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OGO radio astronomy instrument for cosmic noise sky brightness distribution mapping by electrically short antenna ionospheric focusing
The support provided by the Deep Space Network to the Viking Project from 1 June 1978 to 30 April 1980 is described. The project was supported by the worldwide network of Deep Space Stations with 26- and 64-meter-diameter antennas, together with a ground communications system, for the transmission of commands, telemetry, radio metric data, and operational instructions between the stations and the network operation control center in Pasadena, California. Assistance was substantially less than in the previous phases of the Viking Project in order to provide adequate support to the Pioneer and Voyager Projects.
The International Cometary Explorer (ICE) is to investigate the magnetic and electric fields, plasmas, and particles in the Comet Giacobini-Zinner (G-Z) and to study its interaction with solar wind. The ICE can pass through the comet only once and it will take 90 minutes to cross from one side of the tail to the other. Since the Comet G-Z often changes its orbit due to nongravitational forces changing its direction and velocity, ICE's position needs to be adjusted. The probe is aimed 10,000 km from the nucleus in order to be provided the best passage through the Comet G-Z. The 64-meter dishes of JPL's Deep-Space Network (DSN) will receive data transmitted on two adjacent S-band frequencies at the rate of 1024 bits per second. Also NASA has arranged for the radio telescope at Arecibo to record the transmission. The Japanese 64-meter tracking antenna at Usada, equipped with an ultrasensitive receiver for one ICE frequency, will provide pre-encounter and post-encounter tracking. The ICE data may provide information about the dust tail in the Comet G-Z which could be compared to previous research.
The new subreflector mount (quadripod) for the 64-meter to 70-meter antenna extension project was the result of many trial designs aimed at reducing radio frequency spherical and plane wave blockage and minimizing structural weight while satisfying strength and natural frequency requirements. An optimum design emerged which has a gain improvement of 0.32 dB over the present 64-meter design. Some of the trial designs made and the final optimum configuration selected are described.
During Voyager's Neptune encounter, the National Radio Astronomy Observatory's Very Large Array (VLA) will be arrayed with Goldstone antennas to receive the transmitted telemetry data from the spacecraft. The telemetry signal from the VLA will drop out periodically, resulting in a periodic drop in the received signal-to-noise ratio (SNR). The Image Statistics Decoder (ISD), which assumes a correlation between pixels, can improve the bit error rate (BER) for images during these dropout periods. Simulation results have shown that the ISD, in conjunction with the Goldstone-VLA array can provide a 3-dB gain for uncompressed images at a BER of 5.0 x 10(exp -3).
Pattern measurements at 802GHz of a single element in 256-element integrated horn imaging array are presented. The integrated-horn antenna consists of a dipole-antenna suspended on a 1-micron dielectric membrane inside a pyramidal cavity etched in silicon. The theoretical far-field patterns, calculated using reciprocity and Floquet-modes representation of the free-space field, agree well with the measured far-field patterns at 802GHz. The associated directivity for a 1.40 lambda horn aperture, calculated from the measured E and H-plane patterns is 12.3dB + or - 0.2dB. This work demonstrates that high-efficiency integrated-horn antennas are easily scalable to terahertz frequencies and could be used for radio-astronomical and plasma-diagnostic applications.
An integrated corner-cube antenna has been designed, fabricated, and measured at 119 microns. The structure consists of a traveling-wave antenna integrated on a 1-micron dielectric membrane and suspended in a longitudinal cavity etched in silicon wafers. The patterns at 119 microns agree well with millimeter-wave patterns measured on a scaled antenna at 222 GHz. A directivity of 18 +/- 0.5 dB is calculated from E- and H-plane measurements. This work demonstrates that high-efficiency integrated corner-cube antennas are easily scalable to terahertz frequencies and could be used for radio-astronomical and plasma-diagnostic applications.
This article describes an approach for measuring the angular position of a spacecraft with reference to a nearby calibration source (quasar) with an accuracy of a few tenths of a nanoradian using a very long baseline interferometer of two antennas that measures the interferometer phase with a modest accuracy. It employs (1) radio frequency phase to determine the spacecraft position with high precision and (2) multiple delay measurements using either frequency tones or telemetry signals at different frequency spacings to resolve ambiguity of the location of the fringe (cycle) containing the direction of the spacecraft.
Multiband dipole antennas based on hexagonal and pentagonal fractals have been analyzed by computational simulations and functionally demonstrated in experiments on prototypes. These antennas are capable of multiband or wide-band operation because they are subdivided into progressively smaller substructures that resonate at progressively higher frequencies by virtue of their smaller dimensions. The novelty of the present antennas lies in their specific hexagonal and pentagonal fractal configurations and the resonant frequencies associated with them. These antennas are potentially applicable to a variety of multiband and wide-band commercial wireless-communication products operating at different frequencies, including personal digital assistants, cellular telephones, pagers, satellite radios, Global Positioning System receivers, and products that combine two or more of the aforementioned functions. Perhaps the best-known prior multiband antenna based on fractal geometry is the Sierpinski triangle antenna (also known as the Sierpinski gasket), shown in the top part of the figure. In this antenna, the scale length at each iteration of the fractal is half the scale length of the preceding iteration, yielding successive resonant frequencies related by a ratio of about 2. The middle and bottom parts of the figure depict the first three iterations of the hexagonal and pentagonal fractals along with typical dipole-antenna configuration based on the second iteration. Successive resonant frequencies of the hexagonal fractal antenna have been found to be related by a ratio of about 3, and those of the pentagonal fractal antenna by a ratio of about 2.59.
The degradation of antenna performance during hypersonic re-entry is a well known phenomenon that can lead to complete radio blackout. Recent additions to the Empire code establish it as a tool for the study and analysis of the problem. Coupling to the Sandia Parallel Aerodynamics and Reentry Code (SPARC) enables the electromagnetic analysis of realistic re-entry plasma profiles. The geometric flexibility afforded by both Empire and SPARC allow the consideration of arbitrary vehicle and antenna configurations. We have used this tool to study antenna performance during re-entry when the boundary layer becomes turbulent. A concise description of line-of-sight transmissions, which employs advanced statistical methods, was developed. New insights into the low altitude reflectometer readings of RAM-C2 are offered. Techniques for the reconstruction of the re-entry plasma profile from reflectometer data were explored.
A K-band reflected-wave ruby maser was used on the 64-meter (DSS-43) antenna at the Tidbinbilla Tracking Station, near Canberra, Australia. Spectral line observations were carried out near 22 GHz for water vapor sources and near 24 GHz for ammonia sources. The water vapor observations were made in the direction of known southern OH and H2O maser sources. All of the previously detected water line sources examined were detected. In addition, two new water vapor maser sources were discovered, G301.1+1.1and G308.9+0.1. The spectrum of G301.0+1.1 is presented six ammonia sources were found: G291.3-0.7, G305.4+0.2, G322.2+0.6, G327.3-0.5, G333.6-0.2, and G268.4-0.8. Spectra of two of these sources, G291.3-0.7 (RCW 57) and G305.4+0.2, are presented. Both show clearly the presence of the quadrupole splitting satellite lines that will allow the determination of NH3 optical depths in these clouds.
The Owens Valley (OVRO) Solar Array was recently expanded to 5 antennas. Using frequency synthesis, the 5-element OVRO Solar Array has up to 450 effective baselines, which can be employed as necessary to make maps at frequencies in the range 1 to 18 GHz. Fortuitously, the last of the 5 antennas was completed and brought into operation on 7 Jun., just in time for the Gamma Ray Observatory (GRO)/Max 1991 observing campaign. Many events were observed jointly with OVRO and the BATSE experiment on GRO, including the six larger events that are presented in tabular form. Unfortunately, the X flares that occurred during the campaign all occurred outside the OVRO time range. The UV coverage of the newly expanded solar array, combined with frequency synthesis, should give a more complete view of solar flares in the microwave range by providing simultaneous spatial and spectral resolution. A promising application of MEM (maximum entropy) is also being pursued that will use smoothness criteria in both the spatial and spectral domains to give brightness temperature maps at each observed frequency (up to 45 frequencies every 10 s). Such maps can be compared directly with the theory of microwave emission to yield plasma parameters in the source - notably the number and energy distribution of electrons, for comparison with the x ray and gamma ray results from GRO.
The instrumentation of the RAE-2 spacecraft is described. The instruments include a pair of long travelling-wave antennas, a 37-m dipole, two radiometers making one frequency scan every 144 sec, and two rapid-sampling total-power burst receivers which cover the range from 0.025 to 13.1 MHz in 32 discrete steps. Effects of terrestrial noise on RAE-1 and RAE-2 observations are discussed, and it is noted that RAE-2 is uniquely capable of observing repeated lunar occultations of strong radio sources at very low frequencies. Some observational programs are briefly noted, including observations of the galactic background distribution, measurements of lunar occultations of solar radio bursts, and searches for more radio sources among the planets, galactic objects, and extragalactic sources.
A review is given of the 38 rocket, satellite, and planetary payloads dedicated to ionospheric/magnetospheric radio sounding since 1961. Between 1961 and 1995, eleven sounding-rocket payloads from four countries evolved from proof-of-concept flights to sophisticated instruments. Some involved dual payloads, with the sounder transmitter on one and the sounder receiver on the other. The rocket sounders addressed specific space-plasma-wave questions, and provided improved measurements of ionospheric electron-density (N(sub e)) field-aligned irregularities (FAI). Four countries launched 12 ionospheric topside-sounder satellites between 1962 and 1994, and an ionospheric sounder was placed on the Mir Space Station in 1998. Eleven magnetospheric radio sounders, most of the relaxation type, were launched from 1977 to 2000. The relaxation sounders used low-power transmitters, designed to stimulate plasma resonances for accurate local Ne determinations. The latest magnetospheric sounder designed for remote sensing incorporated long antennas and digital signal processing techniques to overcome the challenges posed by low Ne values and large propagation distances. Three radio sounders from three countries were included on payloads to extraterrestrial destinations from 1990 to 2003. The scientific accomplishments of space-borne radio sounders included (1) a wealth of global N(sub e) information on the topside ionosphere and magnetosphere, based on vertical and magnetic-field-aligned N(sub e) profiles; (2) accurate in-situ N(sub e) values, even under low-density conditions; and (3) fundamental advances in our understanding of the excitation and propagation of plasma waves, which have even led to the prediction of a new plasma-wave mode.
Antenna radiation patterns for Saturn I /Sa-5/ launch vehicle very high frequency telemetry system and minitrack-VOT system
Ion sheaths near radiating antennas in ionosphere
Numerical predictions of effective operating periods for RAE-A satellite vidicon camera used for measuring antenna boom tip positions
The Surface Electrical Properties Experiment (SEP) was flown to the moon in December 1972 on Apollo 17 and used to explore a portion of the Taurus-Littrow region. SEP used a relatively new technique, termed radio frequency interferometry (RFI). Electromagnetic waves were radiated from two orthogonal, horizontal electric dipole antennas on the surface of the moon at frequencies of 1, 2, 4, 8, 16, and 32 Mhz. The field strength of the EM waves was measured as a function of distance with a receiver mounted on the Lunar Roving Vehicle and using three orthogonal, electrically small, loops. The interference pattern produced by the waves that travelled above the moon's surface and those that travelled below the surface was recorded on magnetic tape. The tape was returned to earth for analysis and interpretation. Several reprints, preprints, and an initial draft of the first publication of the SEP results are included. These documents provide a rather complete account of the details of the theory of the RFI technique, of the terrestrial tests of the technique, and of the present state of our interpretation of the Apollo 17 data.