Analysis on Determining Warning Threshold of Space Objects

Collision Probability with Gaussian Mixture Orbit Uncertainty

A new approximation is proposed for calculating the first flight collision probabilities in cluster-type fuel lattices, based on the subcell model. In this method the unit cluster is divided into subregions of fuel pins (with or without cladding) arranged in rings, associated coolant, and homogeneous annular regions surrounding the fuel region. The fuel pins and associated coolant are treated separately, and each is distinguished ringwise as a different subregion. The collision probability is then calculated for a neutron proceeding from one subregion to another. The method treats rigorously the fuel annulus where a neutron starts with consideration given to the non-uniform structure of the annulus. The other fuel annuli, however, are treated approximately as if each annulus were homogeneous. The values of the homogenized cross sections of the annuli are determined in such manner that the number of outgoing neutrons from the homogenized annuli equals that from the actual non-uniform fuel annuli. The colli...

Collision probability calculation is critical to space situational awareness or space traffic management. To determine the collision probability, the conjunction time needs to be determined first, but both collision probability and conjunction time usually exist large uncertainties. In this paper, a continuous representation of the polynomial chaos expansion (PCE)-based surrogate model is used to describe the uncertainty of space objects along with time. This PCE model facilitates the propagation of sampling points representing orbital uncertainty at any time. A machine learning-based Bayesian optimization method is employed to determine the conjunction time and then the collision probability. A data-driven Gaussian process regression model is built to approximate the Hausdorff distance, which is a distance metric between two space objects with uncertainty and is used as an objective function for Bayesian optimization. The proposed PCE model and Bayesian optimization do not require the Gaussian assumption and provide a general framework to calculate the conjunction time and collision probability. Two numerical experiments are used to show the effectiveness of the proposed algorithm and its close performance to the traditional Monte Carlo sampling-based method.

The feasibility of a radar instrument working at 95 GHz placed on ISS (International Space Station) to detect very small debris has been investigated and analyzed in this paper. First of all a study about the debris population around the ISS orbit has been taken under consideration by analyzing the debris flux and by determining the preliminary design and mission parameters for Warden instrument, as for instance the pointing angle of the antenna reflector. A technology survey has been also performed to individuate the state of the art in the millimeter wave frequencies band, with particular reference to the transmitter, the front-end, the master oscillator and for A/D converters and DSPs (Digital Signal Processors) suitable for space. The proposed solution for the ISS on board experiment was basically composed of two segments: the on-orbit segment, that is the payload and the ground segment. The on-orbit segment deals with a radar sensor working at 95 GHz which represents a good trade-off between satisfying the limited power consumption available on ISS ExPA (Express Pallet) adapter and having significant range and detection performance necessary for the success of the overall mission, with particular reference to the scientific results. In the overall radar system design major emphasis has been given mainly to the weights, the overall dimensions, and to the EMC problems due to the simultaneous presence of other experiments on the same ExPA. Once fixed the transmitted power, the pulse length and the probability of detection different performances in range are predicting depending on the dimension of the debris and on the approaching speed. For example a detection range (90% PD) of about 180 Km is predicted for a debris of 50 cm running at a relative speed of 10 Km/sec (F=95 GHz, 1 m Cassegrain monopulse antenna, 1000W peak power, 40 /spl mu/sec pulse length, 2.5-100 KHz staggered p.r.f.) Concerning the ground segment, a preliminary architecture has been proposed based upon the extensive use of existing infrastructures and facilities and including a WARDEN control system mainly for all concerns on board payload support, a mission control facility for the general planning of the ground and space resources, and a debris data processing devoted to perform all the activities relevant to the supply of products and services based on payload according to user request. In conclusion the proposed Warden experiment offers several opportunities both in technological field by giving the possibility to verify the sue of millimeter waves components in space environment helpful for future ESA components qualification plan, and in scientific field to validate the concept of a future stand-alone flying on-orbit space-based radar devoted to the detection of very small debris population (0.5 /spl divide/ 1 cm as diameter).

Space environmental effects on materials are very severe and complex because of the synergistic interaction of orbital environments such as high-energy radiation particles, atomic oxygen, micrometeoroids, orbital debris, and ultraviolet irradiation interacting synergistically, along with thermal exposure. In addition, surface degradation associated with contamination can negatively impact optics performance. Materials flight experiments are critical to understanding the engineering performance of materials exposed to specific space environments. Likewise, the spacecraft designer must have an understanding of the specific environment in which a spacecraft will operate, enabling appropriate selection of materials to maximize engineering performance, increase mission lifetimes, and reduce risk. This article will present a methodology for assessing the engineering performance of materials baselined for a specific spacecraft or mission. In addition, an overview of the space environment, from low Earth orbit to interplanetary space, will be provided along with an overview on the effects of the space environment on materials performance. The majority of this article is devoted to materials flight experiments from the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA), and from the National Aeronautics and Space Administration (NASA). Some of the experiments reviewed include ESA's Materials Exposure and Degradation Experiment on the International Space Station (ISS), JAXA's Micro-Particles Capturer and Space Environment Exposure Device experiments on the ISS Service Module and on the ISS Japanese Experiment Module Exposed Facility, and NASA's Long Duration Exposure Facility satellite and the Materials International Space Station Experiment series flown on the exterior of ISS.

In this paper, a discontinuous Bubnov-Galerkin isogeometric analysis discrete ordinate (DBG-IGA-SN) form of the subgroup projection and resonance spectrum expansion (RSE) methods within the DRAGON5 code is presented. The DBG-IGA-SN method uses non-uniform rational B-spline (NURBS) basis functions to spatially discretize the neutron transport equation. The NURBS basis functions, which are used to represent both the solution field and the geometry, are able to exactly represent pin cell geometries even on the coarsest spatial representation. This is not possible with traditional Lagrangian finite elements. This is the first instance of a DBG-IGA-SN discretization of the RSE method. We compared the numerical accuracy of the DBG-IGA-SN method to the existing collision probability (CP) method within DRAGON5 against Serpent and CP ultrafine-group reference solutions for a series of uranium-oxide and mixed-oxide Rowlands pins. In DRAGON5, the CP method is frequently used for resonance self-shielding calculations. We use it in this work as a deterministic method standard for comparison to assess DBG-IGA-SN performance. We found that our implementation of the DBG-IGA-SN method achieved similar numerical accuracy compared to the CP method overall. The infinite multiplication factor errors were no greater than 107 pcm for the uranium-oxide cases and 152 pcm for the mixed-oxide cases with a Serpent reference, with a variation of about 10 pcm between DBG-IGA-SN and CP. For the CP ultrafine-group method reference cases, the infinite multiplication factor errors did not surpass 108 pcm and 127 pcm for the uranium-oxide and mixed-oxide cases, respectively. In addition, DBG-IGA-SN had lower infinite multiplication factor numerical errors than CP in all cases, in one case by 21 pcm. We also found that the RSE method had higher errors in the multiplication factors and reaction rates than the subgroup projection method for both the uranium-oxide and mixed-oxide cases when using the CP ultrafine-group method reference. Future work will investigate the relative performance of the DBG-IGA-SN for larger, more complex cases, where strengths of the method, such as its scalability and ability to model exact geometries and anisotropic scatter, may make it desirable for production resonance self-shielding calculations.

Collision probability is one of the most important factors relating to the productivity of a manufacturing line, and focused investigation of collision probability has recently been taking place. There are two areas of collision probability studies: theoretical studies, which focus on the analysis of collision probability, and algorithmic studies, which focus on the computation of collision probability using simulation. The results of theoretical studies so far have been somewhat limited in comparison to the results of their algorithmic counterparts. Recently, a computation method for collision probability in a series-parallel machines model was presented. In this paper, we present a new method for computing collision probability in the series-parallel machines model. The previous method includes a sorting procedure, and this sorting procedure has an influence on the time complexity of the previous method. On the other hand, the proposed method utilizes a priority queue, and does not require a sorting procedure. Consequently, we offer an efficient method to compute collision probability in the series-parallel machines model. Moreover, we carry out computational experimentation in order to show that our method is actually fast. We also show the computational results relating to an optimal machine allocation.

The presence in space of micrometeoroids and orbital debris, particularly in the lower Earth orbit, presents a continuous hazard to orbiting satellites, spacecraft and the International Space Station. Space debris includes all nonfunctional man-made objects and fragments in Earth orbit. As the amount of debris continues to grow, the probability of collisions that could lead to potential damage will consequently increase. In this book chapter, the feasibility of self-healing of impacted composites in space is discussed.

The International Space Station (ISS) provides a unique opportunity for demonstrating instrument and other technologies in the space environment. The ISS orbits the Earth at about 370 km altitude and 51.6o inclination. Its ground track passes over about 90% of the Earth’s population and scientifically interesting surface features. At assembly complete, the ISS can externally accommodate experiments at eight locations on the U.S. Truss. Another ten experiments can be accommodated on the Kibo Japanese Experiments Module Exposed Facility (JEF) of which the U.S. is allocated five sites. The European Columbus Orbital Facility can also accommodate four unpressurized experiments with two allocated for U.S. research use. These locations provide excellent views of either Earth (nadir-mounted orientation) or space (zenith-mounted orientation). This paper will address potential applications of ISS as a platform for demonstrating technologies for future Earth and space science missions.

The decision for the International Space Station (ISS) to maneuver to avoid a potential collision with another space object will be based on the probability of collision, P C. The calculation of P C requires the covariance of both objects at conjunction. It is well known that the covariance computed by US Space Command is optimistic (too small), especially at altitudes where atmospheric drag is the dominant perturbation, because its computation assumes there are no dynamic model errors. In this paper the effect of errors in the covariance on P C and the sensitivity of P C to the encounter geometry are investigated.

Comparison of dose and risk estimates between ISS Partner Agencies for a 30-day lunar mission

To estimate the space radiation risks for the future planned Mars missions, the radiation fields in the spacecraft and in the habitats on Mars must be fully known. For radiation risk estimations, benchmarking and improving particle and ion transport codes which are currently used for space radiation and shielding calculations, radiation detection and monitoring of the space radiation field as a function of the solar activity, the orbital parameters and the different shielding configurations of the International Space Station (ISS) have been performed and are still ongoing. There are also many ongoing measurements of the spatial and temporal distribution of the radiation field at the ISS. In addition to the measurements at the ISS, important information about radiation environment in deep space was achieved with the Mars Science Laboratory (MSL) spacecraft, containing the Curiosity rover, which was launched to Mars on 26 November 2011, and traveled for 253 days, 560 million kilometers to Mars. The Radiation Assessment Detector (RAD) on the spacecraft showed that the dose equivalent for even the shortest round-trip Earth-Mars journeys, with current propulsion systems and current available shielding, is 0.7 +/- 0.1 Sv, depending on the solar cycle and duration of the mission. Although the dose rate on the surface of Mars is lower than in deep space, measurements with RAD showed that an astronaut would still get around 40% of the dose rate in deep space. If the astronauts are exposed to large Solar Particle Events (SPEs), the dose can reach lethal doses. Effective countermeasures should therefore be developed before performing a manned mission to Mars. The use of human phantoms in space that simulate an astronaut's body, has provided detailed information of the depth-dose distributions, and radiation quality, inside the human body in space. This information is essential for developing more accurate space radiation transport and risk models to be used for evaluating short and long-term radiation risks in deep space and on Mars. Although reports state that background radiation in some high background radiation areas approaches that of the Martian surface, new estimates show that the maximum annual radiation dose in these areas can be much higher than that of the Martian surface. Given this consideration, study of the health effects of exposure to high levels of natural radiation can help scientist better evaluate the risk of radiation in deep space manned missions. This paper presents a short review of some important published space dosimetry and phantom experiments, and discusses some recently proposed counter measures to reduce the health risks of the astronauts on deep space missions.

This study investigates the performance and molecular stability of ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced hydrogen-rich polybenzoxazine composites exposed to the space environment on the International Space Station (ISS). The composite is designed specifically for spacecraft applications requiring lightweight radiation shielding against galactic cosmic rays and solar particle events. Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), dynamic mechanical analysis (DMA), and short beam shear testing were used to evaluate both surface degradation and bulk property retention. Chemical degradation due to direct sunlight exposure is limited to the uppermost 30 nm of the composite surface, with formation of hydroxyl and carbonyl groups. No significant changes in the glass transition temperature (T g), short beam shear strength, or density are observed between space-exposed and control samples. Thermoluminescence dosimetry data indicated significant attenuation of incident radiation. This study confirms the potential of the UHMWPE composite material for use as a multifunctional structure and radiation shield for extended space missions. Graphical Abstract

The set of materials interactions with the space flight environment that have produced the largest impacts on the verification and acceptance of flight hardware and on flight operations of the International Space Station (ISS) Program during the May 2000 to May 2002 time frame are described in this paper. In-flight data, flight crew observations, and the results of ground-based test and analysis directly supporting programmatic and operational decision-making are reported.

Stepping stones toward global space exploration