Reentry Blackout Research Articles

Mitigation of reentry blackout via gas injection in arc-heating facility

Communication blackouts during atmospheric reentry pose significant challenges to the safety and adaptability of spacecraft missions. This phenomenon, caused by the attenuation of electromagnetic waves by the plasma surrounding the spacecraft, disrupts communication with ground stations or orbiting satellites. Therefore, it is crucial to decrease the plasma density in the vicinity of the spacecraft to ensure an unobstructed electromagnetic wave communication path. This study proposes a methodology that involves the injection of gas from the vehicle’s wall to create an insulating layer near the surface. This thin layer maintains lower temperatures and reduced plasma density, enabling electromagnetic wave propagation without attenuation. Practical experiments were conducted in an arc-heating facility to simulate atmospheric reentry conditions. The results of the experiments provided empirical evidence of the effectiveness of the technique in mitigating communication blackout phenomena. Numerical fluid analysis within the wind tunnel chamber validated the formation of an air film layer near the experimental model owing to the injected gas. Schlieren imaging revealed distinctive jet shapes, which corroborated the findings of the numerical analysis. The wind tunnel tests that simulated atmospheric reentry environments confirmed the formation of an air film layer through gas injection, which substantiates the reduction in communication blackout. These results have the potential to improve communication reliability in space transport.

Computational Study on Air Film Approach in Reentry Blackout Mitigation

Communication blackouts during the atmospheric reentry phase are a significant challenge, as flight data are lost due to interruptions caused by plasma gas generated by aerodynamic heating. This study explores a novel mitigation method using an air film, a thin insulating coolant layer on the surface. The researchers successfully reduced the reentry blackout by employing a gas injection system. Through a coupled approach using computational fluid dynamics and a frequency-dependent finite-difference time-domain method, the plasma flow properties and electromagnetic propagation were analyzed around a test model in a wind tunnel in DLR (German Aerospace Center). The numerical results indicated that the injected nitrogen gas formed an insulating air film layer on the surface. The thin layer advected backward, maintaining a low temperature without ionization, and covered the object in the wake region. The electromagnetic waves propagated and reached a distant area because the electron density was low. It means that the air film layer acted as a propagation window for the telecommunication waves. Thus, communication blackouts will be avoidable because electromagnetic waves can transmit through the air-film layer. It concluded that the air film effect, developed as a thermal protection technique, is a novel mitigation scheme for reentry blackouts.

SIPAM-4 scheme improves bit error rate performance in MISO X-ray communication system

X-ray communication (XCOM) technology, which uses X-ray as the carrier wave, is expected to solve the problem of reentry blackout region communication with its good penetration characteristics. In order to mitigate the effects of non-linear distortion of the gated X-ray tube (GMXT), the multiple-input single-output (MISO) technique has been introduced in XCOM systems. A pulse amplitude modulation scheme based on superimposed intensity (SIPAM) was proposed and achieved by configuring GMXTs with on/off keying modulation in MISO XCOM system. The feasibility of the proposed SIPAM scheme in XCOM was numerically investigated through Monte Carlo simulations. As the divergence angle of the GMXT increases, the optical power distribution tends to be more uniform in the receiving plane. It can greatly relax the requirements for link alignment. After that, we conduct a proof-of-concept experiment for the SIPAM with four levels (SIPAM-4) scheme by employing two GMXTs and an LYSO-SiPM-based X-ray detector. The experimental results show that when the bit error rate is within the forward error correction limit of 3.8 × 10−3, the SIPAM-4 scheme can reach a maximum communication rate of 1.20 Mbps, which is 20% higher than the conventional PAM-4 scheme. It can be included that the proposed MISO based the SIPAM-4 modulation scheme could improve the performance of the X-ray communication system.

Unsteady simulation of Mitigation of Reentry Blackout by Air film

During reentry into the planetary atmosphere, the vehicle is surrounded by ionized and dissociated plasma caused by aerodynamic heating. The high-dense plasma near the vehicle blocks the electromagnetic wave propagation for telecommunication, and then, communication with the ground station is prevented. This problem is known as a reentry blackout. One method of mitigation of reentry blackout is air film technique, in which low-temperature gas is blown out of the vehicle to form a path for electromagnetic waves propagation. In this study, to clarify the effect of air film for blackout mitigation, the plasma flow around an experimental model conducted in the DLR was reproduced by a computational fluid dynamics approach. In the present analysis, three cases with different mass flow rates were analyzed. In the two cases with low mass flow rates, oscillations of the air film were observed. In the case with the highest mass flow rate, the results approached steady state with time. This indicated that a high mass flow rate can ensure a stable low electron number density region and mitigate reentry blackouts. In the future, it is necessary to apply the effect of air film to the reentry capsule shape and evaluate the effect on the mitigation of communication blackout and aerodynamic characteristics.

Study on the mechanism of communication blackout mitigation using air-film effects

During the atmospheric reentry phase, the communication between a vehicle and a ground station is interrupted. This phenomenon is called reentry blackout. A strong shock wave in front of the capsule can cause aerodynamic heating and ionize the gas. This plasma can block the propagation of electromagnetic waves emitted from its surface. It is necessary to reduce the number density of electrons near the capsule to mitigate the communication blackout. We focused on a new mitigation approach, which is the effect of air film. Cold gas injected from the surface forms a thin heat insulating layer. Electromagnetic waves can propagate inside the layer because of the low degree of ionization. In this study, we investigate the blackout mitigation effects using computational fluid dynamics (CFD) at a large-scaled arc- heated wind tunnel. The computational results indicated that injection gas forms the air film and works as a propagation path of the electromagnetic waves.

Performance analysis of LYSO–SiPM detection module for X-ray communication during spacecraft reentry blackout

In view of the demand for high-energy and high-bandwidth signal detection in X-ray communication (XCOM) during spacecraft reentry blackout, a detection module using fast-decay LYSO scintillator coupled with Silicon photomultiplier (SiPM) was proposed in this study. The theoretical model based on the Monte Carlo simulation and Personick’ theory was established and the detector prototype was built. Moreover, the signal to noise ratio (SNR) and bit error rate (BER) performance were investigated. Results present that the SNR of 19.8 dB, 29.9 dB and 35.5 dB could be reached for X-ray with the energy of 17 keV, 59.5 keV and 122 keV respectively. This energy response characteristic is much suitable for the X-ray signal detection during spacecraft reentry blackout. Additionally, the deviation of SNR corresponding to the BER between the theoretical and experimental results does not exceed 0.3 dB when the data rate is 100 kbps, which proves the validity of the theoretical model. Furthermore, the numerical analysis shows that the scheme demonstrates high SNR and low BER performance in high bandwidth and low signal receiving power, which explains the superiorities in X-ray signal detection of the design. This work provides the theoretical basis and design reference for the LYSO–SiPM X-ray signal detection module.

Experimental demonstration and mechanism of mitigating reentry blackout via surface catalysis effects

The reentry blackout phenomenon, which is the communication cut-off between the re-entry vehicle and ground station, is a crucial problem that needs to be addressed. To improve safety during reentry, a new mitigation method was proposed using the surface catalysis effect. However, this method has not been investigated extensively by experimental methods. In this study, we experimentally demonstrated the mitigation method using a 1 MW arc-heated wind tunnel and numerically clarified the mitigation mechanism. As a demonstration experiment, communication tests were conducted to compare the two cases. In the first case, a ceramic surface was used as a low catalytic wall, whereas in the second case, a copper surface was used as a high catalytic wall in the arc-heated wind tunnel. The experimental results indicated that the blackout occurred when alumina was used as the low catalytic wall. On the other hand, for the high catalytic wall using copper, blackout was avoided. The tests were reproduced in the wind tunnel using a numerical simulation technique. From the simulation results, the mitigation mechanism suggested that: (a) the number of nitrogen and oxygen atoms decreased due to catalysis; (b) forward reactions of electron impact ionization were suppressed due to the decrease in the number of atoms; and (c) the suppression of reactions decreased the number of electrons, thereby mitigating the reentry blackout. In addition, the numerical simulations performed on the reentry plasma around the re-entry capsule suggested that the mitigation mechanisms between the arc-heated wind flow and reentry plasma were similar despite the different airflow conditions.

Effects of Dynamic Plasma Sheath on Electromagnetic Wave Propagation and Bit Error Rate Under External Magnetic Field

The “magnetic window” is considered to be an effective technique for alleviating a vehicle’s atmospheric reentry blackout, whereas the dynamic variation characteristic of the plasma sheath is critical for the vehicle’s communication. In this article, the effects of dynamic plasma sheath on electromagnetic wave propagation and the bit error rate (BER) of two typical modulation signals under an external magnetic field are investigated. First, the hybrid matrix method is used to calculate the transmission coefficients of right-handed circularly polarized (RHCP) waves with different magnetic fields and plasma electron density fluctuation. Then, the average BER of two typical modulations signals, namely M-ary phase-shift keying (MPSK) and noncoherent M-ary frequency shift keying modulation (NC-MFSK) is numerically simulated based on the magnetized plasma sheath channel response. The results show that the magnitude in dB scale and phase of the RHCP transmission coefficient follow Gaussian distribution when the probability density function of the electron density is a Gaussian distribution. The BER performance of binary phase-shift keying (BPSK) and NC-MFSK is relevant to the incident wave frequency, the plasma stopband, and the intensity of electron density variation. Owing to the insensitivity of phase jitter, the NC-8FSK has a better performance than BPSK, followed by NC-4FSK and NC-2FSK.

DSMC modeling of rarefied ionization reactions and applications to hypervelocity spacecraft reentry flows

The DSMC modeling is developed to simulate three-dimensional (3D) rarefied ionization flows and numerically forecast the communication blackout around spacecraft during hypervelocity reentry. A new weighting factor scheme for rare species is introduced, whose key point is to modify the corresponding chemical reaction coefficients involving electrons, meanwhile reproduce the rare species in resultants and preserve/delete common species in reactants according to the weighting factors. The resulting DSMC method is highly efficient in simulating weakly inhomogeneous flows including the Couette shear flow and controlling statistical fluctuation with high resolution. The accurate reliability of the present DSMC modeling is also validated by the comparison with a series of experimental measurements of the Shenzhou reentry capsule tested in a low-density wind tunnel from the HAI of CARDC. The obtained electron number density distribution for the RAM-C II vehicle agrees well with the flight experiment data, while the electron density contours for the Stardust hypervelocity reentry match the reference data completely. In addition, the present 3D DSMC algorithm can capture distribution of the electron, N+ and O+ number densities better than the axis-symmetric DSMC model. The introduction of rare species weighting factor scheme can significantly improve the smoothness of the number density contours of rare species, especially for that of electron in weak ionization case, while it has negligible effect on the macroscopic flow parameters. The ionization characteristics of the Chinese lunar capsule reentry process are numerically analyzed and forecasted in the rarefied transitional flow regime at the flying altitudes between 80 and 97 km, and the simulations predict communication blackout altitudes which are in good agreement with the actual reentry flight data. For the spacecraft reentry with hypervelocity larger than the second cosmic speed, it is forecasted and verified by the present DSMC modeling that ionization reactions will cover the windward capsule surface, leading to reentry communication blackout, and the communication interruption must be considered in the communication design during reentry in rarefied flow regimes.

Communication Test and Elucidation of Mechanism on Mitigation of Reentry Blackout by Surface Catalysis Effects in 1WM Arc-Heated Wind Tunnel

Communication Test and Elucidation of Mechanism on Mitigation of Reentry Blackout by Surface Catalysis Effects in 1WM Arc-Heated Wind Tunnel

Simulation and experiment of X-ray communication in re-entry dusty plasma region

Compared with the other wireless communication band, X-ray carrier has the merits of lower wavelength, higher frequency and photon energy, which could provide a novel method to solve the communication problems of re-entry blackout region. In this paper, transmission characteristics of X-ray carrier in the re-entry dusty plasma medium were analyzed first, simulation results indicate that dusty particles were more likely to impede the microwave signal than X-ray carrier. Then an alkali metal plasma source was designed to simulate the re-entry dusty plasma sheath for simplification. Transmission co-efficiency under different X-ray energy were tested, which pointed out that X-ray signal would obtain more than 79.4% transmission co-efficiency on condition of dynamic and dusty plasma medium. Finally, we give our proposal and potential capability of X-ray communication in the re-entry plasma condition.

Power budget and performance analysis of X-ray communication during the Earth re-entry of spacecraft

X-ray communication (XCOM) is a novel method that exploits X-rays as a carrier for data transmission. The high penetration of X-rays enables XCOM to avoid radio blackout during the atmospheric re-entry into Earth. To guarantee stable and robust XCOM, this study provides a power budget for XCOM. The Monte Carlo method was used to evaluate the transmission properties of X-ray beams in near-earth space, and a link model in the re-entry blackout region were established. Moreover, we established a noise model for the X-ray detector and evaluated the mathematical relationship between the transmitting power, and the bit-error-rate (BER). Results indicated that the X-rays with energies of 30–50 keV are highly suitable at an altitude of 35 km, and that robust communication performance could be obtained by using soft X-rays in the upper atmosphere. Adopting optimal X-ray energies according to different altitudes of spacecraft re-entry is, thus, of great significance. We calculated the minimum transmitting power of the X-ray source for a targeted BER and found that, when the link distance is 295 km and the X-ray energy is 50 keV, the power consumption of the X-ray source must be 140 W to achieve BER of less than 10−6 level.

Re-entry blackout elimination and communication performance analysis based on laser-plasma-induced X-ray emission

X-ray communication (XCOM) offers important advantages to both civilian and military space projects. Rapid advance in high-intensity laser interaction with plasma has become a driving force for providing a new X-ray carrier generation based on the laser wakefield acceleration scheme. XCOM has the potential to eliminate RF shielding on the ground and communicate with the re-entry supersonic spacecraft during blackout occurrence. In this process, the plasma sheath is formed around the surface due to air compression and ablation, which blocks the traditional communication signals. In this paper, the hazardous substance was proactively exploited and coupled with the modulated laser. Particle-In-Cell simulation results indicate the ultra-bright controllable X-ray emission with a small angular divergence (0.04 rad×0.03 rad), a tunable X-ray energy range (4.60 keV to 321.48 keV), and high photon yields. Additionally, the data rate of the communication via the X-ray carrier during re-entry was estimated up to ∼20.7 Mbps by considering the transmission model, encoding schemes and photon information efficiency. Combined with an existing or developing X-ray detection technique, this regime can eliminate re-entry blackout and also provide a novel modulated X-ray source to acquire high-rate, low transmit power, and highly secure space-based data links.

New transmission mode of electromagnetic wave in high-density rod cavity structure

During reentry of hypersonic spacecraft into the atmosphere, a break in the radio communication due to the presence of a plasma sheath on the spacecraft can occur. The break is commonly known as reentry communication blackout. Normally, for high density plasma, it is difficult for the electromagnetic waves of L and S bands to penetrate through. They may be decayed rapidly or reflected. That is why reentry communication blackout happens. In recent years, initiative methods are used to reduce the effects of reentry communication blackout such as by designing ideal shape for reentry vehicle, sprinkling special substances on the surface of the vehicle to improve efficiency of electromagnetic wave, adding magnetic field within the blackout area, etc. However, these methods not only fail to fully resolve the problems caused by blackout but also bring some new ones. Therefore, to resolve the problems, transmission mechanism of electromagnetic waves in plasmons should be analyzed. In this paper, we use the finite difference time domain, consider the mechanism of electromagnetic waves in a structure consisting of high-density plasma rods, and refer to the two-dimensional (2D) photonic crystal and surface wave local coupling theory. A new type of high-density plasma micro-rod cavity structure is designed. The special structure, consisting of metal cavity, high-density plasma rod, and dielectric medium filled within the cavity, is quite different from traditional 2D sub-wavelength plasma rod arrays. This kind of design takes advantage of cavity structure to couple electromagnetic wave within the plasma rod so that the surface wave diffraction transmission mode can be changed into a local coupling enhancement penetrating mode. In this paper, we investigate the plasma micro-rod cavity structures with two shapes:cylinder and square, respectively. It is found that electromagnetic waves of L and S bands can have unusual transmission properties in certain frequency ranges, such that electromagnetic waves can pass through the interior of the high-density plasma rod.

Reentry blackout prediction for atmospheric reentry demonstrator mission considering uncertainty in chemical reaction rate model

A numerical simulation model of plasma flows and electromagnetic waves around a vehicle was developed to predict a radio frequency blackout. Plasma flows in the shock layer and the wake region were calculated using a computational fluid dynamics technique with a three-dimensional model. A finite-catalytic wall condition known to affect plasma properties, such as the number density of electrons, was considered for accurate prediction. A parametric study was performed to investigate the effect of uncertainty in the chemical reaction rate model on evaluating a radio frequency blackout. The behavior of electromagnetic waves in plasma was investigated using a frequency-dependent finite-difference time-domain method. Numerical simulations of reentry blackout were performed for the Atmospheric Reentry Demonstrator mission at various altitudes. The plasma flows and the complex movement of electromagnetic waves around the Atmospheric Reentry Demonstrator vehicle were clarified. The predicted signal loss profile was then directly compared with the experimental flight data to validate the present models. The numerical results generally reproduced the trends over altitudes of the measured data. It is suggested that the present simulation model can be used to investigate the radio frequency blackout and signal loss of electromagnetic waves in the communication of a reentry vehicle. It was confirmed that high associative ionization reaction rates contribute to reducing the electron density in the wake region and radio frequency blackout. It is suggested that the accuracy of predicting the signal loss improved when considering the uncertainty in the chemical reaction model for associative ionizations.

Mitigating reentry radio blackout by using a traveling magnetic field

A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF) is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positioning System (GPS) and the typical telemetry system are also discussed. Compared with the constant magnetic-window method, the TMF method needs lower magnetic field strength and is easier to realize in the engineering field.

Single-frequency reflection characterisation of shock tube excited plasma

Plasma has been of great interest to engineers and scientists during the past few decades due to its wide applications. Besides, the plasma-sheath-caused lose of communication (i.e. re-entry blackout) that happens when a spacecraft re-enters the earth atmosphere is still a problem to be solved. The microwave characterisation of shock tube excited plasma has been an important method for exploring the transmission and reflection of microwave signals in plasma. The existing frequency sweep or multi-frequency technologies are not desirable for the characterisation of high-speed time-varying plasma generated in shock tubes. Hence, in this paper a novel signal-frequency approach is proposed to measure both electron density and collision frequency of plasma in shock tube. As frequency sweep is not required in this method, it is extremely suitable for characterising the shock tube excited high-speed time-varying plasma. The genetic algorithm is applied to extract electron density and collision frequency from the reflection coefficient. Simulation results demonstrate excellent accuracy for electron density within 1010∼1012 cm−3 and collision frequency within 5×1010∼1012 Hz. This work paves the way for a fast and compact microwave reflection measurement of shock tube generated plasma.

An electromagnetic method for removing the communication blackout with a space vehicle upon re-entry into the atmosphere

When a hypersonic vehicle travels in the Earth and Mars atmosphere, the surface of the vehicle is surrounded by a plasma layer, which is an envelope of ionized air, created from the compression and heat of the atmosphere by the shock wave. The vehicles will lose contact with ground stations known as the reentry communication blackout. Based on the magnetohydrodynamic framework and electromagnetic wave propagation theory, an analytical model is proposed to describe the effect of the effectiveness of electromagnetic mitigation scheme on removing the reentry communication blackout. C and Global Positioning System (GPS) bands, two commonly used radio bands for communication, are taken as the cases to discuss the effectiveness of the electromagnetic field mitigation scheme. The results show that the electron density near the antenna of vehicles can be reduced by the electromagnetic field, and the required external magnetic field strength is far below the one in the magnetic window method. The directions of the external electric field and magnetic field have a significant impact on the effectiveness of the mitigation scheme. Furthermore, the effect of electron collisions on the required applied electromagnetic field is discussed, and the result indicates that electron collisions are a key factor to analyze the electromagnetic mitigation scheme. Finally, the feasible regions of the applied electromagnetic field for eliminating blackout are given. These investigations could have a significant benefit on the design and optimization of electromagnetic mitigation scheme for the blackout problem.

Investigation of plasma–surface interaction effects on pulsed electrostatic manipulation for reentry blackout alleviation

The reentry blackout phenomenon affects most spacecraft entering a dense planetary atmosphere from space, due to the presence of a plasma layer that surrounds the spacecraft. This plasma layer is created by ionization of ambient air due to shock and frictional heating, and in some cases is further enhanced due to contamination by ablation products. This layer causes a strong attenuation of incoming and outgoing electromagnetic waves including those used for command and control, communication and telemetry over a period referred to as the ‘blackout period’. The blackout period may last up to several minutes and is a major contributor to the landing error ellipse at best, and a serious safety hazard in the worst case, especially in the context of human spaceflight. In this work, we present a possible method for alleviation of reentry blackout using electronegative DC pulses applied from insulated electrodes on the reentry vehicle’s surface. We study the reentry plasma’s interaction with a DC pulse using a particle-in-cell (PIC) model. Detailed models of plasma–insulator interaction are included in our simulations. The absorption and scattering of ions and electrons at the plasma–dielectric interface are taken into account. Secondary emission from the insulating surface is also considered, and its implications on various design issues is studied. Furthermore, we explore the effect of changing the applied voltage and the impact of surface physics on the creation and stabilization of communication windows. The primary aim of this analysis is to examine the possibility of restoring L- and S-band communication from the spacecraft to a ground station. Our results provide insight into the effect of key design variables on the response of the plasma to the applied voltage pulse. Simulations show the creation of pockets where electron density in the plasma layer is reduced three orders of magnitude or more in the vicinity of the electrodes. These pockets extend to distances up to three times the electrode length normal to the vehicle surface. Based on our results, we postulate that pulsed electrostatic manipulation (PEM) may be a viable candidate for reentry blackout alleviation in the future.

Characteristics of electromagnetic wave propagation in time-varying magnetized plasma in magnetic window region of reentry blackout mitigation

The “magnetic window” is considered a promising means to eliminate reentry communication blackout. However, the turbulence of plasma sheath results in phase jitter and amplitude turbulence of electromagnetic (EM) wave and may influence the eliminating effect. Therefore, the effect of fluctuating property of reentry plasma sheath on EM wave propagation when a magnetic field is used for eliminating blackout is investigated. For this purpose, a time-varying electron density model, which includes both temporal variation and spatial turbulence, is proposed. Hybrid matrix method is also employed to investigate the interaction between time-varying magnetized plasma and EM wave. The EM wave transmission coefficients in time-varying magnetized and unmagnetized plasmas are likewise compared. Simulation results show that amplitude variation and phase jitter also exist on transmitted EM wave, and the turbulent deviation increases as the degree of plasma fluctuates. Meanwhile, the fluctuation of transmitted EM wave attenuates at low-frequency passband and increases at high-frequency passband with the increasing magnetic field. That is, comparing with unmagnetized time-varying plasma, the fluctuation effect can be mitigated by using a magnetic field when the EM wave frequency is at low-frequency passband. However, the mitigating effect can be influenced by the nonuniformity of magnetic field.