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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 595 records · Page 33
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NASA NTRS1973

Engineering studies related to geodetic and oceanographic remote sensing using short pulse techniques

For the Skylab S-193 radar altimeter, data processing flow charts and identification of calibration requirements and problem areas for defined S-193 altimeter experiments are presented. An analysis and simulation of the relationship between one particular S-193 measurement and the parameter of interest for determining the sea surface scattering cross-section are considered. For the GEOS-C radar altimeter, results are presented for system analyses pertaining to signal-to-noise ratio, pulse compression threshold behavior, altimeter measurement variance characteristics, desirability of onboard averaging, tracker bandwidth considerations, and statistical character of the altimeter data in relation to harmonic analysis properties of the geodetic signal.

Miller, L. S.↗
NASA NTRS1974

Design of an X-ray telescope system for an orbiting astronomical observatory

The design and construction is described of a package of X-ray telescopes launched in the NASA satellite Copernicus (OAO-3), which began stellar observations in September 1972. It contains three grazing incidence reflectors covering a range of wavelengths from 0.3 to 8 nm, and having a combined collecting area of 40.9 sq cm, with angular resolutions up to 1 minute of arc. This is believed to be the first satellite application of such reflectors in stellar X-ray astronomy. A collimated detector of wavelengths 0.1-0.3 nm has a 17.8 sq cm collecting area. A visible light star tracker detects package misalignment if this should occur.

Bowles, J. A.↗
NASA NTRS1973

Processing of the laser Doppler velocimeter signals

The laser Doppler velocimeter (LDV) is a probeless technique that provides a remote measurement of mean and fluctuating velocities. The measurement is actually obtained from small particles embedded in the flow which scatter light from an illuminating laser beam interference pattern. A portion of this scattered light is collected by a photomultiplier which yields an electronic signal whose frequency is directly proportional to the velocity of the small particles. The purpose of this paper is to describe and critically compare three techniques most used to process this electronic signal. These techniques are: (1) spectrum analyzer - a frequency scanning filter (frequency domain instrument), (2) wide-band frequency tracker - a frequency lock loop (frequency domain instrument), and (3) high-speed frequency counter - an interval timer (time domain instrument). The study determines the ability of each technique to process the LDV signal and yield velocity data to be used in determining the flow characteristics.

Meyers, J. F.↗
NASA NTRS1974

Rigid body mode pointing accuracy and stability criteria for an orbiting spacecraft

The effect of gravity gradient torque disturbances (which is an order of magnitude greater than the other torque disturbances and is sinusoidal with a frequency of two cycles per orbit) on pointing accuracy can be predicted very precisely. However, since the sensor noise such as star tracker and gyro inherent noise, is random, their effect can only be predicted statistically. The most common method used is computer simulation with appropriate sensor model and adjusting spacecraft control laws for minimum pointing error, as presented by Harris (1972). The general investigation outlined theoretically relates spacecraft controls to pointing accuracy in terms of the sensor noise power spectrum. The results are presented in graphical form.

Sandhu, G. S.↗
NASA NTRS1974

Analysis of experimental NRL radar altimeter data

An X-band radar capable of continuously variable transmitted pulse durations down to 1 nsec is being flown to investigate the interaction of radar altimeter signals with the sea surface. There is good agreement between the observed radar altimeter leading edge rise time for a 1-nsec transmitted pulse and the rise time predicted from the radar parameters and the sea state determined by a laser profilometer. Using a threshold tracker on 29-pulse averages for a transmitted pulse of 24 nsec, it was found that the range noise varied linearly with the power level of the threshold over a considerable range. The altimeter range quantization was 9.35 cm, and a minimum range noise of 3.9 cm was obtained. A comparison of pulse-to-pulse correlation observed in the radar data with that predicted by a Monte Carlo simulation is used to obtain a measure of sea surface scatterer motion.

Walsh, E. J.↗
NASA NTRS1975

Multibeam-antenna feed system to isolate orthogonally polarized beams

System is polarization tracker and comprises variable polarizer, polarization control, and receiver servo loop. System simultaneously receives desired signal and undesired signal which are approximately orthogonal. They can be either paired as left and right circular polarizations or as cross-linear polarizations.

Ohlson, J. E.↗
NASA NTRS1974

Mariner Mars 1971 attitude control subsystem

The Mariner Mars 1971 attitude control subsystem (ACS) is discussed. It is comprised of a sun sensor set, a Canopus tracker, an inertial reference unit, two cold gas reaction control assemblies, two rocket engine gimbal actuators, and an attitude control electronics unit. The subsystem has the following eight operating modes: (1) launch, (2) sun acquisition, (3) roll search, (4) celestial cruise, (5) all-axes inertial, (6) roll inertial, (7) commanded turn, and (8) thrust vector control. In the celestial cruise mode, the position control is held to plus or minus 0.25 deg. Commanded turn rates are plus or minus 0.18 deg/s. The attitude control logic in conjunction with command inputs from other spacecraft subsystems establishes the ACS operating mode. The logic utilizes Sun and Canopus acquisition signals generated within the ACS to perform automatic mode switching so that dependence of ground control is minimized when operating in the sun acquisition, roll search, and celestial cruise modes. The total ACS weight is 65.7 lb, and includes 5.4 lb of nitrogen gas. Total power requirements vary from 9 W for the celestial cruise mode to 54 W for the commanded turn mode.

Edmunds, R. S.↗
NASA NTRS1974

Stellar tracking attitude reference system

A satellite precision attitude control system was designed, based on the use of STARS as the principal sensing system. The entire system was analyzed and simulated in detail, considering the nonideal properties of the control and sensing components and realistic spacecraft mass properties. Experimental results were used to improve the star tracker noise model. The results of the simulation indicate that STARS performs in general as predicted in a realistic application and should be a strong contender in most precision earth pointing applications.

Klestadt, B.↗
NASA NTRS1974

Airborne Visible Laser Optical Communications (AVLOC) experiment

A series of optical communication experiments between a high altitude aircraft at 18.3 km (60,000 ft) and a ground station were conducted by NASA from summer 1972 through winter 1973. The basic system was an optical tracker and transmitter located in each terminal. The aircraft transceiver consisted of a 5-mW HeNe laser transmitter with a 30-megabit modulator. The ground station beacon was an argon laser operating at 488 nm. A separate pulsed laser radar was used for initial acquisition. The objective of the experiment was to obtain engineering data on the precision tracking and communication system performance at both terminals. Atmospheric effects on the system performance was also an experiment objective. The system description, engineering analysis, testing, and flight results are discussed.

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NASA NTRS1974

Design and performance of a 39cm balloon-borne telescope

A system for stabilizing a balloon-borne telescope using a star sensor device is described. Guide stars from minus four to plus four magnitude can be used and the sensor may be offset with respect to the telescope by as much as plus or minus five degrees in elevation and cross elevation to enable parts of the sky containing no suitable guide stars to be viewed. Acquisition of the guide star and setting of the offset coordinates is carried out by ground command and both may be changed in flight. The main design parameters of the equipment are summarized. Block diagrams and circuit diagrams of the star tracker are provided.

Tomlinson, H. S.↗
NASA NTRS1974

An orientable, stabilized balloon-borne gondola for around-the-world flights

A system capable of pointing a balloon-borne telescope at selected celestial objects to an accuracy of approximately 10 arc minutes for an extended period (weeks to months) without reliance on telemetry is described. A unique combination of a sun/star tracker, an on-board computer, and a gyrocompass is utilized for navigation, source acquisition and tracking, and data compression and recording. The possibilities for intelligent activities by the computer are also discussed.

Ricker, G. R.↗
NASA NTRS1974

AIROscope: Ames infrared balloon-borne telescope

A balloon-borne telescope system designed for astronomical observations at infrared wavelengths is discussed. The telescope is gyro-stabilized with updated pointing information derived from television, star tracker, or ground commands. The television system furnishes both course and fine acquisition after initial orientation using a pair of fluxgate servo compasses. Command and control is by a UHF link with 256 commands available. Scientific and engineering data are telemetered to the ground station via narrow band F.M. in the L band. The ground station displays all scientific, engineering and status information during the flights and records the command and telemetry digital bit stream for detailed analysis. The AIROscope telescope has a 28-inch diameter primary mirror and Dall-Kirkham optics. The beam is modulated by oscillating a secondary mirror at 11 or 25 Hz with provision for left or right beam fixed positions by command.

Koontz, O. L.↗
NASA NTRS1974

The stellar and solar tracking system of the Geneva Observatory gondola

Sun and star trackers have been added to the latest version of the Geneva Observatory gondola. They perform an image motion compensation with an accuracy of plus or minus 1 minute of arc. The structure is held in the vertical position by gravity; the azimuth is controlled by a torque motor in the suspension bearing using solar or geomagnetic references. The image motion compensation is performed by a flat mirror, located in front of the telescope, controlled by pitch and yaw servo-loops. Offset pointing is possible within the solar disc and in a 3 degree by 3 degree stellar field. A T.V. camera facilitates the star identification and acquisition.

Huguenin, D.↗
NASA NTRS1974

AIROscope stellar acquisition

The acquisition system which operates in conjunction with a balloon-borne TV system, boresighted to a telescope is described. It has two main functions, a star field monitor and an offset star tracker. The design of the system was strongly influenced by the TV camera, which uses the same interlaced scanning system as is employed in commercial television broadcasting. To reduce power and bandwidth requirements, the star field information transmitted in our system consists only of the horizontal and vertical coordinates of each star and its brightness. As a star field monitor the system provides video thresholding, camera blemish suppression, coordinate digitization in 3 axes, circuity to recognize as single star the dispersed video signals resulting from one star overlapping adjacent scanning lines and storage of all signals for readout by the telemetry at appropriate times.

Deboo, G. J.↗
NASA NTRS1974

Study of radar pulse compression for high resolution satellite altimetry

Pulse compression techniques are studied which are applicable to a satellite altimeter having a topographic resolution of + 10 cm. A systematic design procedure is used to determine the system parameters. The performance of an optimum, maximum likelihood processor is analysed, which provides the basis for modifying the standard split-gate tracker to achieve improved performance. Bandwidth considerations lead to the recommendation of a full deramp STRETCH pulse compression technique followed by an analog filter bank to separate range returns. The implementation of the recommended technique is examined.

Dooley, R. P.↗
NASA NTRS1974

Design/cost tradeoff studies. Appendix A. Supporting analyses and tradeoffs, book 2. Earth Observatory Satellite system definition study (EOS)

Attitude reference systems for use with the Earth Observatory Satellite (EOS) are described. The systems considered are fixed and gimbaled star trackers, star mappers, and digital sun sensors. Covariance analyses were performed to determine performance for the most promising candidate in low altitude and synchronous orbits. The performance of attitude estimators that employ gyroscopes which are periodically updated by a star sensor is established by a single axis covariance analysis. The other systems considered are: (1) the propulsion system design, (2) electric power and electrical integration, (3) thermal control, (4) ground data processing, and (5) the test plan and cost reduction aspects of observatory integration and test.

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NASA NTRS1975

Modification, fabrication, testing and delivery of ITT model F4012 RP tube/coil assembly

Results of the improvement program for the ITT model F4012 RP image dissector tube and coil are presented. This program undertaken to improve the characteristics of this assembly to make it more accurate for the Large Space Telescope trackers' applications. Comparisons are given of the performance of the new components and the original design goals. Recommendations for further tests and/or design changes to further improve the F4012 tube/coil assembly performance are given.

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