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NASA NTRS1980

Considerations in the placement of phase calibration tones

In the use of tones to calibrate unwanted instrumental phases for very long baseline interferometry experiments, certain problems exist which are related to the placement of these phase calibrator tones. (1) A bias exists in an analytically generated stopping function used during correlation if its frequency satisfies the following condition; f = (f sub s)x(m)/n, where f sub s = sampling frequency, m = any integer, and n = any odd integer. (2) Due to the quantized representation of sine waves in the stopping function, odd harmonics of the fundamental frequencies are generated. Several mechanisms are available through which these harmonics can cause errors in the residual phase extracted from the recorded tones. (3) When multiple tones are injected into a pass band, intermodulation products can occur. The magnitude of these effects is discussed along with strategies designed to avoid them.

Young, L. E.↗

NASA NTRS1979

Timing and frequency considerations in the worldwide testing of a spread spectrum communication system

During 1978 and 1979, an Air Force C-135 test aircraft was flown to various locations in the North and South Atlantic and Pacific Oceans for satellite communications experiments. A part of the equipment tested on the aircraft was the SEACOM spread spectrum modem. The SEACOM modem operated at X band frequency from the aircraft via the DSCS II satellite to a ground station. For data to be phased successfully, it was necessary to maintain independent time and frequency accuracy over relatively long periods of time (up to two weeks) on the aircraft and at the ground station. To achieve this goal, two Efratom atomic frequency standards were used. The performance of these frequency standards as used in the spread spectrum modem is discussed, including the effects of high relative velocity, synchronization and the effects of the frequency standards on data performance is discussed. The aircraft environment, which includes extremes of temperature, as well as long periods of shutdown followed by rapid warmup requirements, is also discussed.

Woodring, D. G.↗

NASA NTRS1980

Design considerations for optical heterodyne receivers: A review

The current state of knowledge concerning optical heterodyne receivers is reviewed. Following a discussion of noise processes in the heterodyne receiver and the manner in which sensitivity is increased through time integration of the detected signal, an expression for the mean square signal current is derived by mixing a coherent local oscillator with a partially coherent, quasimonochromatic source. Then the manner in which the IF signal calculation can be transferred to any convenient plane in the optical front end of the receiver is demonstrated. Using these techniques, a relatively simple equation is obtained for the coherently detected signal from an extended incoherent source and applied to the heterodyne detection of an extended thermal source and to the backscatter lidar problem where the antenna patterns of both the transmitter beam and heterodyne receiver must be taken into account. Finally, the detection of a coherent source is considered and, in particular, a distant point source such as a star or laser transmitter in a long range heterodyne communications system is discussed.

Degnan, J. J.↗

NASA NTRS1980

Navigation network operational considerations

The development of the philosphy necessary for the initial operations costing of the three candidate navigation network designs is described. The effect of the need to minimize costs upon the operations and maintenance concepts, the simplification of operations by adopting the very long base interferometry principle as a basis for the scenarios, and the estimation of the annual load factor based upon an assumed mission set are detailed.

Hird, E.↗

NASA NTRS1975

The prevention of electronical breakdown and electrostatic voltage problems in the space shuttle and its payloads. Part 2: Design guides and operations considerations

The specific electrical discharge problems that can directly affect the shuttle vehicle and its payloads are addressed. General design guidelines are provided to assist flight hardware managers in minimizing these kinds of problems. Specific data are included on workmanship practices and system testing while in low pressure environments. Certain electrical discharge problems that may be unique to the design of the shuttle vehicle itself and to its various mission operational models are discussed.

Whitson, D. W.↗

NASA NTRS1980

Propulsion/airframe integration considerations for high altitude hypersonic cruise vehicles

A study has been conducted to determine the implications of top-mounted inlet nacelles on propulsion performance and cruise range. The top-mounted nacelle would be less visible from ground-based radar below and ahead of the aircraft. For this study, the nacelle is integrated with a high altitude Mach 5 turbojet/ramjet-powered airplane concept requiring a large nacelle. Results of the study suggest nacelle installation advantages and improved inlet mass flow ratio for the top-mounted nacelle, but at the expense of a higher installed drag at transonic and supersonic speeds.

Weidner, J. P.↗

NASA NTRS1980

Acoustic considerations of flight effects on jet noise suppressor nozzles

Insight into the inflight acoustic characteristics of high-velocity jet noise suppressor nozzles for supersonic cruise aircraft (SCA) is provided. Although the suppression of jet noise over the entire range of directivity angles is of interest, the suppression of the peak noise level in the rear quadrant is frequently of the most interest. Consequently, the paper is directed primarily to the inflight effects at the peak noise level. Both single and inverted-velocity-profile multistream suppressor nozzles are considered. The importance of static spectral shape on the noise reduction due to inflight effects is stressed.

Von Glahn, U.↗

NASA NTRS1980

Cosmological considerations on the diffuse gamma-ray isotropic background

Bignami et al (1979) have recently studied the problem of the origin of the diffuse gamma-ray isotropic radiation. They have concluded that within standard cosmology with Lambda = 0 and p = 0, BL Lacertae objects and Seyfert galaxies can account for most of the diffuse radiation if they have not evolved in time. For QSOs, an evolutionary factor is allowed by the data. From the study of radio data, however, it is known that strong evolutionary effects are expected. The discrepancy cannot be explained by changing the geometry of the universe. Contrary to the case of standard cosmology, it is found that in order to fit the diffuse gamma-ray background, the evolutionary function required is almost identical to the one previously determined from the study of the log N-log S relation.

Canuto, V. M.↗

NASA NTRS1980

Practical design considerations for a flightworthy higher harmonic control system

The paper discusses the design of a higher harmonic blade pitch control system for flight testing on an OH-6A helicopter. Alternative designs for both the mechanical and electronic subsystems are also presented. Among the recommendations set forth are: (1) use electronic analog methods instead of FFT software, delegating spectral analysis and self testing to an Electronic Control Unit; (2) use a digital rather than analog computer for increased flexibility in solution processing; and (3) locate HHC actuators in the nonrotating system and separate these actuators from the primary control system. It is concluded that a target weight for a prototype control system would be less than 1% of design gross weight and the production weight of the future HHC system may be 0.5 of the weight of the aircraft.

Wood, E. R.↗

NASA NTRS1980

Some considerations in the evaluation of Seasat-A scatterometer /SASS/ measurements

A study is presented of the geophysical algorithms relating the Seasat-A scatterometer (SASS) backscatter measurements with a wind parameter. Although these measurements are closely related to surface features, an identification with surface layer parameters such as friction velocity or the roughness length is difficult. It is shown how surface truth in the form of wind speeds and coincident stability can be used to derive friction velocity or the equivalent neutral wind at an arbitrary height; it is also shown that the derived friction velocity values are sensitive to contested formulations relating friction velocity to the roughness length, while the derived values of the equivalent neutral wind are not. Examples of geophysical verification are demonstrated using values obtained from the Gulf of Alaska Seasat Experiment; these results show very little sensitivity to the type of wind parameter employed, suggesting that this insensitivity is mainly due to a large scatter in the SASS and surface truth data.

Halberstam, I.↗

NASA NTRS1980

Photovoltaic power system reliability considerations

This paper describes an example of how modern engineering and safety techniques can be used to assure the reliable and safe operation of photovoltaic power systems. This particular application was for a solar cell power system demonstration project in Tangaye, Upper Volta, Africa. The techniques involve a definition of the power system natural and operating environment, use of design criteria and analysis techniques, an awareness of potential problems via the inherent reliability and FMEA methods, and use of a fail-safe and planned spare parts engineering philosophy.

Lalli, V. R.↗

NASA NTRS1980

Thermophysical and system integration considerations in aerobraking design

The aerobraking concept for decelerating spacecraft into low-energy orbits is summarized. Data and comparisons are given for aerobraking approaches to Venus, Earth, Mars, and Titan. Calculations are based on adaption of a craft similar to the Venus Orbiting Imaging Radar vehicle to an aerobraking configuration. Special attention is given to integration of the aerobraking parts into the system and protection of the craft from heat loads due to the aerobraking maneuvers.

French, J. R.↗

NASA NTRS1979

Economic considerations in space industrialization

The industrial categories of the United States economy are surveyed to identify those which can function using dominantly lunar raw materials or lunar derived feedstocks (LDF) and solar energy. Sixty-four standard industrial categories (SIC) appear to be compatible with LDF inputs; another 166 SIC's might be adaptable to LDF and space industry if substitution of materials and/or terrestrial supplements were introduced. Analytic tools are presented to use in deciding optimal strategies by which a generalized economy can be developed in space in an optimal manner within given constraints of capital, products derived at a given time, local production costs, cost of import from earth and other factors.

Ayres, R. U.↗

NASA NTRS1951

Blockage Corrections for Three-Dimensional-Flow Closed-Throat Wind Tunnels, with Consideration of the Effect of Compressibility

Theoretical blockage corrections are presented for a body of revolution and for a three-dimensional, unswept wing in a circular or rectangular wind tunnel. The theory takes account of the effects of the wake and of the compressibility of the fluid, and is based on the assumption that the dimensions of the model are small in comparison with those of the tunnel throat. Formulas are given for correcting a number of the quantities, such as dynamic pressure and Mach number, measured in wind tunnel tests. The report presents a summary and unification of the existing literature on the subject

Herriot, J. G.↗

NASA NTRS1980

Consideration for high accuracy radiation efficiency measurements for the Solar Power Satellite (SPS) subarrays

The transmit beam and radiation efficiency for 10 metersquare subarray panels were quantified. Measurement performance potential of far field elevated and ground reflection ranges and near field technique were evaluated. The state-of-the-art of critical components and/or unique facilities required was identified. Relative cost, complexity and performance tradeoffs were performed for techniques capable of achieving accuracy objectives. It is considered that because of the large electrical size of the SPS subarray panels and the requirement for high accuracy measurements, specialized measurement facilities are required. Most critical measurement error sources have been identified for both conventional far field and near field techniques. Although the adopted error budget requires advances in state-of-the-art of microwave instrumentation, the requirements appear feasible based on extrapolation from today's technology. Additional performance and cost tradeoffs need to be completed before the choice of the preferred measurement technique is finalized.

Kozakoff, D. J.↗

NASA NTRS1978

Preliminary report: Biomedical considerations for future manned space flights

The behavioral, psychological, and sociological aspects of space travel, particularly with emphasis on longer duration missions, are discussed along with the biomedical aspects of space flight. These factors may strongly interact with the various psycho-social factors and as such they stand as an immensely important area of concern in and of themselves. A foundation for understanding weightlessness related medical problems through a discussion of the history of symptoms reported specific details on the major areas of concern and approaches to their investigation are presented. Also, discussion is given to the possibility of various countermeasures. Some indication of the effects of various biomedical changes in performance are also covered.

Akins, F. R.↗

NASA NTRS1979

Performance considerations in long-term spaceflight

Maintenance of skilled performance during extended space flight is of critical importance to both the health and safety of crew members and to the overall success of mission goals. An examination of long term effects and performance requirements is therefore a factor of immense importance to the planning of future missions. Factors that were investigated include: definition of performance categories to be investigated; methods for assessing and predicting performance levels; in-flight factors which can affect performance; and factors pertinent to the maintenance of skilled performance.

Akins, F. R.↗

NASA NTRS1981

Operational considerations in utilization of microwave landing system approach and landing guidance

The characteristics and performance of MLS equipment utilized by the TCV B-737. Several classes of MLS service and approach procedures are discussed in light of TCV experience. Since the early uses of MLS involves procedures identical to ILS, most of the discussion is concerned with exploitation of MLS capabilities not possessed by ILS. Examples are given of how this could be done by using MLS to enhance the safety and utility of procedures presently in use for noise abatement. Some areas which require definition of new procedures and conventions are indicated.

White, W. F.↗