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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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14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The Block V Receiver fast acquisition algorithm for the Galileo S-band mission

A fast acquisition algorithm for the Galileo suppressed carrier, subcarrier, and data symbol signals under low data rate, signal-to-noise ratio (SNR) and high carrier phase-noise conditions has been developed. The algorithm employs a two-arm fast Fourier transform (FFT) method utilizing both the in-phase and quadrature-phase channels of the carrier. The use of both channels results in an improved SNR in the FFT acquisition, enabling the use of a shorter FFT period over which the carrier instability is expected to be less significant. The use of a two-arm FFT also enables subcarrier and symbol acquisition before carrier acquisition. With the subcarrier and symbol loops locked first, the carrier can be acquired from an even shorter FFT period. Two-arm tracking loops are employed to lock the subcarrier and symbol loops parameter modification to achieve the final (high) loop SNR in the shortest time possible. The fast acquisition algorithm is implemented in the Block V Receiver (BVR). This article describes the complete algorithm design, the extensive computer simulation work done for verification of the design and the analysis, implementation issues in the BVR, and the acquisition times of the algorithm. In the expected case of the Galileo spacecraft at Jupiter orbit insertion PD/No equals 14.6 dB-Hz, R(sym) equals 16 symbols per sec, and the predicted acquisition time of the algorithm (to attain a 0.2-dB degradation from each loop to the output symbol SNR) is 38 sec.

Aung, M.↗
NASA NTRS1977

Survey of the BY Draconis syndrome among dMe stars

Results are reported for a BVr photometric survey of 22 dK, dKe, dM, and dMe stars conducted to search for slow quasi-sinusoidal fluctuations in V (the BY Draconis syndrome). The (B-V) and (V-r) color indices are determined in an attempt to detect wavelength-dependent color changes produced by starspots and to infer starspot temperatures. It is found that nine of the stars exhibit variations in V of the order of 0.05 to 0.10 magnitude on a time scale of days or weeks, that at least three more display changes in mean light level over a period of years, that the stars generally tend to become redder at minimum light, and that some of the stars show no detectable color changes over their photometric cycle. The color data are taken to suggest a probable temperature difference of about 200 to 500 K between the stellar photospheres and starspots if the V variations are attributed to dark spots. It is concluded that the BY Draconis syndrome is clearly a very common occurrence among dMe stars.

Bopp, B. W.↗
NASA NTRS1978

Evidence for a supermassive object in the nucleus of the galaxy M87 from SIT and CCD area photometry

Results are presented for broadband three-color (BVR) photometric observations of the peculiar elliptical radio galaxy M87, which were obtained with digital two-dimensional SIT and CCD detector systems on the Palomar 60-in. and 200-in. telescopes. The observations and the reduction procedures for the digital data are outlined, the luminosity profile of M87 is given, and a nuclear luminosity spike is found to be centered within 0.02 arcsec of the center of M87. Attempts are made to fit various theoretical models to the luminosity profile, and a satisfactory fit is obtained between the observed profile and a model involving a massive black hole in the galactic nucleus. A model-independent dynamical analysis of the central regions is performed which indicates that the nucleus of M87 contains a supermassive object of about 5 billion solar masses with a radius of no more than 100 pc and an M/L ratio of at least 60. The possible nature of this object is considered, and it is concluded that M87 is probably the most plausible candidate for a massive black hole in a galactic nucleus.

Young, P. J.↗
NASA NTRS1986

Signal-to-noise ratios for possible stellar occultations by Pluto

Successful observation of a stellar occultation by Pluto would make it possible to obtain information regarding the presence of an atmosphere at the planet. If an atmosphere is found, the determination of its structure might be feasible. Two or more occultation chords could make it possible to obtain the precise diameter of Pluto. Mink and Klemola (1985) have presented a list of ten stars which might be occulted by Pluto during the period 1985-1990. In this paper, BVR photometry of the occultation candidate stars are presented, and a calculation is conducted of the S/N which could be achieved with a 1-m telescope. It is pointed out that from a photometric standpoint, the best potential occultation (after that of P2) would be that of P8. However, even the faintest stars on the list should give interesting results if their occultations by Pluto can be observed with a 1-m telescope and sensitive photometric equipment.

Bosh, A. S.↗
NASA NTRS1994

BVRJK observations of Northern Hemisphere old novae

BVR photometry has been accomplished for 65 objects in the Duerbeck atlas along with J photometry of 52 and K of 30 objects. The (B - V), (V - R), and (V - J) colors are compiled with those available in the literature to assess the color change of novae as a function of time since outburst. Using available reddening values results in a list of 42 (B - V), 28 (V - R), and 38 (V - J) dereddened colors for novae that are from 1 to 319 years past outburst. The results indicate all the colors cluster about zero, with no obvious transition to red values as would be expected for novae undergoing a hibernation scenario. This indicates the accretion disk is sustained for at least 200 years after outburst. It is also apparent that red novae with giant secondaries and/or unusual properties readily stand out from the normal novae in color.

Szkody, Paula↗
NASA NTRS1994

First Hubble Space Telescope observations of the brightest stars in the Virgo galaxy M100 = NGC 4321

As part of both the Early Release Observations from the Hubble Space Telescope (HST) and the Key Project on the Extragalactic Distance Scale, we have obtained multiwavelength BVR Wide Field/Planetary Camera-2 (WFPC2) images for the face-on Virgo cluster spiral galaxy M100 = NGC 4321. We report here preliminary results from those observations, in the form of a color-magnitude diagram for approximately 11,500 stars down to V approximately 27 mag and a luminosity function for the brightest blue stars which is found to have a slope of 0.7, in excellent agreement with previous results obtained for significantly nearer galaxies. With the increased resolution now available using WFPC2, the number of galaxies in which we can directly measure Population I stars and thereby quantify the recent evolution, as well as test stellar evolution theory, has dramatically increased by at least a factor of 100. Finally, we find that the stars are present in M100 at the colors and luminosities expected for the brightest Cepheid variables in galaxies.

Freedman, Wendy L.↗
NASA NTRS1998

Observations of the Neuton Star RXJ0002.9 + 6246

The High Resolution Imager (HRI) observation of the CTB1 region requested in the original proposal was performed and data received. The primary target, the candidate neutron star, was detected at the predicted intensity. As proposed, both timing and spatial extent analysis has been performed on the extracted photons. The preliminary timing analysis showed no evidence for the faint pulsations seen in the PSPC data. As the pulse fraction was rather small, this was not an unexpected result. We have, however, recently developed more sophisticated timing analysis capabilities and are in the process of reanalyzing the data to more accurately constrain the pulse fraction, if indeed any evidence for pulsation is found. We have supplemented the HRI observations with optical observations. Filter images, in BVR & I, have been obtained as well as spectra for candidate counterparts. As of this writing, the original analysis holds, i.e. the x-ray flux is not consistent with the L(sub x)/L(sub opt) ratios expected from the candidate stars within the 3 sigma positional error circles. HRI confirmation of the flux as well as the refinement of the position have allowed us to limit the candidate list and refine the original L(sub x)/L(sub opt) analysis.

Hailey, Charles J.↗
NASA NTRS1996

The 0.8 day orbit of the precataclysmic binary EUVE J1016-053

The optical counterpart of the new extreme ultraviolet source EUVE J1016-053 (=RE 1016-053) is known to show intermittent sharp Balmer and HE I emission and traces of an M dwarf associated with a white dwarf optical spectrum. We present extensive optical spectroscopy showing the emission lines vary in velocity and intensity on a period of 0d.78929 +/- 0d.00003. The phase of the emission-line strengths lags that of the velocities by 0.237 +/- 0.013 cycle, consistent with the quarter-cycle offset expected if emission arises from the side of the secondary facing the hot white dwarf. EUVE J1016-053 is another example of an extreme ultraviolet illumination-effect binary, which only recently emerged from a common-envelope phase of binary evolution. Based on spectroscopic measurements and new BVR photometry, we find that the M dwarf secondary's contribution to the combined light is smaller than previously reported, probably because of the difficulty of avoiding contamination from a third star 3".2 distant. The velocity of the weak H II absorption is in antiphase to the emission, suggesting that it originates in the white dwarf photosphere. The mass function implied by the emission-line motion is f(M) = 0.28 +/- 0.08 M solar. Assuming the He II absorption does follow the white dwarf, the mass ratio MWD/MdM is 1.8 +/- 0.5, and the gravitational redshift is 45 +/- 14 km s-1. The modulation of the emission lines suggests the inclination i > 40 degrees, but plausible masses demand this inclination be well above the value.

Non-NASA Center↗
NASA NTRS2004

GRB 021211 as a Faint Analogue of GRB 990123: Exploring the Similarities and Differences in the Optical Afterglows

We present BVR(sub c)JHK(sub s) photometry of the optical afterglow of the gamma-ray burst GRB 021211 taken at the Magellan, MMT, and WIYN observatories between 0.7 and 50 days after the burst. We find an intrinsic spectral slope at optical and near-infrared wavelengths of 0.69 +/- 0.14 at 0.87 days. The optical decay during the first day is almost identical to that of GRB 990123 except that GRB 021211's optical afterglow was intrinsically approximately 38 times fainter and the transition from the reverse shock to the forward shock may have occurred earlier than it did for GRB 990123. We find no evidence for a jet break or the cooling break passing through optical frequencies during the first day after the burst. There is weak evidence for a break in the J-band decay between 0.89 and 1.87 days which may be due to a jet. The optical and infrared data are consistent with a relativistic fireball where the shocked electrons are in the slow cooling regime and the electron index is 2.3 +/- 0.1. The burst appears to have occurred in a homogeneous ambient medium. Our analysis suggests that the jet of GRB 021211 may have a small opening angle (1.4 deg-4.4 deg) and that the total gamma-ray energy is much less than the canonical value of 1.33 x 10(exp 51) erg. If, this is the case then most of the energy of the burst may be in another form such as a frozen magnetic field, in supernova ejecta, or in a second jet component. The host galaxy of GRB 021211 is subluminous and has a star formation rate of at least 1 solar mass/yr.

Holland, Stephen T.↗
NASA NTRS2005

Thermal Assessment of Swift BAT Instrument Thermal Control System in Flight

THE BAT is the primary instrument on the Swift spacecraft. The Swift mission is part of the National Aeronautics and Space Administration (NASA) Medium-Size Explorer (MIDEX) Program, and is managed by Goddard Space Flight Center (GSFC). It is designed to detect gamma ray burst over a broad region of the sky in a low Earth orbit of 600-km altitude and quickly align the telescopes on the spacecraft to the gamma ray source. It was successfully launched into orbit on November 20, 2004. The Swift mission is a first of its kind of multi-wavelength transient observatory for gamma ray burst astronomy. Its mission life is 2 years. The inclination is 22 deg maximum. The spacecraft bus voltage to the instruments is in the 24 V to 35 V range. The instruments will be turned off when the voltage is below 27 V. The BAT is mounted to the optical bench through five titanium flexures. The BAT has been developed at GSFC. Its telescope assembly consists of 256 Detector Modules (DMs) in the Detector Array. There are 16 Detector Array Blocks. Each Block holds 16 DMs, 3 Block Voltage Regulator (BVR) units and 3 Block Command & Data Handling (BCDH) units. The power dissipation of each Block has been measured to be 13 W. Therefore the total power dissipation of the 16 Blocks is 208 W. The DAP is 1.3 m (4.3 ft) x 1 m (3.3 ft), accommodates all the 16 Blocks. It also provides the mounting surface and the positional stability for the Blocks. The DMs are located at the top (+X side) of the DAP and is enclosed by graded-Z shields on the sides and a coded mask at the top. The BVRs and BCDHs are located at the bottom (-X side) of the DAP. Eight Blocks are located at the front (-Z side or radiator side) of the DAP, and eight are located at the rear (+Z side) of the DAP. The DMs and top of DAP are insulated with a 7-layer multi-layer insulation (MLI). There is a 5.08 cm (2 in) x 5.08 cm (2 in) MLI cutout over each Block heater controller so that heat radiates from the heater controller to the mask. The exterior of the mask, graded-Z shields and bottom of DAP is insulated with a 15-layer MLI.

Choi, Michael K.↗
NASA NTRS2005

Optical and X-ray studies of chromospherically active stars: FR Cancri, HD 95559 and LO Pegasi

We present a multiwavelength study of three chromospherically active stars, namely FR Cnc (= BD +16 degrees 1753), HD 95559 and LO Peg (=BD +22 degrees 4409), including newly obtained optical photometry, (for FR Cnc) low-resolution optical spectroscopy, as well as archival IR and X-ray observations. The BVR photometry carried out during the years 2001 - 2004 has found significant photometric variability to be present in all three stars. For FR Cnc, a photometric period 0.826685 +/- 0.000034 d has been established. The strong variation in the phase and amplitude of the FR Cnc light curves when folded on this period implies the presence of evolving and migrating spots or spot groups on its surface. Two independent spots with migration periods of 0.97 and 0.93 years respectively are inferred. The photometry of HD 95559 suggests the formation of a spot (group) during the interval of our observations. We infer the existence of two independent spots or groups in the photosphere of LO Peg, one of which has a migration period of 1.12 years. The optical spectroscopy of FR Cnc carried out during 2002-2003, reveals the presence of strong and variable Ca I1 H and K, H(sub beta) and H(sub alpha) emission features indicative of high level of chromospheric activity. The value of 5.3 for the ratio of the excess emission in H(sub alpha) to H(sub beta), EH(sub alpha)/EH(sub beta), suggests that the chromospheric emission may arise from an extended off-limb region. We have searched for the presence of color excesses in the near-IR JHK bands of these stars using 2MASS data, but none of them appear to have any significant color excess. We have also analyzed archival X-ray observations of HD 95559 and LO Peg carried out by with the ROSAT observatory. The best fit models to their X-ray spectra imply the presence of two coronal plasma components of differing temperatures and with sub-solar metal abundances. The inferred emission measures and temperatures of these systems are similar to those found for other active dwarf stars. The kinematics of FR Cnc suggest that it is a very young (35 - 55 Myrs) main-sequence star and a possible member of the IC 2391 supercluster. LO Peg also has young disk-type kinematics and has been previously suggested to be a member of the 100 Mys old Local Association (Pleiades Moving Group). The kinematics of HD 95559 indicate it is a possible member of the 600 Myrs old Hyades supercluster.

Pandey, J. C.↗
NASA NTRS2017

The Use of a Satellite Communications System for Command and Control of the National Aeronautics and Space Administration Surrogate Unmanned Aerial System Research Aircraft

The NASA Langley Research Center has transformed a Cirrus Design SR22 general aviation (GA) aircraft into an Unmanned Aerial Systems (UAS) Surrogate research aircraft which has served for several years as a platform for unmanned systems research and development. The aircraft is manned with a Safety Pilot and a Research Systems Operator (RSO) that allows for flight operations almost any-where in the national airspace system (NAS) without the need for a Federal Aviation Administration (FAA) Certificate of Authorization (COA). The UAS Surrogate can be remotely controlled from a modular, transportable ground control station (GCS) like a true UAS. Ground control of the aircraft is accomplished by the use of data links that allow the two-way passage of the required data to control the aircraft and provide the GCS with situational awareness. The original UAS Surrogate data-link system was composed of redundant very high frequency (VHF) data radio modems with a maximum range of approximately 40 nautical miles. A new requirement was developed to extend this range beyond visual range (BVR). This new requirement led to the development of a satellite communications system that provided the means to command and control the UAS Surrogate at ranges beyond the limits of the VHF data links. The system makes use of the Globalstar low earth orbit (LEO) satellite communications system. This paper will provide details of the development, implementation, and flight testing of the satellite data communications system on the UAS Surrogate research aircraft.

Howell, Charles T.↗
NASA NTRS1996

Standardized, Low Cost Communications for Planetary Mission

For Deep Space Missions, the Radio-Frequency (RF) communications link provides both communications and navigation services. In this article we discuss the increased efficiency and reduced cost that can result from the potential consolidation of the two services into one suite of equipment, and the utilization of guaranteed delivery standard protocols to improve the communications service.

Deep↗