Debris Collision Research Articles

COLLISIONAL DEBRIS AS LABORATORIES TO STUDY STAR FORMATION

In this paper we address the question whether star formation is driven by local processes or the large scale environment. To do so, we investigate star formation in collisional debris where the gravitational potential well and velocity gradients are shallower and compare our results with previous work on star formation in non-interacting spiral and dwarf galaxies. We have performed multiwavelength spectroscopic and imaging observations (from the far-ultraviolet to the mid-infrared) of 6 interacting systems, identifying a total of 60 star-forming regions in their collision debris. Our analysis indicates that in these regions a) the emission of the dust is at the expected level for their luminosity and metallicity, b) the usual tracers of star formation rate display the typical trend and scatter found in classical star forming regions, and c) the extinction and metallicity are not the main parameters governing the scatter in the properties of intergalactic star forming regions; age effects and variations in the number of stellar populations, seem to play an important role. Our work suggests that local properties such as column density and dust content, rather than the large scale environment seem to drive star formation. This means that intergalactic star forming regions can be used as a reliable tool to study star formation.

The complex exposure histories of the Pitts and Horse Creek iron meteorites: Implications for meteorite delivery models

Abstract— The concentrations of cosmogenic radionuclides and noble gases in Pitts (IAB) and Horse Creek (ungrouped) provide unambiguous evidence that both irons have a complex exposure history with a first‐stage irradiation of 100–600 Myr under high shielding, followed by a second‐stage exposure of ˜1 Myr as small objects. The first‐stage exposure ages of ˜100 Myr for Horse Creek and ˜600 Myr for Pitts are similar to cosmic‐ray exposure ages of other iron meteorites, and most likely represent the Yarkovsky orbital drift times of irons from their parent bodies in the main asteroid belt to one of the nearby chaotic resonance zones. The short second‐stage exposure ages indicate that collisional debris from recent impact events on their precursor objects was quickly delivered to Earth. The short delivery times suggests that the recent collision events occurred while the precursor objects of Horse Creek and Pitts were either very close to the chaotic resonance zones or already in Earth‐crossing orbits. Since the cosmogenic noble gas records of Horse Creek and Pitts indicate a minimum radius of a few meters for the precursor objects, but do not exclude km‐sized objects, we conclude that these irons may represent fragments of two near‐Earth asteroids, 3103 Eger and 1986 DA, respectively. Finally, we used the cosmogenic nuclide concentrations in Horse Creek, which contains 2.5 wt% Si, to test current model calculations for the production of cosmogenic 10Be, 26Al, and neonisotopes from iron, nickel, and silicon.

Search for tidal dwarf galaxy candidates in a sample of ultraluminous infrared galaxies

Context.Small star-forming galaxies made out of collisional debris have been found in a variety of merging systems. So far only a few of them are known in Ultraluminous Infrared Galaxies (ULIRGs) although they show clear signs of interactions. Whether external star formation may take place in such objects in an open question.

The predicted growth of the low-Earth orbit space debris environment — an assessment of future risk for spacecraft

Space debris is a worldwide-recognized issue concerning the safety of commercial, military, and exploration spacecraft. The space debris environment includes both naturally occuring meteoroids and objects in Earth orbit that are generated by human activity, termed orbital debris. Space agencies around the world are addressing the dangers of debris collisions to both crewed and robotic spacecraft. In the United States, the Orbital Debris Program Office at the NASA Johnson Space Center leads the effort to categorize debris, predict its growth, and formulate mitigation policy for the environment from low-Earth orbit (LEO) through geosynchronous orbit. The current paper presents recent results derived from the NASA long-term debris environment model, LEGEND. It includes the revised NASA sodium potassium droplet model, newly corrected for a factor of two over-estimation of the droplet population. The study indicates a LEO environment that is already collisionally active among orbital debris larger than 1 cm in size. Most of the modelled collision events are non-catastrophic (i.e. they lead to a cratering of the target, but no large scale fragmentation). They take place between impactors smaller than 10 cm and targets larger than 10 cm. Given the small size of the impactor these events would likely be undetectable by present-day measurement means. The activity continues into the future as would be expected. Impact rates of about four per year are predicted by the current study within the next 30 years, with the majority of targets being abandoned intacts (spent upper stages and spacecraft). Still, operational spacecraft do showa small collisional activity that increases over time as the small fragment population increases. And such an event would be potentially mission-ending for the spacecraft.

Dark Matter in Galactic Collisional Debris

Our ideas about galaxy formation and the nature of dark matter have been changed by the unexpected observation that galaxies that formed from the collisions of other galaxies contain dark matter.

Stochastic analysis of survivability of double tether

A stochastic method to estimate survivability of a double tether system is described in this paper. Double tether is a pair of parallel strings connected at every certain distance, in order to improve the survivability against collisions of space debris. First, probabilities of cut off on a tether is modeled, which is caused by a collision of space debris. Next, survivability of a double tethered system is formulated. And then, survivability of single and double tether systems are evaluated and compared according to an environmental model of space debris.

Missing Mass in Collisional Debris from Galaxies

Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.

Instability of the present LEO satellite populations

Several studies conducted during 1991–2001 demonstrated, with some assumed launch rates, the future unintended growth potential of the Earth satellite population, resulting from random, accidental collisions among resident space objects. In some low Earth orbit (LEO) altitude regimes where the number density of satellites is above a critical spatial density, the production rate of new breakup debris due to collisions would exceed the loss of objects due to orbital decay. A new study has been conducted in the Orbital Debris Program Office at the NASA Lyndon B. Johnson Space Center, using higher fidelity models to evaluate the current debris environment. The study assumed no satellites were launched after December 2005. A total of 150 Monte Carlo runs were carried out and analyzed. Each Monte Carlo run simulated the current debris environment and projected it 200 years into the future. The results indicate that the LEO debris environment has reached a point such that even if no further space launches were conducted, the Earth satellite population would remain relatively constant for only the next 50 years or so. Beyond that, the debris population would begin to increase noticeably, due to the production of collisional debris. Detailed analysis shows that this growth is primarily driven by high collision activities around 900–1000 km altitude – the region which has a very high concentration of debris at present. In reality, the satellite population growth in LEO will undoubtedly be worse than this study indicates, since spacecraft and their orbital stages will continue to be launched into space. Postmission disposal of vehicles (e.g., limiting postmission orbital lifetimes to less than 25 years) will help, but will be insufficient to constrain the Earth satellite population. To better preserve the near-Earth environment for future space activities, it might be necessary to remove existing large and massive objects from regions where high collision activities are expected.

2449 応力波伝ぱ現象の分子シミュレーションによる検討(G03-11 解析・計算技術,G03 材料力学)

In order to study the microscopic deformation behavior of materials, numerical simulations such as the molecular dynamics (MD) method, Monte Carlo method and so forth have been developed. In comparison with the ab initio MD, the empirical MD can treat a large number of atoms and suits to study the microscopic mechanism of hyper-velocity or instantaneous phenomena such as the collision of space debris into the artificial sattellite and the penetration or spall fracture due to the projectile. It also leads to understanding of macroscopic phenomena. In this study, we adopted the embedded atom method (EAM) potential for the investigation of the behavior of fcc metal (aluminum) subjected to impact loading and especially examined the stress wave propagation problem.

The surface properties of small asteroids from thermal-infrared observations

While the physical characterization of near-Earth objects (NEOs) is progressing at a much slower rate than that of discovery, a substantial body of thermal-infrared data has been gathered over the past few years. A wide variety of taxonomic classes in the NEO population have now been sampled by means of thermal-infrared spectrophotometric observations. The resulting albedo information, together with the distribution of taxonomic types from spectroscopic investigations and the rapidly increasing catalog of orbits and absolute magnitudes derived from NEO search programs, such as LINEAR, facilitates more accurate estimates of the size distribution of the NEO population and the magnitude of the impact hazard. Despite our rapidly increasing knowledge of the NEO population, many questions and uncertainties remain, such as: How does the albedo distribution of NEOs compare with that of main-belt asteroids, and does space weathering play a role? How does the surface structure and regolith coverage of NEOs vary with size and taxonomic type? What fraction of NEOs are extinct comets? A property of particular interest is the surface thermal inertia of small asteroids, which is an indicator of the presence or lack of a thermally-insulating surface layer. Large asteroids can accumulate regolith, but can very small asteroids retain thermally-insulating collisional debris or at least a dust layer? Knowledge of thermal inertia is important for accurate calculations of the Yarkovsky effect, which can significantly influence the orbital evolution of potentially hazardous NEOs, and for the design of instruments for lander missions. Contrary to earlier expectations, evidence appears to be accumulating that even sub-kilometer asteroids often have a significant thermally-insulating surface layer. Recent results from thermal-infrared investigations of NEOs are reviewed and implications for the surface properties of small asteroids discussed.

3323 九州大学における小型人工衛星の開発(S86-1 小型宇宙システム(1),S86 小型宇宙システム)

Two satellite projects named QTEX and QTEX-PR are being advanced by Kyushu University now. QTEX was a small tethered satellite, and this project started by the students in Space System Dynamics Laboratory in 2002. QTEX has three missions, a proof of tether reel mechanism, an investigation of the tether survivability against space debris collision, and an experiment of orbit transfer technology by the tether cutting. QTEX consists of two similar satellites which named a mother and a daughter satellite, apart from an separation system and a tether reel mechanism in the mother satellite. We advanced the development of the daughter satellite in order to take hold a bus system of QTEX, and we named this daughter satellite "QTEX-PR". This paper will explain about QTEX-PR project.

A top-down scenario for the formation of massive Tidal Dwarf Galaxies

Among those objects formed out of collisional debris during galaxy mergers, the prominent gaseous accumulations observed near the tip of some long tidal tails are the most likely to survive long enough to form genuine recycled galaxies. Using simple numerical models, [CITE] claimed that tidal objects as massive as could only form, in these simulations, within extended dark matter (DM) haloes. We present here a new set of simulations of galaxy collisions to further investigate the structure of tidal tails. First of all, we checked that massive objects are still produced in full N-body codes that include feedback and a large number of particles. Using a simpler N-body code with rigid haloes, we noticed that dissipation and self-gravity in the tails, although important, are not the key factors. Exploiting toy models, we found that, for truncated DM haloes, material is stretched along the tail, while, within extended haloes, the tidal field can efficiently carry away from the disk a large fraction of the gas, while maintaining its surface density to a high value. This creates a density enhancement near the tip of the tail. Only later-on, self-gravity takes over; the gas clouds collapse and start forming stars. Thus, such objects were fundamentally formed following a kinematical process, according to a top-down scenario, contrary to the less massive Super Star Clusters that are also present around mergers. This conclusion leads us to introduce a restrictive definition for Tidal Dwarf Galaxies (TDGs) and their progenitors, considering only the most massive ones, initially mostly made of gas, that were able to pile up in the tidal tails. More simulations will be necessary to precisely determine the fate of these proto–TDGs and estimate their number.

Electromagnetic radiation from collisions at almost the speed of light: An extremely relativistic charged particle falling into a Schwarzschild black hole

We investigate the electromagnetic radiation released during the high energy collision of a charged point particle with a four-dimensional Schwarzschild black hole. We show that the spectra is flat, and well described by a classical calculation. We also compare the total electromagnetic and gravitational energies emitted, and find that the former is suppressed in relation to the latter for very high energies. These results could apply to the astrophysical world in the case that charged stars and small charged black holes are out there colliding into large black holes, and to a very high energy collision experiment in a four-dimensional world. In this latter scenario the calculation is to be used for the moments just after black hole formation, when the collision of charged debris with the newly formed black hole is certainly expected. Since the calculation is four dimensional, it does not directly apply to TeV-scale gravity black holes, as these inhabit a world of six to eleven dimensions, although our results should qualitatively hold when extrapolated with some care to higher dimensions.

Dust production from collisions in extrasolar planetary systems

Dust particles observed in extrasolar planetary discs originate from undetectable km-sized bodies but this valuable information remains uninteresting if the theoretical link between grains and planetesimals is not properly known. We outline in this paper a numerical approach we developed in order to address this issue for the case of dust producing collisional cascades. The model is based on a particle-in-a-box method. We follow the size distribution of particles over eight orders of magnitude in radius taking into account fragmentation and cratering according to dierent prescriptions. Particular attention is paid to the smallest particles, close to the radiation pressure induced cut-o size Rpr, which are placed on highly eccentric orbits by the stellar radiation pressure. We applied our model to the case of the inner (<10 AU) Pictoris disc, in order to quantitatively derive the population of progenitors needed to produce the small amount of dust observed in this region ('10 22 g). Our simulations show that the collisional cascade from kilometre-sized bodies to grains significantly departs from the classical d N/ R 3:5 dR power law: the smallest particles (R' Rpr) are strongly depleted while an overabundance of grains with size2Rpr and a drop of grains with size100Rpr develop regardless of the disc's dynamical excitation, Rpr and initial surface density. However, the global dust to planetesimal mass ratio remains close to its d N / R 3:5 dR value. Our rigorous approach thus confirms the depletion in mass in the inner Pictoris disc initially inferred from questionable assumptions. We show moreover that collisions are as ucient source of dust in the inner Pictoris disc. They are actually unavoidable even when considering the alternative scenario of dust production by slow evaporation of km-sized bodies. We obtain an upper limit of0.1 M for the total disc mass below 10 AU. This upper limit is not consistent with the independent mass estimate (at least 15 M) in the frame of the Falling Evaporating Bodies (FEB) scenario explaining the observed transient features activity. Furthermore, we show that the mass required to sustain the FEB activity implies a so important mass loss that the phenomena should naturally end in less than 1 Myr, namely in less than one twentieth the age of the star (at least 2 10 7 years). In conclusion, these results might help converge towards a coherent picture of the inner Pictoris system: a low-mass disc of collisional debris leftover after the possible formation of planetary embryos, a result which would be coherent with the estimated age of the system.

A Technique for Estimating the Space Debris Density from the Data of Onboard Recording Systems

A three-dimensional mathematical model and a program complex for modeling the external effect of small-sized space debris particles on a spacecraft are developed. On the basis of the rectangular contributions method a new technique is developed for restoring the density of small-sized space debris from a small number of recorded debris collisions with recording sensors. From the form of the density function the total number of points having reached the spacecraft surface is restored. The comparative results of modeling are presented.

Effect of mitigation measures on the long-term evolution of the debris population

The relative effectiveness of mitigation measures on the long-term evolution of the orbital debris population was investigated in detail by using a new version of the Space Debris Mitigation (SDM) analysis tool, developed under ESA/ESOC contract. Starting from new initial conditions, updated to 1999, and from a future traffic model, the influence of the selective adoption of mitigation practices was determined over a 100-year time span. The analysis included the suppression of the release of mission-related objects, the on-orbit explosion avoidance and the de-orbiting of upper stages in low earth orbit. A particular effort was devoted to study the long-term effect of different strategies of spacecraft disposal at the end of the operational life. The end-of-life disposal of low earth satellites in orbits of given residual lifetime, in between 0 and 50 years, was simulated to assess its potential long-term benefits for the debris environment below 2000 km. Moreover, for geostationary and low earth satellites above 1400 km, the re-orbiting to higher altitudes was considered as well. The results show clearly that the explosion avoidance in orbit is quite effective and should be strictly applied. However, some form of de-orbiting will be needed to roughly stabilize the long-term debris collision risk in low earth orbit.

DESIGN AND DEPLOYMENT OF A SPACE ELEVATOR

The space elevator was first proposed in the 1960s as a method of getting into space. The initial studies of a space elevator outlined the basic concept of a cable strung between Earth and space but concluded that no material available at the time had the required properties to feasibly construct such a cable. With the discovery of carbon nanotubes in 1991 it is now possible to realistically discuss the construction of a space elevator. Although currently produced only in small quantities, carbon nanotubes appear to have the strength-to-mass ratio required for this endeavor. However, fabrication of the cable required is only one of the challenges in construction of a space elevator. Powering the climbers, surviving micrometeor impacts, lightning strikes and low-Earth–orbit debris collisions are some of the problems that are now as important to consider as the production of the carbon nanotube cable. We consider various aspects of a space elevator and find each of the problems that this endeavor will encounter can be solved with current or near-future technology.

Impact fragments from asteroids by mutual collisions and cosmic dust bombardments

We estimated a production rate of collisional debris from asteroids, both for the case of mutual collisions of asteroids and for the case of impacts of interstellar dust onto asteroids. The total mass of fragments produced by mutual collisions for km-sized asteroids, occurred once per 10 6 years, is higher than that by the impacts of interstellar dust. However, it is found that the production of small grains from a km-sized asteroid by impacts of interstellar dust becomes about 10 5 to 10 6 kg during 10 6 years. Consequently, the impacts of interstellar dust have a potential ability to supply a significant amount of dust in the diffuse dust cloud in the asteroid belt.

Short-Term Debris Risk to Large Satellite Constellations

A debris collision hazard analysis is carried out on a large 800-satellite constellation, representative of the initial Teledesic cone guration, using the Space Debris Simulation (SDS) software. Usage of the software focuses on the short- to medium-term effects of explosive and collision-induced breakups. Two potentially constellationthreatening scenarios are considered: 1 ) constellation member fragmentation and 2 ) constellation launch-vehicle breakup. The constellation collision probability and the debris impact-energy to target-mass ratio are used as indicatorsoftheseverityoftherisk posed totheconstellation.Itisfound that,inthecaseinvestigated,thecollisional risk to the constellation is low in the short term. Of the scenarios examined, it is the collision-induced breakup of a constellation satellite that poses the greatest danger, in terms of the possibility of a secondary fragmentation. The SDS software is proven to be a useful tool in the analysis of the short-term, relative threat posed by debris impact to large constellation systems.

Microimpact phenomena on Australasian microtektites: Implications for ejecta plume characteristics and lunar surface processes

Abstract— Detailed investigations of the microimpact phenomena on Australasian microtektites from four samples from the Central Indian Basin reveal an array of features, such as very low‐velocity captured droplets, welded projectiles, angular fragments and dust, craters generated by projectiles defining an oblique trajectory, high‐velocity “pitless” craters, and the conventional hypervelocity craters with well‐defined central pits and radial and concentric cracks—found commonly on lunar surface materials. The microimpacts are a consequence of interparticle collisions within the ejecta plume (as suggested by their chemistry) subsequent to a major impact and, therefore, reveal processes inherent in an impact‐generated plume. All the impact phenomena observed here have taken place while the targets and projectiles were in flight and are therefore secondary impacts in lunar terms. However, some of the resultant features are analogous to lunar micro‐craters attributed to primary impacts by cosmic dust. Therefore, ballistic sedimentation on the Moon is likely to contain plume collisional debris as well.