design is, as usual, closely linked to many other subsystems and must deal with constraints and requirements from these subsystems. Additionally, however, and of special interest, the use of the linear aerospike engine is a departure from the gimbaled engines traditionally used for thrust vector control (TVC) in launch vehicles and poses certain design challenges. This paper discusses the unique problem of designing the X-33 attitude control system with the linear aerospike engine, requirements development, modeling and analyses that verify the design.

Hall, Charles E.↗

NASA NTRS1999

Theories of the Universe: A One Semester Course for Honors Undergraduates

For the last two years The University of Alabama in Huntsville (UAH) has delivered a one semester course entitled Theories of The Universe as a seminar for undergraduate honors students. The enrollment is limited to fifteen students to encourage a maximum amount of interaction and discussion. The course has been team-taught enlisting the support of four scientists from the NASA Marshall Space Flight Center as well as UAH faculty from the history, philosophy, biology and physics departments. The course mixes history, mythology, philosophy, religion, and, of course, science and astronomy. The course traces mankind's view of the universe and how that has changed from about 30,000 years BCE to the current observations and models. Starting with a brief history of mankind we trace the evolution of ideas including Prehistoric European, Babylonian, Egyptian, Asian, North, Central and South American, African, Chinese, Greek, Middle Ages, Copernican, Galileo, Kepler, the Renaissance and Enlightenment, Newton, Einstein, and Hawking etc. Namely, we try to touch on just about every different view to puzzles of quantum cosmology, missing mass and the cosmological constant. By the end of the course, students should have a good understanding of: (1) the human desire and need for understanding; (2) the interplay between observations, modeling and theory development, and the need for revisions based on further observations; (3) the role of developing technology in advancing knowledge; (4) the evolution of our views of the universe and our relation to it; and (5) where we are today in our quest. Students are required to write two term papers and present them to the class. The final exam is a open discussion on our views of what we have learned.

Dimmock, John O.↗

NASA NTRS1998

A Status of the Advanced Space Transportation Program from Planning to Action

A Technology Plan for Enabling Commercial Space Business was presented at the 48th International Astronautical Congress in Turin, Italy. This paper presents a status of the program's accomplishments. Technology demonstrations have progressed in each of the four elements of the program; (1) Low Cost Technology, (2) Advanced Reusable Technology, (3) Space Transfer Technology and (4) Space Transportation Research. The Low Cost Technology program element is primarily focused at reducing development and acquisition costs of aerospace hardware using a "design to cost" philosophy with robust margins, adapting commercial manufacturing processes and commercial off-the-shelf hardware. The attributes of this philosophy for small payload launch are being demonstrated at the component, sub-system, and system level. The X-34 "Fastrac" engine has progressed through major component and subsystem demonstrations. A propulsion system test bed has been implemented for system-level demonstration of component and subsystem technologies; including propellant tankage and feedlines, controls, pressurization, and engine systems. Low cost turbopump designs, commercial valves and a controller are demonstrating the potential for a ten-fold reduction in engine and propulsion system costs. The Advanced Reusable Technology program element is focused on increasing life through high strength-to-weight structures and propulsion components, highly integrated propellant tanks, automated checkout and health management and increased propulsion system performance. The validation of rocket based combined cycle (RBCC) propulsion is pro,-,ressing through component and subsystem testing. RBCC propulsion has the potential to provide performance margin over an all rocket system that could result in lower gross liftoff weight, a lower propellant mass fraction or a higher payload mass fraction. The Space Transfer Technology element of the program is pursuing technology that can improve performance and dramatically reduce the propellant and structural mass of orbit transfer and deep space systems. Flight demonstration of ion propulsion is progressing towards launch. Ion propulsion is the primary propulsion for Deep Space 1; a flyby of comet West-kohoutek-lkemura and asteroid 3352 McAuliffe. Testing of critical solar-thermal propulsion subsystems have been accomplished and planning is continuing for the flight demonstration of an electrodynamic tether orbit transfer system. The forth and final element of the program, Space Transportation Research, has progressed in several areas of propulsion research. This element of the program is focused at long-term (25 years) breakthrough concepts that could bring launch costs to a factor of one hundred below today's cost or dramatically expand planetary travel and enable interstellar travel.

Lyles, Garry↗