"SAR-Lupe" is a fully diploid SAR satellite reconnaissance system consisting of 5 satellites with the highest spatial resolution in the world today, as far as known to us. The system was handed over to the end-user in November 2008 and is successfully working 24 hours per day, 12 months per year, 10 years long. This paper will present some more details on the SAR-Lupe system, how it came to life, and how it probably will be continued in Germany.

Lockheed Martin Space Systems Company has completed the Large Optical Test and Integration Site (LOTIS) at its Sunnyvale, CA campus. Central to the LOTIS testing facility is a 6.5-meter diameter optical collimator housed in a large, temperature controlled and vibration isolated high-vacuum chamber. A measurement has been made of the atmospheric turbulence inside the LOTIS vacuum chamber testing environment at ambient pressure and temperature near floor level where distorting turbulence may be most persistent. Turbulence is one of the many components that define the overall LOTIS Collimator optical testing capabilities at ambient air pressure. Experimental measurements have been made with a non-phase-shifting Fizeau interferometer along a 50-foot horizontal propagation path in double pass. Results presented here represent root-mean-square (RMS) wavefront error over an 18-inch aperture and the corresponding atmospheric coherence length, r_o (Fried's parameter). In addition, an analysis was performed to calculate the optical line-of-sight jitter response of the LOTIS Collimator system and facility due to base-level vibration disturbances. Vibration survey measurements were made using accelerometers mounted to the vacuum chamber foundation to create a Power Spectral Density (PSD) plot of the measured seismic and vacuum chamber mechanically induced vibration disturbances. The measured PSD was used as the base input to a system-level finite element model that included the LOTIS Collimator, the Flat Mirror Positioning structure and a generic Unit Under Test all mounted on the LOTIS Vibration Isolation Bench to assess the whole system jitter response. Results presented here represent the RMS jitter in nanoradians through the optical path of the LOTIS Collimator due to base-level induced seismic and chamber mechanical vibrations.

Autonomous satellite on-orbit servicing is a very challenging task when the satellite to be serviced is tumbling and has an unknown dynamics model. This paper addresses an adaptive control approach which can be used to assist the control of a servicing satellite to rendezvous and dock with a tumbling satellite whose dynamics model is unknown. A proximity-rendezvous and docking operation can be assumed to have three steps: 1) pre-dock alignment, 2) soft docking and latching/locking-up, and 3) post-docking stabilization. The paper deals with the first and third steps. Lyapunovbased tracking law and adaptation law are proposed to guarantee the success of the nonlinear control procedures with dynamics uncertainties. A dynamics simulation example is presented to illustrate the application of the proposed control approach. Simulation results demonstrated that the adaptive control method can successfully track any required angular velocity trajectory even when the dynamics model of the target satellite is unknown.

A suite of instruments including a 100 kHz 4-channel radiometer, a rapid scanning Fourier-transform infrared spectrometer, and two high-speed visible imagers was used to observe the detonation of several novel insensitive munitions being developed by the Air Force Research Laboratory. The spectral signatures exhibited from several different explosive compositions are discernable and may be exploited for event classification. The spectra are initially optically thick, resembling a Planckian distribution. In time, selective emission in the wings of atmospheric absorption bands becomes apparent, and the timescale and degree to which this occurs is correlated with aluminum content in the explosive formulation. By analyzing the high-speed imagery in conjunction with the time-resolved spectral measurements, it may be possible to interpret these results in terms of soot production and oxidation rates. These variables allow for an investigation into the chemical kinetics of explosions and perhaps reveal other phenomenology not yet readily apparent. With an increased phenomenological understanding, a model could be created to explain the kinetic behavior of the temperature and by-product concentration profiles and thus improve the ability of military sensing platforms to identify explosive types and sources.

Sofradir is one of a leading company of the world for the development and production of infrared detectors. Main applications of these detectors are tactical and commercial applications but also space applications. In particular, Sofradir started to work in the field of space applications and especially in the earth observation domain in the beginning of the 1990th. Thanks to the work done with the support of the French Ministry of Defense and the European Space Agency, Sofradir has acquired a large know-how and became a major supplier for space industry. Nowadays, Sofradir technologies offer possibilities to develop a large panel of high reliable detectors like long linear arrays or two dimensional arrays covering bandwidth from visible to 15 μm based on qualified Mercury Cadmium Telluride (MCT) technology. As a matter of fact, Sofradir is involved in several projects for future space missions (SPIRALE, Sentinel-2 for GMES, MTG, SGLI...) covering a spectral range from visible to long wavelength infrared. In this paper, we present a review of Sofradir technology for the development and manufacturing of infrared detectors for space applications. A particular emphasis is made on the different programs currently run with a presentation of the associated results in terms of performances and qualifications for space use.

The terrestrial remote sensing community is interested in segmented aperture space telescopes with geometries similar to NASA's James Webb Space Telescope (JWST). However, the unorthodox design has caused a decrease in image quality introduced by piston, tip, and tilt phasing errors of the segments and lightweight mirror aberrations. Traditionally image quality has been determined using the Generalized Image Quality Equation (GIQE), however Fiete et.al.1 have shown that there are inherent problems with the GIQE method when working with apertures that are not circularly symmetric. In this paper an image utility technique utilizing a multispectral motion detection algorithm is used to show how changes in mirror phasing and varying degrees of lightweight mirror aberrations affect a systems utility for detecting motion.

Space borne overhead non-imaging (non-focusing) infrared (ONIR) sensors require on-orbit calibration to validate performance of sensor payloads. Typically this is accomplished by the use of ground based observations including laser illumination of the calibrated sensor. This provides a-priori knowledge of the laser characteristics and atmospheric propagation thereby providing the sensor operators a method for deducing the true system level performance. Of concern is the need to avoid laser illumination of other satellites to prevent inadvertent damage or temporary mission degradation. The complex predictive avoidance process is necessarily bureaucratic and time-consuming due to the need to entertain the interests of multiple stakeholders. Herein is described a method for mutual calibration of co-orbital ONIR sensors by use of incoherent off-board illumination of a sample with known spectral reflectivity. The method will not involve laser illumination, will be less threatening to neighboring spacecraft, and will not require predictive avoidance processes.

This paper provides the results of a proposed methodology for removing sensor bias from a space-based infrared (IR) tracking system through the use of stars detected in the background field of the tracking sensor. The tracking system consists of two satellites flying in a lead-follower formation tracking a ballistic target. Each satellite is equipped with a narrow-view IR sensor that provides azimuth and elevation to the target. The tracking problem is made more difficult due to a constant, non-varying or slowly varying bias error present in each sensor's line of sight measurements. As known stars are detected during the target tracking process, the instantaneous sensor pointing error can be calculated as the difference between star detection reading and the known position of the star. The system then utilizes a separate bias filter to estimate the bias value based on these detections and correct the target line of sight measurements to improve the target state vector. The target state vector is estimated through a Linearized Kalman Filter (LKF) for the highly non-linear problem of tracking a ballistic missile. Scenarios are created using Satellite Toolkit^(C) for trajectories with associated sensor observations. Mean Square Error results are given for tracking during the period when the target is in view of the satellite IR sensors. The results of this research provide a potential solution to bias correction while simultaneously tracking a target.

The traditional approach to satellite design is a customized and highly optimized satellite bus. The primary design driver is to minimize mass but often at the expense of schedule and non-recurring engineering costs. The result after years of development is a high performance system with minimal flexibility. Consequently, there is a need for responsive, small satellites that are able to accommodate different missions, changing threats, and emerging technologies for which the traditional development approach is unable to satisfy. Instead, systems must be modular and/or robust. One of the subsystems that will be challenging for the development of modular and/or robust architectures is the thermal control subsystem (TCS). To design a traditional TCS, virtually every aspect of the mission, the satellite, and the components must be known before an intense design program can be completed. However, the mission, payload, components, and requirements are largely unknown before mission initiation. To provide a baseline for the TCS design and to help bound the problem for the development of robust thermal systems, the range of external and internal heat loads for small satellites were evaluated. From this analysis, the realistic worst design cases were identified along with other requirements for robust thermal control systems. Finally, the paper will discuss the merits of various thermal architectures and the challenges associated with achieving the requirements for robust thermal control for responsive satellite buses.

The performance of mission-critical components and systems within spacecraft and satellites requires the ability to control the local thermal environment. Under conditions of relatively constant component and system loading, this would involve radiative dissipation of both internally and externally generated heat loads and altering thermal balances to provide heating where necessary. As the local thermal load changes with component use, the need arises to alter the heat transfer rates and dissipation within the spacecraft. It is also desirable to be able to evaluate, reconfigure or repair space-based thermal control systems using only ground station commands. These needs can be met using a Plug-and-Play variable-emittance control system where operational analysis and reconfiguration is accomplished via an improved Universal Serial Bus (USB) or space-wire controlled architecture. This paper presents a modular, USB/space-wire-driven thermal control system using a solid-state thin-film infrared variable-emittance device (EclipseVED^TM) from Eclipse Energy Systems, Inc. The paper discusses critical issues including connectivity, device-control scale-up for the advancement of an integrated variable-emittance system, comparison of device weight to other variable emittance systems, the capacity to replace or repair devices in-flight, the survivability of the system in space and the importance of individual device control.

Single Crystal Silicon (SCSi) is proving to be an excellent material for the fabrication of lightweight optical components for use in space. As part of the feasibility studies performed prior to space flight applications, it is important to determine the mechanical properties of complex structures manufactured from individual sections of SCSi. As an additional integral building block for future multi-component SCSi structures, the behavior of the McCarter Machine proprietary frit-bonded metal insert technology was examined. Here we report vibration test results, the objective of which was to measure the structural damping characteristics of a typical silicon structure and verify its structural stability after exposure to random vibration. The tests were designed to better understand SCSi, not only as a mirror substrate, but also as a structural material. The success of this test, combined with the already proven McCarter Machine manufacturing techniques, give us the ability to now manufacture new lightweight and stable opto-mechanical assemblies entirely out of SCSi. But since requirements for larger and more sophisticated SCSi structures are limited by the practical size of available boules, the behavior of these frit-bonded SCSi structures needs to be better understood. This understanding will be obtained from planned testing of larger frit bonded SCSi opto-mechanical structural components and assemblies.

In this paper, we present a comparative study of several nonlinear filters, namely, extended Kalman Filter (EKF), unscented KF (UKF), particle filter (PF), and recursive linear minimum mean square error (LMMSE) filter for the problem of satellite trajectory estimation. We evaluate the tracking accuracy of the above filtering algorithms and obtain the posterior Cramer-Rao lower bound (PCRLB) of the tracking error for performance comparison. Based on the simulation results, we provide recommendations on the practical tracking filter selection and guidelines for the design of observer configurations.

This paper presents simulation results of nonlinear filtering algorithms applied to the cooperative object tracking problem. Cooperative tracking refers to observing a object from multiple mobile sensor platforms that communicate with each other, either directly or through a central node. Inter-agent communication also enables cooperative guidance, which can be used to achieve agent formation configurations advantageous to object tracking.

The probability hypothesis density (PHD) and cardinalized PHD (CPHD) filters were introduced in 2000 and 2006, respectively, as approximations of the full multitarget Bayes detection and tracking filter. Both filters are based on the "standard" multitarget measurement model that underlies most multitarget tracking theory. This paper is part of a series of theoretical studies that addresses PHD and CPHD filters for nonstandard multitarget measurement models. In this paper I derive the measurement-update equations for CPHD and PHD filters that estimate models of unknown, dynamically changing data, such as background clutter. A companion paper generalizes these results to multitarget detection and tracking in unknown, dynamic clutter.

The probability hypothesis density (PHD) and cardinalized PHD (CPHD) filters were introduced in 2000 and 2006, respectively, as approximations of the full multitarget Bayes detection and tracking filter. Both filters are based on the "standard" multitarget measurement model that underlies most multitarget tracking theory. This paper is part of a series of theoretical studies that addresses PHD and CPHD filters for nonstandard multitarget measurement models. In a companion paper I derived the measurement-update equations for CPHD and PHD filters for extracting clusters from dynamically evolving data sets. This paper uses these results to derive CPHD and PHD filters for detecting and tracking multiple targets obscured by unknown, dynamically changing clutter.

The current military trend toward many diverse platforms and sensors available for use within a surveillance environment requires the ability to efficiently and effectively task these sensors. This results in a requirement for functionality within the surveillance problem for sensor resource management. This functionality requires the automatic generation of appropriate tasks, the mapping of these tasks to a set of feasible sensors, the calculation of the benefit achieved for executing the task, and the eventual optimal scheduling of these tasks. As part of a recent research effort, we have developed a closed loop sensor resource management environment. As part of this simulation testbed environment we have addressed two key problems. The first is the development of genetic algorithm approach for solving the sensor scheduling problem. Our approach solves a sensor scheduling problem involving multiple sensors as well as several constraints related to scheduling time windows, resource limitations, and linked/repeating tasks. The second area of development is the automatic generation of the tasks to be scheduled. This automated task generation includes the generation of tasks for different missions which in our problem include both surveillance as well as high priority task requests. In each case, our task generation capability creates a sensor independent score that is used in the scheduling algorithm. This paper will describe the sensor management problem in general as well as give a description of our genetic algorithm scheduling approach. We will also describe our approach for generating tasks for multiple missions and the generation of the corresponding task benefit. We will conclude with a discussion of the results obtained during our effort and directions for future research.

We derive new algorithms for Low Earth Orbit (LEO) event estimation based on joint search and sensor management of space based EO/IR sensors. Our approach is based on particle representation of hypothesized probability densities and the Posterior Expected Number of Objects of Interest sensor management objective function. We address scientific and practical challenges of this LEO estimation problem in the context of space situational awareness. These challenges include estimating changes in satellites trajectories, estimating current trajectories (localization), and estimating future collisions with other LEO space objects. Simulations and the results obtained using actual LEO satellites are presented.

We present a game-theoretic approach to Level 2/3/4 fusion for the purpose of Space Situational Awareness (SSA) along with prototypical SW implementation of this approach to demonstrate its effectiveness for possible future space operations. Our approach is based upon innovative techniques that we are developing to solve dynamic games and Nperson cooperative/non-cooperative games, as well as a new emerging homological sensing algorithms which we apply to control disparate network of space sensors in order to gain better SSA.

Over recent decades, the space environment becomes more complex with a significant increase in space debris and a greater density of spacecraft, which poses great difficulties to efficient and reliable space operations. In this paper we present a Hierarchical Sensor Management (HSM) method to space operations by (a) accommodating awareness modeling and updating and (b) collaborative search and tracking space objects. The basic approach is described as follows. Firstly, partition the relevant region of interest into district cells. Second, initialize and model the dynamics of each cell with awareness and object covariance according to prior information. Secondly, explicitly assign sensing resources to objects with user specified requirements. Note that when an object has intelligent response to the sensing event, the sensor assigned to observe an intelligent object may switch from time-to-time between a strong, active signal mode and a passive mode to maximize the total amount of information to be obtained over a multi-step time horizon and avoid risks. Thirdly, if all explicitly specified requirements are satisfied and there are still more sensing resources available, we assign the additional sensing resources to objects without explicitly specified requirements via an information based approach. Finally, sensor scheduling is applied to each sensor-object or sensor-cell pair according to the object type. We demonstrate our method with realistic space resources management scenario using NASA's General Mission Analysis Tool (GMAT) for space object search and track with multiple space borne observers.

Starting in late 2007 and continuing through the present, NFIRE (Near-Field Infrared Experiment), a Missile Defense Agency (MDA) experimental satellite and TerraSAR-X, a German commercial SAR satellite have been conducting mutual crosslink experiments utilizing a secondary laser communication payload built by Tesat-Spacecom. The narrow laser beam-widths and high relative inter-spacecraft velocities for the two low-earth-orbiting satellites imply strict pointing control and dynamics aboard both vehicles. The satellites have achieved rapid communication acquisition times and maintained communication for hundreds of seconds before losing line of sight to the counter satellite due to earth blockage. Through post-mission analysis and other related telemetry we will show results for pointing accuracy, disturbance environments and pre-engagement prediction requirements that support successful and reliable operations.

Laser altimetry and deep space communications are two typical applications requiring very low noise optical receivers in order to achieve detection of weak and short optical pulse. Avalanche photodiode is the detector of choice for its high quantum efficiency, compact size, reduced electronics complexity and its ability to operate in a radiation-hard environment. Optimal operating condition in terms of APD gain and temperature is the key to maximize the signal to noise ratio. This paper describes the model and the measured performance of a hybrid optical receiver using a TE cooled Silicon Avalanche Photodiode. Receiver performance in terms of responsivity and NEP will be presented as a function of temperature, signal power and APD Gain. A brief discussion of radiation impact on noise is also presented. A NEP of only 5fW/sqrt(Hz) has been obtained with a bandwidth of 200MHz in linear mode at a wavelength of 1060nm.

This paper presents a space-based, space-surveillance study wherein the goal is to demonstrate the feasibility and scalability of the modeling and simulation of a distributed multi-agent multiple satellites tracking and prediction system. A flexible and modular system architecture that enables collaborative and efficient teaming among distributed agents is delineated. Hierarchical objective methodology is deployed to align the mission objectives with the diverse agents' capabilities and resources. A set of satellite platform and sensor configuration/models is considered. Detailed mathematical models of the satellite orbits including the mutual visibility function are simulated for combinations of GEO and LEO orbits. An Unscented Kalman Filter (UKF)/Distributed Unscented Information Filter (DUIF) for high-accuracy orbital determination and tracking is demonstrated to show that the LEO orbit estimation from the GEO satellite with only angle measurements based on UKF is an excellent approach. Simulation studies show that the rate of filter convergence depends on sample time period, initial error, process error, measurement errors as well as the relative geometry of the LEO and GEO satellite orbits.

Constellations of EO/IR space based sensors can be extremely valuable for space situational awareness. In this paper, we present trade-off analysis and comparisons of different Low Earth Orbit (LEO) EO/IR sensor platform constellations for space situational awareness tasks. These tasks include early observation of changing events, and localization and tracking of changing LEO orbits. We derive methods and metrics for evaluation, testing, and comparisons of different sensor constellations based on realistic models and computationally efficient methods for simulating realistic scenarios.

Distributed Sensor Concept-DISCO was proposed for multiplication of individual weapon capability through cooperative target engagement. DISCO creates practically distributed in space sensor network that performs sensing by exchanging of pre-track frame and GNC data. Concept of operations for DISCO is based on complete absence of any kind of host vehicle with its weight allocated for unique and costly propulsion, communication and avionics, and, in the same time DISCO preserves the original idea of multiplicity of lightweight effective weapon dispensed from an unitary payload Three major benefits of DISCO are: immediate PBO deployment; absence of any kind of carrier or "central" vehicle or bus; multiplicity of weapon. DISCO sensor network supports target handover without active ranging but by triangulating. Digital video-signal processing that supports DISCO is Recursive Adaptive Frame Integration of Limited data. Each sensor disseminates to and receives frame, calibration and GNC data from other sensors in the network. In this paper efficiency of DISCO weapon system is discussed for acquisition, accurate handover and track correlation.

The idea of open source software originally began in the early 1980s, but it never gained widespread support until recently, largely due to the explosive growth of the Internet. Only the Internet has made this kind of concept possible, bringing together millions of software developers from around the world to pool their knowledge. The tremendous success of open source software has prompted many corporations to adopt the culture of open source and thus share information they previously held secret. The government, and specifically the Department of Defense (DoD), could also benefit from adopting an open source culture. In acquiring satellite systems, the DoD often builds walls between program offices, but installing doors between programs can promote collaboration and information sharing. This paper addresses the challenges and consequences of adopting an open source culture to facilitate technology collaboration for DoD space acquisitions. DISCLAIMER: The views presented here are the views of the author, and do not represent the views of the United States Government, United States Air Force, or the Missile Defense Agency.