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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 199 records · Page 11
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NASA NTRS1972

Smoothing of functions of range and range rate measurements from earth orbiting satellites

It is shown that for satellites in circular Earth orbits with altitudes of 500 kilometers to 1500 kilometers, and for satellites in elliptical orbits with an approximate 4000 kilometer height of perigee, a high degree least squares polynomial (e.g., a 9th or 10th degree in some cases) is required to smooth both range and range rate data for purposes of input to orbit determination programs. In order to circumvent this problem, functions of range and range rate are smoothed with lower degree least squares polynomials (e.g., 3rd and 4th degree) and it is shown that under the above geometric constraints the standard deviation of fit can be reduced to levels commensurate with typical S-band tracking system resolution which is 1 to 2 meters in range and 0.005 meters/second in range rate for a 1 per second data rate. Also shown are the effects of Gaussian random noise, biases, and periodic noise. This analysis includes numerous examples applied to the 44 point data smoothing interval currently used in much of the operational preprocessing at the Goddard Space Flight Center.

Grenchik, T. J.↗
NASA NTRS1972

Airborne electronically steerable phased array

The results are presented of the second stage of a program for the design and development of a phased array capable of simultaneous and separate transmission and reception of radio frequency signals at S-band frequencies. The design goals of this stage were the development of three major areas of interest required for the final prototype model. These areas are the construction and testing of the low-weight, full-scale 128-element array of antenna elements, the development of the RF manifold feed system, and the construction and testing of a working module containing diplexer and transmit and receive circuits.

Source record↗
NASA NTRS1973

On the Feasibility of Efficient Multiamplitude Communication

Bandwidth constraints in earth-satellite communication systems force consideration of uncoded M-ary modulation to obtain increased data rates. M-ary phase shift keying (MPSK) at first glance seems most promising because of the high transmitter efficiency achieved through Class C operation. Multiple phase-and-amplitude modulation candidates such as quadrature amplitude shift keying (QASK) appear less promising because the transmitter must operate at lower efficiency (in linear or multimode operation). However, initial studies indicate that QASK offers significant raw dc-power savings over MPSK, despite the reduced transmitter efficiency. For example, at S-band both solid-state and traveling wave tube (TWT) QASK transmitters can provide a 3-dB average dc-power savings over comparable 16-ary phase shift keying (PSK) for the same bit rate and error probability. The reason for this savings is that QASK requires much less average signal-to-noise ratio than 16-ary PSK for the same error rate.

Smith, J. G.↗
NASA NTRS1972

Dynamic mass modeling and geophysical analysis of lunar maria based on Apollo tracking data

A series of lunar gravity analyses were carried out using unified S-band tracking network data obtained from Apollos 8, 10, 11, 12, 14, and 15. The progress obtained to date is summarized as it relates to the estimation of lunar mass distributions and their geologic interpretation. The analyses reported are of two distinct types. The first type consists of data obtained at two ranges of altitude to estimate the total mass associated with various lunar features employing a point mass assumption. The second type consists of detailed analyses of Apollo 14 tracking data.

Strange, W. E.↗
NASA NTRS1972

Bistatic-radar investigation

The purpose of the reported experiment was to determine the principal electromagnetic and structural properties of the lunar surface from the observation of command and service module (CSM) radio transmissions that were reflected from the lunar surface and received on earth. These transmissions emanate from the CSM communication systems at wavelengths of 13 cm (S-band) and 116 cm (very high frequency (VHF)). Lunar crustal properties such as dielectric constant, average slope and slope probability, density, small-scale surface roughness, and embedded rocks to a depth of 20 m may be determined. The results are proving to be most useful in understanding the processes that have produced and modified the crust and in distingushing between adjacent and subjacent geological units. The experimental observations are also of intrinsic interest in the study of electromagnetic scattering.

Howard, H. T.↗
NASA NTRS1973

Furlable spacecraft antenna development

Recent activities at JPL directed toward the development of large furlable spacecraft antennas using conical main reflectors are described. Development of two basic antenna configurations conceived at JPL and utilizing conical main reflectors was pursued. A 4.3-m (14-ft)-diameter model based on the two-reflection conical-Gregorian concept and a 1.8-m (6-ft)-diameter model based on the four-reflection Quadreflex concept have been made and RF-tested. RF gain measurements for the 4.3-m (14-ft)-diameter conical-Gregorian model were 48.83 db at X-band (8.448 GHz) and 37.82 db at S-band (2.297 GHz). These gains correspond to efficiencies of 53.6 and 57.5%, respectively. RF gain measurements for the 1.8-m (6-ft)-diameter Quadreflex model were 47.59 db at Ku-band (16.33 GHz) and 41.30 db at X-band (8.448 GHz), corresponding to efficiencies of 58.6 and 51.5%, respectively.

Oliver, R. E.↗
NASA NTRS1973

Adaptive ground implemented phase array

The simulation of an adaptive ground implemented phased array of five antenna elements is reported for a very high frequency system design that is tolerant to the radio frequency interference environment encountered by a tracking data relay satellite. Signals originating from satellites are received by the VHF ring array and both horizontal and vertical polarizations from each of the five elements are multiplexed and transmitted down to ground station. A panel on the transmitting end of the simulation chamber contains up to 10 S-band RFI sources along with the desired signal to simulate the dynamic relationship between user and TDRS. The 10 input channels are summed, and desired and interference signals are separated and corrected until the resultant sum signal-to-interference ratio is maximized. Testing performed with this simulation equipment demonstrates good correlation between predicted and actual results.

Spearing, R. E.↗
NASA NTRS1973

Very long baseline interferometry

S-band stations with dual tracking capability have been used to gather double differential very long baseline interferometry data on Apollo 16 and Apollo 17. This was accomplished by simultaneously receiving both monochromatic radio signal emissions at each of two separated receiving stations, transmitting these data to a central processing facility, and calculating the differences between Doppler angular rates to determine the motion of the lunar roving vehicle.

Salzberg, I. M.↗
NASA NTRS1973

Stanford bistatic radar experiment (S-170) on Apollos 14, 15, and 16

No special equipment was placed onboard the vehicles for the bistatic radar experiments which were carried out during the lunar orbit phases of the Apollo 14, 15, and 16 flights. Radio frequency transmissions from the orbiting command service module were directed toward the moon and received on the earth after reflection from the lunar surface. Two wavelengths, 13 cm (2287.5 MHz, S-band) and 116 cm (259.7 MHz, VHF), were used. Data were obtained at the two wavelengths simultaneously during periods when the spacecraft was maneuvered to maintain a predetermined, although changing, attitude with respect to the earth and moon. Data were also obtained at the 116 cm wavelength during periods of inertial hold and SIM bay attitude maneuvers.

Howard, H. T.↗
NASA NTRS1972

Intensive probing of clear air convective fields by radar and instrumented drone aircraft.

Clear air convective fields were probed in three summer experiments (1969, 1970, and 1971) on an S-band monopulse tracking radar at Wallops Island, Virginia, and a drone aircraft with a takeoff weight of 5.2 kg, wingspan of 2.5 m, and cruising glide speed of 10.3 m/sec. The drone was flown 23.2 km north of the radar and carried temperature, pressure/altitude, humidity, and vertical and airspeed velocity sensors. Extensive time-space convective field data were obtained by taking a large number of RHI and PPI pictures at short intervals of time. The rapidly changing overall convective field data obtained from the radar could be related to the meteorological information telemetered from the drone at a reasonably low cost by this combined technique.

Rowland, J. R.↗
NASA NTRS1972

The atmosphere of Mars from Mariner 9 radio occultation measurements.

Mariner-9 S-band radio occultation measurements conducted during November and December 1971 are described in terms of new information that was obtained about the shape and atmosphere of Mars. The arrival of the spacecraft coincided with a severely obscuring global dust storm, and the effect of the dust in the atmosphere was reflected in the reduced temperature gradients that were measured in the daytime near-equatorial atmosphere, indicating (1) heating of the atmosphere by solar radiation absorbed by dust and (2) simultaneous cooling of the surface. In general, surface atmospheric pressures measured in the equatorial regions are in very good agreement with previous radio-occultation and earth-based measurements. A global disparity in pressures strongly suggests that the physical shape of Mars is more oblate than the shape of its gravitational equipotential surface.

Kliore, A. J.↗
NASA NTRS1972

The Mariner Mars 1971 orbiter.

The Mariner Mars 1971 (MM '71) orbiter spacecraft, launched toward Mars in the spring of 1971, was designed to offer the first opportunity for sustained observations in the near vicinity of another planet of our solar system. The MM '71 spacecraft, like its predecessors, is fully attitude stabilized about three axes, using the sun and Canopus as references, an orientation which allows use of photovoltaic solar panels for primary power and permits two-way communication to the earth through a high-gain directional antenna. Midcourse and orbit insertion maneuvers use the sun-Canopus orientation as a reference direction for initiating commanded turns. Scientific instruments employed during Mars orbital operations are mounted on a two-degree-of-freedom platform controlled by commands from the central computer and sequencer. Science measurements to be obtained by the MM '71 spacecraft include television visual imaging, infrared radiometry, infrared spectroscopy, ultraviolet spectroscopy, S-band radio occultation, and celestial mechanics.

Scull, J. R.↗
NASA NTRS1973

The variation of atmospheric temperatures at microwave frequencies.

Discussion of the effects of varying meteorological conditions on microwave propagation and on total system temperatures. Microwave atmospheric temperatures at X- and K-bands measured continuously for more than a year are compared with data obtained simultaneously by routine S-band spacecraft tracking.

Reid, M. S.↗
NASA NTRS1973

Measurements of the dielectric properties of seawater and NaCl solutions at 2.65 GHz.

Measurements at 2.653 GHz of the dielectric properties of seawater samples collected over the world's oceans and NaCl solutions over the concentration range from 0.3 to 0.7 N have been made over the temperature range from 5.5 to 24 C to an accuracy of 0.2% in the real part of epsilon and 0.4% in the imaginary part of epsilon. The measurements demonstrate that the dielectric properties of seawater can be determined from its chlorinity alone but are substantially different from those of the 3.35 wt % NaCl solution, which has been taken in all previous work as a model for seawater. The data are presented in a form that is well fitted by a linear dependence on chlorinity. The accuracy of the measurements removes the uncertainty in the dielectric properties of seawater as a significant source of error in S-band radiometric determination of ocean surface temperature.

Ho, W.↗
NASA NTRS1973

An experimental study of the temporal statistics of radio signals scattered by rain

A fixed-beam bistatic CW experiment designed to measure the temporal statistics of the volume reflectivity produced by hydrometeors at several selected altitudes, scattering angles, and at two frequencies (3.6 and 7.8 GHz) is described. Surface rain gauge data, local meteorological data, surveillance S-band radar, and great-circle path propagation measurements were also made to describe the general weather and propagation conditions and to distinguish precipitation scatter signals from those caused by ducting and other nonhydrometeor scatter mechanisms. The data analysis procedures were designed to provide an assessment of a one-year sample of data with a time resolution of one minute. The cumulative distributions of the bistatic signals for all of the rainy minutes during this period are presented for the several path geometries.

Hubbard, R. W.↗
NASA NTRS1973

A one way Doppler tracking system for satellite to satellite tracking

An S-band tracking system employing one way Doppler applicable to the tracking and data relay system (TDRS) was evaluated. This evaluation is limited to the measurement system parameters. The analysis assumes state-of-the-art components such as spacecraft oscillator long term stability of one part in 10 to the 8th power and ground station oscillator stability of one part in 10 to the 11th power. Signal characteristics comparable with the present ranging systems are utilized in the analysis. Predicated upon measurement system parameters, position uncertainties for the low orbiting spacecraft vary from 5 meters to 2 kilometers along track, 4 meters to 1 kilometer cross track, and 1 meter to 180 meters radially depending upon the tracking geometry and the high satellite position and velocity error assumptions.

Bryan, J. W.↗
NASA NTRS1973

Very long baseline interferometry /VLBI/ applications to secular geodynamics and earth strain measurement

An instrumental technique from radio astronomy known as very long baseline interferometry (VLBI) offers significant promise for the solution of the problem of accurate long-distance, three-dimensional surveying and determination of whole earth geodynamical phenomena. The methods of VLBI make it possible for receiving stations to be independently operated at arbitrary separations using extragalactic radio sources as their frame of time-invariant angular reference. Feasibility demonstrations at S-band (13 cm) wavelengths have been performed, and accuracies of a few centimeters for three-dimensional surveying over a short distance (16 km) have been demonstrated. VLBI operation on longer baselines (8400 km) has been performed between Goldstone, California, and Madrid, Spain, in order to develop the capability for determination of universal time variations, in addition to the measurements of this intercontinental baseline. Systems analysis indicates that necessary calibrations can be developed so as to make possible the implementation of a transportable radio interferometer station concept.

Macdoran, P. F.↗