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At least 451 records · Page 25

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NASA NTRS1982

Unsteady aerodynamics and motions of the Pioneer Venus probes

Helicopter drop tests were made of models of the Pioneer Venus probe descent configurations to characterize their unsteady forces and angular dynamics in equilibrium descent. The axial and normal forces were found to be unsteady in magnitude by about 10 and 5% of the mean axial force, respectively. A cycle of the axial variation takes place in flight distances of from 15 to 40 diameters. The unsteadiness almost certainly is associated with the wake. Angular motions which do not converge to zero angle of attack even in very long duration descent are excited by the unsteady pitching moments. The nearly spherical large probe model was aerodynamically more unsteady than the round-nosed conical small probe model. Data returned from Venus by the Pioneer Venus probes show unsteady axial forces and angular motions similar to those seen in the drop tests.

Seiff, A.↗

NASA NTRS1981

Measurement of very large flow angles with non-nulling seven-hole probes

This paper describes a method for measuring local direction and total and static pressures of a flow by means of a fixed probe, provided that the local air flow does not make an angle of more than 80 degrees with the axis of the probe. The probe is easily manufactured from standard-sized tubing materials. The power series calibration method used with the probe results in explicit polynomial expressions for the desired aerodynamic properties. The calibration method is easily programmed on a data acquisition system. This paper includes an example of a complete incompressible calibration.

Gallington, R. W.↗

NASA NTRS1984

Temperature-Averaging Thermal Probe

Temperature-averaging thermal probe measures long-term temperature fluctuations in fluid environment. Consists of temperature probe embedded inside thermally massive material. Probe measurements used to estimate powerplant heating and cooling loads, map temperature profiles, and calibrate more-sensitive temperature probes.

Kalil, L. F.↗

NASA NTRS1985

Temperature structure in the lower atmosphere of Venus - New results derived from Pioneer Venus entry probe measurements

The Pioneer Venus Small-Probe Net Flux Radiometer temperature sensor and its calibration, the thermal model of the sensor head, the procedure for deriving atmospheric temperature from the sensor temperatures, and the new temperature results for each entry probe are reported. The new results are compared with those of the Small-Probe Atmospheric Structure experiment and with simple models of diurnal and latitudinal temperature contrasts. A dynamical inconsistency between these results and low-latitude measurements by the Sounder probe is described, and possible ways to resolve it are considered.

Sromovsky, L. A.↗

NASA NTRS1986

A fast-response aspirating probe for measurements of total temperature and pressure in transonic cryogenic wind tunnel

A newly developed, 3-mm-diam, dual hot-wire aspirating probe was used to measure the time-resolved stagnation temperature and pressure in a transonic cryogenic wind tunnel. The probe consists of two coplanar constant temperature hot wires at different overheat ratios operating in a 1.5-mm-diam channel with a choked exit. Thus, the constant Mach number flow by the wires is influenced only by free-stream stagnation temperature and pressure. Diffusion of the free-stream Mach number to a lower value in the channel reduces the dynamic drag on the hot-wire. Frequency response of the present design is dc to 20 kHz. The probe was used to measure the unsteady wake shed from an oscillating airfoil tested in the 0.3-m Transonic Cryogenic Tunnel at NASA-Langley Research Center. The hot-wire lasted for more than ten hours before breaking, proving the ruggedness of the probe and the usefulness of the technique in a high dynamic pressure, transonic cryogenic wind tunnel. Typical data obtained from the experiment are presented after reduction to stagnation pressure and temperature.

Ng, W.-F.↗

NASA NTRS1986

Responses of a hot film and a pressure probe to acoustic excitation in mean flow

The responses of a hot film sensor and a pressure probe to acoustic excitation in steady flow up to a Mach number of 0.5 were measured and compared with the responses of a microphone, flush mounted in the wall of the flow duct. When compared in terms of fluctuating pressure, the response of the pressure probe was less than that of the wall microphone by about 2.1 dB or less at the 0.5 Mach number, while the response of the ho film probe was as much as 6.0 dB above that of the wall sensor, at the Mach numbers 0.3 and 0.5. In terms of fluctuating Reynolds number, the response of the hot film probe was greater than that of the wall-mounted sensor by at most 5.0 dB at the same Mach numbers. Removing the response contribution from fluctuating temperature in the hot film mathematical model improved the agreement between the two transducer responses for both comparisons.

Jones, M. G.↗

NASA NTRS1988

Wind measurements by electromagnetic probes

The emerging technology of electromagnetic probing of the atmosphere to measure winds used in a space vehicle ascent winds load calculations is presented. The frequency range, altitude, and resolution for the following probes are presented: lidars, microwave radars, and clear-air Doppler radars (popularly known as wind profilers). The electromagnetic probing of the atmosphere by clear-air radars and lasers is the new technology to supplement balloon-borne wind sensors used to determine ascent wind loads of space vehicles. The electromagnetic probes measure the wind velocity using the Doppler effect. This is the radar technology used in MSFC's Radar Wind Profiler, and is similar to the technology used in conventional Doppler systems except that the frequency is generally lower, antenna is bigger, and dwell time much longer. Designed for unattended and automated instrumentation in providing measurements of the wind in the troposphere, the profiler employs Doppler radar technology and is currently being put in operation at NASA Kennedy Space Center, Florida.

Susko, Michael↗

NASA NTRS1988

A Saturn atmospheric probe - A proposed augmentation to the Cassini mission

The Saturn probe augmentation of the Cassini mission is studied with particular attention given to the scientific rationale for such an augmentation and any associated issues of technical feasibility, system requirements, performance penalties, and costs. A minimal science complement probe, which concentrates only on atmospheric composition and structure with a total mass requirement of slightly less than 200 kg, is described as well as a full science complement probe with a total mass requirement of about 240 kg. It is noted that either of these Saturn probe configurations can be added to the currently planned mission within the launch performance limitations of the Titan 34D7/Centaur G(prime) launch vehicle.

Swenson, Byron L.↗

NASA NTRS1989

Calibration of seven-hole pressure probes for use in fluid flows with large angularity

Described here is the calibration of a non-nulling, conical, seven-hole pressure probe over a large range of flow onset angles. The calibration procedure is based on the use of differential pressures to determine the three components of velocity. The method allows determination of the flow angle to within 0.5 deg and velocity magnitude to approximately 1.0 percent. Also included is an examination of the factors which limit the use of the probe, a description of the measurement chain, an error analysis, and a typical experimental result. In addition, a new general analytical model of pressure probe behavior is described and the validity of the model is demonstrated by comparing it with experimentally measured calibration data for a three-hole yaw meter and a seven-hole probe.

Zilliac, Gregory G.↗

NASA NTRS1990

Laser diffraction particle sizing: Instrument probe volume relocation and elongation

The effective probe volume of laser diffraction particle sizing instruments depends on many instrument parameters. In particular the probe volume axial boundaries and its location along laser beam are essentially defined by the onset of a vignetting effect where light scattered at large angles from small particles misses the transform lens. This vignetting effect results in a probe volume that must be inconveniently close to the lens in order to detect smaller diameter particles (less than 100 micrometers). With the addition of an appropriately designed Keplerian telescope, the probe volume may be relocated and elongated. The theory of operation of this supplemental optical system is described. Design considerations for these supplemental optical systems are described, including recommendations for lens specifications, assembly and use. An image transfer system is described which has been designed for use on a Malvern 2600HSD instrument. Experimental validation of this image transfer system is described.

Anderson, Robert C.↗

NASA NTRS1990

Investigation of the arcjet plume near field using electrostatic probes

The near field plum of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in) and 15 cm (5.9 in) and radial distances extending to 10 cm (3.9 in) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Sankovic, John M.↗

NASA NTRS1990

Investigation of the Arcjet near Field Plume Using Electrostatic Probes

The near field plume of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in.) and 15 cm (5.9 in.) and radial distances extending to 10 cm (3.9 in.) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in.) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Sankovic, John M.↗

NASA NTRS1990

Design and spacecraft-integration of RTGs for solar probe

The design, analysis, and spacecraft integration of radioisotope thermoelectric generators (RTG) to power the Solar Probe under study at NASA JPL is described. The mission of the Solar Probe is to explore the solar corona by performing in situ measurements at up to four solar radii to the sun. Design constraints for the RTG are discussed. The chief challenge in the design and system integration of the Solar Probe's RTG is a heat rejection problem. Two RTG orientations, horizontal and oblique, are analyzed for effectiveness and results are summarized in chart form. A number of cooling strategies are also investigated, including heat-pipe and reflector-cooled options. A methodology and general computer code are presented for analyzing the performance of arbitrarily obstructed RTGs with both axial and circumferential temperature, voltage, and current variation. This methodology is applied to the specific example of the Solar Probe RTG obstructed by a semicylindrical reflector of 15-inch radius.

Schock, A.↗

NASA NTRS1991

A system for testing airdata probes at high angles of attack using a ground vehicle

A system to calibrate airdata probes at angles of attack between 0 and 90 deg was developed and tested at the NASA Ames Dryden Flight Research Facility. This system used a test fixture mounted to the roof of a ground vehicle and included an onboard instrumentation and data acquisition system for measuring pressures and flow angles. The data could be easily transferred to the facility mainframe computer for further analysis. The system was designed to provide convenient and inexpensive airdata probe calibrations for projects which require airdata at high angles of attack, such as the F-18 High Alpha Research Program. This type of probe was tested to 90 deg angle of attack in a wind tunnel and using the ground vehicle system. The results of both tests are in close agreement. An airdata probe with a swiveling pilot-static tube was also calibrated with the ground vehicle system. This paper presents the results of these tests and gives a detailed description of the test system.

Geenen, Robert J.↗

NASA NTRS1991

A new probe for measuring small electric fields in plasmas

A dipolar double probe has been developed for in situ measurements of small electric fields in laboratory plasmas. The probe measures dc to ac electric fields (f values between 0 and 20 MHz) with high sensitivity (Emin about 10 microV/cm) and responds to both space charge electric fields and inductive electric fields. Using voltage-to-frequency conversion, the probe signal is obtained free of errors and loading effects by a transmission line. Various examples of useful applications for the new probe are presented, such as measurements of dc ambipolar fields, ac space-charge fields of ion acoustic waves, ac inductive fields of whistler waves, and mixed inductive and space-charge electric fields in current-carrying magnetoplasmas.

Stenzel, R. L.↗

NASA NTRS1992

Galileo Probe Nephelometer Experiment

The objective of the Nephelometer Experiment aboard the Probe of the Galileo mission is to explore the vertical structure and microphysical properties of the clouds and hazes in the atmosphere of Jupiter along the descent trajectory of the Probe (nominally from 0.1 to greater than 10 bars). The measurements, to be obtained at least every kilometer of the Probe descent, will provide the bases for inferences of mean particle sizes, particle number densities (and hence, opacities, mass densities, and columnar mass loading) and, for nonhighly absorbing particles, for distinguishing between solid and liquid particles. These quantities, especially the location of the cloud bases, together with other quantities derived from this and other experiments aboard the Probe, will not only yield strong evidence for the composition of the particles, but, using thermochemical models, for species abundances as well. The measurements in the upper troposphere will provide 'ground truth' data for correlation with remote sensing instruments aboard the Galileo Orbiter vehicle.

Ragent, B.↗

NASA NTRS1992

Calibration of hemispherical-head flow angularity probes

The hemisphere-cylinder flow angularity probes were calibrated over a Mach number range of 0.5 to 2.0 at pitch and yaw angles of -5 to +5 deg. Each probe had five pressure orifices in the hemispherical head - one on the axis and four located 45 deg from the axis and equally spaced circumferentially. The probes were identical within fabrication tolerances. Details of probe design, test procedures and data analysis are described and selected test results are presented.

Clark, Edward L.↗

NASA NTRS1990

PROBE (Precision Reflector Orbital Build Experiment): A proposed flight experiment to study EVA assembly of precision segmented reflectors

PROBE (Precision Reflector Orbital Build Experiment) is a Shuttle flight demonstration experiment designed to study extravehicular activity (EVA) assembly of precision segmented reflectors. PROBE will support missions being considered for NASA's Global Change Technology Initiative as well as other missions in astrophysics and spacecraft optical communications requiring large precision reflectors. Such reflectors are envisioned to consist of a low-mass backup truss to which the optical surface is attached. Because of their large size, these reflectors will be constructed on-orbit from smaller pieces which can be packaged in the launch vehicle. The technology to be developed with PROBE also has application for construction of solar dynamic collectors which are planned for the enhanced configuration of Space Station Freedom. Viewgraphs of PROBE are presented.

Heard, Walter↗