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NASA NTRS1991

Methodology for object-oriented real-time systems analysis and design: Software engineering

Successful application of software engineering methodologies requires an integrated analysis and design life-cycle in which the various phases flow smoothly 'seamlessly' from analysis through design to implementation. Furthermore, different analysis methodologies often lead to different structuring of the system so that the transition from analysis to design may be awkward depending on the design methodology to be used. This is especially important when object-oriented programming is to be used for implementation when the original specification and perhaps high-level design is non-object oriented. Two approaches to real-time systems analysis which can lead to an object-oriented design are contrasted: (1) modeling the system using structured analysis with real-time extensions which emphasizes data and control flows followed by the abstraction of objects where the operations or methods of the objects correspond to processes in the data flow diagrams and then design in terms of these objects; and (2) modeling the system from the beginning as a set of naturally occurring concurrent entities (objects) each having its own time-behavior defined by a set of states and state-transition rules and seamlessly transforming the analysis models into high-level design models. A new concept of a 'real-time systems-analysis object' is introduced and becomes the basic building block of a series of seamlessly-connected models which progress from the object-oriented real-time systems analysis and design system analysis logical models through the physical architectural models and the high-level design stages. The methodology is appropriate to the overall specification including hardware and software modules. In software modules, the systems analysis objects are transformed into software objects.

Schoeffler, James D.↗
NASA NTRS1992

Fault-tolerant wait-free shared objects

A concurrent system consists of processes and shared objects. Previous research focused on the problem of tolerating process failure. We study the complementary problem of tolerating failures. We divide object failures into two broad classes: responsive and non-responsive. With responsive failures, a faulty object responds to every invocation, but responses may be incorrect. With non-responsive failures, a faulty object may also 'hang' without responding. For each class, we consider crash, and arbitrary types of failures. For each type of failure, we are seeking a universal implementation for fault-tolerant wait-free shared objects. We present (deterministic) implementations for all types of responsive failures, including arbitrary failures. In contrast, we show that even the most benign type of non-responsive failures requires the use of randomization. Of special interest is the problem of implementing fault-tolerant objects using only objects of the same type. We present such fault-tolerant self-implementations for many common object types. Graceful degradation is a desirable property of fault-tolerant implementations: the implemented object never fails more severely than the base objects it is derived from, even if all the base objects fail. For several failure models, we show whether this property can be achieved, and, if so, how. In addition to the above possibility/impossibility results, we also consider the resources complexity of fault-tolerant implementations. In many cases, we present lower bounds and give matching algorithms.

Jayanti, Prasad↗
NASA NTRS1998

An Object-Oriented Interface to the CCSDS Ground Telecommand Services

The Telecommand Data Routing and Channel Services defined by the Consultative Committee for Space Data Systems (CCSDS) are flexible enough to support a myriad of commanding models. Because the standard is so broad, the traditional approach has been to implement only the portion of the standard needed by the particular spacecraft being tested/operated. Tasked with providing Telecommand Services for an entire class of spacecraft, where each spacecraft may choose any valid CCSDS commanding model, NASA Code 584 designed a common architecture capable of handling the full CCSDS protocol. The solution uses another CCSDS standard - the Standard Formatted Data Unit (SFDU) as the interface to the Telecommand Services. SFDUs provide a consistent way of labelling data objects, as well as allowing data objects to encapsulate other data objects. The resulting interface is: - Flexible: The full Data Routing and Channel Services are available via a single interface. The client (i.e. the command source) may enter commands at any layer within the protocol stack, specify any of the data aggregation or segmentation methods, and dynamically set any configuration parameter defined in the standard. - Object-oriented: Each object specifies both the data and the actions to be performed with the data. An object may contain other objects. - Expandable: New capabilities are added by defining new objects. Objects pass thru the protocol layers until they reach the applicable layer. The resulting design is: - Modular: The logic for each protocol layer is contained in a separate Application Program Interface (API). The objects used for the external interface are also used for communication between layers. - Distributable: The design can be split along any layer boundary for distribution across multiple machines. The objects ensure data consistency across platforms. This paper describes the SFDU-based interface and the resulting protocol implementation. The implementation is currently used by NASA (National Aeronautics and Space Administration) for integration & test of the microwave Anisotropy Probe (MAP) and Earth observer-I (EO-l) spacecraft. It will be used for post-launch operations of these spacecraft as well as the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft.

Ray, Timothy Joseph↗
NASA NTRS1985

Optical and radio properties of X-ray selected BL Lacertae objects

The eight BL Lac objects from the HEAO 1 A-2 all-sky survey and from the Einstein medium-sensitivity survey (MSS) form a flux-limited complete X-ray selected sample. The optical and radio properties of the MSS BL Lac objects are presented and compared with those of the HEAO 1 A-2 sample and with those of radio-selected BL Lac objects. The X-ray selected BL Lac objects possess smaller polarized fractions and less violent optical variability than radio-selected BL Lac objects. These properties are consistent with the substantial starlight fraction seen in the optical spectra of a majority of these objects. This starlight allows a determination of definite redshifts for two of four MSS BL Lac objects and a probable redshift for a third. These redshifts are 0.2, 0.3, and 0.6. Despite the differences in characteristics between the X-ray selected and radio-selected samples, it is concluded that these eight objects possess most of the basic qualities of BL Lac objects and should be considered members of that class. Moreover, as a class, these X-ray selected objects have the largest ratio of X-ray to optical flux of any active galactic nuclei yet discovered.

Stocke, J. T.↗
NASA NTRS1989

Robot Acting on Moving Bodies (RAMBO): Interaction with tumbling objects

Interaction with tumbling objects will become more common as human activities in space expand. Attempting to interact with a large complex object translating and rotating in space, a human operator using only his visual and mental capacities may not be able to estimate the object motion, plan actions or control those actions. A robot system (RAMBO) equipped with a camera, which, given a sequence of simple tasks, can perform these tasks on a tumbling object, is being developed. RAMBO is given a complete geometric model of the object. A low level vision module extracts and groups characteristic features in images of the object. The positions of the object are determined in a sequence of images, and a motion estimate of the object is obtained. This motion estimate is used to plan trajectories of the robot tool to relative locations rearby the object sufficient for achieving the tasks. More specifically, low level vision uses parallel algorithms for image enhancement by symmetric nearest neighbor filtering, edge detection by local gradient operators, and corner extraction by sector filtering. The object pose estimation is a Hough transform method accumulating position hypotheses obtained by matching triples of image features (corners) to triples of model features. To maximize computing speed, the estimate of the position in space of a triple of features is obtained by decomposing its perspective view into a product of rotations and a scaled orthographic projection. This allows use of 2-D lookup tables at each stage of the decomposition. The position hypotheses for each possible match of model feature triples and image feature triples are calculated in parallel. Trajectory planning combines heuristic and dynamic programming techniques. Then trajectories are created using dynamic interpolations between initial and goal trajectories. All the parallel algorithms run on a Connection Machine CM-2 with 16K processors.

Davis, Larry S.↗
NASA NTRS2002

Formation and Migration of Trans-Neptunian Objects

We consider that trans-Neptunian objects (TNOs) with diameter d greater than 100 kilometers moving now in not very eccentric orbits could be formed directly by the compression of large rarefied dust condensations (with a greater than 30 AU), but not by the accretion of smaller solid planetesimals. Probably, some planetesimals with d approximately 100- 1000 kilometers in the feeding zone of the giant planets and even large main-belt asteroids also could be formed directly by such compression. Some smaller objects (TNOs, planetesimals, asteroids) could be debris of larger objects, and other such objects could be formed directly by compression of condensations. A small portion of planetesimals from the feeding zone of the giant planets that entered into the trans-Neptunian region could left in eccentrical orbits beyond Neptune and became so called "scattered objects". Our computer runs in which gravitational interactions of bodies were taken into account with the use of the spheres method, showed that the embryos of Uranus and Neptune could increase their semimajor axes from less than 10 AU to their present values, moving permanently in orbits with small eccentricities, due to gravitational interactions with the migrating planetesimals. Later on, Thommes et al. considered a similar model using direct numerical integration. The total amount of water delivered to the Earth during the formation of the giant, planets was about the mass of water in the Earth oceans. The end of such bombardment could be caused mainly by the planetesimals that became scattered objects. For the present mass of the trans-Neptunian belt, the collisional lifetime of 1-kilometer TNO is about the age of the Solar system, but only a small portion (less than 1%) of 100-km TNOs could be destroyed during this age. The probability of destruction of a typical TNO (with 30 less than a,less than 50 AU) by scattered objects can be of the same order of magnitude as that by typical TNOs. TNOs could be even more often destroyed during planet formation than during last 4 Gyr. The analysis of the results of the orbital evolution of Jupiter-crossing objects (JCOs) and TNOs showed that, in principle, the trans-Neptunian belt can provide up to 100% of Earth-crossing objects, but, of course, some of them came from the main asteroid belt. Most of the collisions of former JCOs with the Earth were from orbits with aphelia inside Jupiter's orbit and belonged to a small portion of objects which moved in such orbits for a long time. About 1 of 300 JCOs collided with the Sun. The ratio of the total mass of icy planetesimals that migrated from the feeding zone of the giant planets and collided with the planet to the mass of this planet was greater (by a factor of 3 in our runs) for Mars than that for Earth and Venus.

Ipatov, S. I.↗
NASA NTRS2009

Adaptive Morphological Feature-Based Object Classifier for a Color Imaging System

Utilizing a Compact Color Microscope Imaging System (CCMIS), a unique algorithm has been developed that combines human intelligence along with machine vision techniques to produce an autonomous microscope tool for biomedical, industrial, and space applications. This technique is based on an adaptive, morphological, feature-based mapping function comprising 24 mutually inclusive feature metrics that are used to determine the metrics for complex cell/objects derived from color image analysis. Some of the features include: Area (total numbers of non-background pixels inside and including the perimeter), Bounding Box (smallest rectangle that bounds and object), centerX (x-coordinate of intensity-weighted, center-of-mass of an entire object or multi-object blob), centerY (y-coordinate of intensity-weighted, center-of-mass, of an entire object or multi-object blob), Circumference (a measure of circumference that takes into account whether neighboring pixels are diagonal, which is a longer distance than horizontally or vertically joined pixels), . Elongation (measure of particle elongation given as a number between 0 and 1. If equal to 1, the particle bounding box is square. As the elongation decreases from 1, the particle becomes more elongated), . Ext_vector (extremal vector), . Major Axis (the length of a major axis of a smallest ellipse encompassing an object), . Minor Axis (the length of a minor axis of a smallest ellipse encompassing an object), . Partial (indicates if the particle extends beyond the field of view), . Perimeter Points (points that make up a particle perimeter), . Roundness [(4(pi) x area)/perimeter(squared)) the result is a measure of object roundness, or compactness, given as a value between 0 and 1. The greater the ratio, the rounder the object.], . Thin in center (determines if an object becomes thin in the center, (figure-eight-shaped), . Theta (orientation of the major axis), . Smoothness and color metrics for each component (red, green, blue) the minimum, maximum, average, and standard deviation within the particle are tracked. These metrics can be used for autonomous analysis of color images from a microscope, video camera, or digital, still image. It can also automatically identify tumor morphology of stained images and has been used to detect stained cell phenomena (see figure).

McDowell, Mark↗
NASA NTRS2015

An Upper Bound on Orbital Debris Collision Probability When Only One Object has Position Uncertainty Information

Upper bounds on high speed satellite collision probability, P (sub c), have been investigated. Previous methods assume an individual position error covariance matrix is available for each object. The two matrices being combined into a single, relative position error covariance matrix. Components of the combined error covariance are then varied to obtain a maximum P (sub c). If error covariance information for only one of the two objects was available, either some default shape has been used or nothing could be done. An alternative is presented that uses the known covariance information along with a critical value of the missing covariance to obtain an approximate but useful P (sub c) upper bound. There are various avenues along which an upper bound on the high speed satellite collision probability has been pursued. Typically, for the collision plane representation of the high speed collision probability problem, the predicted miss position in the collision plane is assumed fixed. Then the shape (aspect ratio of ellipse), the size (scaling of standard deviations) or the orientation (rotation of ellipse principal axes) of the combined position error ellipse is varied to obtain a maximum P (sub c). Regardless as to the exact details of the approach, previously presented methods all assume that an individual position error covariance matrix is available for each object and the two are combined into a single, relative position error covariance matrix. This combined position error covariance matrix is then modified according to the chosen scheme to arrive at a maximum P (sub c). But what if error covariance information for one of the two objects is not available? When error covariance information for one of the objects is not available the analyst has commonly defaulted to the situation in which only the relative miss position and velocity are known without any corresponding state error covariance information. The various usual methods of finding a maximum P (sub c) do no good because the analyst defaults to no knowledge of the combined, relative position error covariance matrix. It is reasonable to think, given an assumption of no covariance information, an analyst might still attempt to determine the error covariance matrix that results in an upper bound on the P (sub c). Without some guidance on limits to the shape, size and orientation of the unknown covariance matrix, the limiting case is a degenerate ellipse lying along the relative miss vector in the collision plane. Unless the miss position is exceptionally large or the at-risk object is exceptionally small, this method results in a maximum P (sub c) too large to be of practical use. For example, assuming that the miss distance is equal to the current ISS alert volume along-track (+ or -) distance of 25 kilometers and that the at-risk area has a 70 meter radius. The maximum (degenerate ellipse) P (sub c) is about 0.00136. At 40 kilometers, the maximum P (sub c) would be 0.00085 which is still almost an order of magnitude larger than the ISS maneuver threshold of 0.0001. In fact, a miss distance of almost 340 kilometers is necessary to reduce the maximum P (sub c) associated with this degenerate ellipse to the ISS maneuver threshold value. Such a result is frequently of no practical value to the analyst. Some improvement may be made with respect to this problem by realizing that while the position error covariance matrix of one of the objects (usually the debris object) may not be known the position error covariance matrix of the other object (usually the asset) is almost always available. Making use of the position error covariance information for the one object provides an improvement in finding a maximum P (sub c) which, in some cases, may offer real utility. The equations to be used are presented and their use discussed.

Frisbee, Joseph H., Jr.↗
NASA NTRS1986

Towards a general object-oriented software development methodology

An object is an abstract software model of a problem domain entity. Objects are packages of both data and operations of that data (Goldberg 83, Booch 83). The Ada (tm) package construct is representative of this general notion of an object. Object-oriented design is the technique of using objects as the basic unit of modularity in systems design. The Software Engineering Laboratory at the Goddard Space Flight Center is currently involved in a pilot program to develop a flight dynamics simulator in Ada (approximately 40,000 statements) using object-oriented methods. Several authors have applied object-oriented concepts to Ada (e.g., Booch 83, Cherry 85). It was found that these methodologies are limited. As a result a more general approach was synthesized with allows a designer to apply powerful object-oriented principles to a wide range of applications and at all stages of design. An overview is provided of this approach. Further, how object-oriented design fits into the overall software life-cycle is considered.

Seidewitz, ED↗
NASA NTRS1989

Engineering the object-relation database model in O-Raid

Raid is a distributed database system based on the relational model. O-raid is an extension of the Raid system and will support complex data objects. The design of O-Raid is evolutionary and retains all features of relational data base systems and those of a general purpose object-oriented programming language. O-Raid has several novel properties. Objects, classes, and inheritance are supported together with a predicate-base relational query language. O-Raid objects are compatible with C++ objects and may be read and manipulated by a C++ program without any 'impedance mismatch'. Relations and columns within relations may themselves be treated as objects with associated variables and methods. Relations may contain heterogeneous objects, that is, objects of more than one class in a certain column, which can individually evolve by being reclassified. Special facilities are provided to reduce the data search in a relation containing complex objects.

Dewan, Prasun↗
NASA NTRS1990

Considerations of persistence and security in CHOICES, an object-oriented operating system

The current design of the CHOICES persistent object implementation is summarized, and research in progress is outlined. CHOICES is implemented as an object-oriented system, and persistent objects appear to simplify and unify many functions of the system. It is demonstrated that persistent data can be accessed through an object-oriented file system model as efficiently as by an existing optimized commercial file system. The object-oriented file system can be specialized to provide an object store for persistent objects. The problems that arise in building an efficient persistent object scheme in a 32-bit virtual address space that only uses paging are described. Despite its limitations, the solution presented allows quite large numbers of objects to be active simultaneously, and permits sharing and efficient method calls.

Campbell, Roy H.↗
NASA NTRS1992

Object-oriented programming with mixins in Ada

Recently, I wrote a paper discussing the lack of 'true' object-oriented programming language features in Ada 83, why one might desire them in Ada, and how they might be added in Ada 9X. The approach I took in this paper was to build the new object-oriented features of Ada 9X as much as possible on the basic constructs and philosophy of Ada 83. The object-oriented features proposed for Ada 9X, while different in detail, are based on the same kind of approach. Further consideration of this approach led me on a long reflection on the nature of object-oriented programming and its application to Ada. The results of this reflection, presented in this paper, show how a fairly natural object-oriented style can indeed be developed even in Ada 83. The exercise of developing this style is useful for at least three reasons: (1) it provides a useful style for programming object-oriented applications in Ada 83 until new features become available with Ada 9X; (2) it demystifies many of the mechanisms that seem to be 'magic' in most object-oriented programming languages by making them explicit; and (3) it points out areas that are and are not in need of change in Ada 83 to make object-oriented programming more natural in Ada 9X. In the next four sections I will address in turn the issues of object-oriented classes, mixins, self-reference and supertyping. The presentation is through a sequence of examples. This results in some overlap with that paper, but all the examples in the present paper are written entirely in Ada 83. I will return to considerations for Ada 9X in the last section of the paper.

Seidewitz, ED↗
NASA NTRS1994

The optical polarization properties of X-ray-selected BL Lacertae objects

We discuss the optical polarization properties of X-ray-selected BL Lacertae objects (XSBLs) as determined from 3 yr of monitoring the polarization of 37 BL Lac objects and candidates. The observed objects include a complete X-ray flux limited sample drawn from the Einstein Extended Medium Sensitivity Survey (EMSS). We find that the majority of the XSBLs classified solely on the appearance of their optical spectra are true members of the class of BL Lacertae objects since they possess intrinsically polarized and variable continua. The duty cycle of polarized emission (fraction of time spent with the degree of polarization greater than 4%) from XSBLs is 44%. The maximum observed percent polarizations are of order 10%, considerably below the maximum values observed for radio-selected BL Lacertae objects and blazars (30%-40%). While XSBLs have variable polarized emission, the majority (approximately equal to 85%) have preferred polarization position angles on timescales at least as long as 3 yr. This reflects stability in the geometry of the region emitting the linearly polarized optical emission. We describe the spectral dependence of the degree of polarization and discuss some of the possible mechanisms producing the observed characteristics. While dilution of the polarized emission by the host galaxy starlight is certainly present in some objects, we demonstrate that the average polarization properties of XSBLs derived from our observations are not drastically affected by this effect. While the confirmed BL Lac objects are shown to be photometric variables, the objects in our monitored sample did not display the larger than 1 mag variations generally used to characterize the optical variability of radio-selected BL Lacertae objects or blazars in general.

Jannuzi, Buell T.↗
NASA NTRS1994

Higher-Order Neural Networks Applied to 2D and 3D Object Recognition

A Higher-Order Neural Network (HONN) can be designed to be invariant to geometric transformations such as scale, translation, and in-plane rotation. Invariances are built directly into the architecture of a HONN and do not need to be learned. Thus, for 2D object recognition, the network needs to be trained on just one view of each object class, not numerous scaled, translated, and rotated views. Because the 2D object recognition task is a component of the 3D object recognition task, built-in 2D invariance also decreases the size of the training set required for 3D object recognition. We present results for 2D object recognition both in simulation and within a robotic vision experiment and for 3D object recognition in simulation. We also compare our method to other approaches and show that HONNs have distinct advantages for position, scale, and rotation-invariant object recognition. The major drawback of HONNs is that the size of the input field is limited due to the memory required for the large number of interconnections in a fully connected network. We present partial connectivity strategies and a coarse-coding technique for overcoming this limitation and increasing the input field to that required by practical object recognition problems.

Spirkovska, Lilly↗
NASA NTRS2004

Astrometric Follow-Up of Faint Near Earth Objects

The observing program at Mt. Hopkins using the 48" reflector and funded by the Near- Earth Object Observation Program continues to excel. As in the past, all requested observing time was granted. Minor improvements continue to be made. For example, the telescope is set up to track and non-sidereal rates. This allows the user to track on the target object, rather than relying exclusively on the shift- and-stack technique. Other improvements made by the staff include automatic focus routines, automatic seeing-measurement routines, and improvement in dome seeing and mirror stabilization. The net result is better focus, better seeing, and the ability to expose longer in order to acquire the faintest and most important objects. During the proposal period, this program ranked again very high worldwide in terms of faint Near Earth Objects observed. During this latest proposal cycle, fewer objects were observed than previous cycles, but this was due to the strict targeting of only the faintest observable objects. The follow-up programs of observatory codes 926 (led by P. Holvorcem) and 291 (led by Dr. B. McMillan) have greatly increased their capacity, and as a result less bright objects are in urgent need of follow-up than in years past. Even with this new object selection and additional competition, code 696 still ranked second to code 291 in terms of objects observed fainter than V = 20. Minimal scripting is now in place to allow the telescope to run autonomously for 30-45 minutes at a time.

Morgan, T.↗
NASA NTRS2006

Towards Robust Designs Via Multiple-Objective Optimization Methods

Fabricating and operating complex systems involves dealing with uncertainty in the relevant variables. In the case of aircraft, flow conditions are subject to change during operation. Efficiency and engine noise may be different from the expected values because of manufacturing tolerances and normal wear and tear. Engine components may have a shorter life than expected because of manufacturing tolerances. In spite of the important effect of operating- and manufacturing-uncertainty on the performance and expected life of the component or system, traditional aerodynamic shape optimization has focused on obtaining the best design given a set of deterministic flow conditions. Clearly it is important to both maintain near-optimal performance levels at off-design operating conditions, and, ensure that performance does not degrade appreciably when the component shape differs from the optimal shape due to manufacturing tolerances and normal wear and tear. These requirements naturally lead to the idea of robust optimal design wherein the concept of robustness to various perturbations is built into the design optimization procedure. The basic ideas involved in robust optimal design will be included in this lecture. The imposition of the additional requirement of robustness results in a multiple-objective optimization problem requiring appropriate solution procedures. Typically the costs associated with multiple-objective optimization are substantial. Therefore efficient multiple-objective optimization procedures are crucial to the rapid deployment of the principles of robust design in industry. Hence the companion set of lecture notes (Single- and Multiple-Objective Optimization with Differential Evolution and Neural Networks ) deals with methodology for solving multiple-objective Optimization problems efficiently, reliably and with little user intervention. Applications of the methodologies presented in the companion lecture to robust design will be included here. The evolutionary method (DE) is first used to solve a relatively difficult problem in extended surface heat transfer wherein optimal fin geometries are obtained for different safe operating base temperatures. The objective of maximizing the safe operating base temperature range is in direct conflict with the objective of maximizing fin heat transfer. This problem is a good example of achieving robustness in the context of changing operating conditions. The evolutionary method is then used to design a turbine airfoil; the two objectives being reduced sensitivity of the pressure distribution to small changes in the airfoil shape and the maximization of the trailing edge wedge angle with the consequent increase in airfoil thickness and strength. This is a relevant example of achieving robustness to manufacturing tolerances and wear and tear in the presence of other objectives.

Man Mohan, Rai↗
NASA NTRS2007

Optical Properties of High Area-to-Mass Objects at GEO

There exists at GEO a significant population of faint debris (R > 15th magnitude) with high area-to-mass ratios (AMR) (1 to 30 sq m/kg). Their orbital elements (particularly eccentricity and inclination) are observed to change on the time-scale of a week. The consensus is that these objects may be fragments of multi-layer insulation (MLI) blankets. Their orbits are primarily perturbed by solar radiation pressure. In this paper we will report preliminary results from an international collaboration to investigate the unresolved optical properties of these objects. This population was originally discovered by the ESA Space Debris Telescope, and the bulk of the objects to be described here are based on discoveries made with this telescope. Additional objects were supplied by both Russia and the US Air Force. Follow-up optical observations were obtained for a sample of a dozen objects by MODEST (the Michigan Orbital DEbris Survey Telescope) located at Cerro Tololo Inter-American Observatory in Chile. Sequences of calibrated observations in filters B, V, Broad R, and I were obtained under photometric conditions. Multi-color photometric observations in B, V, R, and I band of the same objects were also acquired at the Zimmerwald 1-meter telescope, located near Bern, Switzerland. Light curves of selected high AMR objects will be shown with a temporal resolution of a few seconds and typically span about 10 minutes. Photometric observations of these objects were acquired at the Crimean Astrophysical Observatory (CrAO). This data set includes light curves of objects having high variability of brightness and observed with 2.6 m and 0.64 m class instruments. We will present an analysis of the observed magnitudes and colors, and their correlations (or lack of correlation) with orbital elements, and with predicted values for MLI fragments. This represents the first such collaborative observational program on faint debris at GEO.

Seitzer, Patrick↗
NASA NTRS2014

Bi-static Optical Observations of GEO Objects

A bi-static study of objects at Geosynchronous Earth Orbit (GEO) was conducted using two ground-based wide-field optical telescopes. The University of Michigan's 0.6-m MODEST (Michigan Orbital Debris Survey Telescope) located at the Cerro Tololo Inter- American Observatory in Chile was employed in a series of coordinated observations with the U.S. Naval Observatory's (USNO) 1.3-m telescope at the USNO Flagstaff Station near Flagstaff, Arizona, USA. The goals of this project are twofold: (1) Obtain optical distances to known and unknown objects at GEO from the difference in the observed topocentric position of objects measured with respect to a reference star frame. The distance can be derived directly from these measurements, and is independent of any orbital solution. The wide geographical separation of these two telescopes means that the parallax difference is larger than ten degrees, and (2) Compare optical photometry in similar filters of GEO objects taken during the same time period from the two sites. The object's illuminated surfaces presented different angles of reflected sunlight to the two telescopes.During a four hour period on the night.of 22 February 2014 (UT), coordinated observations were obtained for eight different GEO positions. Each coordinated observation sequence was started on the hour or half-hour, and was selected to ensure the same cataloged GEO object was available in the field of view of both telescopes during the thirty minute observing sequence. GEO objects were chosen to be both controlled and uncontrolled at a range of orbital inclinations, and the objects were not tracked. Instead both telescopes were operated with all drives off in GEO survey mode to discover un-cataloged objects at GEO. The initial results from this proof-of-concept observing run will be presented, with the intent of laying the foundation for future large-scale bi-static observing campaigns of the GEO regime.

Seitzer, Patrick↗