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Numerical Computation of ExoMars Schiaparelli Communications Blackout Compared with Flight
Abstract and Figures
The European Space Agency flew an entry, descent and landing demonstrator module called Schiaparelli, that entered the atmosphere of Mars on the 19th October 2016. The UHF or-biter relay links with Schiaparelli suffered a period of ∼57.2-seconds of degradation. An end-to-end aerothermodynamic and electromagnetic analysis has been performed using FGE's in-house simulation tools. Multiple points are considered along a best-estimate trajectory reconstructed from available flight telemetry [1]. For the aerothermodynamics, the chemical composition of the shock layer has been modelled using the Park '94 reaction dataset [2]. The combined computation of the electron density in the hypersonic flow and the propagation characteristics determined by the electromagnetic simulations, has enabled an assessment of the blackout period. Due to the inherent assumptions in modelling the dissociated, hypersonic CO 2 environment , the comparison between the numerical simulations and flight data provides a unique validation of the numerical capability to model blackout. This is a valuable secondary validation of trajectory reconstruction exercises. Compared to flight data, the results align well with the onset of blackout but predict a premature exit by approximately 10 to 15-seconds. These discrepancies could be attributed to complications caused by a combination of factors, including high Doppler dynamics and any attenuation, reflection, or spectral broadening effects from the remaining charged particles. The analysis presented has established the validity of the end-to-end approach, but its accuracy depends strongly on the modelling used for the calculations.
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The present work aims to derive a set of thermomechanical relaxation rate parameters and chemical reaction rate coefficients relevant to future interplanetary missions. It also attempts to assess the impact of thermochemical nonequilibrium phenomena on radiative heating rates for the stagnation point of the Martian entry vehicle.
Propagation of radio signals through sufficiently dense plasma will
become disrupted during a space vehicle's hypersonic entry phase into a
planetary atmosphere. The Mars Phoenix communication links were found to
experience varying levels of reduced received signal strength (brownout)
during the spacecraft's entry into the Martian atmosphere on May 25,
2008. These fades were attributed to charged particles generated inside
the entry vehicle's high-temperature shock layer during the hypersonic
entry. This article presents the results of the analysis of the UHF
carrier signal power emitted by Phoenix as received by three orbiting
relay satellites during the period around peak heating: Mars
Reconnaissance Orbiter, Mars Odyssey, and Mars Express.
During the Mars Pathfinder mission, there was a 30-second period in which the 8.4-GHz (X-band) communications link to Earth was lost during the atmospheric entry phase. An analysis of the Mars Pathfinder reconstructed flight profile using aero-thermodynamic tools provided estimates of the electron densities in the stag- nation and wake regions of the spacecraft. For the wake region, where the low-gain antenna used to communicate with Earth was located, the electron-density esti- mates exceeded the critical X-band electron density during the first 20 seconds of the 30-second blackout period. High Doppler dynamics and low signal-to-noise ratio may have contributed to the blackout during the last 10 seconds. Thus, at least part of the Mars Pathfinder communications blackout during entry was possibly due to the sheath of charged particles generated by heating incurred by the shock. The up- coming Mars Exploration Rover (MER) missions, MER-A and MER-B, scheduled for 2003 launches, are not expected to experience communication blackouts due to charged particles during their entry phases into the Martian atmosphere in 2004. The estimated peak electron densities expected for MER lie about three orders of magnitude below the critical X-band electron density required for blackout.
The issues of code validation and verification are addressed in the
context of a 3D Navier-Stokes method for flows in thermochemical
nonequilibrium. A series of validation and verification cases are
presented. The code uses a second order upwind TVD method for the
inviscid fluxes, and is marched in time by means of a point Gauss-Seidel
relaxation technique. Thermodynamic nonequilibrium is modeled with two
temperatures. Agreement with other codes is good, and with experimental
and flight data is also generally good, although a lack of suitably
detailed experimental data means it is not possible to comprehensively
validate the viscous position of the code.
The characteristics of the waves guided along a plane [I] P. S. Epstein, “On the possibility of electromagnetic surface waves, ” Proc. Nat’l dcad. Sciences, vol. 40, pp. 1158-1165, Deinterface which separates a semi-infinite region of free cember 1954. space from that of a magnetoionic medium are investi- [2] T. Tamir and A. A. Oliner, “The spectrum of electromagnetic waves guided by a plasma layer, ” Proc. IEEE, vol. 51, pp. 317gated for the case in which the static magnetic field is 332, February 1963. oriented perpendicular to the plane interface. It is [3] &I. A. Gintsburg, “Surface waves on the boundary of a plasma in a magnetic field, ” Rasprost. Radwvoln i Ionosf., Trudy found that surface waves exist only when w,<wp and NIZMIRAN L’SSR, no. 17(27), pp. 208-215, 1960. that also only for angular frequencies which lie bet\\-een [4] S. R. Seshadri and A. Hessel, “Radiation from a source near a plane interface between an isotropic and a gyrotropic dielectric,” we and 1/42 times the upper hybrid resonant frequency. Canad. J. Phys., vol. 42, pp. 2153-2172, November 1964. The surface waves propagate with a phase velocity [5] G. H. Owpang and S. R. Seshadri, “Guided waves propagating along the magnetostatic field at a plane boundary of a semiwhich is always less than the velocity of electromagnetic infinite magnetoionic medium, ” IEEE Trans. on Miomave waves in free space. The attenuation rates normal to the Tbory and Techniques, vol. MTT-14, pp. 136144, March 1966. [6] S. R. Seshadri and T. T. \Vu, “Radiation condition for a maginterface of the surface wave fields in both the media are netoionic medium. ” to be Dublished. examined. Kumerical results of the surface wave characteristics are given for one typical case.
Analysis of the AEDB performance during the ExoMars Schiaparelli descent
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ExoMars mission description of TGO and Schiaparelli
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Aerothermodynamics of the ExoMars entry demonstrator module
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Preliminary analysis of entry and descent radio communications of ExoMars 2016 Schiaparelli
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personal communication, June 2017.