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At least 145 records · Page 8

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NASA NTRS1977

The effect of variations in controls and displays on helicopter instrument approach capability

A flight investigation was conducted with a variable stability helicopter to determine the effects of variations in controls and displays on helicopter instrument approach capabilities. The baseline instrument approach task was a decelerating approach to a hover along a 6 deg glide slope. Pilot evaluations were obtained for both the constant speed part of the task and the deceleration and hover part of the task. The attitude stability augmentation system (SAS) was strongly preferred over the rate SAS because the aircraft had a divergent pitch response. From a display variation standpoint, it was not possible to decelerate to a hover in a consistent manner, regardless of the control system employed, with situation information only. In particular, the deceleration and hover part of the task was unacceptable without flight director command information.

Niessen, F. R.↗

NASA NTRS1977

The galactic halo question: New size constraints from galactic gamma-ray data

The SAS-2 gamma-ray data is analyzed making use of recent CO line emission and other data for determining the large-scale distribution of galactic gas. A nonuniform distribution of cosmic rays in the galaxy is implied. This fact rules out large trapping halo models and extragalactic origin models. Detailed models of diffusion halos of various sizes perpendicular to the galactic plane are considered. In such models, the scale perpendicular to the plane has a strong effect in determining the radial distribution of cosmic rays. Such radial distributions are calculated for cylindrical coordinate models. The implied gamma-ray longitude distributions are then calculated and compared with the SAS-2 data for goodness-of-fit. Assuming the sources to be supernova remnants or pulsars, cosmic ray nucleon halo models with scale heights greater than 3 kpc are found to provide a poor fit to the gamma-ray longitude data (probability of 6% or less). Thin halo, or source dominated diffusion models are found to provide a good fit to the gamma-ray data, with an upper limit scale height of approximately 3 kpc.

Stecker, F. W.↗

NASA NTRS1978

Pilot-optimal augmentation synthesis

An augmentation synthesis method usable in the absence of quantitative handling qualities specifications, and yet explicitly including design objectives based on pilot-rating concepts, is presented. The algorithm involves the unique approach of simultaneously solving for the stability augmentation system (SAS) gains, pilot equalization and pilot rating prediction via optimal control techniques. Simultaneous solution is required in this case since the pilot model (gains, etc.) depends upon the augmented plant dynamics, and the augmentation is obviously not a priori known. Another special feature is the use of the pilot's objective function (from which the pilot model evolves) to design the SAS.

Schmidt, D. K.↗

NASA NTRS1978

X-ray observation of IC 4329 A

X-rays from the extreme type 1 Seyfert galaxy IC 4329 A have been observed with the rotating modulation collimator on board SAS 3. In addition to establishing IC 4329 A as an X-ray source, the SAS 3 data require that the source be extended, that there be at least one other nearby source, or both.

Delvaille, J. P.↗

NASA NTRS1978

Analytical design of a high performance stability and control augmentation system for a hingeless rotor helicopter

A stability and control augmentation system (SCAS) was designed based on a set of comprehensive performance criteria. Linear optimal control theory was applied to determine appropriate feedback gains for the stability augmentation system (SAS). The helicopter was represented by six-degree-of-freedom rigid body equations of motion and constant factors were used as weightings for state and control variables. The ratio of these factors was employed as a parameter for SAS analysis and values of the feedback gains were selected on this basis to satisfy three of the performance criteria for full and partial state feedback systems. A least squares design method was then applied to determine control augmentation system (CAS) cross feed gains to satisfy the remaining seven performance criteria. The SCAS gains were then evaluated by nine degree-of-freedom equations which include flapping motion and conclusions drawn concerning the necessity of including the pitch/regressing and roll/regressing modes in SCAS analyses.

Miyajima, K.↗

NASA NTRS1979

Discovery of soft X-ray flux from 2A 1102+384 = Markarian 421

During April 1976 a soft X-ray flux was detected with SAS 3 from the vicinity of 2A 1102+384. The average flux densities were 4.3 x 10 to the -11th and 14 x 10 to the -11th erg/sq cm per sec in the energy bands 0.1-0.28 keV and 1-6 keV, respectively. There is an indication of variability over about 0.5 day in the lowest energy band. An upper limit of 3 x 10 to the 20th H atoms per sq cm is found for the gas column density to the X-ray source. In May 1978, observations with the modulation collimators of SAS 3 yielded an accurate (40 arcsec error radius) position for the X-ray source (2-6 keV) at right ascension 11 h 1 m 39.7 s, declination + 38 deg 28 min 51 sec (equinox 1950). The earlier tentative identification by Ricketts et al. (1976) with the BL Lacertae object B2 1101+38 = Markarian 421 is thus confirmed.

Hearn, D. R.↗

NASA NTRS1979

Gamma-ray evidence for a galactic halo

Gamma-ray evidence for the existence of a cosmic-ray halo around the Galaxy is examined. Gamma-ray data obtained by SAS-2 and COS-B and nonthermal radio continuum data are shown to indicate the nonconfinement of cosmic rays to the spiral arms and thus the existence of a larger propagation disk through which cosmic rays diffuse. The latitudinal distribution of gamma rays observed by SAS-2 is found to be consistent with the existence of a thin disk-shaped electron halo of half-thickness 1.5 kpc. The propagation of nucleons is determined indirectly from their radial distribution in the galactic plane, which is obtained from an analysis of the longitudinal distribution of gamma rays in the plane. The resulting distributions are found to be similar to the distribution of supernovae in the Galaxy, implying a galactic origin for cosmic rays and a half-thickness of less than 3 kpc.

Stecker, F. W.↗

NASA NTRS1983

Irregular X-ray variability in the transient X-ray burst source MXB 1659-29

Irregular variability in the X-ray emission from MXB 1659-29 was observed with SAS 3 during the 1978 transient outburst of the source. No stable period can yet be derived from the low-intensity states, although there is evidence for a quasi-periodicity of either 1.2 or 1.4 hours. The low-intensity states observed in MXB 1659-29 during the transient outburst vary both in width and duration, similar to those in MXB 1916-05. The SAS 3 data are consistent with either the intermittent obscuration of the X-ray emitter by relatively cold gas or with scattering of the X-rays by hotter material.

Cominsky, L.↗

NASA NTRS1982

Solar array system for solar maximum mission

The paper describes the design of the solar array system (SAS) for the Solar Maximum Mission, the unique features of the SAS, and the results of its successful in-orbit operation. It is noted that the array was unique in that: (1) major weight concessions were made to produce a dynamically stiff array; (2) it was the first array designed to be compatible with the NASA Multimission Modular Spacecraft; (3) it is the first jettisonable solar array; and (4) it represents the first use of FEP-bonded overslides on a prime power array. It is concluded that the array performed as predicted with no evidence of the FEP causing any unusual array power degradations. In addition, the deployment and telemetry systems performed as designed.

Meese, R. A.↗

NASA NTRS1984

Production of high-energy gamma rays by cosmic ray interactions in the atmosphere and lunar surface

The production of gamma rays above 10 MeV by the interaction of cosmic rays in the atmosphere and the lunar surface is simulated using Monte Carlo methods. The calculation incorporates a new model of high-energy nucleon-nucleus interactions based on empirical fits to inclusive cross sections for the production of pions and nucleons. The atmospheric gamma ray flux is calculated as a function of direction, energy, and atmospheric depth. These calculations are compared with observations from balloons and from the SAS 2 satellite. Estimates of the flux of earth albedo electrons produced by cosmic ray interactions are presented. The lunar gamma ray albedo is calculated and compared with an upper limit based on SAS 2 measurements.

Morris, D. J.↗

NASA NTRS1984

Advanced CID array multispectral pushbroom scanner

An optical imager, called the Scanning Imaging Spectroradiometer (SIS), was built for NASA in the early 1970's. Later, the Solidstate Array Spectroradiometer (SAS) was developed on the basis on a substitution of a Charge Injection Device (CID) array for the vidicon of the SIS. The Advanced Solidstate Array Spectroradiometer (ASAS) represents an improvement of the SAS. ASAS is a solidstate multispectral optical imaging radiometer which is currently the most versatile instrument of its type in the visible part of the spectrum. The instrument is capable of absolute radiometric measurements in all of its 32 bands. ASAS can be easily mounted in small aircraft as well as high altitude craft such as the U-2, taking into account also the possibility of a use in the Space Shuttle. The instrument consists of three separate subsystems. Attention is given to the optics, the detector array, data storage, data retrieval, and system performance.

Stewart, S. E.↗

NASA NTRS1989

Results of an A109 simulation validation and handling qualities study

The results for the validation of a mathematical model of the Agusta A109 helicopter, and subsequent use of the model as the baseline for a handling qualities study of cockpit centerstick requirements, are described. The technical approach included flight test, non-realtime analysis, and realtime piloted simulation. Results of the validation illustrate a time- and frequency-domain approach to the model and simulator issues. The final A109 model correlates well with the actual aircraft with the Stability Augmentation System (SAS) engaged, but is unacceptable without the SAS because of instability and response coupling at low speeds. Results of the centerstick study support the current U.S. Army handling qualities requirements for centerstick characteristics.

Eshow, Michelle M.↗

NASA NTRS1989

Further observations of the eclipsing X-ray burst source MXB 1659-29

An analysis is presented of data for MXB 1659-29 obtained during October 2-10, 1976 and June 6-11, 1977 using the SAS 3 X-ray Observatory (Lewin et al., 1976) and during September 8-13, 1978 using the A-1 experiment aboard HEAO 1 (Wood et al., 1984). The data confirm the 7.1 hr orbital period and provide evidence for the 15-min X-ray eclipse reported by Cominsky and Wood (1984). A total of 32 X-ray bursts are detected during the SAS 3 observations. By combining the data with previously published results, the orbital period is found to be about 0.29650474 days.

Cominsky, L. R.↗

NASA NTRS1989

Candidate sample acquisition systems for the Rosetta

The Comet Nucleus Sample Return (CNSR) mission, one of the four cornerstones of the ESA scientific program, is one of the most complex space ventures within the next century, both from technological and deep space exploration point of view. In the Rosetta scenario the sample acquisition phase represents the most critical point for the global mission's success. The proposed paper illustrates the main results obtained in the context of the CNSR-SAS ongoing activity. The main areas covered are related to: (1) sample properties characterization (comet soil model, physical/chemical properties, reference material for testing); (2) concepts identification for coring, shovelling, harpooning and anchoring; (3) preferred concept (trade off among concepts, identification of the preferred configuration); and (4) proposed development activity for gaining the necessary confidence before finalizing the CNSR mission. Particular emphasis will be given to the robotic and flexibility aspects of the identified sample acquisition systems (SAS) configuration, intended as a means for the overall system performance enhancement.

Magnani, P. G.↗

NASA NTRS1990

Results of an A109 simulation validation and handling qualities study

Eshow, Michelle M.↗

NASA NTRS1992

Silicon carbide fiber reinforced strontium aluminosilicate glass-ceramic matrix composite

A SrO-Al2O3 - 2SrO2 (SAS) glass ceramic matrix is reinforced with CVD SiC continuous fibers. This material is prepared by casting a slurry of SAS glass powder into tapes. Mats of continuous CVD-SiC fibers are alternately stacked with the matrix tapes. This tape-mat stack is warm-pressed to produce a 'green' composite. Organic constituents are burned out of the 'green' composite, and the remaining interim material is hot pressed.

Bansal, Narottam↗

NASA NTRS1993

MAC to VAX Connectivity: Heartrate Spectral Analysis System

The heart rate Spectral Analysis System (SAS) acquires and analyzes, in real-time, the Space Shuttle onboard electrocardiograph (EKG) experiment signals, calculates the heartrate, and applies a Fast Fourier Transformation (FFT) to the heart rate. The system also calculates other statistical parameters such as the 'mean heart rate' over specific time period and heart rate histogram. This SAS is used by NASA Principal Investigators as a research tool to determine the effects of weightlessness on the human cardiovascular system. This is also used to determine if Lower Body Negative Pressure (LBNP) is an effective countermeasure to the orthostatic intolerance experienced by astronauts upon return to normal gravity. In microgravity, astronauts perform the LBNP experiment in the mid deck of the Space Shuttle. The experiment data are downlinked by the orbiter telemetry system, then processed and analyzed in real-time by the integrated Life Sciences Data Acquisition (LSDS) - Spectral Analysis System. The data system is integrated within the framework of two different computer systems, VAX and Macintosh (Mac), using the networking infrastructure to assist the investigators in further understanding the most complex machine on Earth--the human body.

Rahman, Hasan H.↗

NASA NTRS1991

Cerebral blood flow - Comparison of ground-based and spaceflight data and correlation with space adaptation syndrome

The relationship between the cerebral blood flow velocity and the space adaptation syndrome (SAS), which includes symptoms of motion sickness, stuffy head, and/or headaches, was investigated by measuring (using a transcranial Doppler device) differences between the preflight and the inflight cerebral blood flow velocity in crew members who were motion sick and in those who were not sick during a flight aboard KC-135. It was found that the cerebral artery bloodflow inflight did not differ significantly from that recorded preflight, nor did the severity of SAS symptoms correlate directly with the cerebral blood flow.

Bagian, James P.↗