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NASA NTRS2005

A Simple, Powerful Method for Optimal Guidance of Spacecraft Formations

One of the most interesting and challenging aspects of formation guidance law design is the coupling of the orbit design and the science return. The analyst s role is more complicated than simply to design the formation geometry and evolution. He or she is also involved in designing a significant portion of the science instrument itself. The effectiveness of the formation as a science instrument is intimately coupled with the relative geoniet,ry and evolution of the collection of spacecraft. Therefore, the science return can be maximized by optimizing the orbit design according to a performance metric relevant to the science mission goals. In this work, we present a simple method for optimal formation guidance that is applicable to missions whose performance metric, requirements, and constraints can be cast as functions that are explicitly dependent upon the orbit states and spacecraft relative positions and velocities. We present a general form for the cost and constraint functions, and derive their semi-analytic gradients with respect to the formation initial conditions. The gradients are broken down into two types. The first type are gradients of the mission specific performance metric with respect to formation geometry. The second type are derivatives of the formation geometry with respect to the orbit initial conditions. The fact that these two types of derivatives appear separately allows us to derive and implement a general framework that requires minimal modification to be applied to different missions or mission phases. To illustrate the applicability of the approach, we conclude with applications to twc missims: the Magnetospheric Mu!tiscale mission (MMS), a,nd the TJaser Interferometer Space Antenna (LISA).

Hughes, Steven P.↗

NASA NTRS2006

A Simple, Powerful Method for Optimal Guidance of Spacecraft Formations

One of the most interesting and challenging aspects of formation guidance law design is the coupling of the orbit design and the science return. The analyst's role is more complicated than simply to design the formation geometry and evolution. He or she is also involved in designing a significant portion of the science instrument itself. The effectiveness of the formation as a science instrument is intimately coupled with the relative geometry and evolution of the collection of spacecraft. Therefore, the science return can be maximized by optimizing the orbit design according to a performance metric relevant to the science mission goals. In this work, we present a simple method for optimal formation guidance that is applicable to missions whose performance metric, requirements, and constraints can be cast as functions that are explicitly dependent upon the orbit states and spacecraft relative positions and velocities. We present a general form for the cost and constraint functions, and derive their semi-analytic gradients with respect to the formation initial conditions. The gradients are broken down into two types. The first type are gradients of the mission specific performance metric with respect to formation geometry. The second type are derivatives of the formation geometry with respect to the orbit initial conditions. The fact that these two types of derivatives appear separately allows us to derive and implement a general framework that requires minimal modification to be applied to different missions or mission phases. To illustrate the applicability of the approach, we conclude with applications to two missions: the Magnetospheric Multiscale mission (MMS) , and the Laser Interferometer Space Antenna (LISA).

Hughes, Steven P.↗

NASA NTRS2006

Computer Modeling of Protocellular Functions: Peptide Insertion in Membranes

Lipid vesicles became the precursors to protocells by acquiring the capabilities needed to survive and reproduce. These include transport of ions, nutrients and waste products across cell walls and capture of energy and its conversion into a chemically usable form. In modem organisms these functions are carried out by membrane-bound proteins (about 30% of the genome codes for this kind of proteins). A number of properties of alpha-helical peptides suggest that their associations are excellent candidates for protobiological precursors of proteins. In particular, some simple a-helical peptides can aggregate spontaneously and form functional channels. This process can be described conceptually by a three-step thermodynamic cycle: 1 - folding of helices at the water-membrane interface, 2 - helix insertion into the lipid bilayer and 3 - specific interactions of these helices that result in functional tertiary structures. Although a crucial step, helix insertion has not been adequately studied because of the insolubility and aggregation of hydrophobic peptides. In this work, we use computer simulation methods (Molecular Dynamics) to characterize the energetics of helix insertion and we discuss its importance in an evolutionary context. Specifically, helices could self-assemble only if their interactions were sufficiently strong to compensate the unfavorable Free Energy of insertion of individual helices into membranes, providing a selection mechanism for protobiological evolution.

Rodriquez-Gomez, D.↗

NASA NTRS1995

Optimization of Coherent Lidar Performance Using Graded- Reflectance Transmitter Resonator Optics in the Low Equivalent Fresnel Number Region

Using a diffractive eigenmode treatment to model the laser output, we show that graded-reflectance resonator optics offer significant efficiency benefits over conventional hard-edge coupled unstable resonators in the context of coherent detection lidar applications. Extending previous work pertinent to the high equivalent Fresnel number regime, we have modelled the optimum performance of a notional super-Gaussian coupled cavity as a function of the key resonator parameters in the low equivalent Fresnel number regime.

lidar graded-reflectance transmitter resonator↗

NASA NTRS2011

NASA Schedule Management Handbook

The purpose of schedule management is to provide the framework for time-phasing, resource planning, coordination, and communicating the necessary tasks within a work effort. The intent is to improve schedule management by providing recommended concepts, processes, and techniques used within the Agency and private industry. The intended function of this handbook is two-fold: first, to provide guidance for meeting the scheduling requirements contained in NPR 7120.5, NASA Space Flight Program and Project Management Requirements, NPR 7120.7, NASA Information Technology and Institutional Infrastructure Program and Project Requirements, NPR 7120.8, NASA Research and Technology Program and Project Management Requirements, and NPD 1000.5, Policy for NASA Acquisition. The second function is to describe the schedule management approach and the recommended best practices for carrying out this project control function. With regards to the above project management requirements documents, it should be noted that those space flight projects previously established and approved under the guidance of prior versions of NPR 7120.5 will continue to comply with those requirements until project completion has been achieved. This handbook will be updated as needed, to enhance efficient and effective schedule management across the Agency. It is acknowledged that most, if not all, external organizations participating in NASA programs/projects will have their own internal schedule management documents. Issues that arise from conflicting schedule guidance will be resolved on a case by case basis as contracts and partnering relationships are established. It is also acknowledged and understood that all projects are not the same and may require different levels of schedule visibility, scrutiny and control. Project type, value, and complexity are factors that typically dictate which schedule management practices should be employed.

Source record↗

NASA NTRS2011

Evidence Report, Risk of Inadequate Design of Human and Automation/Robotic Integration

The success of future exploration missions depends, even more than today, on effective integration of humans and technology (automation and robotics). This will not emerge by chance, but by design. Both crew and ground personnel will need to do more demanding tasks in more difficult conditions, amplifying the costs of poor design and the benefits of good design. This report has looked at the importance of good design and the risks from poor design from several perspectives: 1) If the relevant functions needed for a mission are not identified, then designs of technology and its use by humans are unlikely to be effective: critical functions will be missing and irrelevant functions will mislead or drain attention. 2) If functions are not distributed effectively among the (multiple) participating humans and automation/robotic systems, later design choices can do little to repair this: additional unnecessary coordination work may be introduced, workload may be redistributed to create problems, limited human attentional resources may be wasted, and the capabilities of both humans and technology underused. 3) If the design does not promote accurate understanding of the capabilities of the technology, the operators will not use the technology effectively: the system may be switched off in conditions where it would be effective, or used for tasks or in contexts where its effectiveness may be very limited. 4) If an ineffective interaction design is implemented and put into use, a wide range of problems can ensue. Many involve lack of transparency into the system: operators may be unable or find it very difficult to determine a) the current state and changes of state of the automation or robot, b) the current state and changes in state of the system being controlled or acted on, and c) what actions by human or by system had what effects. 5) If the human interfaces for operation and control of robotic agents are not designed to accommodate the unique points of view and operating environments of both the human and the robotic agent, then effective human-robot coordination cannot be achieved.

Zumbado, Jennifer Rochlis↗

NASA NTRS2005

Pressure Dependence of Insulator-Insulator Contact Charging

The mechanism of insulator-insulator triboelectric (contact) charging is being studied by the Electrostatics and Surface Physics Laboratory at KSC. The hypothesis that surface ion exchange is the primary mechanism is being tested experimentally. A two-phase model based on a small partial pressure of singly charged ions in an ambient ideal gas in equilibrium with a submonolayer adsorbed film will provide predictions about charging as a function Of ion mass, pressure, temperature, and surface adsorption energy. Interactions between ions will be considered in terms of coulombic and screened potential energies. This work is yielding better understanding of the triboelectrification of insulators, which is an important problem in. space exploration technology. The work is also relevant to important industrial processes such as xerography and the application of paints and coatings. Determining a better understanding of the fundamental mechanism of insulator-insulator triboelectrification will hopefully lead to better means of eliminating or at least mitigating its hazards and enhancing its useful applications.

Hogue, Michael D.↗

NASA NTRS2012

Atomic Data and Spectral Line Intensities for Ca IX

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ca IX. We include in the calculations the 33 lowest configurations in the n = 3, 4, 5 complexes, corresponding to 283 fine structure levels in the 3l3l ', 3l4l'' and 3l4l''' configurations, where l,l' = s, p, d, l '' = s, p, d, f and l''' = s, p, d, f, g. Collision strengths are calculated at five incident energies for all transitions: 5.8, 13.6, 24.2, 38.6 and 57.9 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.0055 Ry and 0.23 Ry depending on the levels involved. Calculations have been carried out using the Flexible Atomic Code and the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates calculated in the present work, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14)/cubic cm range and at an electron temperature of log T(sub e)(K)=5.8, corresponding to the maximum abundance of Ca IX. Spectral line intensities are calculated, and their diagnostic relevance is discussed.

Landi, E.↗

NASA NTRS2011

Atomic Data and Spectral Line Intensities for Ni XV

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ni XV.Weinclude in the calculations the 9 lowest configurations, corresponding to 126 fine structure levels: 3s23p2, 3s3p3, 3s23p3d, 3p4, 3s3p23d, and 3s2 3p4l with l =, s, p, d, f. Collision strengths are calculated at five incident energies for all transitions: 7.8, 18.5, 33.5, 53.5, and 80.2 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.004 and 0.28 Ry depending on the levels involved. Calculations have been carried out using the Flexible Atomic Code and the distorted-wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates calculated in the present work, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14)/cu cm range and at an electron temperature of log T(sub e)(K) = 6.4, corresponding to the maximum abundance of Ni XV. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.

Landi, E.↗

NASA NTRS2012

NIRPS: A Year of Progress and Challenge

In the past 14 months NIRPS has gone from an idea on a sheet of paper to a working organization, performing tasks of national scale. NIRPS is beginning to establish itself among the Propulsion Community. Need is recognized for a coordination and integration function across the US Government s propulsion activities. NIRPS acts as a collaboration agent - serves as a catalyst and multi-agency facilitator NIRPS is leading a high-priority Government-wide task. 2012 Defense Authorization Act, Sec 1095; Develop National Rocket Propulsion Strategy. Beginning to perform in accordance with Grand Challenges. Performing to an Executable plan, adjusting to to Center and Agency priorities. Challenges remain to building a sustainable Institute. Effective integration and Coordination with other Government Agencies. Continued Active engagement with Industry and Academia. Building an Efficient and Responsive Governance System for a growing Institute.

Thomas, Dale↗

NASA NTRS2013

Development of a SMA-Based Slat-Cove Filler for Reduction of Aeroacoustic Noise Associated With Transport-Class Aircraft Wings

Airframe noise is a significant part of the overall noise produced by typical, transport-class aircraft during the approach and landing phases of flight. Leading-edge slat noise is a prominent source of airframe noise. The concept of a slat-cove filler was proposed in previous work as an effective means of mitigating slat noise. Bench-top models were deployed at 75% scale to study the feasibility of producing a functioning slat-cove filler. Initial results from several concepts led to a more-focused effort investigating a deformable structure based upon pseudoelastic SMA materials. The structure stows in the cavity between the slat and main wing during cruise and deploys simultaneously with the slat to guide the aerodynamic flow suitably for low noise. A qualitative parametric study of SMA-enabled, slat-cove filler designs was performed on the bench-top. Computational models were developed and analyses were performed to assess the displacement response under representative aerodynamic load. The bench-top and computational results provide significant insight into design trades and an optimal design.

Turner, Travis L.↗

NASA NTRS2014

Ballistic Performance Model of Crater Formation in Monolithic, Porous Thermal Protection Systems

Porous monolithic ablative systems insulate atmospheric reentry vehicles from reentry plasmas generated by atmospheric braking from orbital and exo-orbital velocities. Due to the necessity that these materials create a temperature gradient up to several thousand Kelvin over their thickness, it is important that these materials are near their pristine state prior to reentry. These materials may also be on exposed surfaces to space environment threats like orbital debris and meteoroids leaving a probability that these exposed surfaces will be below their prescribed values. Owing to the typical small size of impact craters in these materials, the local flow fields over these craters and the ablative process afford some margin in thermal protection designs for these locally reduced performance values. In this work, tests to develop ballistic performance models for thermal protection materials typical of those being used on Orion are discussed. A density profile as a function of depth of a typical monolithic ablator and substructure system is shown in Figure 1a.

Miller, J. E.↗

NASA NTRS2014

Increased Tensile Strength of Carbon Nanotube Yarns and Sheets through Chemical Modification and Electron Beam Irradiation

The inherent strength of individual carbon nanotubes offers considerable opportunity for the development of advanced, lightweight composite structures. Recent work in the fabrication and application of carbon nanotube (CNT) forms such as yarns and sheets has addressed early nanocomposite limitations with respect to nanotube dispersion and loading; and has pushed the technology toward structural composite applications. However, the high tensile strength of an individual CNT has not directly translated to macro-scale CNT forms where bulk material strength is limited by inter-tube electrostatic attraction and slippage. The focus of this work was to assess post processing of CNT sheet and yarn to improve the macro-scale strength of these material forms. Both small molecule functionalization and e-beam irradiation was evaluated as a means to enhance tensile strength and Youngs modulus of the bulk CNT material. Mechanical testing results revealed a tensile strength increase in CNT sheets by 57 when functionalized, while an additional 48 increase in tensile strength was observed when functionalized sheets were irradiated; compared to unfunctionalized sheets. Similarly, small molecule functionalization increased yarn tensile strength up to 25, whereas irradiation of the functionalized yarns pushed the tensile strength to 88 beyond that of the baseline yarn.

composites↗

NASA NTRS2012

Managing the Perception of Advanced Technology Risks in Mission Proposals

Through my work in the project proposal office I became interested in how technology advancement efforts affect competitive mission proposals. Technology development allows for new instruments and functionality. However, including technology advancement in a mission proposal often increases perceived risk. Risk mitigation has a major impact on the overall evaluation of the proposal and whether the mission is selected. In order to evaluate the different approaches proposals took I compared the proposals claims of heritage and technology advancement to the sponsor feedback provided in the NASA debriefs. I examined a set of Discovery 2010 Mission proposals to draw patterns in how they were evaluated and come up with a set of recommendations for future mission proposals in how they should approach technology advancement to reduce the perceived risk.

proposals↗

NASA NTRS2015

Multi-Objective Hybrid Optimal Control for Interplanetary Mission Planning

Preliminary design of low-thrust interplanetary missions is a highly complex process. The mission designer must choose discrete parameters such as the number of flybys, the bodies at which those flybys are performed, and in some cases the final destination. Because low-thrust trajectory design is tightly coupled with systems design, power and propulsion characteristics must be chosen as well. In addition, a time-history of control variables must be chosen which defines the trajectory. There are often many thousands, if not millions, of possible trajectories to be evaluated. The customer who commissions a trajectory design is not usually interested in a point solution, but rather the exploration of the trade space of trajectories between several different objective functions. This can be very expensive process in terms of the number of human analyst hours required. An automated approach is therefore very desirable. This work presents such an approach by posing the mission design problem as a multi-objective hybrid optimal control problem. The methods is demonstrated on hypothetical mission to the main asteroid belt and to Deimos.

Trajectory Design↗

NASA NTRS2015

Reconfigurable, Cognitive Software-Defined Radio

Software-defined radio (SDR) technology allows radios to be reconfigured to perform different communication functions without using multiple radios to accomplish each task. Intelligent Automation, Inc., has developed SDR platforms that switch adaptively between different operation modes. The innovation works by modifying both transmit waveforms and receiver signal processing tasks. In Phase I of the project, the company developed SDR cognitive capabilities, including adaptive modulation and coding (AMC), automatic modulation recognition (AMR), and spectrum sensing. In Phase II, these capabilities were integrated into SDR platforms. The reconfigurable transceiver design employs high-speed field-programmable gate arrays, enabling multimode operation and scalable architecture. Designs are based on commercial off-the-shelf (COTS) components and are modular in nature, making it easier to upgrade individual components rather than redesigning the entire SDR platform as technology advances.

Bhat, Arvind↗

NASA NTRS2018

Estimating Software Reliability for Space Launch Vehicles in Probabilistic Risk Assessment (PRA)

It is acutely recognized in the Probabilistic Risk assessment (PRA) field that software plays a defining role in overall system reliability for all modern systems across a wide variety of industries. Regardless if the software is embedded firmware for working components or elements, part of a Human-Machine-Interface, or automated command and control logic, the success of the software to fulfill its function under nominal and off-nominal environments will be a dominant contributor to system reliability. It is also recognized that software reliability prediction and estimation is one of the more challenging and questionable aspects of any PRA or system analyses due to the nature of software and its integration with physics based systems. Irrespective of this dichotomy, any incorporation of software reliability methods requires that the contributions are accountable, quantitative, and tractable. This paper provides a brief overview of software reliability methods, establishes some minimum requirements that the methods should incorporate for completeness, and provides a logic structure for applying software reliability. Model resolution will be discussed that supports current testing plans and trade studies. We will provide initial recommendations for use in the NASA PRA and present a future dynamic option for software and PRA. Space Launch Vehicle Software is recognized to be reliable in static conditions, yet relatively vulnerable to a set of failure modes in changing environments/flight phases. Two quantitative methods were chosen to incorporate software reliability into a Space Launch Vehicle PRA accounting for phase adjustments. One method predicts latent software failure using statistical methods, and the second provides estimates of coding errors and software operating system failures based on test and historical data, respectively. Software uncertainty will also be discussed. We determined that recommendations for PRA software reliability should be modeled at the software module level where multiple software components compose a module and combinations of the software architecture can lead to a functional failure.

Novack, Steven↗

NASA NTRS2018

Estimating Software Reliability for Space Launch Vehicles in Probabilistic Risk Assessment (PRA)

It is acutely recognized in the Probabilistic Risk Assessment (PRA) field that software plays a defining role in overall system reliability for all modern systems across a wide variety of industries. Regardless of whether the software is embedded firmware for working components or elements, part of a Human-Machine-Interface, or automated command and control logic, the success of the software to fulfill its function under nominal and off-nominal environments will be a dominant contributor to system reliability. It is also recognized that software reliability prediction and estimation is one of the more challenging and questionable aspects of any PRA or system analyses due to the nature of software and its integration with physics based systems. Irrespective of this dichotomy, any incorporation of software reliability methods requires that the contributions are accountable, quantitative, and tractable. This paper provides a brief overview of software reliability methods, establishes some minimum requirements that the methods should incorporate for completeness, and provides a logic structure for applying software reliability. Model resolution will be discussed that supports current testing plans and trade studies. We will provide initial recommendations for use in the National Aeronautics and Space Administration (NASA) PRA and present a future dynamic option for software and PRA. Space Launch Vehicle software is recognized to be reliable in static conditions, yet relatively vulnerable to a set of failure modes in changing environments/flight phases. Two quantitative methods were chosen to incorporate software reliability into a Space Launch Vehicle PRA accounting for phase adjustments. One method predicts latent software failure using statistical methods, and the second provides estimates of coding errors and software operating system failures based on test and historical data. Software uncertainty will also be discussed. It is determined that recommendations for PRA software reliability should be modeled at the software module level where multiple software components compose a module and combinations of the software architecture can lead to a functional failure.

Steven D. Novack↗