Debris Flux Research Articles

Discharge of debris from ice at the margin of the Greenland ice sheet

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

Volcanic triggering of late Pliocene glaciation: evidence from the flux of volcanic glass and ice-rafted debris to the North Pacific Ocean

Mass accumulation rates (MAR) of different components of North Pacific deep-sea sediment provide detailed information about the timing of the onset of major Northern Hemisphere glaciation that occurred at 2.65 Ma. An increase in explosive volcanism in the Kamchatka–Kurile and Aleutian arcs occurred at this same time, suggesting a link between volcanism and glaciation. Sediments recovered by piston-coring techniques during ODP Leg 145 provide a unique opportunity to undertake a detailed test of this possibility. Here we use volcanic glass as a proxy for explosive volcanism and ice-rafted debris (IRD) as a proxy for glaciation. The MAR of both glass and IRD increase markedly at 2.65 Ma. Further, the flux of the volcanic glass increased just prior to the flux of ice-rafted material, suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid-Pliocene glacial intensification.

Direct simulation of meteoroids and space debris flux on LDEF spacecraft surfaces

The meteoroid flux on all faces of the long duration exposure facility (LDEF) is predicted by a direct simulation Monte Carlo (DSMC) model, which for the first time provides a self-consistent method to model the collision behaviour between both meteoroids and debris with oriented spacecraft surfaces. This new model includes the modified Divine's meteoroid population, and Taylor's velocity distribution, to include the effects of planetary shielding and gravitational enhancement by the Earth. Results obtained when only meteroid impact is considered show good agreement with observed data and provide some correlation with previous models. When the space debris population is also included, the total particle flux on different faces of LDEF fits well with the observed measurements. Information concerning Earth shielding, gravity capturing and atmospheric effects can be obtained by comparing the ratio of the number of meteoroids moving towards the Earth to the total number of the meteoroids, obtained from the DSMC model with measured data. Approximately 25% of the meteoroids flux is predicted as not returning into the interplanetary space due to these effects.

Direct Simulation of Apex Enhancement on the Flux onto European Retrievable Carrier

The extended direct simulation Monte Carlo method is employed to model fluxes of meteoroid and space debris onto surfaces of the sun-pointing spacecraft European Retrievable Carrier. Apex enhancement of the Earth motion on flux is considered by including a parameter to describe the anisotropic velocity directionality in the meteoroid distribution. The anisotropy of the measured fluxes onto different surfaces is well explained by this approach, and results are consistent with measured data. Also, the effect of the apex enhancement of the Earth motion on the morphology of the impacts is analyzed, and a good agreement with measured data is achieved. Our simulation allows an estimation of the extent to which the directionality distribution of the meteoroid velocity unit vectors deviates from the isotropic distribution.

Centurial‐millenial ice‐rafted debris pulses from ablating marine ice sheets

We use an ice‐sheet model to show that (i) margins of marine ice‐sheets can be expected to be frozen to the bed, except where ice‐streams discharge; (ii) 20–50km retreats induced by ablation rates of 2 m/yr provide sufficient debris flux through the grounding line to produce large sedimentation events. Such ablation would reduce ice‐shelf extent markedly, permitting debris to reach the calving front and be transported by icebergs leading to ice‐rafted debris (IRD) events. Ice shelf break‐up takes around a century (start of IRD pulse), while the creation of warm‐based conditions (end of IRD pulse) due to upwards motion of warm ice takes a few more centuries. Such IRD pulses are unlikely to explain Heinrich events, which are associated with relatively cold periods within glaciations. Surges are not necessary conditions for the production of large IRD events.

The Space Dust (SPADUS) instrument aboard the Earth-orbiting ARGOS spacecraft: II–results from the first 16 months of flight

In a companion paper (Tuzzolino et al., Planet. Space Sci., 2001, to appear) hereafter called Part I, we present a detailed description of the Space Dust (SPADUS) instrument being carried aboard the Earth-orbiting Advanced Research and Global Observation Satellite ( ARGOS). In this paper, we focus on examples of the flight data obtained by SPADUS during the first 16 months of the ARGOS mission. We present results obtained from the SPADUS polyvinylidene fluoride (PVDF) dust trajectory system, which measures dust particle flux, mass distribution, velocity and trajectory, as well as results obtained from the SPADUS Ancillary Diagnostic Sensor (ADS) subsystem, which measures energetic charged particles. Included are both raw data and reduced data for the time period from ARGOS launch (February 23, 1999) to June 8, 2000. The PVDF dust trajectory system detected a total of 258 dust impacts over this interval of approximately 470 days. Of these, 24 were D1–D2 type events—where particles impacted and penetrated a D1 sensor, then impacted a D2 rear array sensor—allowing for time-of-flight measurements. Of the 24 D1–D2 impacts on SPADUS, we identified 11 orbital debris particles, 7 interplanetary impactors, and 6 ambiguous impacts. Examples of particle orbits for both debris particles and interplanetary particles are detailed, and the results obtained for orbital debris flux and mass distribution are compared with predictions from an orbital debris model. We also describe transient particle streams detected by the SPADUS trajectory system resulting from the passage of ARGOS through streams of debris particles in Earth orbit.

The MASTER-99 space debris and meteoroid environment model

MASTER-99 is a space debris and meteoroid environment model produced by TU Braunschweig (D), eta_max space (D), and DERA (UK) under an ESA contract. The model allows to compute particulate impact fluxes on any terrestrial target orbit up to geostationary altitudes. Flux contributions can be discriminated with respect to debris source types (catalog objects, explosion and collision fragments, NaK droplets, solid rocket motor dust and slag, impact ejecta, and surface degradation products), meteoroid source types (Divine-Staubach populations, and annual stream events), and with respect to origin and impact direction of each flux contributing particulate. Impact fluxes of meteoroids and debris down to 1 μm sizes can be determined for spherical targets, for tumbling plates, or for oriented, planar surfaces which are controlled according to standard attitude steering laws. MASTER-99 is distributed by ESA/ESOC on a CD ROM which includes user documentation, and the necessary data files, executables, and GUI driven installation scripts for the most common operating systems and computer platforms. MASTER-99 is delivered together with PROOF-99, a program for radar and optical observation forecasting. Based on the MASTER-99 population larger than 1 mm, it predicts debris detections from ground-based or space-based sensors (radars or telescopes) of user-defined system performances.

Long-term collision risk prediction for low earth orbit satellite constellations

In the light of recent changes to planned Low Earth Orbit (LEO) satellite constellation designs and enhancements made to the DERA IDES model, we have conducted a new study on long-term debris environment evolution. This includes the collision interactions of constellation systems with the orbital debris environment over the next 50 years. In this new study, we use the IDES model to simulate long-term evolution in four ‘business as usual’ future traffic scenarios, which differ by the presence and absence of foreseen satellite constellation traffic and debris mitigation measures. The IDES model is capable of taking high spatial resolution snapshots of the debris flux environment at regular time intervals. By accessing these snapshots, the IDES model is able to predict the long-term variation of debris flux incident on a specific target orbit. This technique is harnessed to predict the average debris flux trends for a typical LEO constellation satellite. Furthermore, we estimate the average debris-induced satellite failure rates for a whole constellation system. Finally, we discuss our new findings on the long-term effects of constellations on the debris environment and vice versa.

A model of ablation-dominated medial moraines and the generation of debris-mantled glacier snouts

AbstractMedial moraines form striking dark stripes that widen non-linearly, steepen laterally and increase in relief down-glacier from the equilibrium line. Coalescence of these low-ablation-rate features can feed back strongly on the mass balance of a glacier snout. Ablation-dominated medial moraines originate from debris delivered to glacier margins, producing a debris-rich septum between tributary streams of ice below their confluence. Emergence of this ice below the equilibrium line delivers debris to the glacier surface, which then moves down local slopes of evolving morainal topography. A quantitative description of moraine evolution requires specification of the debris concentration field within the glacier, treatment of the melt-rate dependence on debris thickness, and characterization of processes that transport debris once it emerges onto the ice surface. Debris concentration at glacier tributary junctions scales with the erosion rates and the lengths of the tributary-valley walls, and inversely with the tributary ice speeds. Melt rate is damped exponentially by debris, with a ∼10 cm decay scale. Debris flux across the glacier surface scales with the product of debris thickness and local slope. Analytical and numerical results show that medial moraines should develop cross-glacier profiles with parabolic crests and linear slopes, and should widen with age and hence distance down-glacier. Debris should be both thin and uniform over the moraine. Observed faster-than-linear growth of moraine widths with distance reflects the increasing ablation rate down-glacier. Increase in medial moraine cover reduces the local average ablation rate, allowing the glacier to extend further down-valley than meteorology alone would suggest. This feedback is especially effective when moraines merge.

Collision Risk Mitigation in Geostationary Orbit

The short- and long-term effects of spacecraft explosions, as a function of the end-of-life re-orbit altitude above the geostationary orbit (GEO), were analyzed in terms of their additional contribution to the debris flux in the GEO ring. The simulated debris clouds were propagated for 72 yrs, taking into account all the relevant orbital perturbations.

Regional patterns of Pleistocene ice‐rafted debris flux in the North Pacific

IRD mass accumulation rate (MAR) records are presented for Deep Sea Drilling Project site 580 and Ocean Drilling Program sites 882 and 887 and are combined with results from previous IRD MAR studies to provide a synthesis of North Pacific Pleistocene ice rafting. Important regional differences in the ice rafting histories of the NW and NE Pacific are highlighted by this synthesis and include (1) significant variations in IRD fluxes across the North Pacific, which identify two major IRD sources, coastal Alaska and coastal Siberia/Kamchatka Peninsula, and (2) significant variations in the timing of IRD supply across the North Pacific, particularly in response to global‐scale climatic forcing. These regional differences indicate that local and regional controls on iceberg input, transport, and melting exert a major influence on ice rafting throughout the North Pacific. This suggests that a single generalized ice rafting record for the North Pacific does not adequately describe the complexity of this basin's Pleistocene history.Data used to calculate LSRs and IRD MARs for sites 380, 882, and 887 are available on diskette or via anonymous FTP from kosmos.agu.org, directory APEND (Usemame = anonymous, Password = guest). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009 or by phone at 800‐966‐2481; $15.00. Payment must accompany order.

A space based radar on a micro-satellite for in-situ detection of small orbital debris

The increase in the number of satellites in the Near Earth Orbit is exponential. The consequent increase in pollution of the orbital environment is of growing concern to the international community. There are currently only two observation systems available for measurement of orbital debris. Ground based radar and telescopes can detect objects larger than about 7 cm. Passive space based systems provide an accurate statistical estimation of flux for debris smaller than about 0.1 mm in size. Consequently, there is no way of obtaining information about debris in the millimeter-size range. Considering that the relative speed between objects in space is commonly in the km/s range, millimeter sized debris carry enough energy to be deadly to astronauts or to totally destroy the functioning of any satellite. Then National space agencies have recommended launching orbital spacecraft carrying debris detection experiments for gaining a better understanding of small debris. CNES (the French Space Agency) is developing a new family of micro-satellites, that will make possible to put into orbit a totally new system of radar that could measure in-situ flux of debris. We present results of this system analysis, which would cumulate the advantages of both ground-based radar and in orbit passive experiments. The proposed method for detection is quite original and allows the radar to act like a band-pass filter with respect to the debris diameter. The optimum frequency is shown to be in the Ka-band. Two points are critical in the definition of the radar: the average power available and the false alarm probability in the detection criterion. Therefore, we present a special receiver chain in order to optimize the signal-to-noise ratio. The estimate of the radial velocity through Doppler frequency measurement may be used to discriminate orbital debris from meteoroids. This system could be built today using an existing Continuous Wave amplifier. Several hundreds of objects per year could be detected yielding an accurate statistical estimation. The orbital debris radar would be a major contribution to our knowledge of millimeter sized debris. This experiment would contribute to making the current models more accurate at all inclinations. The micro-satellite concept would make the orbital debris radar mission cheap enough for considering a constellation of such satellites.

Meteoroids and small sized debris in low earth orbit and at 1 AU: Results of recent modelling

We present consolidated flux data from the Long Duration Exposure Facility (LDEF) and develop an isotropic meteoroid model applicable to predicting damage to the LDEF surfaces. The model is shown to work well, and is used to derive the resultant component of orbital debris incident on the LDEF east (ram) and west (wake) faces. Overall, orbital debris dominates the measured fluxes at small sizes (aluminium penetration depth F max < 30 μm) whereas meteoroids dominate above this size (see also McDonnell et al., 1997). The east and west face comparison shows that at least 2 distinct populations of debris exist with different size distributions. Analysis of data from the European Retrievable Carrier (EuReCa) shows the interplanetary meteoroid flux to be biased towards the Earth-apex direction (in the measured size regime). An enhanced meteoroid model is derived which is consistent with both EuReCa and LDEF data, and which does not affect the debris fluxes derived from LDEF data.

Assessing the Risk of Orbital Debris Impact

A Space Debris Impact Risk Analysis Tool (SDIRAT) was developed and implemented to assess the orbital debris impact risk on a specified target in Earth orbit, in terms of flux, relative velocity, impact velocity, direction of the incoming particles, debris mass and diameter. Based on a deterministic approach, SDIRAT uses a realistic orbital debris population where each representative particle is identified by its rectangular coordinates (position and velocity) at a reference epoch. Using this information, some geometrical algorithms were developed and implemented to evaluate the contribution of each particle to the incoming flux. The position of the particle with respect to a specified target drives the selection criteria to reject, or select, it as a possible projectile. On the other hand, the relative velocity vector can be used to estimate the impact direction of the incoming flux. SDIRAT was conceived as a general tool for a variety of scenarios, such as low circular and elliptical orbits, up to the geosynchronous ring. This paper presents some examples of possible applications, including the computation of the incoming debris flux on SAX (low Earth orbit), SIRIO (geosynchronous orbit) and the IRIS upper stage (elliptical orbit). Other applications assess the impact risk for the Soviet Radar Ocean Reconnaissance Satellites Cosmos 1900 and Cosmos 1932.

On the new latitude-dependent “average” model to study future debris environment

The AVERAGE model which was used by Su and Kessler (1985) adopted the latitude-averaged spatial density to study the evolution of the space debris environment. However, the latitudinal variation of the space debris density from explosion fragments of space objects at certain inclinations can produce spatial densities at some latitudes two-order of magnitude larger than that at other latitudes. Thus the AVERAGE model is now upgraded to include latitude-dependence of the space debris distribution. The latitudinal variation of the debris density from the current 1998 cataloged database is first obtained to compare with the fictitious debris flux counts observed by a ground radar with the same cataloged satellite database. The result indicates that the new AVERAGE model is in good agreement with the observation and is being implemented to study the future evolution of the orbital debris environment.

Secondary impact generated particles: Implications for the orbital debris population

Every time a debris or a meteoroid hits a part of a satellite in orbit, a great amount of secondary particles is ejected in the neighborhood of the impact site. This phenomenon is important for brittle materials, such as used for solar generators. The secondary particles that do not impact other parts of the spacecraft are added to the primary debris population and increase the small debris flux. We present an ejecta production model that gives the size and the velocity distribution of ejected particles as a function of primary impact parameters. We derive the parameters of all ejecta created during one orbital revolution of a satellite. An orbital evolution program is used to extrapolate the secondary debris position at later times. Preliminary results show that spall fragments ejected at low velocities remain in the vicinity of the parent satellite. The ejecta trajectories are similar and their inclination is very close to those of the parent satellite. Their orbital evolution depends mainly on the size of the debris and on the altitude of the parent body: the smallest particles in low earth orbit quickly reenter the earth atmosphere, while the largest spalls have a very slow decay. The antagonistic action of debris production and debris decay by drag leads to an equilibrium for particles within a given size range. Quantitative results on densities and fluxes compared to the primary debris population are presented for the peculiar case of heliosynchronous orbits.

Parametric Studies of Ablation and Venting from the Central Cavity of the HYLIFE-II Reactor

Gas dynamics in the heavy-ion inertial-fusion-energy power plant, HYLIFE-II, have been modeled using the code TSUNAMI. Simulations were run and results compared using both ideal-gas and the partial-ionization equations of state. Developed by Zeldovich and Raizer, the partial-ionization model approximates the Saha equation for multiply ionized species in a gas mixture. Results from a cylindrically symmetric simulation indicate an initial, low density, burst of high energy particles enters the final-focus transport beam line within 28 microseconds after the blast, much faster than the proposed 1 millisecond shutter closing time. After approximately 300 microseconds the chamber debris flux levels off to one eighth its peak value and maintains this level until the shutter closes. Uncertainty in IFE target design motivated the adjustment of two target parameters: target mass and the ratio of x-ray to debris kinetic energy. Although initial jet x-ray ablation is considered, neither secondary radiation nor condensation were modeled. Therefore results are conservative.

A rock glacier/debris‐covered glacier system at galena creek, absaroka mountains, wyoming

At Galena Creek, the ice/debris system has alternated between rock glacier and debris‐covered glacier modes due to changes in the size of the accumulation area. In the rock glacier mode, coarse debris is concentrated at the base of couloirs along the lower edge of a small, steep accumulation area where it becomes part of the surface debris mantle of the rock glacier. In the debris‐covered glacier mode, debris is primarily incorporated englacially within an expanded accumulation area. Englacial debris originating on the sides of the cirque is concentrated at the margins of the glacier; debris originating from the cirque headwall is concentrated where it emerges in the ablation area and forms a debris cover. As the equilibrium line rises during warm periods, the debris‐covered glacier is transformed into a rock glacier. The marginal englacial debris is exposed progressively up‐glacier resulting in ice‐cored debris ridges which extend into the cirque and are analogous to the ice‐cored lateral moraines of many subpolar alpine glaciers. The debris‐covered terminus continues to flow as a rock glacier lobe. The debris ridges/lateral moraines record previous positions of a debris‐covered glacier margin and can be used to map past accumulation areas and to infer the position of the associated glacier terminus. At least three of these features are cross‐cut by the rock glacier. Age estimates for three glacial advances are made using reasonable surface velocities and the distance between a rock glacier lobe and the inferred position of its associated glacier terminus. The estimated ages correlate with regional alpine glacier chronologies. These observations, which are not unique to the Absaroka Range, have general utility for understanding how changes in the relative flux of ice and debris control the morphology of the resulting deposits and for placing rock glacier deposits within alpine glacier chronologies.

Compositional Evolution of Saturn's Rings Due to Meteoroid Bombardment

In this paper we address the question of compositional evolution in planetary ring systems subsequent to meteoroid bombardment. The huge surface area to mass ratio of planetary rings ensures that this is an important process, even with current uncertainties on the meteoroid flux. We develop a new model which includes both direct deposition of extrinsic meteoritic “pollutants” and ballistic transport of the increasingly polluted ring material as impact ejecta. Our study includes detailed radiative transfer modeling of ring particle spectral reflectivities based on refractive indices of realistic constituents.Voyager data have shown that the lower optical depth regions in Saturn's rings (the C ring and Cassini division) havedarker and less redparticles than the optically thicker A and B rings. These coupled structural–compositional groupings have never been explained; we present and explore the hypothesis that global scale color and compositional differences in the main rings of Saturn arise naturally from extrinsic meteoroid bombardment of a ring system which was initially composed primarily, but not entirely, of water ice. We find that the regional color and albedo differences can be understood if all ring material was initially water ice colored by tiny amounts of intrinsic reddish, plausibly organic, absorber, which then evolved entirely by addition and redistribution of extrinsic, nearly neutrally colored, plausibly carbonaceous material. The regional compositional differences result from different susceptibilities to pollution of regions with very different surface mass density.We further demonstrate that the detailed radial profile of color across the abrupt B ring–C ring boundary can constrain key unknown parameters in the model. We carefully reanalyze and revise meteoroid flux estimates by975863and estimate the duration of the exposure to extrinsic meteoroid flux of this part of the rings, at least, to be on the order of 108years. This conclusion is easily extended by inference to the Cassini division and its surroundings as well. This geologically young “exposure age” is compatible with time scales estimated elsewhere based on the evolution of ring structure due to ballistic transport and also with other “short time scales” estimated on the grounds of gravitational torques. However, uncertainty in the flux of interplanetary debris and in the ejecta yield may preclude ruling out a ring age as old as the Solar System at this time.

Radiometrically determined sedimentary fluxes in the sub-polar North Atlantic during the last 140,000 years

We have examined the record of sediment input during the last 140 000 years in a deep-sea core from 49°27′N, 22°16′W in the eastern North Atlantic. Using uranium-series disequilibria to constrain time, we have calculated mass fluxes of total sediment, as well as mass and particle fluxes of major sedimentary components. Sediment accumulation rates were generally lower and relatively constant during broadly defined interglacial intervals, driven primarily by the burial of biogenic material. Accumulation rates were higher and more variable during glacial intervals, and were influenced primarily by terrigenous material. Peaks in bulk mass fluxes were associated with particular episodes (Heinrich events) within the last glacial and during each of the last two deglaciations. The flux of ice-rafted debris, as uniquely identified by coarse detrital fragments, was higher during layers representing each of the glacial Heinrich events, with modest increases during events H3 and H6, and dramatic increases during the others, confirming the widespread interpretation of these layers as episodes of enhanced iceberg delivery. The burial flux of foraminifera was markedly lower during each of the glacial Heinrich events, also confirming the original identification of these layers as barren intervals. Ice-rafting events within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site. Variations in the burial rates of non-carbonate sediments were largely responsible for overall changes in sediment accumulation throughout the last climate cycle. Ice-rafting was apparently an important delivery mechanism for this terrigenous material. The instantaneous chronometer established here for the last 140 000 years in the subpolar North Atlantic allows the transformation of existing and subsequent data from relative values to absolute burial fluxes.