Contribution of CO2 IR Radiation to Martian Entries Radiative Wall Fluxes Support to the ESA EXOMARS Mission for Exploration of Planet Mars M. Lino da Silva Instituto de Plasmas e Fus ˜ ao Nuclear, Instituto Superior T´ ecnico Framework of the ESA EXOMARS Mission I ExoMars (Exobiology on Mars) is a European-led robotic mission to Mars currently under development by the European Space Agency (ESA) and NASA. I ExoMars is the first mission in ESA’s Aurora Exploration Programme, aimed at extending Europe’s capabilities in planetary exploration. I Mission originally conceived as a rover with a static ground station, to be launched in 2011 aboard a Soyuz Fregat rocket. I Delays in the definition of the mission led to a modified framework: The new ESA/NASA Mars Joint Exploration Initiative signed in July 2009. I Other technological challenges, also as a consequence of the contribution by IPFN, showed that the original mission profile was inpractical. I Two missions defined: The launch of an ESA Entry, Descent, and Landing Demonstrator in 2016, and the launch of the robotic ESA-rover onboard a NASA Spacecraft in 2018. I Prime contractor (Fluid Gravity Eng. (UK)) tasked with producing the CFD flowfields. I IPFN has been tasked with the simulation of the radiative properties of the plasma surrounding the EXOMARS spacecraft during its atmospheric entry, using its in-house line-by-line code SPARTAN. Figure: Artist concept of the EXOMARS Spacecraft Entry Figure: Simulation and experimental validation of the hypersonic flowfield around EXOMARS; G¨ ottingen HEG Plasma Windtunnel c DLR Figure: Spacecraft scale model tested in a shock-tube facility; TCM2 Shock-Tube c Universit´ e de Provence I Objective: Simulation of the local radiative properties of the plasma (emission and absorption coefficients) for a large spectral range (VUV to IR) and radiative transfer from the plasma towards the wall points using a Ray-Tracing routine. Hardware Used for Simulations I Calculations carried in a Linux Debian Intel x86 8-core machine with 32GB of RAM and 2+2TB storage space. I Radiative field with a size of 25–50GB. Large I/O overheads need special computational techniques. I Creation of a 28GB ramdrive with an associated stack systm for preallocating radiative data. Computational Fluid Radiative Dynamics Modelling of the EXOMARS Entry I Simulations on initial mission profile (larger vehicle) and new profile (smaller vehicle), for 6 entry trajectory points. I 5 chemical species in the flowfield: CO 2 , CO, O 2 , C and O. I Population of radiative states obtained from a Boltzmann distribution, considering two temperatures (T,T vib ). I Need to define a coarser radiative grid due to storage constraints (line-by-line calculations yield spectra with millions of points). Figure: Sample temperature field and wake for a 5km/s Martian entry Radiative Systems Accounted by the Simulation species system upper state – bands species database model electronic lower state (v 0 max , v 00 max ) levels Martian-like molecular systems atomic photoionization CO X-X X 1 Σ + - X 1 Σ + (20; 20) C Topbase level Q a 361 Fourth-Positive A 1 Π - X 1 Σ + (20; 20) O Topbase level Q a 245 Third-Positive b 3 Σ + - a 3 Π (2; 20) Angstrom B 1 Σ + - A 1 Π (2; 20) molecular photoionization Triplet d 3 Π - a 3 Π (20; 20) Asundi a 03 Π - a 3 Π (20; 20) O 2 – total Q a – CO – total Q a – CO 2 – – 613 bands CO 2 – total Q a – Earth-like molecular systems molecular photodissociation O 2 Schumann-Runge B 3 Σ - u - X 3 Σ - g (10; 10) O 2 – T-dependent Q a – Atomic lines atomic photodetachment species database model electronic C - – total Q a – levels O - – total Q a – C NIST – 272 O NIST – 377 Ray -Tracing and Radiative Transfer Procedures Fundamental equations for radiative transfer towards the spacecraft wall: dI dl = ε ν - α(ν)l I w (ν) = 2 Z π 0 Z π/2 0 I w (θ, φ) cos (θ) sin (θ) sin (dθ) dφ I w (W/m 2 ) = Z ∞ 0 I w (ν)(W/m 2 cm -1 )dν Figure: Sample rays over a spacecraft wall point I Sampling of 22,500 rays for 50 wall points (450 per wall point, covering a half-hemisphere of ’ 5 ◦ solid angle). I The radiative fluxes from the different hemispherical angles are then summed, accounting for the inclination relative to the wall. Results and Discussion I Simulations highlighted the predominance of CO 2 IR radiation, which accounts for over 95% of the overall wall fluxes. I Previous works neglected IR contributions, therefore severely underestimating radiative fluxes. I The radiative peak occurs at lower velocities than the convective pek, in the case where CO 2 is heated without dissociating. I Radiative fluxes in the spacecraft backcover exceeded 1W/cm 2 , mandating the application of additional thermal protections, and invalidating the first mission profile. I Approach can be straightforwardly extended to other studies, such as radiative transfer inside a Tokamak. Figure: Integated radiative wall fluxes I w (left), spectral-dependent wall fluxes I w (ν) (right), for the 50 sampled wall points Instituto de Plasmas e Fus ˜ ao Nuclear Workshop, 12 November 2010