The Michigan Orbital DEbris Survey Telescope (MODEST) is normally used to survey the geosynchronous orbit (GEO) environment to obtain a statistical assessment of the debris population. Due to the short time that the object is in the field-of-view (usually five minutes), it is common practice to assume a circular orbit when calculating the orbit from this limited observational arc. Some objects in the GEO regime are GEO-transfer orbit (GTO) objects which are observed at their apogee or objects with varying eccentricities such as those with high area-to-mass ratios. For these objects, an assumed circular orbit (ACO) prediction would not be accurate. After MODEST was modernized in March 2005 and brought under computer control, it became possible to use the telescope in modes other than tracking at the sidereal rate. Three data runs were conducted to test the orbit determination program, the ability to transfer data effectively between site locations, and to determine if objects could be re-acquired with this method. We report in this paper our initial efforts to determine full orbits based on follow-up observations after the initial detection in survey mode. Our long-term goal is to construct a system which can detect and follow-up an object in any orbit at GEO. This paper reports our first steps towards that goal. During the three data collections, only circular orbit objects were obtained. Although this allowed for testing of the process, further tests must be conducted in an effort to target GTO and high area-to-mass objects.

This paper presents laboratory measurements and analysis of optical spectral bidirectional reflectance distribution functions of materials commonly found on the surfaces of spacecraft. A goniospectrometer sensitive to light with wavelengths between 350 and 1100 nm was constructed, and four classes of materials were studied in a variety of illumination and observational geometries: triple-junction photovoltaic cells, aluminum, white-coated metallic surface, and aluminized polyimide films. The measurements were analyzed to study how specific materials could be characterized based on their spectral bidirectional reflectance distribution function and how it varies with changing illumination and observational geometry. In the end, the experiment yielded two significant outcomes. First, the results provide a better understanding of how the spectral energy distribution of light reflected from these materials behaves as the illumination and observational geometry is varied. This result will be particularly useful in the interpretation of spectra and color photometric measurements of artificial objects in Earth orbit. Second, and more important, this experiment convincingly demonstrates that any spectral library of materials commonly found on spacecraft must include measurements taken throughout the widest range of observational geometries. With this in mind, the measurements collected during this experiment now serve as the first entries in an open-access spectral library of spacecraft material.

The Michigan Orbital DEbris Survey Telescope (MODEST) is normally used to survey the geosynchronous orbit (GEO) environment to obtain a statistical assessment of the debris population. Due to the short time that the object is in the field-of-view (usually five minutes), it is common practice to assume a circular orbit when calculating the orbit from this limited observational arc. Some objects in the GEO regime are GEO-transfer orbit (GTO) objects which are observed at their apogee or objects with varying eccentricities such as those with high area-to-mass ratios. For these objects, an assumed circular orbit (ACO) prediction would not be accurate. After MODEST was modernized in March 2005 and brought under computer control, it became possible to use the telescope in modes other than tracking at the sidereal rate. Three data runs were conducted to test the orbit determination program, the ability to transfer data effectively between site locations, and to determine if objects could be re-acquired with this method. We report in this paper our initial efforts to determine full orbits based on follow-up observations after the initial detection in survey mode. Our long-term goal is to construct a system which can detect and follow-up an object in any orbit at GEO. This paper reports our first steps towards that goal. During the three data collections, only circular orbit objects were obtained. Although this allowed for testing of the process, further tests must be conducted in an effort to target GTO and high area-to-mass objects.

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NASA's Orbital Debris measurements program has a goal to characterize the small debris environment in the geosynchronous orbit (GEO) region using optical telescopes ("small" refers to objects too small to catalog and track with current operational systems). Traditionally, observations of GEO and near-GEO objects involve following the object with the telescope long enough to obtain an orbit suitable for tracking purposes. Telescopes operating in survey mode, however, randomly observe objects that pass through their field-of-view. Typically, these short-arc observation are inadequate to obtain detailed orbits, but can be used to estimate approximate circular orbit elements (semi-major axis, inclination, and ascending node). From this information, it should be possible to make statistical inferences about the orbital distributions of the GEO population bright enough to be observed by the system. The Michigan Orbital Debris Survey Telescope (MODEST) has been making such statistical surveys of the GEO region for five years. During that time, the telescope has made sufficient observations in enough areas of the GEO belt to have achieved nearly complete coverage. That means that almost all objects in all possible orbits in the GEO and near-GEO region had a non-zero chance of being observed. Some regions (such as those near zero inclination) have had good coverage, while others are poorly covered. Nevertheless, it is possible to remove these statistical biases and reconstruct the orbit populations within the limits of sampling error. In this paper, these statistical techniques and assumptions are described, and the techniques are applied to the current MODEST data set to arrive at our best estimate of the GEO orbit population distribution.