The accurate calibration of the line of sight (LOS) is very important for a high-resolution imaging satellite, especially in a system as Co3D, whose mission is to produce 3D elevation models. A calibration error immediately translates into an altimetry error. Co3D has a matrix and the reading of the lines is done in rolling shutter, each line is read at a different date. So, the geometry of the image is affected by the dynamic perturbations of the attitude during the acquisition time.The objective of the study is to propose a calibration method accurate to 0.1 pixel at 90 percentile. The images needed for calibration must only require one or two satellite passes over the same site, and be compatible with the pointing agility. The method must be robust to residual errors in attitude knowledge.The assumptions of the simulations have been modified in this article to keep the performance of Co3D confidential.

PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which is being developed by the French space agency CNES, is the first primary frequency standard specially designed for operation in space. PHARAO is the main instrument of the ESA mission ACES (Atomic Clock Ensemble in Space) [1]. ACES payload will be installed on-board the International Space Station to perform fundamental physics experiments. Last year [2], some results on two flight model (FM) sub-systems have been presented: Microwave Source performances and Cesium Tube operating as a cold atom clock by using the other engineering model sub-systems. All the FM sub-systems have now passed the qualification process and the whole FM of the cold cesium clock, PHARAO, has been assembled and will undergo extensive tests during the first semester of 2014. The results on the cold atoms manipulation and the metrological evaluation are presented.

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature, and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.

CNES, LKB and SYRTE are developing a primary frequency standard, called PHARAO, which is specially designed for space applications.The clock signal is referenced on the frequency measurement of the hyperfine transition performed on a cloud of cold cesium

The notching profile defines the loading conditions for satellite subsystem shake tests. Its model-based design is a critical issue in the space field and must be defined early in order to initiate as soon as possible discussions between launch authorities and subcontractors. This discussion revolves around the following dilemma: how conservative can the loading be and still be safe for the subsystem interfaces? Indeed, the significant lack of knowledge present in the non-validated model can result in overloading conditions. This paper will propose a global strategy for the model-based design of notching profiles which accounts for epistemic modeling uncertainties using an info-gap approach. The latter provides a generic framework for evaluating and comparing the performances of competing profile designs as well as addressing issues of lack of knowledge in both deterministic and probabilistic model parameters. The proposed methodologies will be illustrated on an academic test case.

PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which is being developed by the French space agency CNES, is the first primary frequency standard specially designed for operation in space. PHARAO is the main instrument of the ESA mission ACES (Atomic Clock Ensemble in Space) [1]. ACES payload will be installed on-board the International Space Station to perform fundamental physics experiments. Last year [2], some results on two flight model (FM) sub-systems have been presented: Microwave Source performances and Cesium Tube operating as a cold atom clock by using the other engineering model sub-systems. All the FM sub-systems have now passed the qualification process and the whole FM of the cold cesium clock, PHARAO, has been assembled and will undergo extensive tests during the first semester of 2014. The results on the cold atoms manipulation and the metrological evaluation are presented.

Uncertainty quantification is an integral part of the model validation process and is important to take into account during the design of mechanical systems. Sources of uncertainty are diverse but generally fall into two categories: aleatory uncertainties due to random processes and epistemic uncertainty resulting from a lack of knowledge or erroneous assumptions.This work focuses on the impact of uncertain levels of prestress on the behavior of solar arrays in their stowed configuration. In this context, snubbers are inserted between two adjacent panels to maintain contact and absorb vibrations during launch. However, under high excitation loads, a loss of contact between the two panels may occur. This results in impacts that can cause extensive damages to fragile elements.

This paper presents all the updating activities performed on the finite element model of PLEIADES. The model updating is usually limited to a correction of modal data, by changing the most sensitive physical design parameters. In this paper, the modelization errors are localized and corrected thanks to a residual energy criteria: the Constitutive Relation Error (CRE). This method was originally developed by the LMT Cachan, and then implemented by the FEMTO Institute (Besançon, FRANCE) for application in an industrial context. The updating of PLEIADES is based on a modal approach: The experimental modes are identified using the Real Time Modal Vibration Identification (RTMVI) method. First, the model of the payload is updated with respect to a subsystem test performed on the instrument. Next, the model is condensed and included in the satellite model. The final step is to update the entire model using tests at satellite level. Primodal, a structural analysis tool developed by TOPMODAL (Toulouse, FRANCE) is used for correlation and updating. 131 DOI 10.1007/978-1-4419-9302-1_12, © T. Proulx (ed.), Advanced Aerospace Applications, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series 4, The Society for Experimental Mechanics, Inc. 2011

Following a campaign of structural dynamic measurements on an industrial structure, the question often arises: “Is my structure non-linear?”. A response to this question is important to the extent that the presence of a nonlinearity, even local, can significantly affect the global dynamic behavior of a structure. Several techniques that enable engineers to detect a non-linear behavior can be found in the literature. These methods are applied mostly in the frequency domain and give the best results with a stepped sine excitation. The goal of this paper is to propose an alternative methodology. It is based on the principal component analysis and uses time responses obtained with a random excitation. This will be first applied to an academic simulated system, and then tests are carried out on a simplified solar array system.

This paper presents all the updating activities performed on the finite element model of PLEIADES. The model updating is usually limited to a correction of modal data, by changing the most sensitive physical design parameters. In this paper, the modelization errors are localized and corrected thanks to a residual energy criteria: the Constitutive Relation Error (CRE). This method was originally developed by the LMT Cachan, and then implemented by the FEMTO Institute (Besançon, FRANCE) for application in an industrial context. The updating of PLEIADES is based on a modal approach: The experimental modes are identified using the Real Time Modal Vibration Identification (RTMVI) method. First, the model of the payload is updated with respect to a subsystem test performed on the instrument. Next, the model is condensed and included in the satellite model. The final step is to update the entire model using tests at satellite level. Primodal, a structural analysis tool developed by TOPMODAL (Toulouse, FRANCE) is used for correlation and updating.

The aim of this paper is to perform a comparative study between different distance measures or metrics for use in nonlinear model updating using vibration test data. Four metrics derived from both frequency and time domain updating approaches are studied, including the harmonic balance method, the constitutive equation error, the restoring force surface and the Karhunen-Loeve decomposition. In the first section, a benchmark model with local nonlinear stiffness is defined in order to illustrate each method. Secondly, each nonlinear updating metric is succinctly reviewed. Finally, the relative performances of the different metrics are investigated based on numerical simulations. These results allow us to characterize the applicability and limitations of the different approaches.

The RTMVI modal identification method was introduced 10 years ago in order to extract modes from frequency response functions (FRF) obtained from sinesweep shaker table vibration tests as opposed to classical modal survey tests. Recently, a study funded by the CNES [1] was carried out with the goal of extending the capabilities of the RTMVI method and in particular the ability to identify coupled modes and to assess the quality and reliability of the FRF and the identified modes. Several state-of-the-art methods in the time and frequency domains were initially evaluated as potential complementary methods to be coupled with the RTMVI approach. However in the end, an extended MDOF version of the RTMVI algorithm proved to be most suitable and best performing solution, and was therefore implemented and validated. This paper presents the formulation and implementation of the new RTMVI/MDOF method along with an industrial application to illustrate its effectiveness.

Friswell, M.I., Mottershead, J.E., (1995) Finite Element Model Updating in Structural Dynamics, , Kluwer Academy Publishers