Space Situational Awareness (SSA) requires the ability for secure communication of information and sensing of objects in space, reliable estimation on ground information from space, and command and control of sensor resources to space. Inherent in the secure, reliable, and robust coordination with space assets is the ability to monitor and detect jammer activities. This paper presents a ground jammer localization method by fusing multiple parameters (including time difference of arrival (TDOA), frequency and direction of arrival (DOA)) collected using two satellites via an extended Kalman filter (EKF) with a two-step initialization process. The first step uses DOA fusion and the second step uses DOA-TDOA fusion. The two-step initialization guarantees the convergence of the EKF and therefore the high localization accuracy. The simulation shows that the ground jammer can be localized using the space assets within 100 meters, which is accurate enough for many applications.

For tracking a target in a heavily cluttered environment, the Probabilistic Data Association Filter (PDAF) is very efficient and can significantly reduce track losses. However, as shown in this paper, the PDAF will experience difficulties at the initial stage of the filtering when the track is not accuracy enough, and the filter tends to diverge under even modest clutter density. To address this problem we propose a technique of splitting the track of the target into sub-tracks that run in parallel when the original track has low accuracy. Each sub-track occupies a portion of the uncertainty region of the original track. As a result, the sub-tracks maintained using the PDAF will be more selective over the incoming measurements (including detection and false alarms), and have less loss in tracking accuracy and improved robustness. This approach is similar to the Gaussian Sum filter in the literature. The major contribution of this paper is to propose a systematic method to effectively divide a less accurate track in a high dimensional state space into a set of sub-tracks to effectively improve the robustness of the PDAF. The splitting of the track will incur a significant amount of additional computation cost. To reduce the number of sub-tracks a likelihood ratio test is also proposed for the problem considered to drop unlikely sub-tracks. Simulation results are presented to demonstrate the performance of the proposed algorithm.

The problem of automated scheduling a constellation of satellites to achieve maximum information content is a challenging problem. This optimization problem is further complicated when one attempts to meet collection requirements on various sites all while operating within a power budget. The goal of this research is to find the schedules for a set of satellite sensors that observe a set of fixed ground locations while incorporating visibility, solar angles, time of day, site priority, desired goal time between collects for each site, and satellite power. Our solution approach utilizes a top-down approach that accounts for information over the entire scheduling window. The higher layers use relaxed satellite information in ever decreasing time windows, while the lowest resolution scheduling layer uses a Lagrangian relaxation based approach which incorporates the power constraint in the objective function. The final step of our approach is to search locally for better solutions using a k-switch local search method to improve on the optimization objective function. This paper will focus on the technical discussion of the hierarchical approach and generation of the final solution via Lagrangian relaxation. The information content or benefit of the top-down, Lagrangian relaxation technique will also be compared to other scheduling techniques to provide a measure of performance. We will provide performance results for our approach using simulated data and sensors.

A potentially high payoff for the ballistic missile defense system (BMDS) is the ability to fuse the information gathered by various sensor systems. In particular, it may be valuable in the future to fuse measurements made using ground based radars with passive measurements obtained from satellite-based EO/IR sensors. This task can be challenging in a multitarget environment in view of the widely differing resolution between active ground-based radar and an observation made by a sensor at long range from a satellite platform. Additionally, each sensor system could have a residual pointing bias which has not been calibrated out. The problem is further compounded by the possibility that an EO/IR sensor may not see exactly the same set of targets as a microwave radar. In order to better understand the problems involved in performing the fusion of metric information from EO/IR satellite measurements with active microwave radar measurements, we have undertaken a study of this data fusion issue and of the associated data processing techniques. To carry out this analysis, we have made use of high fidelity simulations to model the radar observations from a missile target and the observations of the same simulated target, as gathered by a constellation of satellites. In the paper, we discuss the improvements seen in our tests when fusing the state vectors, along with the improvements in sensor bias estimation. The limitations in performance due to the differing phenomenology between IR and microwave radar are discussed as well.

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nano-satellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. In this paper, we first give an overview of the STARE program. We then describe the details of the optical imaging payload for the STARE pathfinder CubeSats, including the optical design and the sensor characterization. Finally, we discuss the track detection algorithm that will be used on the images acquired by the payload.

In order to maintain space situational awareness, it is necessary to maintain surveillance of objects in Earth orbit. A system of space-based imaging sensors could make much more detailed inspections of the existing resident space objects (RSOs). However, in order to preserve bandwidth, it is desirable to send the groundstation only a subset of all images which are taken by the inspection system. This paper presents a change detection algorithm which can detect changes in the appearance of an RSO. A new inspection image is compared to a previously taken base image. In each image, the translation vector and rotation matrix between the camera and the RSO, or pose, is slightly different. Assuming that the points making up each image of the RSO are within a single plane, it is possible to generate a planar homography which is a linear mapping between the two images. The homography is used to estimate the rotation and translation between the camera coordinate systems. This knowledge can be used to warp the inspection image so that it appears as though it was taken from the same coordinate system as the base image. Finally, basic morphological image processing and image thresholding techniques are used to perform change detection. The algorithm was evaluated by applying it to raytraced inspection images exhibiting varying lighting and pose conditions. Simulation results show that the algorithm can reliably detect damage to the RSO or the rendezvous of a suspicious object.

Satellites are subject to harsh lighting conditions which make visual inspection difficult. Automated systems which detect changes in the appearance of a satellite can generate false positives in the presence of intense shadows and specular reflections. This paper presents a new algorithm which can detect visual changes to a satellite in the presence of these lighting conditions. The position and orientation of the satellite with respect to the camera, or pose, is estimated using a new algorithm. Unlike many other pose estimation algorithms which attempt to reduce image reprojection error, this algorithm minimizes the sum of the weighted 3-dimensional error of the points in the image. Each inspection image is compared to many different views of the satellite, so that pose may be estimated regardless of which side of the satellite is facing the camera. The features in the image used to generate the pose estimate are chosen automatically using the scale-invariant feature transform. It is assumed that a good 3-dimensional model of the satellite was recorded prior to launch. Once the pose between the camera and the satellite have been estimated, the expected appearance of the satellite under the current lighting conditions is generated using a raytracing system and the 3-dimensional model. Finally, this estimate is compared with the image obtained from the camera. The ability of the algorithm to detect changes in the external appearance of satellites was evaluated using several test images exhibiting varying lighting and pose conditions. The test images included images containing shadows and bright specular reflections.

This paper develops and evaluates a pursuit-evasion orbital game approach for satellite interception and collision avoidance. Using a coupled zero-sum differential pursuit-evasion game, the pursuer minimizes the satellite interception time, and the evader tries to maximize interception time for collision avoidance. For the satellite interception problem we design an algorithm for pursuer and one for collision avoidance, where the game solution controls the evader satellite. The interception-avoidance (IA) game approach provides a worst-case solution, which is the robust lower-bound performance case. We divide our IA algorithm into two parts: first, the pursuer will rotate its orbit to the same plane of the evader; and second, the two spacecraft will play a zero-sum pursuit-evasion (PE) game. A two-step setup saves energy during the PE game because rotating a pursuer orbit requires more energy than maneuvering within the orbit plane. For the PE orbital game, an optimum open loop feedback saddle-point equilibrium solution is calculated between the pursuer and evader control structures. Using the open-loop feedback control rule, each player will calculate their distributed control track state. Numerical simulations are calculated to demonstrate the performance.

Sensor allocation is an important and challenging problem within the field of multi-agent systems. The sensor allocation problem involves deciding how to assign a number of targets or cells to a set of agents according to some allocation protocol. Generally, in order to make efficient allocations, we need to design mechanisms that consider both the task performers' costs for the service and the associated probability of success (POS). In our problem, the costs are the used sensor resource, and the POS is the target tracking performance. Usually, POS may be perceived differently by different agents because they typically have different standards or means of evaluating the performance of their counterparts (other sensors in the search and tracking problem). Given this, we turn to the notion of trust to capture such subjective perceptions. In our approach, we develop a trust model to construct a novel mechanism that motivates sensor agents to limit their greediness or selfishness. Then we model the sensor allocation optimization problem with trust-in-loop negotiation game and solve it using a sub-game perfect equilibrium. Numerical simulations are performed to demonstrate the trust-based sensor allocation algorithm in cooperative space situation awareness (SSA) search problems.

In this paper we present collision event modeling, detection, and tracking using a space-based Low Earth Orbit (LEO) EO/IR constellation of platforms. The implemented testbed is based on our previous work on dispersed and disparate sensor management for tracking Space Objects (SOs). The known SOs' LEO trajectory parameters are tracked by using a first order state perturbation model, and the estimates are updated using Monte Carlo sampling techniques. Using multi-hypothesis testing we estimate if the tracked RSO is on a collision trajectory with a satellite. Trajectories that can lead to a collision are then constantly observed and tracked using observations from EO/IR sensors located on LEO platforms. The developed algorithms are tested and evaluated on a simulated testbed. Open problems and future work are discussed.

Given the increasingly dense environment in both low-earth orbit (LEO) and geostationary orbit (GEO), a sudden change in the trajectory of any existing resident space object (RSO) may cause potential collision damage to space assets. With a constellation of electro-optical/infrared (EO/IR) sensor platforms and ground radar surveillance systems, it is important to design optimal estimation algorithms for updating nonlinear object states and allocating sensing resources to effectively avoid collisions among many RSOs. Previous work on RSO collision avoidance often assumes that the maneuver onset time or maneuver motion of the space object is random and the sensor management approach is designed to achieve efficient average coverage of the RSOs. Few attempts have included the inference of an object's intent in the response to an RSO's orbital change. We propose a game theoretic model for sensor selection and assume the worst case intentional collision of an object's orbital change. The intentional collision results from maximal exposure of an RSO's path. The resulting sensor management scheme achieves robust and realistic collision assessment, alerts the impending collisions, and identifies early RSO orbital change with lethal maneuvers. We also consider information sharing among distributed sensors for collision alert and an object's intent identification when an orbital change has been declared. We compare our scheme with the conventional (non-game based) sensor management (SM) scheme using a LEO-to-LEO space surveillance scenario where both the observers and the unannounced and unplanned objects have complete information on the constellation of vulnerable assets. We demonstrate that, with adequate information sharing, the distributed SM method can achieve the performance close to that of centralized SM in identifying unannounced objects and making early warnings to the RSO for potential collision to ensure a proper selection of collision avoidance action.

Relative guidance for autonomous rendezvous and docking is a key technology for many current and future space missions, such as the unmanned on-orbit service. In these missions, it is normally required that the chaser spacecraft can plan a trajectory to the target rapidly, and control the chaser's attitude to align with the docking port of the target. This paper presents a recently developed bio-inspired virtual motion camouflage methodology to compute the optimal or near optimal orbit and attitude trajectories for relative guidance of rendezvous and docking missions rapidly. In this approach, the dimension of the optimization parameters and then the computational cost of the online trajectory planning can be reduced significantly. Multiple simulations are provided to demonstrate the capabilities of the algorithm.

One of the most challenging and risky missions for spacecraft is to perform Rendezvous and Docking (RvD) autonomously in space. To ensure a safe and reliable operation, such a mission must be carefully designed and thoroughly verified before a real space mission can be launched. This paper describes the impact-contact dynamics simulation capability of a new, robotics-based, hardware-in-the-loop (HIL) RvD simulation facility which uses two industrial robots to simulate 6-DOF dynamic maneuvering of two docking satellites. The facility is capable of physically simulating the final approaching within 25-meter range and the entire docking/capturing process in a satellite on-orbit servicing mission. The paper briefly discusses the difficulties of using industrial robots for HIL contact dynamics simulation and how these problems are solved. Admittance control strategy is proposed to control the robotic system to make the robot dynamically behave like the spacecraft during a physical interception. The control strategy works as an outer loop on the top of the existing control system of the industrial robot and hence, it does not require altering the joint control hardware and software which are inaccessible for an industrial robot. A simulation study has shown that the methodology can accurately simulate the impact-contact dynamics behavior of the spacecraft in a docking operation.

For three years, students at New Mexico State University have pursued flight experiments for validation of a newly developed inertia property identification algorithm. The robotics-based algorithm was developed and studied using computer simulations only. It has not been fully validated experimentally because of the difficulty to physically test full six degrees of freedom system dynamics in microgravity conditions on the ground. In the attempt to experimentally validate the algorithm, two experiments onboard NASA's C-9 microgravity flights have been performed. Although these flight experiments have been an invaluable experience, the zero-gravity environment desired to fully validate the algorithm has not yet been achieved. The full validation requires 6 DOF, a zero-gravity motion condition which is virtually inconceivable for ground-based testing or aircraft-based testing. Therefore, the student team is developing a suborbital experiment to further test the algorithm. The experiment has been scheduled to fly in the summer of 2011. This paper describes the activities of this suborbital flight project.

By starting with established and flown hardware (high Technology Readiness Level (TRL)), and implementing a concurrent engineering environment and seamless team, a mission architect can achieve high reliability and high performance while operating under constrained cost and short implementation schedule. We will describe methods, including those used by the telescope team on the recent Wide-field Infrared Survey Explorer (WISE) mission, to manage cost and realize aggressive schedules. These lessons may be evoked for telescopes addressing defense, security and sensing, as well as those for NASA science.

Military experts often refer to space as the ultimate high ground under the premise that placing systems in orbit provides advantages consistent with the military doctrine of high ground. Although space provides the ultimate "observation post", it has none of the other advantages traditionally associated with high ground. Army Field Manual (FM) 34-130 states the other advantages of holding key terrain: commanding avenues of approach, overcoming obstacles, and affording cover and concealment as additional benefits of high ground. Yet systems in orbit incur none of these additional advantages. Finally, international restrictions and reciprocity concerns limit the employment of weapons in space nullifying many of the unique capability advantages that would otherwise support the "high ground" aspect of space. As the ultimate observation post, satellites provide a large quantity of vital data to military decision makers. This massive amount of data needs to have as much context as possible to convert this data to useful knowledge. To use space assets optimally, the military needs to learn from the past and make space and cyber products distributed and tactical. It is absolutely essential to distribute the right information to the lowest level (tactical elements) of the organization or the "boots on the ground" in a timely manner.

Previously difficult or impossible shapes can now be placed on visible imaging optical surfaces using Narrow Ion Beam Figuring (NIBF). This technique, unlike classical Ion Beam Figuring (IBF), does not substantially roughen the surface. Furthermore, the method can be used to take optical surfaces to sub-nanometer surface errors and to sub-micron radian slope errors. A specific set of applications uses NIBF surfaces at a reimaged pupil plane to impart special characteristics on image creation. Such optics has steep local slope changes over only 1mm scale.

The traditional model for space-based earth observations involves long mission times, high cost, and long development time. Because of the significant time and monetary investment required, riskier instrument development missions or those with very specific scientific goals are unlikely to successfully obtain funding. However, a niche for earth observations exploiting new technologies in focused, short lifetime missions is opening with the growth of the small satellite market and launch opportunities for these satellites. These low-cost, short-lived missions provide an experimental platform for testing new sensor technologies that may transition to larger, more long-lived platforms. The low costs and short lifetimes also increase acceptable risk to sensors, enabling large decreases in cost using commercial off the shelf (COTS) parts and allowing early-career scientists and engineers to gain experience with these projects. We are building a low-cost long-wave infrared spectral sensor, funded by the NASA Experimental Project to Stimulate Competitive Research program (EPSCOR), to demonstrate the ways in which a university's scientific and instrument development programs can fit into this niche. The sensor is a low-mass, power efficient thermal hyperspectral imager with electronics contained in a pressure vessel to enable the use of COTS electronics, and will be compatible with small satellite platforms. The sensor, called Thermal Hyperspectral Imager (THI), is based on a Sagnac interferometer and uses an uncooled 320x256 microbolometer array. The sensor will collect calibrated radiance data at long-wave infrared (LWIR, 8-14 microns) wavelengths in 230-meter pixels with 20 wavenumber spectral resolution from a 400-km orbit.

ITT Geospatial Systems has space-qualified a visible band interline Charge Coupled Device (CCD) image sensor with 18 million pixels developed using commercial technology. The sensor is comprised of an 4320 (H) x 4144 (V) array of 8 micron square pixels. With multiple analog outputs each operating at 20 MHz the sensor will support 30 frames per second continuous video capture. The pixel incorporates a pinned photodiode, vertical overflow drain and microlens to achieve low dark current, lag-free imaging with highspeed global electronic shutter at high quantum efficiency (QE). The vertical and horizontal CCD's are true two-phase designs which support an integrate-while-read operation. The sensor chip is mounted on an Aluminum Nitride co-fired ceramic package optimized for electrical signal integrity, thermal and optical stability. The architecture supports quadrant redundancy. The complete assembly has been space-qualified to a Technology Readiness Level (TRL) of 6 with Total Ionization Dose (TID) radiation testing at 25 Krad. The sensor exceeds 12-bit of dynamic range and 31% QE with 5 W of total power. The nonlinearity is measured to be 1.0% while the global non-uniformity is less than 2%. The low defect density of the CCD sensor allows high resolution video imaging in a space environment.

Phase retrieval is explored for image reconstruction using outputs from both a simulated intensity interferometer (II) and a hybrid system that combines the II outputs with partially resolved imagery from a traditional imaging telescope. Partially resolved imagery provides an additional constraint for the phase retrieval process, as well as an improved starting point for the algorithm. The benefits of this additional a priori information are explored, and when combined with standard constraints such as positivity and compact support include faster convergence, increased sensitivity, and improved image quality.

Crew Optical Alignment Sights (COAS) are used by spacecraft pilots to provide a visual reference to a target spacecraft for lateral relative position during rendezvous and docking operations. NASA's Orion vehicle, which is currently under development, has not included a COAS in favor of automated sensors, but the crew office has requested such a device be added for situational awareness and contingency support. The current Space Shuttle COAS was adopted from Apollo heritage, weighs several pounds, and is no longer available for procurement which would make re-use difficult. In response, a study was conducted to examine the possibility of converting a commercially available weapons sight to a COAS for the Orion spacecraft. The device used in this study was the XPS series Holographic Weapon Sight (HWS) procured from L-3 EOTech. This device was selected because the targeting reticule can subtend several degrees, and display a graphic pattern tailored to rendezvous and docking operations. Evaluations of the COAS were performed in both the Orion low-fidelity mockup and rendezvous simulations in the Reconfigurable Operational Cockpit (ROC) by crewmembers, rendezvous engineering experts, and flight controllers at Johnson Space Center. These evaluations determined that this unit's size and mounting options can support proper operation and that the reticule visual qualities are as good as or better than the current Space Shuttle COAS. The results positively indicate that the device could be used as a functional COAS and supports a low-cost technology conversion solution.

An all fiber Navigation Doppler Lidar (NDL) system is under development at NASA Langley Research Center (LaRC) for precision descent and landing applications on planetary bodies. The sensor produces high-resolution line of sight range, altitude above ground, ground relative attitude, and high precision velocity vector measurements. Previous helicopter flight test results demonstrated the NDL measurement concepts, including measurement precision, accuracies, and operational range. This paper discusses the results obtained from a recent campaign to test the improved sensor hardware, and various signal processing algorithms applicable to real-time processing. The NDL was mounted in an instrumentation pod aboard an Erickson Air-Crane helicopter and flown over various terrains. The sensor was one of several sensors tested in this field test by NASA's Autonomous Landing and Hazard Avoidance Technology (ALHAT) project.

POSE (relative position and attitude) can be computed in many different ways. Given a sensor that measures bearing to a finite number of spots corresponding to known features (such as a target) of a spacecraft, a number of different algorithms can be used to compute the POSE. NASA has sponsored the development of a flash LIDAR proximity sensor called the Vision Navigation Sensor (VNS) for use by the Orion capsule in future docking missions. This sensor generates data that can be used by a variety of algorithms to compute POSE solutions inside of 15 meters, including at the critical docking range of approximately 1-2 meters. Previously NASA participated in a DARPA program called Orbital Express that achieved the first automated docking for the American space program. During this mission a large set of high quality mated sensor data was obtained at what is essentially the docking distance. This data set is perhaps the most accurate truth data in existence for docking proximity sensors in orbit. In this paper, the flight data from Orbital Express is used to test POSE algorithms at 1.22 meters range. Two different POSE algorithms are tested for two different Fields-of-View (FOVs) and two different pixel noise levels. The results of the analysis are used to predict future performance of the POSE algorithms with VNS data.

Space robot is a special robotic system which is expected to perform important tasks in space, like servicing satellites. But any motion of robotic manipulator will disturb its supporting vehicle in space due to the dynamic coupling. Moreover, the evaluating method of manipulability used on ground can not be directly applied to the space robot. A volume element concept is developed to evaluate the manipulability and disturbance of a space robot system. This paper shows the application of volume element method in two-link planar space robot. The volume element method is a new theoretical approach for the research and analysis of space robot system.

In this article, the dynamic equations of a spherical mobile robot, named BYQ-III, are derived by utilizing the Lagrange method. There is no simplification throughout the whole dynamic analysis and the derived dynamic equations can be used for more precise studies of spherical mobile robots' behavior. Considering any possible differentiable function for the terrain's curve, only assuming that the spherical shell will remain in contact with the ground and the elastic effect of the spherical shell is ignored, the effect of the terrain's unevenness is completely described in the dynamic equation evaluation. Although there are complicated and nonlinear relations between the spherical shell and rough terrain, proper choice of generalized coordinates leads to the general closed form dynamic equations of motion, and finally results in the effective reduction of simulation time. But there is no need for the numerical method to solve the complex dynamic equation due to the closed form derivation. In the dynamic equation all variables are highly coupled together and their individual effect cannot be decoupled exactly. From this proposed complete model a simplified model for controller design can be extracted and the proposed model description can give an insight about the performance of different controllers of the spherical robots' motion. Simulations with the same initial conditions on a flat surface and rough terrain show that a rough terrain has a considerable effect on the dynamic behavior of the spherical robots. And as the unevenness of the terrain increases, its effect in the dynamic analysis becomes greater and cannot be neglected.

In this paper we establish mechanical model of the interaction between spherical mobile robot and lunar soil under the moon environment. Two cases are considered: 1.static case in which the spherical robot sits stationary on the moon surface, 2.dynamic case in which the spherical robot rolls over the moon surface with a constant forward speed. Curves of mathematical model is obtained by the software of Matlab. Then we create the model of lunar soil and the spherical robot in the software of ANSYS. We obtain some difference datas about the relationships between the shape of lunar soil and carrying capability of the spherical robot. We obtain curves with these datas by Matlab curve fitting. Compare curves obtained by Matlab with curves obtained by ANSYS and Matlab curve fitting we can see that these two groups of curves are broadly consistent with each other. These simulation results verify the validity of the mathematical model.

An active co-phasing imaging testbed with high accurate optical adjustment and control in nanometer scale was set up to validate the algorithms of piston and tip-tilt error sensing and real-time adjusting. Modularization design was adopted. The primary mirror was spherical and divided into three sub-mirrors. One of them was fixed and worked as reference segment, the others were adjustable respectively related to the fixed segment in three freedoms (piston, tip and tilt) by using sensitive micro-displacement actuators in the range of 15mm with a resolution of 3nm. The method of twodimension dispersed fringe analysis was used to sense the piston error between the adjacent segments in the range of 200μm with a repeatability of 2nm. And the tip-tilt error was gained with the method of centroid sensing. Co-phasing image could be realized by correcting the errors measured above with the sensitive micro-displacement actuators driven by a computer. The process of co-phasing error sensing and correcting could be monitored in real time by a scrutiny module set in this testbed. A FISBA interferometer was introduced to evaluate the co-phasing performance, and finally a total residual surface error of about 50nm rms was achieved.

Carbon/Carbon has many attributes that make it an attractive material for satellite applications. It is low in density, is dimensionally stable under a wide variety of conditions, has very low thermal expansion, is relatively low in cost, and is a mature technology. Moreover, the material is flexible enough to enable the designer to select such variables as fiber type, fabric architecture, fiber volume, and high temperature processing and thus custom tailor the physical and mechanical properties to his specific requirements. A wide range of properties are available - densities from 1.5 to 1.9 g/cm³, room temperature Coefficients of Thermal Expansion (CTE) from -0.3x10^-6to -1.3x10^-6/K, room temperature thermal conductivities from 7 to 210 W/m.K, and modulus from 60 to 190 GPa. A new type of structure developed by CNRS on the space instrument SODISM uses Carbon/Carbon.