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NASA NTRS2019

Defining Well Clear Separation for Unmanned Aircraft Systems Operating with Non-Cooperative Aircraft

Detect-and-Avoid (DAA) systems are essential to the safe operations of Unmanned Aircraft Systems, and have the objectives of mitigating collisions with and remaining Well Clear of manned aircraft. This paper analyzes four candidate DAA Well Clear definitions for non-cooperative aircraft using mitigated performance metrics of DAA systems. These DAA Well Clear definitions were proposed in previous work based on their unmitigated collision risk and maneuver initiation range. In this work they are evaluated using safety and operational suitability metrics computed from a large number of representative encounters. Results suggest that although the four candidate DAA Well Clear definitions provide comparable safety, the alerting characteristics give preference for the DAA Well Clear definition without a temporal parameter.

Chen, Christine C.↗

NASA NTRS2019

Defining Well Clear Separation for Unmanned Aircraft Systems Operating with Noncooperative Aircraft

Well Clear↗

NASA NTRS2019

Management by Trajectory: Improving Predictability for Airspace Operations

In the present-day National Airspace System, the air traffic management system attempts to predict the trajectory for each flight based on the flight plan and scheduled or controlled departure time. However, gaps in trajectory data and models, coupled with tactical control actions that are not communicated to automation systems or other stakeholders, lead to trajectory predictions that are less accurate than they could be. This affects traffic flow management performance. Management by Trajectory (MBT) is a NASA concept for air traffic management in which every flight operates in accordance with a 4D trajectory that is negotiated between the airspace user and the FAA to account for the airspace user’s goals while complying with NAS constraints. The primary benefit of MBT is an improvement in system performance due to increased trajectory predictability and stability, which result from managing traffic in all four dimensions (2D route, vertical, and time), ensuring that changes to the flight’s trajectory are incorporated into the assigned trajectory, and utilizing improved time or arrival control standards. Importantly, the performance improvements support increasing efficiency without increasing collision risk. This paper provides an overview of MBT and describes fast-time simulation results evaluating the safety, performance, and efficiency effects of MBT.

Fernandes, Alicia B.↗

NASA NTRS1972

Shuttle/Agena study. Volume 2, part 2: Agena tug configurations, Shuttle/Agena interface, performance, safety, cost

An evaluation of the compatibility of the space shuttle and Agena rocket vehicle was conducted. The Agena space tug configuration design is described in terms of the total vehicle system as well as the individual subsystems and major assemblies and components. The complete interface between the Agena space tug and the space shuttle orbiter is defined for in-flight and ground operations. The derivation and design of an evolutionary stage is also presented. This vehicle conforms to the same guidelines and interface requirements as the Agena space tug. Performance data developed for both vehicles for each of the three study baseline missions are included.

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NASA NTRS2007

2006 NASA Range Safety Annual Report

Throughout 2006, Range Safety was involved in a number of exciting and challenging activities and events, from developing, implementing, and supporting Range Safety policies and procedures-such as the Space Shuttle Launch and Landing Plans, the Range Safety Variance Process, and the Expendable Launch Vehicle Safety Program procedures-to evaluating new technologies. Range Safety training development is almost complete with the last course scheduled to go on line in mid-2007. Range Safety representatives took part in a number of panels and councils, including the newly formed Launch Constellation Range Safety Panel, the Range Commanders Council and its subgroups, the Space Shuttle Range Safety Panel, and the unmanned aircraft systems working group. Space based range safety demonstration and certification (formerly STARS) and the autonomous flight safety system were successfully tested. The enhanced flight termination system will be tested in early 2007 and the joint advanced range safety system mission analysis software tool is nearing operational status. New technologies being evaluated included a processor for real-time compensation in long range imaging, automated range surveillance using radio interferometry, and a space based range command and telemetry processor. Next year holds great promise as we continue ensuring safety while pursuing our quest beyond the Moon to Mars.

TenHaken, Ron↗

NASA NTRS2011

NASA Accident Precursor Analysis Handbook, Version 1.0

Catastrophic accidents are usually preceded by precursory events that, although observable, are not recognized as harbingers of a tragedy until after the fact. In the nuclear industry, the Three Mile Island accident was preceded by at least two events portending the potential for severe consequences from an underappreciated causal mechanism. Anomalies whose failure mechanisms were integral to the losses of Space Transportation Systems (STS) Challenger and Columbia had been occurring within the STS fleet prior to those accidents. Both the Rogers Commission Report and the Columbia Accident Investigation Board report found that processes in place at the time did not respond to the prior anomalies in a way that shed light on their true risk implications. This includes the concern that, in the words of the NASA Aerospace Safety Advisory Panel (ASAP), "no process addresses the need to update a hazard analysis when anomalies occur" At a broader level, the ASAP noted in 2007 that NASA "could better gauge the likelihood of losses by developing leading indicators, rather than continue to depend on lagging indicators". These observations suggest a need to revalidate prior assumptions and conclusions of existing safety (and reliability) analyses, as well as to consider the potential for previously unrecognized accident scenarios, when unexpected or otherwise undesired behaviors of the system are observed. This need is also discussed in NASA's system safety handbook, which advocates a view of safety assurance as driving a program to take steps that are necessary to establish and maintain a valid and credible argument for the safety of its missions. It is the premise of this handbook that making cases for safety more experience-based allows NASA to be better informed about the safety performance of its systems, and will ultimately help it to manage safety in a more effective manner. The APA process described in this handbook provides a systematic means of analyzing candidate accident precursors by evaluating anomaly occurrences for their system safety implications and, through both analytical and deliberative methods used to project to other circumstances, identifying those that portend more serious consequences to come if effective corrective action is not taken. APA builds upon existing safety analysis processes currently in practice within NASA, leveraging their results to provide an improved understanding of overall system risk. As such, APA represents an important dimension of safety evaluation; as operational experience is acquired, precursor information is generated such that it can be fed back into system safety analyses to risk-inform safety improvements. Importantly, APA utilizes anomaly data to predict risk whereas standard reliability and PRA approaches utilize failure data which often is limited and rare.

Groen, Frank↗

NASA NTRS1985

Improvements in safety testing of lithium cells

A systematic approach was developed for evaluating the basic safety parameters of high power lithium soluble cathode cells. This approach consists of performing a series of tests on each cell model during the design, prototype and production phases. Abusive testing is performed in a facility where maximum protection is given to test personnel.

Stinebring, R. C.↗

NASA NTRS2001

Performance and Safety of Lithium Ion Cells

This report evaluates the performance and safety of Lithium Ion (Li-Ion) cells when used in batteries. Issues discussed include the cycle life, energy efficiency, tolerance to higher charge voltage, tolerance to extended tapered charge voltage, charge on cycling, specific energy, low temperature discharge, low temperature charge, various charge characteristics, storage characteristics, and more of Li-Ion cells.

Ratnakumar, B. V.↗

NASA NTRS2001

Interrelation Between Safety Factors and Reliability

An evaluation was performed to establish relationships between safety factors and reliability relationships. Results obtained show that the use of the safety factor is not contradictory to the employment of the probabilistic methods. In many cases the safety factors can be directly expressed by the required reliability levels. However, there is a major difference that must be emphasized: whereas the safety factors are allocated in an ad hoc manner, the probabilistic approach offers a unified mathematical framework. The establishment of the interrelation between the concepts opens an avenue to specify safety factors based on reliability. In cases where there are several forms of failure, then the allocation of safety factors should he based on having the same reliability associated with each failure mode. This immediately suggests that by the probabilistic methods the existing over-design or under-design can be eliminated. The report includes three parts: Part 1-Random Actual Stress and Deterministic Yield Stress; Part 2-Deterministic Actual Stress and Random Yield Stress; Part 3-Both Actual Stress and Yield Stress Are Random.

Elishakoff, Isaac↗

NASA NTRS2006

A Silent Safety Program

NASA's Columbia Accident Investigation Board (CAIB) referred 8 times to the NASA "Silent Safety Program." This term, "Silent Safety Program" was not an original observation but first appeared in the Rogers Commission's Investigation of the Challenger Mishap. The CAIB on page 183 of its report in the paragraph titled 'Encouraging Minority Opinion,' stated "The Naval Reactor Program encourages minority opinions and "bad news." Leaders continually emphasize that when no minority opinions are present, the responsibility for a thorough and critical examination falls to management. . . Board interviews revealed that it is difficult for minority and dissenting opinions to percolate up through the agency's hierarchy. . ." The first question and perhaps the only question is - what is a silent safety program? Well, a silent safety program may be the same as the dog that didn't bark in Sherlock Holmes' "Adventure of the Silver Blaze" because system safety should behave as a devil's advocate for the program barking on every occasion to insure a critical review inclusion. This paper evaluates the NASA safety program and provides suggestions to prevent the recurrence of the silent safety program alluded to in the Challenger Mishap Investigation. Specifically targeted in the CAM report, "The checks and balances the safety system was meant to provide were not working." A silent system safety program is not unique to NASA but could emerge in any and every organization. Principles developed by Irving Janis in his book, Groupthink, listed criteria used to evaluate an organization's cultural attributes that allows a silent safety program to evolve. If evidence validates Jams's criteria, then Jams's recommendations for preventing groupthink can also be used to improve a critical evaluation and thus prevent the development of a silent safety program.

Goodin, James Ronald↗

NASA NTRS2001

So What's an RTG and Are They Safe?

When one considers space missions to the outer edges of our solar system and far beyond, our sun cannot be relied on to produce the required spacecraft (s/c) power. Solar energy diminishes as the square of the distance from the Sun. At Mars it is only 43% of that at earth. At Jupiter, it falls off to only 3.6% of Earth's. By the time we get out to Pluto, solar energy is only .066% what it is on Earth. Beyond the orbit of Mars, it is not practical to depend on solar power for a s/c. However, the farther out we go the more power we need to heat the s/c and to transmit data back to Earth over the long distances. On Earth, knowledge is power. In the outer solar system, power is knowledge. Solar arrays only operate at 19% efficiency, are very vulnerable to damage from radiation and temperature extremes, and cannot be used for even nearby missions that operate in extended darkness, or under the surface of a planet or moon. Twenty-six U.S. space missions, from the Transit to Cassini, have used radioisotope power systems and heater units to take s/c to the far reaches of our solar system and have demonstrated an outstanding record of safety and reliability. Radioisotope thermoelectric generators (RTG's) have proven to be safe, reliable, maintenance-free, and capable of providing both thermal and electrical power for decades under the harsh environments of deep space. RTG's have no problem operating in the high radiation belts of space, the extreme temperatures, or the severe dust storms of Mars, and they have proven to be the most reliable power source ever flown on U.S. s/c. For example, the two Pioneer s/c operated for more than two decades and the Voyager s/c may last for 40 years. RTG's are not nuclear reactors, they serve only as power generators and are not involved in the propulsion of the s/c. They operate on the principle of thermoelectric generation that converts heat directly into electricity, they have no moving parts, are extremely reliable, and have met or exceeded all safety and performance expectations. Federal laws and regulations require analysis and evaluation of the safety risks and any potential environmental impacts. Extensive safety testing of RTG's and RTG components has been performed by the U.S. Department of Energy (DOE) to demonstrate the ability to survive accidents related to Space Shuttle launches and assure that the systems would be safe under all accident conditions, including accidents at or near the launch pad or during orbital reentry. Many design improvements have been made over the four decades that RTG's have been flown on space missions. This paper outlines the operation and safety standards of RTG's and the advanced developments expected to be used on future deep space missions such as the Europa Orbiter, Pluto/Kuiper Express, Solar Probe, Europa Lander, and Titan Explorer missions.

Barret, Chris↗

NASA NTRS2007

NASA Range Safety Annual Report 2007

As always, Range Safety has been involved in a number of exciting and challenging activities and events. Throughout the year, we have strived to meet our goal of protecting the public, the workforce, and property during range operations. During the past year, Range Safety was involved in the development, implementation, and support of range safety policy. Range Safety training curriculum development was completed this year and several courses were presented. Tailoring exercises concerning the Constellation Program were undertaken with representatives from the Constellation Program, the 45th Space Wing, and the Launch Constellation Range Safety Panel. Range Safety actively supported the Range Commanders Council and it subgroups and remained involved in updating policy related to flight safety systems and flight safety analysis. In addition, Range Safety supported the Space Shuttle Range Safety Panel and addressed policy concerning unmanned aircraft systems. Launch operations at Kennedy Space Center, the Eastern and Western ranges, Dryden Flight Research Center, and Wallops Flight Facility were addressed. Range Safety was also involved in the evaluation of a number of research and development efforts, including the space-based range (formerly STARS), the autonomous flight safety system, the enhanced flight termination system, and the joint advanced range safety system. Flight safety system challenges were evaluated. Range Safety's role in the Space Florida Customer Assistance Service Program for the Eastern Range was covered along with our support for the Space Florida Educational Balloon Release Program. We hope you have found the web-based format both accessible and easy to use. Anyone having questions or wishing to have an article included in the 2008 Range Safety Annual Report should contact Alan Dumont, the NASA Range Safety Program Manager located at the Kennedy Space Center, or Michael Dook at NASA Headquarters.

Dumont, Alan G.↗

NASA NTRS1972

Manned space flight nuclear system safety. Volume 7: Literature review. Part 1: Literature search and evaluation

A review of the literature used in conducting the manned space flight nuclear system safety study is presented. The objectives of the presentation are to identify and evaluate for potential application to study the existing related literature and to provide the information required to include the related literature in the NASA Aerospace Safety Research and Data Institute. More than 15,000 documents were evaluated and identification forms were prepared for 850 reports.

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NASA NTRS1987

An assessment and validation study of nuclear reactors for low power space applications

The feasibility and safety of six conceptual small, low power nuclear reactor designs was evaluated. Feasibility evaluations included the determination of sufficient reactivity margins for seven years of full power operation and safe shutdown as well as handling during pre-launch assembly phases. Safety evaluations were concerned with the potential for maintaining subcritical conditions in the event of launch or transportation accidents. These included water immersion accident scenarios both with and without water flooding the core. Results show that most of the concepts can potentially meet the feasibility and safety requirements; however, due to the preliminary nature of the designs considered, more detailed designs will be necessary to enable these concepts to fully meet the safety requirements.

Klein, A. C.↗

NASA NTRS1993

Development of a software safety process and a case study of its use

The goal of this research is to continue the development of a comprehensive approach to software safety and to evaluate the approach with a case study. The case study is a major part of the project, and it involves the analysis of a specific safety-critical system from the medical equipment domain. The particular application being used was selected because of the availability of a suitable candidate system. We consider the results to be generally applicable and in no way particularly limited by the domain. The research is concentrating on issues raised by the specification and verification phases of the software lifecycle since they are central to our previously-developed rigorous definitions of software safety. The theoretical research is based on our framework of definitions for software safety. In the area of specification, the main topics being investigated are the development of techniques for building system fault trees that correctly incorporate software issues and the development of rigorous techniques for the preparation of software safety specifications. The research results are documented. Another area of theoretical investigation is the development of verification methods tailored to the characteristics of safety requirements. Verification of the correct implementation of the safety specification is central to the goal of establishing safe software. The empirical component of this research is focusing on a case study in order to provide detailed characterizations of the issues as they appear in practice, and to provide a testbed for the evaluation of various existing and new theoretical results, tools, and techniques. The Magnetic Stereotaxis System is summarized.

Knight, John C.↗

NASA NTRS2021

Evaluation of Sensor Uncertainty Mitigation Methods for Detect-and-Avoid Systems

The impact of sensor noise on the performance of Detect-And-Avoid (DAA) systems can be reduced by implementing various mitigation schemes. This paper evaluates two such methods. One of them is the Sensor Uncertainty Mitigation (SUM) method, implemented in the Detect and Avoid Alerting Logic for Unmanned Systems (DAIDALUS) algorithm, a reference implementation in the DAA minimum operational performance standards. The second method is the Virtual Intruder State Aggregation (VISA), which averages multiple subsequent intruder states extrapolated to the current (most recent) time into a single ``aggregated`` intruder state. The VISA method can be used either individually as a sensor noise mitigation method in its own right, or in combination with DAIDALUS SUM. The performance of these methods is evaluated using three safety and operational suitability metrics and compared with a baseline configuration using static safety buffers. A large number of encounters representative of low-speed unmanned aircraft against non-cooperative manned aircraft, not equipped with a broadcasting transponder or ADS-B out system, are simulated and evaluated. An air-to-air radar model produces representative sensor noise for the DAA system. Results show that increasing the DAIDALUS SUM parameters for horizontal and vertical uncertainty improves the safety metric at the cost of increasing the number of actionable alerts leading to increased workload. A range of SUM parameters is recommended as suitable values for the type of operations considered for this work. VISA was found to be almost as effective as other noise mitigation methods even when it was used alone. Combining VISA with DAIDALUS SUM achieved the best performance among all investigated methods used with DAIDALUS. General trends and optimal SUM configurations were found to be nearly the same for two large and very different encounter data sets.

Detect-and-Avoid Systems↗

NASA NTRS2019

Urban Area Unmanned Aerial Systems Sensor Capabilities for Ensuring Ground Hazards Safety

Unmanned aerial systems (UASs) in urban areas can pose significant safety risks to dynamic ground objects (DGOs) such as people, pets, and bikes; especially for off-nominal emergency traverses and landings. This paper will examine a framework for evaluating the UAS safety benefits which can be achieved by classifying DGO hazards, modeling their behavior, and assigning collision costs. DGOs are assumed to be any ground objects which are either moving or capable of moving. Safety benefits will be assessed by analyzing metrics computed from UAS and DGO trajectories which take into account intent and uncertainties. This paper will establish the theoretical relationships mapping these trajectories and DGO classifications to safety levels. Sensor capabilities will be mapped to DGO trajectory uncertainties, so that safety can be directly estimated from the sensor specifications for a given UAS trajectory.

Bouyssounouse, Xavier↗

NASA NTRS1986

Evaluation of advanced high rate Li-SOCl2 cells

Under NASA sponsorship, JPL is developing advanced, high rate Li-SOCl2 cells for future space missions. As part of this effort, Li-SOCl2 cells of various designs were examined for performance and safety. The cells differed from one another in several aspects, such as: nature of carbon cathode, catalysts, cell configuration, case polarity, and safety devices. Performance evaluation included constant-current discharge over a range of currents and temperatures. Abuse-testing consisted of shortcircuiting, charging, and over-discharge. Energy densities greater than 300 Wh/Kg at the C/2 rate were found for some designs. A cell design featuring a high-surface-area carbon cathode was found to deliver nearly 500 Wh/Kg at moderate discharge rates. Temperature influenced the performance significantly.

Deligiannis, F.↗