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At least 775 records · Page 43

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NASA NTRS1992

Frequency-response techniques for documentation and improvement of rotorcraft simulators

Pilot-in-the-loop characterizations are most naturally formulated in terms of end-to-end frequency responses, so a frequency-response-based method is the natural approach to assessing simulator dynamic fidelity. A comprehensive frequency-response approach used heavily by Ames Research Center researchers was described, and results were presented from a number of simulator fidelity assessment studies. Those studies included UH-60 mathematical model validation and upgrade, ASTOVL linear model extraction, and documentation of the Vertical Motion Simulator (at Ames Research Center) motion and visual system characteristics.

Tischler, Mark B.↗

NASA NTRS1993

Process control and recovery in the Link Monitor and Control Operator Assistant

This paper describes our approach to providing process control and recovery functions in the Link Monitor and Control Operator Assistant (LMCOA). The focus of the LMCOA is to provide semi-automated monitor and control to support station operations in the Deep Space Network. The LMCOA will be demonstrated with precalibration operations for Very Long Baseline Interferometry on a 70-meter antenna. Precalibration, the task of setting up the equipment to support a communications link with a spacecraft, is a manual, time consuming and error-prone process. One problem with the current system is that it does not provide explicit feedback about the effects of control actions. The LMCOA uses a Temporal Dependency Network (TDN) to represent an end-to-end sequence of operational procedures and a Situation Manager (SM) module to provide process control, diagnosis, and recovery functions. The TDN is a directed network representing precedence, parallelism, precondition, and postcondition constraints. The SM maintains an internal model of the expected and actual states of the subsystems in order to determine if each control action executed successfully and to provide feedback to the user. The LMCOA is implemented on a NeXT workstation using Objective C, Interface Builder and the C Language Integrated Production System.

Lee, Lorrine↗

NASA NTRS1992

Active structural control for damping augmentation and compensation of thermal distortion

A large space-based Focus Mission Interferometer is used as a testbed for the NASA Controls and Structures Interaction Program. Impedance-based adaptive structural control and control of thermal disturbances are demonstrated using an end-to-end simulation of the system's optical performance. Attention is also given to integrated optical/structural modeling and a hierarchical, layered control strategy.

Sirlin, S. W.↗

NASA NTRS1991

Lidar windshear detection for commercial aircraft

As part of the NASA/FAA National Integrated Windshear Program, a measurable windshear hazard index that can be remotely sensed from an aircraft is presented. This will provide a pilot information about the wind conditions he will experience at some later time if he continues along the present flight path. The technology analysis and end-to-end performance simulation, which measured S/N and resulting wind velocity errors for competing lidar systems, demonstrated that a Ho:YAG lidar at a wavelength of 2.1 microns and a CO2 lidar at 10.6 microns can give the pilot data about the line-of-sight component of a windshear threat in an area extending from his present position to two to four km in front of the aircraft.

Targ, Russell↗

NASA NTRS1991

The Space Station end-to-end data system - Linking architecture and operations

The paper describes tha data system designed for linking and integrating the Space Station Freedom (SSF) space and ground architecture and for providing instrument data to the user and discusses the operations of the system. Particular attention is given to the objectives, the organization, and the schedule of the SSF Program, the infrastructure elements of the end-to-end data system, the key active functional areas of the system, the types of data, the user scenario, and the SSF's space, space-to-ground, and ground infrastructures as they are active in support of the stipulated user scenario.

Fishkind, Stanley↗

NASA NTRS1992

An integrated modeling and design tool for advanced optical spacecraft

Consideration is given to the design and status of the Integrated Modeling of Optical Systems (IMOS) tool and to critical design issues. A multidisciplinary spacecraft design and analysis tool with support for structural dynamics, controls, thermal analysis, and optics, IMOS provides rapid and accurate end-to-end performance analysis, simulations, and optimization of advanced space-based optical systems. The requirements for IMOS-supported numerical arrays, user defined data structures, and a hierarchical data base are outlined, and initial experience with the tool is summarized. A simulation of a flexible telescope illustrates the integrated nature of the tools.

Briggs, Hugh C.↗

NASA NTRS1991

Solar-diffuser panel and ratioing radiometer approach to satellite sensor on-board calibration

The use of a solar-diffuser panel is a desirable approach to the on-board absolute radiometric calibration of satellite multispectral sensors used for earth observation in the solar reflective spectral range. It provides a full aperture, full field, end-to-end calibration near the top of the sensor's dynamic range and across its entire spectral response range. A serious drawback is that the panel's reflectance, and the response of any simple detector used to monitor its reflectance may change with time. This paper briefly reviews some preflight and on-board methods for absolute calibration and introduces the ratioing-radiometer concept in which the radiance of the panel is ratioed with respect to the solar irradiance at the time the multispectral sensor is viewing the panel in its calibration mode.

Slater, Philip N.↗

NASA NTRS1992

Application of information technology to the National Launch System

The approach to the development of the Unified Information System (UNIS) to provide in a timely manner all the information required to manage, design, manufacture, integrate, test, launch, operate, and support the Advanced Launch System (NLS), as well as the current and planned capabilities are described. STESYM, the Space Transportation Main Engine (STME) development program, is comprised of a collection of data models which can be grouped into two primary models: the Engine Infrastructure Model (ENGIM) and the Engine Integrated Cast Model (ENGICOM). ENGIM is an end-to-end model of the infrastructure needed to perform the fabrication, assembly, and testing of the STEM program and its components. Together, UNIS and STESYM are to provide NLS managers and engineers with the ability to access various types and files of data quickly and use that data to assess the capabilities of the STEM program.

Mauldin, W. T.↗

NASA NTRS1992

Large autonomous spacecraft electrical power system (LASEPS)

NASA - Marshall Space Flight Center is creating a large high voltage electrical power system testbed called LASEPS. This testbed is being developed to simulate an end-to-end power system from power generation and source to loads. When the system is completed it will have several power configurations, which will include several battery configurations. These configurations are: two 120 V batteries, one or two 150 V batteries, and one 250 to 270 V battery. This breadboard encompasses varying levels of autonomy from remote power converters to conventional software control to expert system control of the power system elements. In this paper, the construction and provisions of this breadboard are discussed.

Dugal-Whitehead, Norma R.↗

NASA NTRS1992

Imaging solar flares in hard X-rays using Fourier telescopes

The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.

Campbell, Jonathan W.↗

NASA NTRS1993

An end-to-end pointing budget approach to planetary observing systems with application to EOS

Previously published error budgets have focused on spacecraft error sources for pointing error and have tended to include only spacecraft pointing rather than the ultimate geolocation of each pixel of dam onto a well-defined spot on the surface of the Earth. A systematic approach to geolocation error budgeting, including all contributors in the geolocation process is presented. Its structure allows simultaneous expression of the needs of instrument teams as well as spacecraft design teams. It allows explicit acknowledgement of approximations made for on-board control as well as the ultimate geolocation accuracy achievable after ground processing and exploits the commonality inherent in the on-board and post-processing error budgets. It also includes the uncontrolled and unmeasured spacecraft jitter. This approach can be used to investigate the mission-wide benefit of a variety of design choices, (such as on-board sensing and ground correction of measurements contrasted with on-board correction of measurements). Additionally, in light of increasing accuracy requirements as sensor resolution improves, numerous non-spacecraft contributors to geolocation error are quantified.

Throckmorton, A.↗

NASA NTRS1991

An overview of the halogen occultation experiment (HALOE)

The HALOE experiment will fly on the Upper Atmosphere Research Satellite (UARS) in the last quarter of 1991. The experiment uses the solar occultation limb sounding approach, in combination with gas filter and broadband radiometry to provide measurements of temperature profiles and key gases in the ClO(y), NO(y), and HO(y) chemical families of the middle atmosphere. The instrument has been characterized in great detail to determine gains, spectral response, noise, crosstalk, field-of-view, and thermal drift characteristics. A final end-to-end test using a gas cell to simulate the atmosphere demonstrated measurement repeatability to about 1 percent and agreement between measured and calculated signals to within about 1 percent to 3 percent. This latter agreement provides confidence in knowledge of both the hardware as well as the software.

Russell, James M., III↗

NASA NTRS1992

Small-kernel, constrained least-squares restoration of sampled image data

Following the work of Park (1989), who extended a derivation of the Wiener filter based on the incomplete discrete/discrete model to a more comprehensive end-to-end continuous/discrete/continuous model, it is shown that a derivation of the constrained least-squares (CLS) filter based on the discrete/discrete model can also be extended to this more comprehensive continuous/discrete/continuous model. This results in an improved CLS restoration filter, which can be efficiently implemented as a small-kernel convolution in the spatial domain.

Hazra, Rajeeb↗

NASA NTRS1992

Integrated multidisciplinary analysis of segmented reflector telescopes

The present multidisciplinary telescope-analysis approach, which encompasses thermal, structural, control and optical considerations, is illustrated for the case of an IR telescope in LEO; attention is given to end-to-end evaluations of the effects of mechanical disturbances and thermal gradients in measures of optical performance. Both geometric ray-tracing and surface-to-surface diffraction approximations are used in the telescope's optical model. Also noted is the role played by NASA-JPL's Integrated Modeling of Advanced Optical Systems computation tool, in view of numerical samples.

Briggs, Hugh C.↗

NASA NTRS1991

Imaging the sun in hard X-rays - Spatial and rotating modulation collimators

Several approaches to imaging hard X-rays emitted from solar flares have been proposed or are planned for the nineties including the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC). A survey of current solar flare theoretical literature indicates the desirability of spatial resolutions down to 1 arcsecond, field of views greater than the full solar disk (i.e., 32 arcminutes), and temporal resolutions down to 1 second. Although the sun typically provides relatively high flux levels, the requirement for 1 second temporal resolution raises the question as to the viability of Fourier telescopes subject to the aforementioned constraints. A basic photon counting, Monte Carlo 'end-to-end' model telescope was employed using the Astronomical Image Processing System (AIPS) for image reconstruction. The resulting solar flare hard X-ray images compared against typical observations indicated that both telescopes show promise for the future.

Campbell, Jonathan W.↗

NASA NTRS1992

HAZBOT - A hazardous materials emergency response mobile robot

The authors describe the progress that has been made towards the development of a mobile robot that can be used by hazardous materials emergency response teams to perform a variety of tasks including incident localization and characterization, hazardous material identification/classification, site surveillance and monitoring, and ultimately incident mitigation. In September of 1991, the HAZBOT II vehicle performed its first end-to-end demonstration involving a scenario in which the vehicle: navigated to the incident location from a distant (150-200 ft.) deployment site; entered a building through a door with thumb latch style handle and door closer; located and navigated to the suspected incident location (a chemical storeroom); unlocked and opened the storeroom's door; climbed over the storeroom's 12 in. high threshold to enter the storeroom; and located and identified a broken container of benzene.

Stone, H. W.↗

NASA NTRS1992

Measurements of a deep space station fractional frequency stability to the 10 exp -15 level

This article presents techniques for measuring frequency stability of a deep space station that was configured with a new X-band transmitter subsystem to enable high-quality radio science data to be obtained for a Gravity Wave Experiment. The instrument and test procedures for performing frequency stability measurements in the field are described. Test results from measurements made on various transmit receive subsystems, as well as the overall transmit-receive end-to-end systems below the antenna feed horn are presented. The subsystem test data proved to be useful for assessing the frequency stabilities of various subsystems. This assessment design improvements needed to meet stringent frequency stability requirements for forthcoming gravity wave experiments.

Otoshi, Tom Y.↗

NASA NTRS1992

Operations planning for Space Station Freedom - And beyond

The potential of automated planning and electronic execution systems for enhancing operations on board Space Station Freedom (SSF) are discussed. To exploit this potential the Operations Planning and Scheduling Subsystem is being developed at the NASA Johnson Space Center. Such systems may also make valuable contributions to the operation of resource-constrained, long-duration space habitats of the future. Points that should be considered during the design of future long-duration manned space missions are discussed. Early development of a detailed operations concept as an end-to-end mission description offers a basis for iterative design evaluation, refinement, and option comparison, particularly when used with an advanced operations planning system capable of modeling the operations and resource constraints of the proposed designs.

Gibson, Stephen S.↗