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Abstract: The intentional break-up of the Fengyun-1C spacecraft on 11 January 2007 via a hypervelocity collision with a ballistic object created the most severe artificial debris cloud in Earth orbit since the beginning of space exploration. More than 2000 debris of the order of 10cm or greater in size have been identified by the US Space Surveillance Network. The majority of these debris reside in long-lived orbits. The NASA Orbital Debris Program Office has conducted a thorough examination of the nature of the Fengyun-1C debris cloud, using Space Surveillance Network (SSN) data for larger debris and special Haystack radar observations for smaller debris. These data have been compared with the NASA standard satellite break-up model for collisions, and the results are presented in this paper. The orbital longevity of the debris have also been evaluated for both small and large debris. The consequent long-term spatial density effects on the low Earth orbit regime and the potential effect of the debris cloud on the growth of the near-Earth satellite population have been addressed. [Copyright &y& Elsevier]

A number of optical instruments are involved in making systematic surveys of the geosynchronous Earth orbit (GEO) region. Because of the limited field of view of an optical instrument, it is impossible at any one time to observe objects in all orbit planes in the region. Therefore, the orbit distributions seen are biased relative to the true populations of orbits in space. Because the observations represent a statistical sample of the population, statistical variations must be accounted for. The full procedure to remove the biases is extremely difficult with the limited orbit data measured because objects in GEO can have a wide spectrum of possible orbits. The measurements themselves are often insufficient to distinguish whether the object is in an elliptical or circular orbit. However, by limiting the range of possible orbit types it is possible to simplify the problem and obtain reasonable orbit distribution estimates. These distributions can in turn be used to identify interesting groupings of objects that may be part of an unrecognized breakup event. This paper describes the methods used to remove observational biases, and presents estimates of orbit distributions of uncatalogued objects at GEO visible to the instruments. [Copyright &y& Elsevier]

Abstract: The growing need for real-time impact sensors for deployment on both space vehicles and space habitats (in orbit or on the surface of atmosphere-less bodies such as the Moon) has stimulated sensor development programmes. The sensors should be low mass, low power, easily read-out electronically, cover large areas and be sensitive to impacts which can cause damage up to and including penetration. We propose that piezo-strain acoustic sensors can play an important role in this work. Accordingly we report on a series of hypervelocity impact tests of acoustic sensors mounted on thin plates (aluminium and Duroid plates). The acoustic sensors gave strong signals for impacts of sub mm–mm scale projectiles. We investigated dependences on impactor speed and size, angle of incidence and tested the difference between cratering and penetrating impacts. [Copyright &y& Elsevier]

Abstract: This paper summarizes three micro-satellite impact tests completed in early 2007 through collaboration between Kyushu University and the NASA Orbital Debris Program Office. The previous experiments completed in late 2005 aimed to compare low- and hypervelocity impacts on identical target micro-satellites, whereas the new tests used larger micro-satellites as targets and aimed to investigate the effects of impact directions. Three identical micro-satellites equipped with fully functional electronic devices were prepared as targets. Their dimensions were 20cm by 20cm by 20cm, and the mass of each was approximately 1.3kg. Aluminum alloy solid spheres, with a diameter of 3cm and a mass of 39g, were prepared as projectiles. The impact velocity was approximately 1.7km/s. The impact tests were carried out using the two-stage light gas gun at the Kyushu Institute of Technology. All target micro-satellites were completely fragmented, but there were noticeable differences among the three sets of fragments due to the different impact directions. More than 1000 fragments from each test were collected, measured, photographed, and documented with material descriptions. Preliminary results of the new data and comparisons with the previous data will be presented in the paper. [Copyright &y& Elsevier]

Results will be presented from a new NASA optical survey of objects at geosynchronous orbit (GEO). The goal is to determine the total population of debris objects at GEO to as small a limiting size as possible. This survey uses the University of Michigan''s 0.6/0.9 m Schmidt telescope Michigan Orbital Debris Survey Telescope (MODEST). Located at Cerro Tololo Inter-American Observatory in Chile, the system is equipped with a scanning CCD with a field of view of 1.3° × 1.3°, and can detect objects smaller than 20 cm diameter at GEO. Each night the telescope scans a strip of sky 100° long × 1.3° high. Up to eight independent detections are made of each candidate GEO object in a 5 min time span, yielding measurements of brightness, position, and angular motion. Since February 2001, an extensive series of observations of the GEO regime has been carried out with this system, revealing a considerable population of objects smaller than 1 m in diameter. [Copyright &y& Elsevier]

MIT Lincoln Laboratory has conducted a measurement program for man-made orbital debris since 1991 in response to NASA''s need to characterize the orbital debris population and facilitate manned spaceflight activities. The primary sensors used in that effort are the Haystack and Haystack auxiliary (HAX) radars located at the Lincoln space surveillance complex (LSSC) in Westford, Massachusetts. This paper will describe the results from a new effort conducted at LSSC, the objective of which is to assess the variability in NASA''s current procedure for determination of size from radar data. RCS data have been acquired on 39 NASA-selected resident space objects (RSO). Results are also compared to the size estimates from the FPS-85 radar, an asset of the Space Surveillance Network. [Copyright &y& Elsevier]

Currently, certain physical properties, such as material type and albedo, of orbital debris are assumed when used to determine the size of the objects. A study to ascertain whether or not the assumed values are valid has begun using reflectance spectroscopy as a means of determining the material type of the object. What appears to some as a squiggly line is actually the reflectance of sunlight from the object. By comparing the location, depth, and width of the absorption features on the squiggly lines, the material type of the debris object is identified. Once the material type is known, the albedo of the object can be determined. This paper discusses the results from observations of large rocket bodies and satellites in both lower and geosynchronous Earth orbits (LEO and GEO, respectively) taken at the air force maui optical and supercomputing (AMOS) site located in Maui, Hawaii. Using the 1.6-m telescope and a spectral range of 0.3–0.9 μm, differences between rocket bodies of different types and launch dates, as well as satellites of different types and launch dates are determined. Variations seen in the squiggle lines are due to colors of paint, space weathering, and for the satellites, orientation and size of the solar panels. Future direction of the project will be discussed as well as plans for future observations. [Copyright &y& Elsevier]