High Entry Velocity Research Articles

ABLATION AND CHEMICAL ALTERATION OF COSMIC DUST PARTICLES DURING ENTRY INTO THE EARTH’S ATMOSPHERE

ABSTRACT Most dust-sized cosmic particles undergo ablation and chemical alteration during atmospheric entry, which alters their original properties. A comprehensive understanding of this process is essential in order to decipher their pre-entry characteristics. The purpose of the study is to illustrate the process of vaporization of different elements for various entry parameters. The numerical results for particles of various sizes and various zenith angles are treated in order to understand the changes in chemical composition that the particles undergo as they enter the atmosphere. Particles with large sizes (> few hundred μm) and high entry velocities (>16 km s−1) experience less time at peak temperatures compared to those that have lower velocities. Model calculations suggest that particles can survive with an entry velocity of 11 km s−1 and zenith angles (ZA) of 30°–90°, which accounts for ∼66% of the region where particles retain their identities. Our results suggest that the changes in chemical composition of MgO, SiO2, and FeO are not significant for an entry velocity of 11 km s−1 and sizes <300 μm, but the changes in these compositions become significant beyond this size, where FeO is lost to a major extent. However, at 16 km s−1 the changes in MgO, SiO2, and FeO are very intense, which is also reflected in Mg/Si, Fe/Si, Ca/Si, and Al/Si ratios, even for particles with a size of 100 μm. Beyond 400 μm particle sizes at 16 km s−1, most of the major elements are vaporized, leaving the refractory elements, Al and Ca, suspended in the troposphere.

Olivine settling in cosmic spherules during atmospheric deceleration: An indicator of the orbital eccentricity of interplanetary dust

AbstractA new type of cosmic spherule is reported with textures suggesting settling of olivine during atmospheric deceleration. Numerical simulations of entry heating reveal that relict forsterite, which survives melting, can settle over the 1–2 s of flight at high entry angles and entry velocities up to 16 km s−1. Enhanced crystallization of phenocrysts by heterogeneous nucleation on accumulated relict forsterites is the most likely origin of the observed cumulate textures in cosmic spherules. Such textures in cosmic spherules reveal interplanetary dust with higher encounter velocity with the Earth that correspond to orbital eccentricities >0.3. The relative abundance of cumulate spherules suggests that 14% of ordinary chondrite‐related, S(IV)‐type asteroid dust over the last 800 kyr had relatively high orbital eccentricity owing to secular and planetary perturbations. The textures of cosmic spherules collected from sediments can therefore be used to trace dust orbital variations with time, which may influence terrestrial climate.

Meteorites from meteor showers: A case study of the Taurids

AbstractWe propose that the Taurid meteor shower may contain bodies able to survive and be recovered as meteorites. We review the expected properties of meteorite‐producing fireballs, and suggest that end heights below 35 km and terminal speeds below 10 km s−1 are necessary conditions for fireballs expected to produce meteorites. Applying the meteoroid strength index (PE criteria) of Ceplecha and McCrosky (1976) to a suite of 33 photographically recorded Taurid fireballs, we find a large spread in the apparent meteoroid strengths within the stream, including some very strong meteoroids. We also examine in detail the flight behavior of a Taurid fireball (SOMN 101031) and show that it has the potential to be a (small) meteorite‐producing event. Similarly, photographic observations of a bright, potential Taurid fireball recorded in November of 1995 in Spain show that it also had meteorite‐producing characteristics, despite a very high entry velocity (33 km s−1). Finally, we note that the recent Maribo meteorite fall may have had a very high entry velocity (28 km s−1), further suggesting that survival of meteorites at Taurid‐like velocities is possible. Application of a numerical entry model also shows plausible survival of meteorites at Taurid‐like velocities, provided the initial meteoroids are fairly strong and large, both of which are characteristics found in the Taurid stream.

Mars Entry Bank Profile Design for Terminal State Optimization

One challenge examined in NASA’s DRM 5.0 study is that of entry, descent, and landing (EDL) on Mars for high-ballistic-coefficient, human-class payloads. To define best-case entry scenarios for the evaluation of potential EDL system designs, a study is conducted to optimize the entry-to-terminal-state portion of EDL for a variety of entry velocities, vehicle ballistic coefficients ( �), and lift-to-drag ratios ( L/D ). The terminal state is envisioned as one appropriate for the initiation of terminal descent via parachute or other means. A particle swarm optimizer varies entry flight path angle and ten bank profile points to find maximum-final-altitude trajectories. A baseline set of optimizations is performed, as are fulllift-up and relaxed-deceleration-constraint sets fo r comparison. In total, an estimated 9 million trajectories are analyzed to yield 1800 opt imal trajectories. Parametric plots of maximum achievable altitude are shown, as are examples of optimized trajectories. Characteristic vehicle contours are overlaid on the parametric plots, and conclusions are drawn on the feasibility of vehicles in the L/D vs. � design space. It is shown that entry bank angle control is highly deserving of consideration early in design, particularly for vehicles with mid- or high-L/D values, high entry velocities, and deceleration-li mited trajectories. Key conclusions are also drawn regarding trends in optimal bank profiles and in the constraints which impose particularly severe limits on the design of these trajectories.

Cosmogenic radionuclides in L5 and LL5 chondrites from Queen Alexandra Range, Antarctica: Identification of a large L/LL5 chondrite shower with a preatmospheric mass of approximately 50,000 kg

Abstract– The collection of approximately 3300 meteorites from the Queen Alexandra Range (QUE) area, Antarctica, is dominated by more than 2000 chondrites classified as either L5 or LL5. Based on concentrations of the cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca in the metal and stone fraction of 16 QUE L5 or LL5 chondrites, we conclude that 13 meteorites belong to a single meteorite shower, QUE 90201, with a large preatmospheric size and a terrestrial age of 125 kyr. Members of this shower have properties typical of L (e.g., pyroxene composition) and LL chondrites (e.g., metal abundance and composition), as well as properties intermediate between the L and LL groups (e.g., olivine composition), and is thus best described as an L/LL5 chondrite. Based on comparison with model calculations, the measured radionuclide concentrations in the metal and stone fractions of QUE 90201 indicate irradiation in an object with a preatmospheric radius of approximately 150 cm, representing one of the largest chondrites known so far. Based on the abundance of small L5 and LL5 chondrites at QUE and their distinct mass distribution, we conclude that the QUE 90201 shower includes up to 2000 fragments with a total recovered mass of 60–70 kg, <1% of the preatmospheric mass of approximately 50,000 kg. The mass distribution of the QUE 90201 shower suggests that the meteoroid experienced catastrophic atmospheric fragmentation(s), either because it was a fragile object or it had a high entry velocity.

Computational Examination of Parameters Influencing Practicability of Ram Accelerator

The problems concerning practicability aspects of a ram accelerator, such as intense in-bore projectile ablation, large accelerator tube length to achieve high projectile muzzle velocity, and high entry velocity of projectile in the accelerator tube for starting the accelerator have been examined. Computational models of the processes like phenomenon of projectile ablation, flow in the aero-window used as accelerator tube-end closure device in case of high drive gas filling pressure in the ram accelerator tube have been presented. New projectile design to minimise the starting velocity of the ram accelerator is discussed. Possibility of deployment of ram accelerator in the defence-oriented role has been investigated to utilise its high velocity potential.

Sodium resonance lidar observations during 2001 Leonid meteor shower over Wuhan

Here is the first report on the observation of meteor ablation trails with lidar in China. Four long-lived Na ablation trails were observed during the 18/19 Nov. 2001 Leonid meteor shower with a sodium resonance lidar over Wuhan. The mean altitude of the 4 trails is 97.95 km, consistent with Leonid high entry velocity (∼72 km/s). The peak density averages about 3380±3633 cm−3, and the abundance is (2.33 ±1.49) ×108 cm−2, both of which are higher than those previously observed for sporadic meteor trails. The RMS width is 359 m and the meteor’s age is 81 min, indicating that they are long duration meteor trails. These observation results are quite different from those of sporadic meteor trails, but comparable to the 1998 and 1999 Leonid report. Five night observations from 17 Nov. to 23 Nov. suggest that the 2001 Leonid meteor shower does not have a significant impact on the abundance of the background Na layer.

High resolution radar observations of the 1999, 2000 and 2001 Leonid meteor storms over middle Europe and Northern Scandinavia

Observations of the Leonid meteor storms have been made with all-sky meteor radars at Juliusruh, Germany (54.6°N), at Kiruna, Sweden (67.9°N) and at Andenes, Norway (69.3°N) in 1999, 2000, and 2001. In the Juliusruh and Andenes experiments acquisition parameters were selected to acquire data at the highest possible rate with an optimum time resolution to locate as many meteors as possible as well as to determine the high entry velocities of the Leonid meteors. Height-dependent meteor rates and distributions of the meteor entry velocities were analyzed in the altitude range 80–115 km with a time-resolution of 10 min (1999 and 2000) and 20 min (2001). During each of the three storm periods, the Leonid storm activity was most prominent at altitudes above 100 km with counts much higher than usual and short-time variations in the Leonid activity were clearly revealed by the radars. Temporary peaks in the Leonid activity during the storms depicted in the radar observations were more pronounced than in the ZHR-curve derived from a multitude of visual observers.

Plasma source development for the qualification of thermal protection materials for atmospheric entry vehicles at IRS

During re-entry of a spacecraft into the atmosphere of a celestial body, large amounts of energy are set free near the surface due to the high entry velocity. This energy leads to dissociation and ionization in the boundary layer and results in a high heat flux on the return body. These re-entry conditions must be simulated in ground test facilities to qualify for the necessary heat protection materials. For this purpose, several plasma wind tunnels were constructed at the Institut für Raumfahrtsysteme (IRS) of the University of Stuttgart and various plasma sources were developed to do justice to many qualification requirements for different missions, which will be presented in this paper.

Turbulent premixed, swirling combustion: Direct stress, strained flamelet modelling and experimental investigation

A direct stress model is presented for turbulent, swirling, combustion. Combustion and variable density are accounted for by modifying, and adding to, some of the existing terms of the direct stress model equations, originally developed for non-reacting, constant density flows. The premixed combustion model employs the concept of laminar flamelets that are subject to a distribution of flame strain rates and the energy equation yields the mean turbulent volumetric heat release rate. Model predictions are compared, for three entry velocities and three swirl numbers, with those from the k−∈ model and with measurements in a laboratory burner with the facility for the annular entry of swirling premixture. Thermocouple temperatures were measured for both non-swirling and swirling combustion of CH 4 -air, inside the cylindrical tunnel. Without swirl, two combustion modes were observed: a cone-like turbulent flame at high entry velocity and an annular turbulent jet flame at lower entry velocity. With swirl, only annular jet flames were observed. In general, swirling flames are shorter and thicker. Predictions of measured temperatures are found to be better by the direct stress than by the k−∈ strained flamelet model. The former model adequately predicts the threshold velocity for the different combustion models for non-swirling flows, as well as the length of the turbulent flame.