This paper assumes a requirement for an unmanned multiunit satellite to be assembled in orbit. The requirement to be met is to bring the satellites together so tha t they do not collide but actually rendezvous. The equations of motion of the rendezvous satellite in a relative coordinate system are derived and used to compute a final injection velocity which would effect collision after a time r. The velocity is corrected periodically by a command guidance system and just before impact retrothrust is applied. A terminal infrared homing sj^stem is required to actually accomplish physical contact and joining of the satellites. The first satellite placed in orbit is the "control satellite" and controls all the satellites to be assembled and contains the ccmputer, command guidance equipment, precision orientation equipment, and other features necessary to effect rendezvous. The succeeding satellites contain a propulsion system, a rough at t i tude control system, and a command receiver plus whatever scientific equipment they carry to perform their basic mission. This paper presents the following:

Terminal Guidance System for Satellite Rendezvous

TanDEM-X (TerraSAR-X add-on for digital elevation measurements) is an innovative spaceborne radar interferometer that is based on two TerraSAR-X radar satellites flying in close formation. The primary objective of the TanDEM-X mission is the generation of a consistent global digital elevation model (DEM) with an unprecedented accuracy, which is equaling or surpassing the HRTI-3 specification. Beyond that, TanDEM-X provides a highly reconfigurable platform for the demonstration of new radar imaging techniques and applications. This paper gives a detailed overview of the TanDEM-X mission concept which is based on the systematic combination of several innovative technologies. The key elements are the bistatic data acquisition employing an innovative phase synchronization link, a novel satellite formation flying concept allowing for the collection of bistatic data with short along-track baselines, as well as the use of new interferometric modes for system verification and DEM calibration. The interferometric performance is analyzed in detail, taking into account the peculiarities of the bistatic operation. Based on this analysis, an optimized DEM data acquisition plan is derived which employs the combination of multiple data takes with different baselines. Finally, a collection of instructive examples illustrates the capabilities of TanDEM-X for the development and demonstration of new remote sensing applications.

/pdf/tandem-x-a-satellite-formation-for-high-resolution-sar-z54xhync6a.pdf

TanDEM-X: A Satellite Formation for High-Resolution SAR Interferometry

The Communication program emphasizes theory, research, and application to examine the ways humans communicate, verbally and non-verbally, across a variety of levels and contexts. This is particularly important as communication shapes our ideas and values, gives rise to our politics, consumption and socialization, and helps to define our identities and realities. Its power and potential is inestimable. From the briefest of text messages to the grandest of public declarations, we indeed live within communication and invite you to join us in appreciating its increasing importance in contemporary society. From Twitter and reality television to family relationships and workplace dynamics, communication is about understanding ourselves, our media, our relationships, our culture and how these things connect.

의사 간호사 communication

http://ieeexplore.ieee.org/iel5/4768668/4784008/04784017.pdf

TanDEM-X: A satellite formation for high-resolution SAR interferometry

Synthetic aperture radar (SAR) tomography (TomoSAR) extends the synthetic aperture principle into the elevation direction for 3-D imaging. The resolution in the elevation direction depends on the size of the elevation aperture, i.e., on the spread of orbit tracks. Since the orbits of modern meter-resolution spaceborne SAR systems, like TerraSAR-X, are tightly controlled, the tomographic elevation resolution is at least an order of magnitude lower than in range and azimuth. Hence, super-resolution reconstruction algorithms are desired. The high anisotropy of the 3-D tomographic resolution element renders the signals sparse in the elevation direction; only a few pointlike reflections are expected per azimuth-range cell. This property suggests using compressive sensing (CS) methods for tomographic reconstruction. This paper presents the theory of 4-D (differential, i.e., space-time) CS TomoSAR and compares it with parametric (nonlinear least squares) and nonparametric (singular value decomposition) reconstruction methods. Super-resolution properties and point localization accuracies are demonstrated using simulations and real data. A CS reconstruction of a building complex from TerraSAR-X spotlight data is presented.

/pdf/tomographic-sar-inversion-by-l-1-norm-regularization-the-48rup9r6p3.pdf

Tomographic SAR Inversion by $L_{1}$ -Norm Regularization—The Compressive Sensing Approach

The implementation of synthetic apertures by means of a distributed satellite system requires tight control of the relative motion of the participating satellites. This paper investigates a formation-flying concept able to realize the demanding baselines for aperture synthesis, while minimizing the collision hazard associated with proximity operations. An elegant formulation of the linearized equations of relative motion is discussed and adopted for satellite formation design. The concept of eccentricity/inclination-vector separation, originally developed for geostationary satellites, is here extended to low-Earth-orbit (LEO) formations. It provides immediate insight into key aspects of the relative motion and is particularly useful for orbit control purposes and proximity analyses. The effects of the relevant differential perturbations acting on an initial nominal configuration are presented, and a fuel-efficient orbit control strategy is designed to maintain the target separation. Finally, the method is applied to a specific LEO formation (TanDEM-X/TerraSAR-X), and realistic simulations clearly show the simplicity and effectiveness of the formation-flying concept.

/pdf/proximity-operations-of-formation-flying-spacecraft-using-an-mzv3uy3nwm.pdf

Proximity Operations of Formation-Flying Spacecraft Using an Eccentricity/Inclination Vector Separation

The Prototype Research Instruments and Space Mission Technology Advancement (PRISMA) represents the first
European technology demonstration of formation-flying and on-orbit-servicing techniques. Several hardware and
software experiments, either at subsystem or system levels, have been successfully conducted since the launch of the
dual-satellite mission in June 2010. This paper describes the guidance, navigation, and control functionalities and
presents key flight results from the so-called Spaceborne Autonomous Formation-Flying Experiment (SAFE)
executed in September 2010 and March 2011 as one of the primary PRISMA mission objectives. SAFE is intended to
demonstrate autonomous acquisition, keeping, and reconfiguration of passive relative orbits for advanced remote sensing
and rendezvous applications. As shown in the paper, the onboard Global Positioning System navigation
system provides relative orbit information in real time with an accuracy better than 10 cm and 1 mm/s (threedimensional,
root mean square) in position and velocity, respectively. The impulsive formation control achieves
accuracies better than 10m (three-dimensional, root mean square) for separations below 2 km with minimum usage
of thrusters, ensuring high predictability for simplified mission operations and minimum collision risk for increased safety

Spaceborne Autonomous Formation Flying Experiment on the PRISMA Mission

PRISMA is a technology demonstration mission for satellite formation ﬂying and in-orbit servicing. The space segment comprises the fully maneuverable Main minisatellite and the smaller Target satellite in a low Earth orbit at 700-km altitude. A key mission objective is to demonstrate onboard, fully autonomous, robust, safe, and precise formation ﬂying of spacecraft. This is accomplished by spaceborne global positioning system navigation, guidance, and control functionalities for the maintenance of the relative motion between the two spacecraft. An innovative estimation approach employs a common Kalman ﬁlter for the absolute states of Main and Target, which accounts for the interdependency of absolute and relative navigation without the need for an explicit relative state. As a result, the onboard navigation system provides absolute and relative orbit information in real time with a position accuracy of 2 and 0.1 m, respectively. The formation control achieves accuracies of a few tenths of meters with minimum usage of thrusters. The guidance and control concept is detailed with emphasis on a relative eccentricity and inclination vector separation strategy. The paper derives estimates of the expected relative orbit control performances based upon realworld simulations using typical global positioning system receiver and propulsion system characteristics.

/pdf/autonomous-formation-flying-for-the-prisma-mission-1uu702qzov.pdf

Autonomous Formation Flying for the PRISMA Mission

This paper presents system design and on-orbit results from the Advanced Rendezvous Demonstration using Global Positioning System and Optical Navigation (ARGON). ARGON has been conducted during the extended phase of the Prototype Research Instruments and Space Mission Technology Advancement (PRISMA) mission in April 2012. It represents one of the first rendezvous technology experiments using line of sight measurements from optical navigation and was motivated by the new generation of on-orbit-servicing and debris-removal missions which are discussed at national and international level. Its primary goal was to demonstrate the capability of an active servicer spacecraft to safely approach and rendezvous a non-cooperative passive client using angles-only optical navigation in a ground-in-the-loop fashion. To this end, a dedicated flight dynamics system has been developed for routine processing of the camera images collected on-board, for estimation of the relative orbit of the servicer with respect to the cl...

Simone D'Amico

Papers

Proximity Operations of Formation-Flying Spacecraft Using an Eccentricity/Inclination Vector Separation

Spaceborne Autonomous Formation Flying Experiment on the PRISMA Mission

Autonomous Formation Flying for the PRISMA Mission

Noncooperative Rendezvous Using Angles-Only Optical Navigation: System Design and Flight Results

Comprehensive Survey and Assessment of Spacecraft Relative Motion Dynamics Models