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On the 7th of December, 1995 the Galileo spacecraft arrived at Jupiter. It began its mission by collecting data radioed from the Probe as it descended into Jupiter's atmosphere. A Short time later it fired its main engine for about 45 minutes, slowing the craft enough to be captured by Jupiter's gravity. The vessel named for the discovery of Jupiter's natural satellites thus became the first known artificial satellite of the giant planet.
Ambient electron concentrations derived from observations with the Radio Astronomy Explorer 1 antenna capacitance probe have been compared with upper hybrid resonance measurements from the same spacecraft. From this comparison an empirical correction factor for the capacitance probe measurements has been derived. The differences between the two types of measurements is attributed to sheath effects.
No abstract available
The equatorial atmosphere of Titan was probed by means of two coherently related radio signals transmitted from Voyager 1 at 13.0 and 3.6 cm wavelengths during the November 12, 1980 occultation of the spacecraft by the Saturn satellite. An analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of Titan. The gas refractivity data, which extend from the surface to about 200 km altitude, were interpreted in two different ways. In the first, it is assumed that N2 makes up virtually all of the atmosphere, with small amounts of CH4 and other hydrocarbons present. In the second interpretation of the refractivity data, it is assumed that the 3.5 km altitude level corresponds to the bottom of a CH4 cloud layer and that N2 and CH4 were perfectly mixed below this level.
The invention is a method and apparatus for monitoring the presence, concentration, and the movement of fluids. It is based on utilizing electromagnetic measurements of the complex permittivity of the fluids for detecting and monitoring the fluid. More particularly the apparatus uses one or more microwave probes which are placed at the locations where the measurements are to be made. A radio frequency signal is transmitted to the probe and the reflected signal is phase and amplitude detected at a rapid rate for the purpose of identifying the fluids, based on their dielectric constant at the probe. The apparatus can be used for multiple purposes including measures of flow rates, turbulence, dispersion, fluid identification, and changes in flow conditions of multiple fluids or multiple states of a single fluid in a flowline or a holding container. The apparatus includes a probe consisting of two electrical conductors separated by an insulator. A radio frequency signal is communicated to the probe and is reflected back from the portion of the probe exposed to the fluid. The radio frequency signal also provides a reference signal. An oscillator generates a second signal which combined with each of the reference signal and the reflected signal to produce signals of lower frequencies to facilitate filtering and amplifying those signals. The two signals are then mixed in a detector to produce an output signal that is representative of the phase and amplitude change caused by the reflection of the signal at the probe exposed to the fluid. The detector may be a dual phase detector that provides two such output signals that are in phase quadrature. A phase shifter may be provided for selectively changing the phase of the reference signal to improve the sensitivity of at least one of the output signals for more accurate readings and/or for calibration purposes. The two outputs that are in quadrature with respect to each other may be simultaneously monitored to account for drift errors. The output signals are digitized and provided to a computer at a sample rate which may be very high. The computer is operable to identify the fluid based on its complex permittivity as may be useful for identifying the flow rates, determining the fluid mixture ratio, detecting impurities in the fluid, and so forth. Novelty is believed to reside in the use of the real part of complex permittivity to measure small difference in permittivity of the fluid.
Microwave radio observations of planetary atmospheres to partially circumvent the hindrances imposed by the planetary radiation belt and the dense ionosphere
A technique is described for measuring electron concentrations in the lower portion of the ionosphere above Punta Chilca. A radio-propagation experiment for measuring Faraday rotation is combined with a dc/Langmuir probe experiment for measuring electron current. The results obtained from the analysis of radio and probe data from Nike Apache 14.532, which was launched at 20:26 UT on May 28, 1975, at a solar zenith angle of 60 deg are presented. A comparison of the profiles of electron concentration indicates that the value of the maximum ionization in the D region under quiet conditions is proportional to the square of the cosine of the solar zenith angle.
In an extension of previously reported work on ices containing H2O, CO, CO2, SO2, H2S, and H2, we present measurements of the physical and infrared spectral properties of ices containing CH3OH and NH3. The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed depletion of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH-containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.
In an extension of previously reported work on ices containing H20, CO, CO2, SO2, H2S, and H2, We present measurements of the physical and infrared spectral properties of ices containing CH30H and NH3.The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed 87 of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH-containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.
Radio communication with space probes requires sending signals through the Earth's ionosphere and usually the solar wind. During planetary flybys, the signal may also pass through the ionosphere of another planet. These ionized media can perturb the radio signal in a variety of ways. Examples of these perturbations are variations in the electrical length between the spacecraft and the ground station, Faraday rotation of linearly polarized signals, amplitude and phase scintillations, and spectral and angular broadening. These plasma effects can have undesirable influences on telemetry performance and thus need to be understood from a communications engineering viewpoint. The plasma effects are, however, useful from a scientific viewpoint, since the effects on the communications link can often be inverted to estimate the physical conditions in the plasma.
Abstract. Stellar occultation observations from space can probe the stratosphere and mesosphere at a fine vertical scale around the globe. Unlike other measurement techniques like radiosondes and aircraft, stellar occultation has the potential to observe the atmosphere above 30 km, and unlike radio occultation, stellar occultation probes fine-scale phenomena with potential to observe atmospheric turbulence. We imaged the refractive bending angle of a star centroid for a series of occultations by the atmosphere. Atmospheric refractivity, density, and then temperature are retrieved from the bending observations with the Abel transformation and Edlén's law, the hydrostatic equation, and the ideal gas law. The retrieval technique is applied to data collected by two nanosatellites operated by Terran Orbital. Measurements were primarily taken by the GEOStare SV2 mission, with a dedicated imaging telescope, supplemented with images captured by spacecraft bus sensors, namely the star trackers on other Terran Orbital missions. The bending angle noise floor is 10 and 30 arcsec for the star tracker and GEOStare SV2 data, respectively. The most significant sources of uncertainty are due to centroiding errors due to the fairly low-resolution stellar images and telescope pointing knowledge derived from noisy satellite attitude sensors. The former mainly affects the star tracker data, while the latter limits the GEOStare SV2 accuracy, with both providing low vertical resolution. This translates to a temperature profile retrieval up to roughly 20 km for both star tracker and GEOStare SV2 datasets. In preparation of an upcoming 2023 mission designed to correct these deficiencies, SOHIP, we simulated bending angle measurements with varying magnitudes of error. The expected maximum altitude of retrieved temperature is 41 km on average for these simulated measurements with a noise floor of 0.39 arcsec. Our work highlights the capabilities of stellar occultation observations from nanosatellites for atmospheric sounding. Future work will investigate high-frequency observations of atmospheric gravity waves and turbulence, mitigating the major uncertainties observed in these datasets.
This paper presents the development of ultra-stable oscillators on deep space missions and selecting oscillators for planetary entry probes, including factors such as duration of the experiment, the available warm-up time and the Allan deviation and phase noise requirements.
Kilometer cosmic radioemission measurements in interplanetary space from Zond 2, Zond 3, and Venera 2 probes
Observations of radio-wave scattering effects probe interstellar electron-density turbulence. But with limited use of complementary data sets only broad conclusions have been obtained. The locations of this turbulence are unknown (phases, objects, etc.), as is the mechanism for its production, although it could play a role in various galactic processes. The IRAS data set was used to search for correlations between scattering and structures traced by infrared emitting dust. The existent HI (21-cm line emission), and 408-MHz radio-continuum all-sky surveys were used to search for correlations between scattering and structures traced by these emissions. Only lines of sight outside the galactic plane were considered (to better delimit the structures which might be causing scattering). No correlation is apparent between 21-cm line emission, or infrared continuum emission and interstellar scattering. However, a correlation exists between the scattering toward extragalactic radio sources and 408-MHz continuum emission.
Context. Giant radio galaxies (GRGs, or colloquially ‘giants’) are the Universe’s largest structures generated by individual galaxies. They comprise synchrotron-radiating active galactic nucleus ejecta and attain cosmological (megaparsec-scale) lengths. However, the main mechanisms that drive their exceptional growth remain poorly understood. Aims. To deduce the main mechanisms that drive a phenomenon, it is usually instructive to study extreme examples. If there exist host galaxy characteristics that are an important cause for GRG growth, then the hosts of the largest GRGs are likely to possess them. Similarly, if there exist particular large-scale environments that are highly conducive to GRG growth, then the largest GRGs are likely to reside in them. For these reasons, we aim to perform a case study of the largest GRG available. Methods. We reprocessed the LOFAR Two-Metre Sky Survey DR2 by subtracting compact sources and performing multi-scale CLEAN de-convolutions at 60" and 90" resolution. The resulting images constitute the most sensitive survey yet for radio galaxy lobes, whose diffuse nature and steep synchrotron spectra have allowed them to evade previous detection attempts at higher resolution and shorter wavelengths. We visually searched these images for GRGs. Results. We have discovered Alcyoneus, a low-excitation radio galaxy with a projected proper length l p = 4.99 ± 0.04 Mpc. Both its jets and lobes are detected at very high significance, and the SDSS-based identification of the host, at spectroscopic redshift z spec = 0.24674 ± 6 × 10 -5 , is unambiguous. The total luminosity density at ν = 144 MHz is L ν = 8 ± 1 × 10 25 W Hz -1 , which is below average, though near median (percentile 45 ± 3%) for GRGs. The host is an elliptical galaxy with a stellar mass M* = 2.4 ± 0.4 × 10 11 M ⊙ and a super-massive black hole mass M• = 4 ± 2 × 10 8 M ⊙ , both of which tend towards the lower end of their respective GRG distributions (percentiles 25 ± 9% and 23 ± 11%). The host resides in a filament of the Cosmic Web. Through a new Bayesian model for radio galaxy lobes in three dimensions, we estimate the pressures in the megaparsec-cubed-scale northern and southern lobes to be P min,1 = 4.8 ± 0.3 × 10 -16 Pa and P min,2 = 4.9 ± 0.6 × 10 -16 Pa, respectively. The corresponding magnetic field strengths are B min,1 = 46 ± 1 pT and B min,2 = 46 ± 3 pT. Conclusions. We have discovered what is in projection the largest known structure made by a single galaxy – a GRG with a projected proper length l p = 4.99 ± 0.04 Mpc. The true proper length is at least l min = 5.04 ± 0.05 Mpc. Beyond geometry, Alcyoneus and its host are suspiciously ordinary: the total low-frequency luminosity density, stellar mass, and super-massive black hole mass are all lower than, though similar to, those of the medial GRG. Thus, very massive galaxies or central black holes are not necessary to grow large giants, and, if the observed state is representative of the source over its lifetime, neither is high radio power. A low-density environment remains a possible explanation. The source resides in a filament of the Cosmic Web, with which it might have significant thermodynamic interaction. The pressures in the lobes are the lowest hitherto found, and Alcyoneus therefore represents the most promising radio galaxy yet to probe the warm–hot inter-galactic medium.
Clear atmosphere angels origin, clear air turbulence detection, radio propagation and atmospheric radar probing
Planetary probes can encounter mission scenarios where communication is not favorable during critical maneuvers or emergencies. Launch, initial acquisition, landing, trajectory corrections, safing. Communication challenges due to sub-optimum antenna pointing or transmitted power, amplitude/frequency dynamics, etc. Prevent lock-up on signal and extraction of telemetry. Examples: loss of Mars Observer, nutation of Ulysses, Galileo antenna, Mars Pathfinder and Mars Exploration Rovers Entry, Descent, and Landing, and the Cassini Saturn Orbit Insertion. A Deep Space Network capability to handle such cases has been used successfully to receive signals to characterize the scenario. This paper will describe the capability and highlight the cases of the critical communications for the Mars rovers and Saturn Orbit Insertion and preparation radio tracking of the Huygens probe at (non-DSN) radio telescopes.
The grant contributed to the publication of 18 refereed papers and 5 conference proceedings. The primary uses of the funding have been for page charges, travel for invited talks related to the grant research, and the support of a graduate student, Charles Keeton. The refereed papers address four of the primary goals of the proposal: (1) the statistics of radio lenses as a probe of the cosmological model (#1), (2) the role of spiral galaxies as lenses (#3), (3) the effects of dust on statistics of lenses (#7, #8), and (4) the role of groups and clusters as lenses (#2, #6, #10, #13, #15, #16). Four papers (#4, #5, #11, #12) address general issues of lens models, calibrations, and the relationship between lens galaxies and nearby galaxies. One considered cosmological effects in lensing X-ray sources (#9), and two addressed issues related to the overall power spectrum and theories of gravity (#17, #18). Our theoretical studies combined with the explosion in the number of lenses and the quality of the data obtained for them is greatly increasing our ability to characterize and understand the lens population. We can now firmly conclude both from our study of the statistics of radio lenses and our survey of extinctions in individual lenses that the statistics of optically selected quasars were significantly affected by extinction. However, the limits on the cosmological constant remain at lambda < 0.65 at a 2-sigma confidence level, which is in mild conflict with the results of the Type la supernova surveys. We continue to find that neither spiral galaxies nor groups and clusters contribute significantly to the production of gravitational lenses. The lack of group and cluster lenses is strong evidence for the role of baryonic cooling in increasing the efficiency of galaxies as lenses compared to groups and clusters of higher mass but lower central density. Unfortunately for the ultimate objective of the proposal, improved constraints on the cosmological constant, the next large survey for gravitational lenses did not release its results during the term of the proposal. The research supported the career development. of six graduate students (polar, Fletcher, Herold, Keeton, Deng and Rusin) and two post-docs (Labor and Munoz).