Radio Blackout Research Articles

Examination of Radio Frequency Blackout for an Inflatable Vehicle During Atmospheric Reentry

Numerical simulations of the plasma flow and electromagnetic wave around a membrane-aeroshell type reentry vehicle were performed using various physical model combinations, and the possibility of radio frequency blackout of transceiver antenna embedded at the rear of the vehicle was investigated. The flowfield was assumed to be in thermochemical nonequilibrium, and it was described by the Navier–Stokes equations with a multitemperature model and the equation of state. The simulations were performed for several altitudes, including the highest heat flux point according to reentry orbit data. Through these computations, the detailed distributions of the flowfield properties in the shock layer and wake region were successfully obtained. To evaluate the possibility of radio frequency blackout during atmospheric reentry, the distribution of the electron number density around the inflatable vehicle was clarified. A frequency-dependent finite-difference time-domain method was used for simulations of electromagnetic waves, and the physical properties were obtained from the computational results of the plasma flow calculation. Electromagnetic wave behaviors in an ionized gas region behind the inflatable vehicle were investigated. It was found that the number density of electrons was sufficiently small and that the electromagnetic waves can propagate with no reflection and less attenuation. These results suggest that radio frequency blackout may not occur during the atmospheric reentry of the inflatable vehicle.

Influence of dust loading on atmospheric ionizing radiation on Mars

Measuring the radiation environment at the surface of Mars is the primary goal of the Radiation Assessment Detector on the NASA Mars Science Laboratory's Curiosity rover. One of the conditions that Curiosity will likely encounter is a dust storm. The objective of this paper is to compute the cosmic ray ionization in different conditions, including dust storms, as these various conditions are likely to be encountered by Curiosity at some point. In the present work, the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety model, recently modified for Mars, was used along with the Badhwar & O'Neill 2010 galactic cosmic ray model. In addition to galactic cosmic rays, five different solar energetic particle event spectra were considered. For all input radiation environments, radiation dose throughout the atmosphere and at the surface was investigated as a function of atmospheric dust loading. It is demonstrated that for galactic cosmic rays, the ionization depends strongly on the atmosphere profile. Moreover, it is shown that solar energetic particle events strongly increase the ionization throughout the atmosphere, including ground level, and can account for the radio blackout conditions observed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on the Mars Express spacecraft. These results demonstrate that the cosmic rays' influence on the Martian surface chemistry is strongly dependent on solar and atmospheric conditions that should be taken into account for future studies.

CHANNEL CHARACTERIZATION AND FINITE-STATE MARKOV CHANNEL MODELING FOR TIME-VARYING PLASMA SHEATH SURROUNDING HYPERSONIC VEHICLES

Efiects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational ∞uid dynamics (CFD) technique, Demetriades's plasma turbulence model and flnite-difierence time-domain (FDTD) algorithm, amplitude variation and phase ∞uctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a flnite-state Markov channel (FSMC) model is proposed, to represent the dynamical efiects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

Kinetics of complex plasma with liquid droplets

This paper provides a theoretical basis for the reduction of electron density by spray of water (or other liquids) in hot plasma. This phenomenon has been observed in a hypersonic flight experiment for relief of radio black out, caused by high ionization in the plasma sheath of a hypersonic vehicle, re-entering the atmosphere. The analysis incorporates a rather little known phenomenon for de-charging of the droplets, viz., evaporation of ions from the surface and includes the charge balance on the droplets and number cum energy balance of electrons, ions, and neutral molecules; the energy balance of the evaporating droplets has also been taken into account. The analysis has been applied to a realistic situation and the transient variations of the charge and radius of water droplets, and other plasma parameters have been obtained and discussed. The analysis through made in the context of water droplets is applicable to all liquids.

Reproducing continuous radio blackout using glow discharge plasma

A novel plasma generator is described that offers large-scale, continuous, non-magnetized plasma with a 30-cm-diameter hollow structure, which provides a path for an electromagnetic wave. The plasma is excited by a low-pressure glow discharge, with varying electron densities ranging from 10(9) to 2.5 × 10(11) cm(-3). An electromagnetic wave propagation experiment reproduced a continuous radio blackout in UHF-, L-, and S-bands. The results are consistent with theoretical expectations. The proposed method is suitable in simulating a plasma sheath, and in researching communications, navigation, electromagnetic mitigations, and antenna compensation in plasma sheaths.

Numerical Prediction of Hypersonic Flowfields Including Effects of Electron Translational Nonequilibrium

The degree of electron thermal nonequilibrium occurring in continuum, hypersonic, slender body, and blunt body flows is investigated. The effect of thermal nonequilibrium between the electron translational and vibrational-electronic modes on the predicted electron density and electron temperature is quantified at flight conditions characteristic of a slender hypersonic vehicle, as well as at a higher energy, superorbital flight condition of a blunt reentry vehicle. The most significant effect of electron thermal nonequilibrium on the flowfield is through the influence of the electron temperature on the magnitude of the chemical reaction rates in the high density shock layer. A twofold reduction in peak plasma density is predicted in the flow around the slender body when the electron nonequilibrium model is used, and this results in better agreement between the simulation results and the experimental electron density measurements. A change in the shape of the electron density profile with the use of the electron nonequilibrium model is predicted along the stagnation streamline of the blunt body flow. In both cases, the changes in predicted electron density are much more pronounced at the higher density flight conditions examined. In all cases, the rise of the electron temperature precedes the rise of the vibrational-electronic temperature along the stagnation streamline. These results have potentially important implications for the prediction of the onset of radio frequency blackout during the flights of next generation hypersonic vehicles, a phenomenon that is governed by the properties of the electron gas.

Electron depletion via cathode spot dispersion of dielectric powder into an overhead plasma

The effectiveness of cathode spot delivered dielectric particles for the purpose of plasma depletion is investigated. Here, cathode spot flows kinetically entrain and accelerate dielectric particles originally at rest into a background plasma. The time variation of the background plasma density is tracked using a cylindrical Langmuir probe biased approximately at electron saturation. As inferred from changes in the electron saturation current, depletion fractions of up to 95% are observed. This method could be exploited as a means of communications blackout mitigation for manned and unmanned reentering spacecraft as well as any high speed vehicle enveloped by a dense plasma layer.

Microwave phase perturbation and ionisation measurement in vegetation fire plasma

Interaction of low temperature high collisional combustion plasma with electromagnetic wave energy results in a phase lag of the incident wave. If normalised collision frequency {(φ eff)/2πf 0} is much greater than unity (1), the phase shift (Δφ) varies linearly with plasma frequency, and hence with ionisation in plasma. Ionisation in vegetation fires (highly collisional atmospheric pressure plasma) has implications on the safety of fire-fighters. During wildfire suppression, radio communication blackout at very/ultra high frequency has been experienced. A cylindrical fire burner was constructed in which various natural vegetation materials could be used as fuel. The burner was equipped with Type K thermocouples to measure fuel combustion temperature and was used as cavity for microwaves with laboratory quality network analyser to measure phase shift. In the experiment, microwaves were caused to propagate combustion zones of eucalyptus litter fires with maximum temperatures of 1142 and 1174 K, respectively. The measured phase shift ranged from 7.34 to 11.63°. Calculated ionisation from the phase shift measurements were from 1.9 to 2.0 × 1016 m− 3.

THEORETICAL AND EXPERIMENTAL STUDIES OF MAGNETIC FIELD ON ELECTROMAGNETIC WAVE PROPAGATION IN PLASMA

A spacecraft will experience the well-known \blackout problem in the re-entry into the Earth's atmosphere, which results in communication failures between the spacecraft and ground control center. It is important to study the blackout mitigation method. The efiects of external magnetic fleld on electromagnetic wave propagation in plasma are studied by theoretical and experimental methods in this paper. The numerical results show that the attenuation of electromagnetic wave in plasma is reduced by the presence of a magnetized fleld. The propagation properties of electromagnetic wave in unmagnetized and magnetized plasma have been studied experimentally with plasma torch, and the experimental results are in good agreement with the theory. Both the theoretical and experimental results indicate that magnetic window is an alternative and promising way to improve the radio blackout issue.

Experimental Results for Communications Blackout Amelioration Using Crossed Electric and Magnetic Fields

Experimental Results for Communications Blackout Amelioration Using Crossed Electric and Magnetic Fields

Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.

Electromagnetic Reduction of Plasma Density During Atmospheric Reentry and Hypersonic Flights

As a vehicle reenters or travels through the atmosphere at hypersonic velocities, the shock-heated air surrounding the vehicle becomes weakly ionized. This plasma layer causes an important systems operation problem known as communications blackout or radio blackout. At sufficiently high plasma density, the plasma layer either reflects or attenuates radiowave communications to and from the vehicle. In this paper, we study the application of electric and magnetic fields to reduce the plasma density. Specifically, an E ? B crossed-field configuration is proposed. Both analytical and numerical results suggest that significant reduction of the plasma density is possible at large altitudes. For instance, plasma density reduction by a factor of 10 is predicted in the case of 81 km and a magnetic field of about 0.1 T. Theoretical results suggest that significant reduction of the plasma density is possible, enabling radio communication across the plasma layer. The benefit of the reduced plasma density in terms of electromagnetic wave absorption across the plasma layer is estimated.

Nonintrusive measurement of ionisation in vegetation fire plasma

Vegetation fires are slightly ionised gaseous medium. Omnipresent alkali metal species in plant's organic structure are the main source of thermally produced electrons in the fires. In the flames, electron-neutral particle collisions dominate other modes of particle interaction. The collision regime absorbs some of the incident energy when the fire is illuminated with electromagnetic waves. The rate of electromagnetic wave absorption in the vegetation fires has implications on the safety of fire-fighters. During wildfire suppression, radio communication blackout at vhf/uhf has been experienced. This may be partly due to thermal ionisation in the fire. In the experiment, the extent of ionisation in vegetation fires is measured using a 2-port vector network analyser. X-band microwaves are caused to propagate combustion zones of eucalyptus bark and guinea grass fires with maximum temperatures of 1114 and 1054 K respectively. Alkali content in the vegetation fuel was different. Measurements show maximum ionisation in flames produced from guinea grass, which had almost twice much potassium as that of eucalyptus bark, to be 2.63 × 10 16 m −3 while that produced in eucalyptus bark flame was 1.46 × 10 16 m −3 .

Modeling of associative ionization reactions in hypersonic rarefied flows

When vehicles reenter the Earth’s atmosphere from space, the hypersonic conditions are sufficiently energetic to generate ionizing reactions. The production of a thin plasma layer around a hypersonic vehicle can block radio waves sent to and from the vehicle, leading to communications blackout. For Earth entry from orbit, the maximum energy involved in molecular collisions requires only associative ionization of air-species to be considered. In the present study, the modeling of such reactions is considered in detail using the direct simulation Monte Carlo (DSMC) method. For typical Earth entry conditions, with a velocity near 8km∕s, it is shown that the average ionizing reaction probabilities are small. Special numerical techniques must therefore be used in the DSMC technique in order to numerically resolve these reactions. Additional simulation problems arise from the relatively small mass of the electrons in comparison to the other atoms and molecules in these flow fields. Artificially increasing the electron mass greatly increases computational efficiency, and the viability of this approach is investigated. Simulation results are presented for conditions corresponding to the RAM-C II hypersonic flight experiment that gathered measurements of electron number density. It is demonstrated that simulation results for electron number density in this energy regime are relatively insensitive to the mass of the electrons. Direct comparison of DSMC results with the RAM-C II measurements for electron number density shows excellent agreement. These satisfactory comparisons represent the first direct verification of the ability of the DSMC technique to successfully predict the weak plasma generated around a hypersonic vehicle.

Autonomy and remote control experiment for lunar rover missions

Teleoperation will be used for rover control during lunar missions. However the interesting places for scientific investigations are located in difficult areas: the south pole, or deep craters in which communications to the earth will be limited and possibly interrupted. To investigate the feasibility of such missions, a testbed has been built in order to check the feasibility of remote control of the rover in the presence of important time delays with low-rate communications, as well as to demonstrate the capability of autonomous motion during communications blackout periods. The testbed consists of a 6x6 vehicle able to move on a moon-representative terrain, either in an autonomous mode or in low-communication-rate teleoperation called TESA. This paper describes the vehicle, its control and the results obtained during the tests.

Autonomy and remote control experiment for lunar rover missions

Teleoperation will be used for rover control during lunar missions. However the interesting places for scientific investigations are located in difficult areas: south pole, deep craters in which communications to the earth will be limited and possibly interrupted. To investigate the feasibility of such missions, a tcstbed has been built in order to check the feasibility of remote control of the rover in presence of important time delays with low rate communications as well as to demonstrate the capability of autonomous motion during communications blackout periods.The testbed consists of a 6x6 vehicle able to move on a moon representative terrain either in an autonomous mode or in low communication rate teleoperation called TESA. This paper describes the vehicle, its control and the results obtained during the tests.

Analysis of Communications Blackout for Pioneer Venus Entry Probes

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Special report: The Great New York Telephone Fire: The Bell System marshaled its impressive resources to assess and repair damage in record time

On February 27, 1975, at approximately 12:15 a.m., a fire broke out in a New York Telephone Company central office, located at 13th Street and Second Avenue in New York City's Borough of Manhattan. The fire, which started in the building's basement cable vault, raged out of control, damaging or totally destroying millions of dollars worth of telephone equipment. The result: an unprecedented, total telephone communications blackout in the affected subscriber area, and its environs, disrupting service to over 160 000 residential and business subscribers.

Comment on "Effects of Nonequilibrium Ablation Chemistry on Viking Radio Blackout"

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Effects of Nonequilibrium Ablation Chemistry on Viking Radio Blackout

The length of the entry blackout period during descent of the Viking Lander into the Mars atmosphere is predicted from calculated profiles of electron density in the shock layer over the aeroshell. Nonequilibrium chemistry plays a key role in the calculation, both in the inviscid flow and in the boundary layer. This is especially true in the boundary layer contaminated with ablation material, for which nonequilibrium chemistry predicts electron densities two decades lower than the same case calculated with equilibrium chemistry.