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NASA NTRS2014

Spacecraft Charging in Geostationary Transfer Orbit

The 700 km x 5.8 Re orbit of the two Van Allen Probes spacecraft provide a unique opportunity to investigate spacecraft charging in geostationary transfer orbits. We use records from the Helium Oxygen Proton Electron (HOPE) plasma spectrometer to identify candidate surface charging events based on the "ion line" charging signature in the ion records. We summarize the energetic particle environment and the conditions necessary for charging to occur in this environment. We discuss the altitude, duration, and magnitude of events observed in the Van Allen Probes from the beginning of the mission to present time. In addition, we explore what information the dual satellites provide on the spatial and temporal variations in the charging environments.

Parker, Linda Neergaard↗

NASA NTRS2016

Image Navigation and Registration Performance Assessment Tool Set for the GOES-R Advanced Baseline Imager and Geostationary Lightning Mapper

The GOES-R Flight Project has developed an Image Navigation and Registration (INR) Performance Assessment Tool Set (IPATS) for measuring Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM) INR performance metrics in the post-launch period for performance evaluation and long term monitoring. For ABI, these metrics are the 3-sigma errors in navigation (NAV), channel-to-channel registration (CCR), frame-to-frame registration (FFR), swath-to-swath registration (SSR), and within frame registration (WIFR) for the Level 1B image products. For GLM, the single metric of interest is the 3-sigma error in the navigation of background images (GLM NAV) used by the system to navigate lightning strikes. 3-sigma errors are estimates of the 99.73rd percentile of the errors accumulated over a 24-hour data collection period. IPATS utilizes a modular algorithmic design to allow user selection of data processing sequences optimized for generation of each INR metric. This novel modular approach minimizes duplication of common processing elements, thereby maximizing code efficiency and speed. Fast processing is essential given the large number of sub-image registrations required to generate INR metrics for the many images produced over a 24-hour evaluation period. Another aspect of the IPATS design that vastly reduces execution time is the off-line propagation of Landsat based truth images to the fixed grid coordinates system for each of the three GOES-R satellite locations, operational East and West and initial checkout locations. This paper describes the algorithmic design and implementation of IPATS and provides preliminary test results.

Image Navigation↗

NASA NTRS2016

Image Navigation and Registration (INR) Performance Assessment Tool Set (IPATS) for the GOES-R Advanced Baseline Imager and Geostationary Lightning Mapper

The GOES-R Flight Project has developed an Image Navigation and Registration (INR) Performance Assessment Tool Set (IPATS) for measuring Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM) INR performance metrics in the post-launch period for performance evaluation and long term monitoring. For ABI, these metrics are the 3-sigma errors in navigation (NAV), channel-to-channel registration (CCR), frame-to-frame registration (FFR), swath-to-swath registration (SSR), and within frame registration (WIFR) for the Level 1B image products. For GLM, the single metric of interest is the 3-sigma error in the navigation of background images (GLM NAV) used by the system to navigate lightning strikes. 3-sigma errors are estimates of the 99.73rd percentile of the errors accumulated over a 24 hour data collection period. IPATS utilizes a modular algorithmic design to allow user selection of data processing sequences optimized for generation of each INR metric. This novel modular approach minimizes duplication of common processing elements, thereby maximizing code efficiency and speed. Fast processing is essential given the large number of sub-image registrations required to generate INR metrics for the many images produced over a 24 hour evaluation period. Another aspect of the IPATS design that vastly reduces execution time is the off-line propagation of Landsat based truth images to the fixed grid coordinates system for each of the three GOES-R satellite locations, operational East and West and initial checkout locations. This paper describes the algorithmic design and implementation of IPATS and provides preliminary test results.

Image Registration↗

NASA NTRS2015

Low-Power Operation and Plasma Characterization of a Qualification Model SPT-140 Hall Thruster for NASA Science Missions

Hall thruster systems based on commercial product lines can potentially lead to lower cost electric propulsion (EP) systems for deep space science missions. A 4.5-kW SPT-140 Hall thruster presently under qualification testing by SSL leverages the substantial heritage of the SPT-100 being flown on Russian and US commercial satellites. The Jet Propulsion Laboratory is exploring the use of commercial EP systems, including the SPT-140, for deep space science missions, and initiated a program to evaluate the SPT-140 in the areas of low power operation and thruster operating life. A qualification model SPT-140 designated QM002 was evaluated for operation and plasma properties along channel centerline, from 4.5 kW to 0.8 kW. Additional testing was performed on a development model SPT-140 designated DM4 to evaluate operation with a Moog proportional flow control valve (PFCV). The PFCV was commanded by an SSL engineering model PPU-140 Power Processing Unit (PPU). Performance measurements on QM002 at 0.8 kW discharge power were 50 mN of thrust at a total specific impulse of 1250 s, a total thruster efficiency of 0.38, and discharge current oscillations of under 3% of the mean current. Steady-state operation at 0.8 kW was demonstrated during a 27 h firing. The SPT-140 DM4 was operated in closed-loop control of the discharge current with the PFCV and PPU over discharge power levels of 0.8-4.5 kW. QM002 and DM4 test data indicate that the SPT-140 design is a viable candidate for NASA missions requiring power throttling down to low thruster input power.

Garner, Charles E.↗

NASA NTRS2022

Characterization of Response Times based on Voice Communication and Traffic Surveillance Data

A barrier to the integration of remotely piloted aircraft operations in the U.S. National Airspace System is the latency of voice communications between the air traffic controller and the remote pilot, and the latency of communication between the aircraft and the remote pilot. The latency can be substantial especially when satellite-based beyond-radio-line-of-sight communication and relay through the aircraft are employed. This study uses voice recordings of controller-pilot communications and aircraft track data to establish a baseline of pilot readback latencies and maneuver detection delays in the current piloted operations. A machine learning pipeline was developed to parse the contents of the air traffic control clearances including the callsigns using natural language processing. After manually validating the results obtained using the pipeline, the average pilot readback latency was found to be about 0.6 seconds. The average latency between the end of maneuver (inferred from track data), initiated by the pilot in response to the clearance, and the end of clearance was found to be about 176 seconds for altitude change commands, 69 seconds for heading change commands, and 182 seconds for speed change commands. The average latency between the beginning of maneuver and the end of clearance was found to be about 17 seconds for altitude change commands, 17seconds for heading change commands, and 25 seconds for speed change commands.

controller-pilot communication, communication late↗

NASA NTRS2022

Characterization of Response Times Based on Voice Communication and Traffic Surveillance Data

controller-pilot communication↗

NASA NTRS2024

Improved Modelling of SEP Event Onset Within the WSA–Enlil–SEPMOD Framework

Multi-spacecraft observations of solar energetic particle (SEP) events not only enable a deeper understanding and development of particle acceleration and transport theories but also provide important constraints for model validation efforts. However, because of computational limitations, a given physics-based SEP model is usually best suited to capture a particular phase of an SEP event, rather than its whole development from onset through decay. For example, magnetohydrodynamic (MHD) models of the heliosphere often incorporate solar transients only at the outer boundary of their so-called coronal domain – usually set at a heliocentric distance of 20–30 R⊙. This means that particle acceleration at coronal mass ejection (CME)-driven shocks is also computed from this boundary onwards, leading to simulated SEP event onsets that can be many hours later than observed, since shock waves can form much lower in the solar corona. In this work, we aim to improve the modelled onset of SEP events by inserting a “fixed source” of particle injection at the outer boundary of the coronal domain of the coupled WSA–Enlil 3D MHD model of the heliosphere. The SEP model that we employ for this effort is Solar Energetic Particle MODel (SEPMOD), a physics-based test-particle code based on a field line tracer and adiabatic invariant conservation. We apply our initial tests and results of SEPMOD’s fixed-source option to the 2021 October 9 SEP event, which was detected at five well-separated locations in the inner heliosphere – Parker Solar Probe, STEREO-A, Solar Orbiter, BepiColombo, and near-Earth spacecraft.

Solar eruptions↗

NASA NTRS1983

Early estimation of resource expenditures and program size

A substantial amount of software engineering research effort was focused on the development of software estimation models. A measure of lines of code was derived based on the origin of the delivered code, L sub dev = N + E + 0.2 (S + O) (where L sub dev = developed lines of code, N = newly implemented lines of code, E = extensively modified lines of code, S = slightly modified lines of code, and O = old unchanged lines of code) that is substituted in the following equation H sub s = aL sup b (where H sub s = staff-hours of effort, L = lines of code, a = a constant, and b = a constant). The limitations of this model are discussed and some alternative estimation models that can be used earlier in the development process are proposed.

Card, D.↗

NASA NTRS1991

Prototype high speed optical delay line for stellar interferometry

The long baselines of the next-generation ground-based optical stellar interferometers require optical delay lines which can maintain nm-level path-length accuracy while moving at high speeds. NASA-JPL is currently designing delay lines to meet these requirements. The design is an enhanced version of the Mark III delay line, with the following key features: hardened, large diameter wheels, rather than recirculating ball bearings, to reduce mechanical noise; a friction-drive cart which bears the cable-dragging forces, and drives the optics cart through a force connection only; a balanced PZT assembly to enable high-bandwidth path-length control; and a precision aligned flexural suspension for the optics assembly to minimize bearing noise feedthrough. The delay line is fully programmable in position and velocity, and the system is controlled with four cascaded software feedback loops. Preliminary performance is a jitter in any 5 ms window of less than 10 nm rms for delay rates of up to 28 mm/s; total jitter is less than 10 nm rms for delay rates up to 20 mm/s.

Colavita, M. M.↗

NASA NTRS2003

Caustics and Caustic-Diffraction in Laser Shadowgraphy of a Sessile Drop and Identification of Profile Near Contact Line

This paper presents an optical method based on the caustics and caustic-difraction in laser shadowgaphy of a sessile drop to identify and estimate the drop profile near the contact line. A parallel laser beam passes through a liquid sessile drop placed on a transparent substrate to produce a shadowgraphic image of the drop on the screen far from the substrate. Along the inflection line of the drop the Gaussian curvature of the wavefront deformed by the drop vanishes, and therefore the inflection line gives caustics in the far field of the wave, which can be seen on the screen. The neighboring light rays at both sides of the inflection line interfere with each other to form interference fringes at the inner side of the caustics. According to the pattern of the caustics, the drop-profile shape can be identified and estimated.

Zhang, Neng-Li↗

NASA NTRS1985

Elevated temperature creep-rupture behavior of the single crystal nickel-base superalloy NASAIR 100

The creep and rupture behavior of 001-line-oriented single crystals of the nickel-base superalloy NASAIR 100 was investigated at temperatures of 925 and 1000 C. In the stress and temperature ranges studied, the steady state creep rate, time to failure, time to the onset of secondary creep, and the time to the onset of tertiary creep all exhibited power law dependencies on the applied stress. The creep rate exponents for this alloy were between seven and eight, and the modulus-corrected activation energy for creep was approximately 350 kjoule/mole, which was comparable to the measured activation energy for Ostwald ripening of the gamma-prime precipitates. Oriented gamma-prime coarsening to form lamellae perpendicular to the applied stress was very prominent during creep. At 1000 C, the formation of a continuous gamma-gamma-prime lamellar structure was completed during the primary creep stage. Shear through the gamma-gamma-prime interface is considerd to be the rate limiting step in the deformation process. Gradual thickening of the lamellae appeared to be the cause of the onset of tertiary creep. At 925 C, the fully developed lamellar structure was not achieved until the secondary or tertiary creep stages. At this temperature, the gamma-gamma-prime lamellar structure did not appear to be as beneficial for creep resistance as at the higher temperature.

Nathal, M. V.↗

NASA NTRS1992

The interstellar deuterium-to-hydrogen ratio - A reevaluation of Lyman absorption-line measurements

The D/H ratio in the local interstellar medium is evaluated based upon previously published measurements of Lyman absorption lines together with the hypothesis that the D/H ratio is constant. A unique value for the D/H ratio of 1.5 (+/- 0.2) x 10 exp -5 by number is shown to be consistent with all published determinations made with the Copernicus and the International Ultraviolet Explorer satellites. The possibility that the D/H ratio may vary substantially in the local interstellar medium is considered and found to be unnecessary.

Mccullough, Peter R.↗

NASA NTRS1974

On the steady flow of gas from the nuclei of Seyfert galaxies

Heating of gas energy released during explosive events produces hot winds in Seyfert nuclei. Steady-state solutions indicate that supersonic velocities up to about 800 km per sec are obtainable. Lyman continuum radiation emitted by the wind ionizes and maintains temperature of cooler gas clouds seen in emission, and dominates energy losses during early stages of expansion. A study of stability of the thermal equilibrium state leads to a two-component model: a hot stable phase (the wind), in pressure equilibrium with a cooler stable phase (clouds). Extreme variations in cloud electron densities are a consequence of the steep decrease with radius of external pressure. Cloud dynamics are related to the radius of formation and internal parameters. Permitted lines of H are emitted by high-density clouds formed at the base of the wind, while forbidden lines arise in radially moving clouds, produced throughout the wind.

Wolfe, A. M.↗

NASA NTRS1993

Solar coronal observations and formation of the He II 304 A line

Although a large body of recent work supports the formation of the He II 304 A resonance line by collisional excitation in the quiet sun, the formation mechanism is less clear in strong coronal active regions and flares. The 1989 May 5 flight of the Goddard Solar Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS-3) provided a data set that is well suited to addressing this question. This paper develops a method of assessment of the line formation mechanism that is based on simple non-LTE theory and is applied to these data. The results support the conclusion of other authors that the 304 A line is formed by collisional excitation in the quiet sun, but that photoionization-recombination (p-r) may play a significant role in coronal active regions, and that p-r is important, and may even be predominant, in many flares.

Jordan, S. D.↗

NASA NTRS1990

Real-time diagnostics of the reusable rocket engine using on-line system identification

A model-based failure diagnosis system has been proposed for real-time diagnosis of SSME failures. Actuation, sensor, and system degradation failure modes are all considered by the proposed system. In the case of SSME actuation failures, it was shown that real-time identification can effectively be used for failure diagnosis purposes. It is a direct approach since it reduces the detection, isolation, and the estimation of the extent of the failures to the comparison of parameter values before and after the failure. As with any model-based failure detection system, the proposed approach requires a fault model that embodies the essential characteristics of the failure process. The proposed diagnosis approach has the added advantage that it can be used as part of an intelligent control system for failure accommodation purposes.

Guo, T.-H.↗

NASA NTRS2004

Comparing Ultraviolet Spectra against Calculations: Year 2 Results

The five-year goal of this effort is to calculate high fidelity mid-W spectra for individual stars and stellar systems for a wide range of ages, abundances, and abundance ratios. In this second year, the comparison of our calculations against observed high-resolution mid- W spectra was extended to stars as metal-rich as the Sun, and to hotter and cooler stars, further improving the list of atomic line parameters used in the calculations. We also published the application of our calculations based on the earlier list of line parameters to the observed mid-UV and optical spectra of a mildly metal-poor globular cluster in the nearby Andromeda galaxy, Messier 3 1.

Peterson, Ruth C.↗

NASA NTRS1974

An introduction to the Marshall information retrieval and display system

An on-line terminal oriented data storage and retrieval system is presented which allows a user to extract and process information from stored data bases. The use of on-line terminals for extracting and displaying data from the data bases provides a fast and responsive method for obtaining needed information. The system consists of general purpose computer programs that provide the overall capabilities of the total system. The system can process any number of data files via a Dictionary (one for each file) which describes the data format to the system. New files may be added to the system at any time, and reprogramming is not required. Illustrations of the system are shown, and sample inquiries and responses are given.

Source record↗

NASA NTRS1978

A new inversion method for remote sounding of planetary atmospheres

An inversion method which is applicable to high resolution observations where the spectral lines are fully resolved is described. The technique is based on matching calculated slopes of the spectral line profiles with slopes of the observed lineshapes, and involves finding an inverse solution to the derivative of the radiative transfer equation with respect to frequency. The method is applied to inversion of ozone absorption lines in the earth's atmosphere and the results are compared with those obtained by a conventional method. Advantages include narrower weighting functions providing a higher vertical resolution; higher atmospheric level which may be probed, more faster and more stable convergence, and more accurate retrieved profiles.

Abbas, M. M.↗