Atmospheric Re-entry Phase Research Articles

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.

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.

Utilization of thermite energy for re-entry disruption of detachable rocket elements made of composite polymeric material

A conceptual approach to improve the safety of rocket-space activity is presented, including minimization of space debris returning from space. The main idea is to eliminate hazards of uncontrolled re-entry of detachable rocket design elements after finishing their mission with the use of the energy of pyrotechnic thermite reaction to disrupt these parts made of composite polymeric material, i.e., carbon fiber reinforced polymer. As an example, the payload fairing half is considered, the conditions for its descent in dense layers of the atmosphere are calculated. Results reveal that depending on the entrance velocity, the target object or completely burn out, or the additional heat source is required for its full destruction. It is proposed that pyrotechnic composition to be installed on the object could serve as additional heat source to provide its combustion or fine dispersion during the atmospheric re-entry phase of the descent trajectory. The possible pyrotechnic compositions to be used are presented and discussed.

Plasma Effect on Radiofrequency Communications for Lifting Reentry Vehicles

The present work investigates plasma effects around two lifting hypersonic vehicles and their implications on the radiofrequency communication blackout performances during the Earth atmospheric reentry phase. In particular, the Intermediate Experimental Vehicle developed by the European Space Agency and a slender, high lift-over-drag space plane, investigated during previous studies, have been taken into account. Chemical nonequilibrium analyses have been carried out by means of a numerical code, updated with a customized chemical model comprised of several reacting species and different reaction mechanisms. Different flight conditions, including the most critical for communications, have been considered for both vehicles. The main outcomes of the study show that, for very similar freestream conditions, the slender space plane exhibits better communication capabilities when compared with the Intermediate Experimental Vehicle. Particularly, the results suggest that the Intermediate Experimental Vehicle would be able to communicate from the lee side for a limited range of the angle of sight, while no communications from the wind side would be possible. On the other hand, for the slender space plane, flying at relatively low angles of attack, communications are possible either from the lee side or the wind side with very wide angles of sight.

Analyzing Reentry Vehicle Control Vane Effect on Stability of a Vehicle in the Atmospheric Outgoing Phase

In this paper, the effect of RV (Reentry Vehicle) control vane on stability of a launch vehicle in the atmospheric outgoing phase will be analyzed. Despite of necessity for stability or control purposes in atmospheric re-entry phase, the RV vane has adverse effects on the stability of the whole launch vehicle in the phase of atmospheric outgoing. For analyzing this, a pilot launch vehicle is selected, the geometry is modeled in GAMBIT, flight data is extracted and using FLUENT, the launch vehicle conditions is simulated and the stability results is extracted for analyzing that shows the adverse effects of RV control vane on whole launch vehicle stability. Finally, some suggestions are offered.

Barriers of Oxidation ans Ageing of Space Shuttle Material

During the atmospheric re-entry phase, the thermal protection of a spacecraft vehicle is submitted to air plasma. The transfer of the kinetic energy of the gases to the surface leads to an important heating of the nose cap and leading edges. The energy released from the recombination of oxygen atoms on the surface produces an additional amount of heat, increasing further the temperature. This excess of heat can damage the protection materials. This last mechanism leads to the oxidation of the surface and an accelerated ageing of the material. The oxidation produces a new surface layer of oxide such as SiO2 (Passive oxidation) and leads to the ablation of the material by the formation of CO, CO2, SiO and to the diffusion of oxygen in the bulk creating micro-cracks in the material (Active oxidation). Thus the composition of the surface and consequently the protection material properties are modified. The atmospheric re-entry conditions are created with a non equilibrium low pressure RF plasma chemical reactor. The ageing of the material and the diffusion of oxygen are studied by mass spectrometry analysis of 18O isotope for temperatures ranging from 300 – 1000 K. Silicon Carbide targets are covered with two different coatings, Chromium oxide, and Chromium oxide/ Silica. Oxygen diffusion in the material bulk for the targets was followed by Secondary Ion Mass Spectroscopy (SIMS).Mass Spectrometry shows the formation of CO and CO2 pointing out the process of ablation. This ablation is much lower in the case of polluted sample (with Chromium oxide). SIMS analyses show that Cr2O3 acts like a barrier in the oxidation of the material by limiting the diffusion of oxygen in the bulk.

Analytical solutions for the equations of motion of a space vehicle during the atmospheric re-entry phase on a 2-D trajectory

A practical and important problem encountered during the atmospheric re-entry phase is to determine analytical solutions for the space vehicle dynamical equations of motion. The author proposes new solutions for the equations of trajectory and flight-path angle of the space vehicle during the re-entry phase in Earth’s atmosphere. Explicit analytical solutions for the aerodynamic equations of motion can be effectively applied to investigate and control the rocket flight characteristics. Setting the initial conditions for the speed, re-entering flight-path angle, altitude, atmosphere density, lift and drag coefficients, the nonlinear differential equations of motion are linearized by a proper choice of the re-entry range angles. After integration, the solutions are expressed with the Exponential Integral, and Generalized Exponential Integral functions. Theoretical frameworks for proposed solutions as well as, several numerical examples, are presented.

Modified Wagner model for the active-to-passive transition in the oxidation of Si3N4

Si3N4 is used as the coating material of space shuttle structures which receive very high thermal fluxes during the atmospheric re-entry phase. Two main regimes govern the oxidation of Si3N4: the passive oxidation, with the formation of a protective silica layer leading generally to a mass gain, and the active oxidation, with vaporization of SiO leading to a mass loss of the sample. To ensure that silicon nitride will efficiently protect a material in given oxidizing environments, its own oxidation behaviour must be previously known. Therefore, the active-to-passive transition of Si3N4 oxidation is a problem of deep scientific importance and of wide technological relevance. In this paper, a modified Wager model for the active-to-passive transition in the oxidation of Si3N4 is presented, which includes the non-equilibrium effects caused by the mass transfer. The present theoretical calculations satisfactorily explained the reported experimental and theoretical data. The influence of flow rate on the active-to-passive transition boundary has been explained using our model. The rate controlling mechanism of the oxidation at the active-to-passive transition point is proposed.

Un exemple d'interaction fluide-fluide: "essorage" par un jet d'air turbulent d'un film liquide entraîné par une plaque en mouvement

Cet article presente une simulation numerique des interactions hydrodynamiques entre une plaque solide en mouvement, un film liquide entraine par cette plaque et un fluide gazeux au repos ou structure en jet plan impactant ce film, dans une hypothese de geometrie cartesienne 2D essentiellement, mais egalement 3D. Cette problematique se rencontre dans des applications procedes materiaux (controle d'epaisseur de depot ou d'etats de surface en siderurgie) ou pour dans les parois protectrices (des vehicules spatiaux en phase de rentree atmospherique ou des reacteurs de fusion nucleaire) et d'une certaine facon dans des problemes de condensation avec balayage par un ecoulement gazeux. Ce probleme allie de nombreuses difficultes physiques et numeriques : traitement des interfaces liquide-gaz et des instabilites qui y prennent naissance, turbulence dans la zone gazeuse et eventuellement dans la zone liquide. Une autre difficulte est inherente aux multiples echelles rencontrees : procede a l'echelle centimetrique-metrique, epaisseur de film a l'echelle millimetrique-micronique, echelles de turbulence variees. Notre travail va tenter de vaincre ces difficultes et de produire des resultats en conditions reelles ... ou du moins au plus pres de celles-ci.