Stardust Sample Return Capsule Research Articles

Geometric Effects on Charring Ablator: Modeling the Full-Scale Stardust Heat Shield

The multidimensional geometric effects within the heat shield of the Stardust sample return capsule are studied over its reentry trajectory, using a material response solver. The solver models material charring, conductive heat transfer, surface energy balance, pyrolysis gas transport, and orthotropic material properties in three dimensions. The material response of the heat shield is computed using isotropic and orthotropic models for conductivity and permeability, and both results are compared to the 1-D model. The orthotropic and isotropic models predict dissimilar responses, especially in regard to the surface blowing rates and pyrolysis gas transport. Although both models yield similar results for the surface temperature near the stagnation region, the temperature distribution within the heat shield differs. The 1-D model appears to greatly underestimate the thermal response deeper in the material, especially late in the trajectory.

Comparison of Transport Properties Models for Flowfield Simulations of Ablative Heat Shields

The goal of this study is to evaluate the effects of different models for calculating the mixture transport properties on flowfield predictions of ablative heat shields. The Stardust sample return capsule at four different trajectory conditions is used as a representative environment for Earth entry. In the first part of the study, the results predicted using Wilke’s missing rule, with species viscosities calculated using Blottner’s curve fits and species thermal conductivities determined using Eucken’s relation, are compared to the results obtained using Gupta’s mixing rule with collision cross-section data. The heat transfer to the vehicle predicted using the Wilke/Blottner/Eucken model is found to be larger than the value obtained using the Gupta/collision cross-section model by as much as 60%. The Wilke/Blottner/Eucken model also produces a larger mass blowing rate due to the oxidation of bulk carbon by as much as 25% compared to the Gupta/collision cross-section model. In the second part of the study, the effects of the mass diffusion model are assessed using the Fick’s, modified Fick’s, self-consistent effective binary diffusion, and Stefan–Maxwell models. The results show that the flowfield properties calculated using the modified Fick’s, self-consistent effective binary diffusion, and Stefan–Maxwell models are in good agreement. However, the Fick’s model produces a larger heat transfer and mass blowing rate compared to the other diffusion models by as much as 20%.

Stardust Interstellar Preliminary Examination VII: Synchrotron X‐ray fluorescence analysis of six Stardust interstellar candidates measured with the Advanced Photon Source 2‐ID‐D microprobe

AbstractThe NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X‐ray fluorescence element mapping and abundance measurements, for elements 19 ≤ Z ≤ 30, on six “interstellar candidates,” potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot‐spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high‐speed particle having an approximately chondritic (CI) element abundance pattern, except for factor‐of‐ten enrichments in K and Zn and an S depletion. This hot‐spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe‐normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al‐deck material from the Stardust sample return capsule, which was within the field‐of‐view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al‐rich surface feature that has a composition generally consistent with the Al‐deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot‐spots having CI‐like Ni/Fe ratios, complicating the search for CI‐like interstellar/interplanetary dust.

Stardust Interstellar Preliminary Examination IV: Scanning transmission X‐ray microscopy analyses of impact features in the Stardust Interstellar Dust Collector

AbstractWe report the quantitative characterization by synchrotron soft X‐ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy‐resolution spectra of major rock‐forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg‐spinel, forsterite, and an iron‐bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low‐density, amorphous Mg‐silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high‐speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty‐two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X‐ray analyses; however, we recorded the effects of synchrotron hard X‐ray radiation on I1043,1,30 and I1047,1,34.

Coupled Radiation-Gasdynamic Model for Stardust Earth Entry Simulation

A three-dimensional radiative aerodynamic computational simulation has been accomplished for the thermodynamically and chemically nonequilibrium flowfield around the Stardust sample return capsule at an angle of attack. In the early phase of study, the axisymmetric computations using the half-moment method indicate a significant radiative-gasdynamic interaction at high-altitude stages of the reentry trajectory. The radiative heating of the space capsule is studied again according to the preentry trajectory simulation of NASA duplicating the flight condition at an angle of attack of 8 deg. The three-dimensional radiative heat transfer is generated by a spectral multigroup ray-tracingmethod including themost dominant radiative mechanisms of absorption and emission. The computational results agree very well with data in literature and bring new insights into the interdisciplinary fluid dynamics phenomenon.

High-Speed Spectrographic Photometry of the Stardust Sample Return Capsule Around Peak Deceleration

The descent of the Stardust Sample Return Capsule on 15 January 2006 was observed with an intensified highframe-rate slitless spectrograph, which was operated in staring mode. Spectra were recorded at 300 frames per second from 09:57:47 to 09:57:57 UTC (Coordinated Universal Time), around the time of peak deceleration of the capsule. At this time, the spectra contained continuum emission from the hot surface and appeared to be featureless otherwise, with the exception of the telluric absorption caused by molecular oxygen in the atmosphere between the capsule and the observer. By averaging all spectra together, however, it was possible to bring outweak emission lines of oxygen and potassium over the time frame 09:57:51–54 UTC and sodium emission during 09:57:48–51 UTC. The spectral sequence was analyzed for signs of variation in the total emission from a possible wobbling of the capsule at periods higher than the spin rate. No such variationwas observed above the detection threshold of 5 amplitude in the line of sight.

Imaging and Slitless Spectroscopy of the Stardust Capsule Reentry Radiation

Observations were made during the reentry of the Stardust sample return capsule on 15 January 2006 in order to calibrate the level of radiation from the capsule surface, from the bow shock, and from its wake. A sensitive cooled charge-coupled device camera was used, equipped with a grating to simultaneously record the first-order spectrum of the capsule and that of the background stars. The radiation of the capsule was dominated by the graybody radiation from the hot surface. This graybody radiation was calibrated against the known radiation of background stars. The purpose of this calibrationwas to provide a cross check for other instruments participating in the airborne Stardust Entry Observing Campaign. In addition, eight short-exposed images were obtained that show the development of billowing and the distortion induced by winds.

Doppler weather radar as a meteorite recovery tool

Abstract– We report the use of Doppler weather radar as a tool for locating meteorites, both at the time of a fall and from archived radar data. This asset is especially useful for meteorite recovery as it can provide information on the whereabouts of falling meteorites in “dark flight” portion of their descent where information on their flight paths cannot be discerned from more traditional meteorite location techniques such as eyewitness accounts. Weather radar data can provide information from detection in three distinct regimes: (A) direct detection of the rapidly moving, optically bright fireball by distant radars, (B) detection of falling debris to include hand‐sample sized rocks, and (C) detection of dust produced by detonation events that can occur tens of minutes and many kilometers laterally removed from the actual fireball locality. We present examples of each, as well as comparisons against man‐made debris from a re‐entering Soyuz rocket and the Stardust Sample Return Capsule. The use of Doppler weather radar as a supplement to traditional meteorite recovery methods holds the promise of improving both the speed and total number of meteorite recoveries, thereby increasing the number of freshly fallen meteorites for scientific study.

Modeling of Stardust Entry at High Altitude, Part 1: Flowfield Analysis

DOI: 10.2514/1.37360 The Stardust sample return capsule entered the Earth’s atmosphere at a very energetic velocity of 12:6 km=s .I n the present study, both continuum (computational fluid dynamics) and particle (direct simulation Monte Carlo) methods are used to analyze the forebody flow of the Stardust sample return capsule at altitudes of 81 and 71 km, where the flow is in the near-continuum regime. At the higher altitude, direct comparisons between baseline computational fluiddynamicsanddirectsimulationMonteCarlomodelsgiveenormousdifferencesinbasic flowfield properties. To study the discrepancy between the solutions, a modified approach for determining the temperature used by computational fluid dynamics to control the dissociation and ionization reactions is investigated. The modified computational fluid dynamics and direct simulation Monte Carlo results are in significantly better agreement with each other, illustrating the strong sensitivity to chemistry modeling under these highly energetic conditions. Significant differences persist in temperatures near the capsule surface and in surface heat flux. Evaluation of local Knudsen numbers indicates that the flow experiences noncontinuum behavior in the shock front andatthecapsulesurfacethatexplainsthesmallerheat fluxpredictedbydirectsimulationMonteCarlo.Atthelower altitude, the flowfield results become less sensitive to details of the chemistry modeling, although noncontinuum effects are again predicted at the stagnation point.

Observations of the Stardust Sample Return Capsule Entry with a Slitless Echelle Spectrograph

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.

Calibrating infrasonic to seismic coupling using the Stardust sample return capsule shockwave: Implications for seismic observations of meteors

Shock waves produced by meteoroids are detectable by seismograph networks, but a lack of calibration has limited quantitative analysis of signal amplitudes. We report colocated seismic and infrasound observations from reentry of NASA's Stardust sample return capsule (SSRC) on 15 January 2006. The velocity of the SSRC (initially 12.5 km/s) was the highest ever for an artificial object, lying near the low end of the 11.2–72 km/s range typical of meteoroids. Our infrasonic/seismic recordings contain an initial N wave produced by the hypersonic shock front, followed ∼10 s later by an enigmatic series of weak, secondary pulses. The seismic signals also include an intervening dispersed wave train with the characteristics of an air‐coupled Rayleigh wave. We determine an acoustic‐seismic coupling coefficient of 7.3 ± 0.2 μm s−1/Pa. This represents an energy admittance of 2.13 ± 0.15%, several orders of magnitude larger than previous estimates derived from earthquake or explosive analogs. Theoretical seismic response was computed using in situ VP and VS measurements, together with laboratory density measurements from samples of the clay‐rich playa. Treatment of the air‐ground interface as an idealized air‐solid contact correctly predicts the initial pulse shape but underestimates its seismic amplitude by a factor of ∼2. Full‐wave synthetic seismograms simulate the air‐coupled Rayleigh wave and suggest that the secondary arrivals are higher‐order Airy phases. Part of the infrasound signal appears to arise from coupling of ground motion into the air, much like earthquake‐induced sounds.

Focused ion beam recovery of hypervelocity impact residue in experimental craters on metallic foils

Abstract— The Stardust sample return capsule returned to Earth in January 2006 with primitive debris collected from comet 81P/Wild‐2 during the flyby encounter in 2004. In addition to the cometary particles embedded in low‐density silica aerogel, there are microcraters preserved in the aluminum foils (1100 series; 100 μm thick) that are wrapped around the sample tray assembly. Soda lime spheres (˜49 μm in diameter) have been accelerated with a light gas gun into flight‐grade aluminum foils at 6.35 km s−1 to simulate the capture of cometary debris. The experimental craters have been analyzed using scanning electron microscopy (SEM) and X‐ray energy dispersive spectroscopy (EDX) to locate and characterize remants of the projectile material remaining within the craters. In addition, ion beam‐induced secondary electron imaging has proven particularly useful in identifying areas within the craters that contain residue material. Finally, high‐precision focused ion beam (FIB) milling has been used to isolate and then extract an individual melt residue droplet from the interior wall of an impact. This has enabled further detailed elemental characterization that is free from the background contamination of the aluminum foil substrate. The ability to recover “pure” melt residues using FIB will significantly extend the interpretations of the residue chemistry preserved in the aluminum foils returned by Stardust.

Aerothermodynamic Analysis of Stardust Sample Return Capsule with Coupled Radiation and Ablation

An aerothermodynamic analysis of the forebody aeroshell of the Stardust Sample Return Capsule is carried out using the axisymmetric viscous shock-layer (VSL) equations with and without fully coupled radiation and ablation. Formulation of the VSL equations with shoulder radius as the length scale and implementation of the Vigneron pressure condition allow resolution of the flowfield over the shoulder. With a predominantly supersonic outflow over the shoulder, a globally iterated solution of VSL equations can be obtained. The stagnation-point results are obtained along a specified trajectory, whereas detailed calculations along the body are provided at the peak heating point. The coupled laminar and turbulent flow solutions with radiation and ablation are obtained using the equilibrium flow chemistry, whereas a nonequilibrium chemistry model is used for solutions without ablation and turbulence. The equilibrium calculations are physically consistent and a practical way to conserve surface (and flow-field) elemental composition for the current small ablation injection rates, where the surface elemtal composition is a mixture of freestream and ablator elements. A maximum stagnation heating of about 1100 W/cm2 is obtained for the no ablation injection case with nonequilibrium flow chemistry and an equilibrium catalytic wall boundary condition. The corresponding radiative quilibrium flow chemistry and an equilibrium catalytic wall boundary condition. The corresponding radiative quilibrium wall temperature is about 3800 K. A similar stagnation heating value is obtained with equilibrium flow chemistry. With ablation injection, this value is reduced by about 35 percent. Reduction in heating due to ablation is slightly less downstream of the stagnation point, along the conical flank, and over the shoulder. For the ablation injection and turbulent flow solutions, with instantaneous transition just downstream of the stagnation line, the heating is reduced by only about 13 percent on the conical flank and shoulder from a non-ablating laminar solution. The reduction in heating by ablation injection appears to be partially offset by augmentation due to turbulence in this case.

Aerodynamics of Stardust Sample Return Capsule

Successful return of interstellar dust and cometary material by the Stardust Sample Return Capsule requires an accurate description of the Earth entry vehicle''s aerodynamics. This desciption must span the hypersonic-rarefied, hypersonic-continuum, supersonic, transonic, and subsonic flow regimes. Data from numerous sources are compiled to accomplish this objective. These include Direct Simulation Monte Carlo analyses, thermochemical nonequilibrium computational fluid dynamics, transonic computational fluid dynamics, existing wind tunnel data, and new wind tunnel data. Four observations are highlighted: 1) a static instability is revealed in the free-molecular and early transitional-flow regime due to aft location of the vehicle''s center-of-gravity, 2) the aerodynamics across the hypersonic regime are compared with the Newtonian flow approximation and a correlation between the accuracy of the Newtonian flow assumption and the sonic line position is noted, 3) the primary effect of shape change due to ablation is shown to be a reduction in drag, and 4) a subsonic dynamic instability is revealed which will necessitate either a change in the vehicle''s center-of-gravity location or the use of a stabilizing drogue parachute.