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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The molecular gas associated with HH46 and HH47

The NASA 64-m and CSIRO 64-m antennas at Tidbinbilla and Parkes, respectively, have been used to observe the star-forming region associated with HH46 and HH47 in the Bok globule known as ESO 210-6A or Sa III. The (1,1), (2,2), and (3,3) transitions of ammonia were observed at the position of the infrared point source, which is the star energizing this complex. Ammonia was not detected at other nearby locations in the globule. The ammonia emission is attributed to a circumstellar toroid or disk with a gas temperature of 17 + or - 2 K, a density of 7 + or - 20,000/cu cm, a size of 6000-7500 Au, and a mass of 0.09-0.14 solar masses, assuming an ammonia abundance of 10 to the -7th. Such a low disk mass may imply more than mere confinement as the mechanism for achieving high collimation observed in the outflow from this region.

Kuiper, T. B. H.↗
NASA NTRS1986

A Southern Hemisphere ammonia survey

A spectral line survey for interstellar NH3 is being carried out using the 64-m telescopes at Parkes and Tidbinbilla. Both telescopes are equipped with K-band maser receivers yielding system temperatures below 100 K. The preliminary survey is being made with the Parkes antenna (beam = 1.35 arcmin), with follow-up mapping of the more interesting sources at Tidbinbilla (beam = 0.9 arcmin). The selected sources have in general been H II regions from the H2CO surveys made at Parkes. Statistical results from initial observations of the (1,1), (2,2), and (3,3) lines in the preliminary survey are presented.

Peters, W. L.↗
NASA NTRS1987

IRAS observations of southern molecular clouds

A report is given of a project to use IRAS Band 3 (60 microns) and Band 4 (100 microns) observations to investigate the far-infrared properties of southern galactic molecular clouds. A method by which dust temperature and total gas column density can be estimated is presented. Results are tabulated for 65 prominent southern far-infrared sources. The dust temperatures are closely grouped between 30 and 50 K, while the column densities range between 2 x 10 to the 20th and 10 to the 22nd/sq cm. Maps of dust temperature and gas column density have been generated for two fields containing far-infrared sources to illustrate the effectiveness of this form of presentation.

Kuiper, T. B. H.↗
NASA NTRS1987

Low frequency VLBI in space using GAS-Can satellites: Report on the May 1987 JPL Workshop

Summarized are the results of a workshop held at JPL on May 28 and 29, 1987, to study the feasibility of using small, very inexpensive spacecraft for a low-frequency radio interferometer array. Many technical aspects of a mission to produce high angular resolution images of the entire sky at frequencies from 2 to 20 MHz were discussed. The workshop conclusion was that such a mission was scientifically valuable and technically practical. A useful array could be based on six or more satellites no larger than those launched from Get-Away-Special canisters. The cost of each satellite could be $1-2M, and the mass less than 90 kg. Many details require further study, but as this report shows, there is good reason to proceed. No fundamental problems have been discovered involving the use of untraditional, very inexpensive spacecraft for this type of mission.

Mahoney, M. J.↗
NASA NTRS1988

The Deep Space Network: An instrument for radio astronomy research

The NASA Deep Space Network operates and maintains the Earth-based two-way communications link for unmanned spacecraft exploring the solar system. It is NASA's policy to also make the Network's facilities available for radio astronomy observations. The Network's microwave communication systems and facilities are being continually upgraded. This revised document, first published in 1982, describes the Network's current radio astronomy capabilities and future capabilities that will be made available by the ongoing Network upgrade. The Bibliography, which includes published papers and articles resulting from radio astronomy observations conducted with Network facilities, has been updated to include papers to May 1987.

Renzetti, N. A.↗
NASA NTRS1988

A dual-frequency 183/380 GHz receiver for airborne applications

A complete dual-frequency cryogenic heterodyne receiver operating at 183 and 380 GHz is described. The cooled mixers are whisker-contacted GaAs Schottky diodes mounted in reduced-height fundamental-mode waveguide. The local oscillators are Gunn-oscillator-driven multipliers using GaAs varactor diodes as the harmonic generators. Quasi-optical techniques are used extensively for coupling the remote and local oscillator signals into the mixers. The overall system double side-band (DSB) noise temperature is 320 K for the 183-GHz receiver and 650 K for the 380 GHz receiver.

Batelaan, Paul D.↗
NASA NTRS1987

A low-frequency synthesis array in earth orbit

The scientific objectives and design concept of a space-based VLBI array for high-resolution astronomical observations at 1-30 MHz are discussed. The types of investigations calling for such an array include radio spectroscopy of individual objects, measurement of the effects of scattering and refraction by the interplanetary medium (IPM) and the ISM, mapping the distribution of low-energy cosmic-ray electrons, and determining the extent of the Galactic halo. Consideration is given to the limitations imposed on an LF VLBI array by the ionosphere, the IPM, and the ISM; the calibration advantages offered by circular polar orbits of slightly differing ascending-node longitude for the array satellites; and collection of the IF data streams from the array satellites by one 'master' satellite prior to transmission to the ground. It is shown that determination of the three-dimensional array geometry by means of intersatellite radio links is feasible if there are at least seven spacecraft in the array.

Jones, Dayton L.↗
NASA NTRS1989

Very-Long-Baseline Interferometry Using Cheap Satellites

Celestial radiation below 25 MHz, heretofore inaccessible, yields new insights. Report discusses feasibility of array of small satellites deployed in high orbit around Earth to monitor celestial radio sources at frequencies less than 25 MHz. Objective to make high-angular-resolution map of such sources over entire sky by use of very-long-baseline interferometry (VLBI).

Mahoney, M. J.↗
NASA NTRS1987

Ammonia mapping of the southern molecular cloud NGC 6334

The ammonia emission in the (J,K = 1,1) and (J,K = 2,2) transitions toward NGC 6334 has been mapped using the Parkes 64-m antenna. Distributions of observed and derived quantities are obtained with a resolution of about 1 pc. The results suggest that velocity anomalies are present near the two OH masers NGC 6334A and B, and that the source of ammonia emission located near the northernmost H2O maser is one of most intense sources of NH3 emission in the Galaxy.

Forster, J. R.↗
NASA NTRS1989

Detection of the 2(0) to 3(-1) transition of C-13H3OH at 14.8 GHz

Observations of the 2(0) to 3(-1) E-type transition of C-13H3OH at 14.78 GHz have been made toward the continuum sources Sgr A, Sgr B2, and W33. For the cases of Sgr B2 and one position in Sgr A, a C-12/C-13 abundance ratio of 40 is obtained which is much higher than the values (20-25) found for other molecules. For W33, the value 50 obtained (50) is lower than that derived from H2CO observations, but is comparable to that noted from CO observations.

Kuiper, T. B. H.↗
NASA NTRS1989

The 32-GHz performance of the DSS-14 70-meter antenna: 1989 configuration

The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency.

Gatti, M. S.↗
NASA NTRS1989

First detection of the O-18 isotope of methanol

Interstellar CH3(O-18)H has been detected using NASA's 70-m antenna at Tidbinbilla. The 2(0)-3(-1) transition at 11.6 GHz was detected in absorption at two positions in the direction of Sgr B2. The profile shapes were similar to those for the corresponding transitions of CH3OH and (C-13)H3OH, containing velocity components centered near 64 and 80 km/s. Abundance ratios were derived using the simplest assumptions. The O-16/O-18 ratio was 210 + or - 40; the value would be larger after correction for radiation trapping but still well below the terrestrial value of 489. The (C-13)H3OH/CH3(O-18)H ratio was 7.5 + or - 1.0, above the value (5.5) derived from terrestrial C-12/C-12 and O-16/O-18 ratios, but close to the isotope abundance ratio (9.0) determined from formaldehyde observations. In view of the complexity of the methanol energy-level diagram, the similarity suggests that excitation of the lowest energy levels is largely collisional.

Gardner, F. F.↗
NASA NTRS1989

Resource letter ETC-1 - Extraterrestrial civilization

This resource letter provides a guide to the literature about intelligent life beyond the human sphere of exploration. It offers a starting point for professionals and academics interested in participating in the debate about the existence of other technological civilizations or in SETI. It can also serve as a reference for teaching. Several extensive bibliographies are cited.

Kuiper, Thomas B. H.↗
NASA NTRS1990

Lunar low-frequency radio array

A simple, inexpensive experiment is proposed for the early lunar mission to make high angular resolution observations in one of the last unexplored parts of the electromagnetic spectrum. An array of nineteen simple crossed-dipole antennas will make images at frequencies below the earth's ionospheric cut-off - from about 100 kHz to 10 MHz. It would serve as a precursor to a major low-frequency telescope which would eventually be built on the back of the moon, away from terrestrial interference.

Kuiper, T. B. H.↗
NASA NTRS1990

A simple low-cost array on the lunar near-side for the early lunar expeditions

A concept of a simple, low-cost array on the lunar near-side is discussed. The concept includes 19 stations laid in a T, with three arms each 36 km long, and separated by 6 km. Each station consists of two 10-m-long orthogonal dipoles, each feeding a receiver of a commercial pocket digital shortwave radio type, and a 3-m spring-loaded mast with a small UHF array at the top for receiving the timing signals and tuning commmands and for sending out the digitized data streams. Each station has 0.25 square meters of solar arrays and 20 kg of lithium batteries. At the array center there is either a digital correlator for processing the signals from each antenna pair to compact the data into a 32-kb/sec channel or a 10-cm telescope for sending back raw data to earth.

Kuiper, T. B. H.↗
NASA NTRS1992

Robust Method For Robotic Mapping

Robot constructs map from experience. Topological model consists of nodes and arcs corresponding to distinctive places and local travel edges linking nearby distinctive places. Model created by linking places and edges. Enables accumulation of metrical information with reduced vulnerability to metrical errors. Applications include robotic sentires, robotic delivery trucks, robotic floor cleaners, and robotic lawnmowers.

Kuipers, Benjamin J.↗
NASA NTRS1991

The composition of heterogeneous control laws

The fuzzy control literature and industrial practice provide certain nonlinear methods for combining heterogeneous control laws, but these methods have been very difficult to analyze theoretically. An alternate formulation and extension of this approach is presented that has several practical and theoretical benefits. An example of heterogeneous control is given and two alternate analysis methods are presented.

Kuipers, Benjamin↗
NASA NTRS1992

Reasoning about energy in qualitative simulation

While possible behaviors of a mechanism that are consistent with an incomplete state of knowledge can be predicted through qualitative modeling and simulation, spurious behaviors corresponding to no solution of any ordinary differential equation consistent with the model may be generated. The present method for energy-related reasoning eliminates an important source of spurious behaviors, as demonstrated by its application to a nonlinear, proportional-integral controlled. It is shown that such qualitative properties of such a system as stability and zero-offset control are captured by the simulation.

Fouche, Pierre↗