Systems engineering has become a commonly practiced discipline in many ground-based telescope projects over the last decade. Invented by the large defense and aerospace companies decades ago, space astronomy projects have long embraced systems engineering. While it is much easier to fix problems after the fact, ground-based projects have taken longer to embrace this approach. As ground-based projects have grown in size and complexity, discovering the benefits of a systems approach has taken time. The up-front costs should be compared to the intended savings at the end of a project in order to find a balance in applying systems engineering tools. Based upon size and complexity of a project, one might expect a different balance in the rigorous application of systems engineering discipline when applied to the ground-based systems of today, The question is, as future ground-based systems increase an order of magnitude in complexity and cost, will this push the systems implementation closer to that of complex space systems? Thoughts will be presented for future giant telescopes based upon experience outside of astronomy, as well as systems implementation on the Gemini 8-meter Telescopes Project and for the new Advanced Technology Solar Telescope (ATST).

The presentation describes the historical background of systems engineering and its development based on the urgent need for systematic management approaches in highly complex and sophisticated scientific (space) and military projects. Not in every project related to technical equipment for astronomical applications a separate expensive systems engineer or systems engineering team is absolutely necessary. The presentation outlines the typical project constellations and boundary conditions requiring the implementation of systems engineering in a project management organisation and explains the benefits and advantages system engineering offers to the project. Whether a project benefits from the sys-tems engineering function or rather consider it as ballast and wasted money depends to a large degree on the people involved in the systems engineering function. The required characteristics for an efficient systems engineer are discussed as well as the personal and professional experience, which are prerequisites to be or become an ideal systems engineer.

The Kepler mission will launch in 2007 and determine the distribution of earth-size planets (0.5 to 10 earth masses) in the habitable zones (HZs) of solar-like stars. The mission will monitor > 100,000 dwarf stars simultaneously for at least 4 years. Precision differential photometry will be used to detect the periodic signals of transiting planets. Kepler will also support asteroseismology by measuring the pressure-mode (p-mode) oscillations of selected stars. Key mission elements include a spacecraft bus and 0.95meter, wide-field, CCD-based photometer injected into an earth-trailing heliocentric orbit by a 3-stage Delta II launch vehicle as well as a distributed Ground Segment and Follow-up Observing Program. The project is currently preparing for Preliminary Design Review (October 2004) and is proceeding with detailed design and procurement of long-lead components. In order to meet the unprecedented photometric precision requirement and to ensure a statistically significant result, the Kepler mission involves technical challenges in the areas of photometric noise and systematic error reduction, stability, and false-positive rejection. Programmatic and logistical challenges include the collaborative design, modeling, integration, test, and operation of a geographically and functionally distributed project. A very rigorous systems engineering program has evolved to address these challenge. This paper provides an overview of the Kepler systems engineering program, including some examples of our processes and techniques in areas such as requirements synthesis, validation & verification, system robustness design, and end-to-end performance modeling.

The Mid-Infrared Instrument (MIRI) is the coldest and longest wavelength (5-28 micron) science instrument on-board the James Webb Space Telescope observatory and provides imaging, coronography and high and low resolution spectroscopy. The MIRI thermal design is driven by a requirement to cool the detectors to a temperature below 7.1 Kelvin. The MIRI Optics Module (OM) is accommodated within the JWST Integrated Science Instrument Module (ISIM) which is passively cooled to between 32 and 40 K. Thermal isolation between the OM and the ISIM is therefore required, with active cooling of the OM provided by a dedicated cryostat, the MIRI Dewar. Heat transfer to the Dewar must be minimised to achieve the five year mission life with an acceptable system mass. Stringent cleanliness levels are necessary in order to maintain the optical throughput and the performance of thermal control surfaces. The ISIM (and MIRI OM) is launched warm, therefore care must be taken during the on-orbit cooldown phase, when outgassing of water and other contaminants is anticipated from composite structures within the ISIM. Given the strong link between surface temperature and contamination levels, it is essential that the MIRI thermal and contamination control philosophies are developed concurrently.

As detailed instrument design progresses, judgements have to be made as to what changes to allow and when models such as thermal, stray-light and mechanical structure analysis have to be re-run. Starting from a well-founded preliminary design, and using good engineering design when incorporating changes, the design detailing and re-run of the models should bring no surprises. Nevertheless there are issues for maintaining the design and model configuration to a reasonably concurrent level. Using modern modeling software packages and foresight in setting up the models the process is made efficient, but at the same time the level of detail and number of cases now needed for instrument reviews is also large in order to minimise risks. We describe examples from the detailed instrument design of the VISTA IR Camera to illustrate these aspects and outline the design and analysis methods used.

While Systems Engineering appears to be widely applied on the very large telescopes, it is lacking in the development of many of the medium and small telescopes currently in progress. The latter projects rely heavily on the experience of the project team, verbal requirements and conjecture based on the successes and failures of other telescopes. Furthermore, it is considered an unaffordable luxury to "close-the-loop" by carefully analysing and documenting the requirements and then verifying the telescope's compliance with them. In this paper the authors contend that a Systems Engineering approach is a keystone in the development of any telescope and that verification of the telescope's performance is not only an important management tool but also forms the basis upon which successful telescope operation can be built. The development of the Southern African Large Telescope (SALT) has followed such an approach and is now in the verification phase of its development. Parts of the SALT verification process will be discussed in some detail to illustrate the suitability of this approach, including oversight by the telescope shareholders, recording of requirements and results, design verification and performance testing. Initial test results will be presented where appropriate.

With the award of the VISTA project to the United Kingdom Astronomy Technology Centre (UK ATC), the need for a formal systems approach and dedicated systems engineering management was identified as a key requirement for the success of that project. The structuring of projects within the UK ATC has been increasingly biased toward a systems engineering approach. ROE projects such as CGS4, while very successful, were based on a traditional engineering discipline approach. The systems responsibility was split between the Project Scientist and the Project Manager. Such an approach can be made to work on internal projects where the entire team and project sponsor are in close proximity. As instrumentation projects have grown larger, become more complex and increasingly geographically distributed through international collaboration, the need for technical discipline enforced by a formal system engineering approach has correspondingly grown. Internal projects also benefit and are becoming increasingly reliant on systems engineering as a means to mitigating both schedule and budget risks. This paper describes and analyses the ongoing introduction of a formal systems approach within the UK ATC. Structuring of projects through a sub-system approach rather than by discipline, formal requirements capture, traceability and the use of systems tools to monitor performance are described. The introduction of systems engineering as a discipline is discussed and progress to date reported. Systems engineering activities in previous projects and ongoing implementation in current projects are analysed. Lessons learnt are described and future development in the systems approach outlined.

In a joint effort, the European Southern Observatory (ESO), the Institute for Lightweight Structures, Technical University of Munich, and EADS Astrium, Germany, have developed a set of software tools for integrated modeling of astronomical telescopes and interferometers. Integrated modeling aims at time-dependent system analysis combining different technical disciplines (optics, mechanical structure, control system with sensors and actuators, environmental disturbances). As example for the application of this modeling technique, we present an integrated model of the Very Large Telescope Interferometer (VLTI). It can be regarded as a "precursor" model for future telescope or interferometer projects. Besides its demonstrator role, it also serves for practical applications. An example is prediction of the dynamic VLTI output performance at interface-level to future scientific instruments, such as GENIE. The basic output of the integrated model is a complete description of the time-dependent electromagnetic field within a broad spectral range and for each interferometer arm. Alternatively, a more elaborated output can be created, such as a fringe pattern resulting from a superposition of several beams after modal filtering by single-mode fibers. The paper shows the architecture of the integrated model with its components such as telescope structures, optics, control loops and disturbance models for wind load, seismic ground acceleration and atmospheric turbulence. Results illustrating the capability of the model approach are presented.

Fundamental measurement procedures are described that enable full end-to-end characterization of the entire imaging path between astronomical objects and their telescope images. The procedures are based on measurements of certain key properties of point-object (unresolved star) images, properties that carry the essential information about the integrated effects of all mechanisms in the imaging path that contribute to the OPD fluctuations. These mechanisms can include, but are not limited to, atmospheric turbulence, dome turbulence, telescope aberrations, the effect of wind-induced oscillations on large multiple-segment primary mirrors, and the (corrective) effects of Adaptive Optics (AO). The measurement procedures are fully general and take into account amplitude scintillation as well as phase variation in the wavefronts. The effects of atmospheric turbulence are fully encrypted in the statistical properties of the OPD fluctuations in the telescope pupil. In turn, these OPD properties are fully encrypted in the measured point-object image properties. Consequently, there is no need to make a priori assumptions about the form of the turbulence structure function, Kolmogorov or otherwise; the measurement procedures naturally provide the appropriate structure function. Whereas telescope aberrations usually contribute fixed amounts to the total OPD fluctuation, other mechanisms, such as atmospheric turbulence, contribute time-varying amounts. The measurement procedures allow the fixed OPD contributions to be separated from the time varying contributions. If AO is used, it is appropriate to have the AO system running during the measurement procedures, which otherwise remain unchanged. The procedures described are fundamental to establishing appropriate end-to-end wavefront error budgets for ground-based telescopes and to establishing telescope resolution expectations as a function of wavelength.

In the context of the LOFAR preliminary design phase and in particular for the specification of the Station Digital Processing (SDP), a performance/cost model of the system was used. We present here the framework and the trajectory followed in this phase when going from requirements to specification. In the phased array antenna concepts for the next generation of radio telescopes (LOFAR, ATA, SKA) signal processing (multi-beaming and RFI mitigation) replaces the large antenna dishes. The embedded systems for these telescopes are major infrastructure cost items. Moreover, the flexibility and overall performance of the instrument depend greatly on them, therefore alternative solutions need to be investigated. In particular, the technology and the various data transport selections play a fundamental role in the optimization of the architecture. We proposed a formal method [1] of exploring these alternatives that has been followed during the SDP developments. Different scenarios were compared for the specification of the application (selection of the algorithms as well as detailed signal processing techniques) and in the specification of the system architecture (selection of high level topologies, platforms and components). It gave us inside knowledge on the possible trade-offs in the application and architecture domains. This was successful in providing firm basis for the design choices that are demanded by technical review committees.

We describe and demonstrate a telescope performance model based on Monte Carlo simulations. As a specific example, we apply this method to our delivered image quality error budgets for the Advanced Technology Solar Telescope (ATST). The ATST site survey database provides us with probability distributions for parameters that affect image quality, like wind velocity and Fried’s seeing parameter. The histograms characterizing these parameters can be sampled many times randomly to yield fact-based predictions of system performance. From this we are able to estimate the fraction of the time that a given site will meet or exceed the performance goals of the telescope. The calculations are performed using Crystal Ball, an after-market add-in for Microsoft Excel marketed by Decisioneering, Inc. of Denver Colorado.

Telescope mount models correct telescope pointing by compensating for repeatable errors. Geometric misalignments and manufacturing errors account for most of the repeatable variation. The pointing performance of a telescope depends strongly on the ability to accurately estimate the repeatable errors in the presence of other sources of uncertainty. This paper reviews the factors contributing to uncertainty in pointing models and describes an approach to eliminating one common but controllable cause of model degradation.

In the past decade, new tools have been offered to the system designers in terms of thermal and mechanical modeling. In addition to an overwhelming increase of computer capabilities, these tools are now mature enough to drive the design of complex astronomical instruments, in particular if these instruments have to be cooled. This is the case of WIRCam, the new wide-field infrared camera to be installed on the CFHT in Hawaii on the Mauna Kea summit. This camera uses four 2Kx2K Rockwell Hawaii-2RG infrared detectors and includes 2 optical barrels and 2 filter wheels. This camera is mounted at the prime focus of the 3.6m CFHT telescope. The mass to be cooled is close to 100 kg. The camera will use a Gifford Mac-Mahon closed-cycle cryo-cooler in order to avoid strenuous daily re-fillings on the telescope due to the camera location. This paper will present the thermal-mechanical model of the camera using Finite-Element Analysis under the I-deas software. The capabilities of the I-deas thermal module (TMG) will be demonstrated for our particular application: including conduction, radiation and free-convection management, variations of the cooling power and thermal characteristics of the materials as a function of the temperature, and studies in permanent regime and transient analysis. The hypotheses used for the thermal model are explained and results of the model are shown to explain the choice of the cryo-cooler. Predicted performances (cooling down time, warm-up time, and mechanical deformations) are presented and compared to measurements. All these models were carried out using a normal PC laptop running I-deas/TMG.

Recent advancements in computational fluid dynamics (CFD) software development (namely incorporation of unstructured meshing, wall functions and advanced turbulence modeling) now make it possible to perform a full three dimensional turbulent airflow analysis without the need for a supercomputer. A commercially available CFD code was used to investigate the effect of the WFCAM (a wide field camera developed by Astronomy Technology Centre at Royal Observatory of Edinburgh) presence in the airflow through the optical path of the United Kingdom Infrared telescope (UKIRT). The necessity of this investigation arises from the fact that WFCAM is placed directly above the primary mirror of the UKIRT telescope. There is very little information available in the literature about the possible adverse effects of this configuration on telescope performance, namely seeing and additional wind loading. The CFD code chosen to carry out the study utilizes a wall function for treatment of the near-wall solution. This approach requires only one node in the boundary layer and results in a significant reduction of required computing capacity. The results presented in the study include the effects of turbulent fluctuations of the airflow, natural and forced convection, and wind loading predictions on the instrument with the telescope at several positions.

A parametric cost model for ground-based telescopes is developed using multi-variable statistical analysis of both engineering and performance parameters. While diameter continues to be the dominant cost driver, diffraction limited wavelength is found to be a secondary driver. Other parameters such as radius of curvature were examined. The model includes an explicit factor for primary mirror segmentation and/or duplication (i.e. multi-telescope phased-array systems). Additionally, single variable models based on aperture diameter were derived.

Because of the complexity of the Terrestrial Planet Finder (TPF) design concepts, the project will rely heavily on the use of engineering and science simulations to predict on-orbit performance. Furthermore, current understanding of these missions indicates that the 3m to 8m class optical systems need to be as stable as picometers in wavefront and sub-milli arcsec in pointing. These extremely small requirements impose on the models a level of predictive accuracy heretofore never achieved, especially in the area of microgravity effects, material property accuracy, thermal solution convergence, and all other second order modeling effects typically ignored. New modeling tools and analysis paradigms are developed which emphasize computational accuracy and fully integrated analytical simulations. The process is demonstrated on sample problems using the TPF Coronagraph design concept. The TPF project is also planning a suite of testbeds through which various aspects of the models and simulations will be verified.

The Terrestrial Planet Finder interferometer design concepts are large and complex systems that must operate in environments that are impractical to reproduce in preflight testing. The structurally- connected design is 36 meters long - longer than all but one thermal vacuum chamber in existence. The formation flying design will be comprised of up to five separate spacecraft, each with a sunshield over 15 meters on a side, and is designed to operate with formation sizes spanning 60-100 meters. System-level verification of the performance of the designs will rely on analytical modeling. The effort to model the many physical aspects of the designs under study is under way. This paper describes the program of modeling for the TPF-I concepts. The program includes a number of types of models, such as the standard stand-alone optics, thermal, and structural models, as well as an end-to-end performance model of the project system called the Observatory Simulation. Aspects of each model are discussed including the purpose, methods of implementation (software applications), and approaches to validation. Program-level considerations (such as model-to-model integration and configuration management) are also discussed. Given that there are at least seven different organizations contributing to model developments and more than twenty separate models, these are special challenges.

The Kepler Mission is designed to characterize the frequency of Earth-sized planets in the habitable zones of solar-like stars in the solar galactic neighborhood by observing >100,000 main-sequence stars in a >100 square degree field of view (FOV) and seeking evidence of transiting planets. As part of the system engineering effort, we have developed an End-To-End Model (ETEM) of the photometer to better characterize the expected performance of the instrument and to guide us in making design trades. This model incorporates engineering information such as the point spread function, time histories of pointing offsets, operating temperature, quantization noise, the effects of shutterless readout, and read noise. Astrophysical parameters, such as a realistic distribution of stars vs. magnitude for the chosen FOV, zodiacal light, and cosmic ray events are also included. For a given set of design and operating parameters, ETEM generates pixel time series for all pixels of interest for a single CCD channel of the photometer. These time series are then processed to form light curves for the target stars and the impact of various noise sources on the combined differential photometric precision can be determined. This model is of particular value when investigating the effects of noise sources that cannot be easily subjected to direct analysis, such as residual pointing offsets, thermal drift or cosmic ray effects. This version of ETEM features extremely efficient computation times relative to the previous version while maintaining a high degree of fidelity with respect to the realism of the relevant phenomena.

High quality multi-disciplinary integrated models are needed for complex opto-mechanical spacecraft such as SIM and TPF in order to predict the system's on-orbit behavior. One major activity in early design is to examine the system's behavior over multiple configurations using an integrated model. A three step procedure for model tuning is outlined that consists of (1) applying engineering insight to the model so that all physical systems are present in the model, (2) using optimization to automatically update system parameters that are uncertain in the model, and (3) evaluating the model at several configurations using the updated parameters. The key contribution of this work is the systematic checking of the validity of the updated parameters by evaluating, both in the model and the experiment, the system at different configurations (step three). It is hypothesized that if the simulation model and experimental data of the additional configurations match well then the tuned system parameters were indeed updated in a way that physically represents the system. This three step process is applied to a testbed at the MIT Space System Laboratory.

Within the scope of the DARWIN Technology and Research Programme, the European Space Agency (ESA) initiated the development of a dynamic system simulator (called FINCH "Fast Interferometer Characterization") for the spaceborne nulling interferometry mission DARWIN.The FINCH project is realized by two parallel activities: (1) a simulator for the Guidance, Navigation and Control (FINCH/GNC) of the free-flying satellite array, and (2) a simulator for the optical subsystems and the beam propagation within the system (FINCH/OPT). While the GNC activity is handled by EADS Astrium, France, the optical part is performed in a joint effort by EADS Astrium, Germany, and the European Southern Observatory (ESO). In this paper we focus on FINCH/OPT aspects and describe: • DARWIN and the corresponding overall end-to-end simulation approach • the completed FINCH/OPT development for modelling of point sources • modelling of extended objects, exact and with suitable approximations • details of optical modelling of DARWIN configurations within FINCH • applications of FINCH

A sound system engineering approach and the appropriate tools to support it are essential in achieving the scientific and financial objectives of the Thirty Meter Telescope project. Major elements of the required tool set are those providing estimates for the performance of the telescope. During the last couple of years, the partners in the consortium developed a wide range of modeling and simulation tools with various levels of fidelity and flexibility. There are models available for time domain and frequency domain simulations and analysis, as well as for lower fidelity, parametric investigations of design trade-offs and for high fidelity, integrated modeling of structure, optics and control. Presented are characteristic simulation results using the existing preliminary point designs of the TMT, with emphasis on the telescope performance degradation due to wind buffeting. Under the conditions modeled, the wind induced image jitter and image quality degradation was found comparable to good atmospheric seeing.

The Euro50 is an astronomical extremely large telescope for optical and infrared wavelength with a 50 m primary mirror. The telescope will have an elaborate control system ("live optics") to correct for atmospheric and telescope aberrations. To study and predict performance of the complete telescope system, an integrated model combining the structural model of the telescope, optics models, the control systems, and the adaptive optics has been established. Wind is taken into account on the basis of wind tunnel measurements and computer fluid dynamics calculations. Atmospheric aberrations are included using a seven-layer atmosphere model. The integrated model is written in Matlab and is run on a cluster computer to achieve acceptable execution times. Dedicated ordinary differential equation solvers have been written and a special toolkit for communication between Matlab processes on different nodes of the cluster computer has been set up. Preliminary results from the complete integrated model, including adaptive optics, are shown.

A parametric model of the dynamic performance of an optical telescope due to wind-buffeting is presented. The model is being developed to support the design of next generation segmented-mirror optical telescopes through enabling rapid design iterations and allowing a more thorough exploration of the design space. A realistic performance assessment requires parametric descriptions of the wind, the structural dynamics, active control of the structure, and the optical response. The current model and its assumptions are presented, with the primary emphasis being on the parameterization of the wind forces. Understanding the temporal spectrum and spatial distribution of wind disturbances inside the telescope enclosure is one of the most challenging aspects in developing the overall parametric model. This involves integrating information from wind tunnel tests, computational fluid dynamics, and measurements at existing observatories. The potential and limitations of control to mitigate the response are also discussed, with realistic constraints on the control bandwidth obtained from the detailed structural model of a particular point design. Finally, initial results are presented on performance trends with a few key parameter variations.

The Terrestrial Planet Finder (TPF) mission, to be launched in 2014 as a part of NASA's Origins Program, will search for Earth-like planets orbiting other stars. One main concept under study is a structurally connected interferometer. Integrated modeling of all aspects of the flight system is necessary to ensure that the stringent dynamic stability requirements imposed by the mission are met. The MIT Space Systems Laboratory has developed a suite of analysis tools known as DOCS (Disturbances Optics Controls Structures) that provides a MATLAB environment for managing integrated models and performing analysis and design optimization. DOCS provides a framework for identifying critical subsystem design parameters and efficiently computing system performance as a function of subsystem design. Additionally, the gradients of the performance outputs with respect to design variables can be analytically computed and used for automated exploration and optimization of the design space. The TPF integrated model consists of a structural finite element model, optical performance model, reaction wheel isolation stage, and attitude/optical control systems. The integrated model is expandable and upgradeable due to the modularity of the state-space subsystem models. Optical performance under reaction wheel disturbances is computed, and the effects of changing design parameters are explored. The results identify redesign options that meet performance requirements with improved margins, reduced cost and minimized risk.

Arroyo is an open source, cross-platform C++ class library project designed for modeling of electromagnetic wave propagation through atmospheric turbulence and adaptive optics systems. This paper describes the functionality available in the library and discusses future plans for this project.

The next generation of ground-based telescopes will have apertures of 20 meters or more and will be increasingly dependent on active and adaptive optics (AO) to deliver good image quality. A numerical model of the complete telescope system, including optical, mechanical, and atmospheric seeing effects, will be a vital tool during the design process. The Thirty Meter Telescope (TMT) / Very Large Optical Telescope (VLOT) Integrated Model (IM) is written in MATLAB and runs on a Windows PC. One goal of the IM is to study the interaction of various AO designs with several telescope configurations. This requires the inclusion of an AO simulation engine; the IDL-based CAOS code was chosen as a starting point. Socket based software was developed to allow MATLAB MEX functions called from the IM to control the CAOS code running on a Linux PC. Software was also developed to allow MATLAB MEX functions to interact with IDL on the same Windows computer using callable IDL.

Wind loading is one of the critical parameters influencing the performance of large telescopes, with potentially more dramatic consequences for proposed future giant telescopes. This study describes a strategy for modeling the effects of wind loading on extremely large telescopes such as the Thirty Meter Telescope (TMT). The optical performance of the telescope is estimated by an integrated model, which incorporates the telescope structure, optics, and control. To model the dynamic force variation on the telescope, a Finite Element Analysis (FEA) model of the telescope is created along with an unsteady Computational Fluid Dynamics (CFD) model of the airflow around the enclosure-telescope configuration, which should have a suitable level of geometric fidelity. Numerical simulations using the CFD model are performed for a chosen wind speed and telescope orientation (azimuth, zenith), through which the dynamic force pattern on the primary and secondary mirrors as well as on the secondary support structure can be determined. Finally the force pattern is applied to the FEA model. This can be achieved either by applying temporally and spatially filtered white noise forces with random distribution deducted from the CFD analysis, or by considering the dynamic force pattern itself from the unsteady CFD calculations. Since the FEA and CFD models usually have different resolution requirements and consequently different, non-uniform spatial sampling grids, a key part of the interface is the conversions necessary to transfer the forces from CFD surface cells to structural nodes.

A variety of aerodynamic studies have been completed to assist in the development of an integrated model for the Thirty Meter Telescope. These studies investigated the characteristics of wind loading on the Canadian Very Large Optical Telescope (VLOT) and produced preliminary data for input into the VLOT integrated model. We describe the details of, and present the results from, the computational fluid dynamic (CFD) analyses and wind tunnel (WT) tests. The validity of the CFD results is assessed through correlation studies that compare the CFD and WT results. Through extensive comparison of the mean and RMS coefficients of pressure and the power spectral density plots of the pressures within the enclosure, excellent correlations between the experimental and computational results are shown.

Modeling extremely large ground based optical telescopes is growing in complexity as the level of design detail is increasing. Our model of a 30m telescope includes a modal system of differential equations that represent the telescope structure, an edge controller to monitor and correct the gaps between mirrors of the hexagonally segmented primary mirror, an optical engine that propagates light through the telescope and calculates performance metrics at the exit pupil of the telescope, and a course optical control that can correct the wavefront for tip and tilt. Simulating one minute of telescope observing time with wind and atmospheric disturbances is a computationally intense proposition. The software tools in our arsenal include MATLAB (The MathWorks, Inc.) and OSLO (Lambda Research Corporation). Descriptions of the simulation components, and the results of telescope simulations are presented.

All current proposals for the construction of Extremely Large (30- to 100-m) ground-based Telescopes (ELTs) assume segmentation of (at least) the primary mirror. This has implications for the low-level structure of their PSFs which are likely to be significant for a number of important scientific applications, including the potential detection and characterization of terrestrial planets orbiting nearby solar-type stars. Several studies of these effects have been carried out; all rely on Fourier methods applied to an approximate model of the telescope entrance pupil. Concerned that these methods may be prone to quite significant errors we have undertaken a physical optics analysis. This numerical simulation uses methods well-established in long-wave optics, with well-defined convergence criteria, to model the PSF of a 50-m segmented-primary telescope. Our results are in very close agreement with those from Fourier methods when an F/16 system is modelled, but significant differences are seen when a more realistic F/1 system is modelled. We also present preliminary results of simulations of an "imperfect telescope". The regular diffraction pattern seen from the perfect mirror is almost completely destroyed even when the form errors and alignment errors of the segments are sufficiently small to maintain a Strehl ratio of 90%.

Primary mirrors of the next generation of extremely large telescopes will be highly segmented. Since these telescopes will be equipped with adaptive optics (AO), it is very important to examine in details what are the consequences of different segmentation schemes on the delivered image quality after AO correction. We do so using our analytical AO simulation code PAOLA {Performance of Adaptive Optics for Large (or Little) Apertures}, upgraded to include AO correction of the primary mirror static aberrations. This study allows us to derive requirements on the geometry of the primary mirror, and the maximum acceptable segments positioning and figuring errors knowing that part of their amplitude will be corrected by the AO system offset. The first important issue is the influence of the segments size and gap width. These parameters have indeed a strong impact on the structure of the wings of the diffraction limited point spread function (PSF), but on the other hand, with the smooth AO residual halo superimposed onto it, the relative importance of the wing structures is decreased. To assess these effects, we consider the case of an AO system working in a near infrared classical mode on a 30-m segmented telescope and examine how the encircled energy radius and image contrast evolve with segment size and gap width. The second important issue is the effect of residual segment positioning & figuring errors after active optics and AO correction. Using appropriate metrics, we characterise the maximum acceptable segment positioning & figuring errors residuals in a classical AO mode, for one of the pupils studied in the first part of our work.

Optical imaging test beds are used increasingly to demonstrate advanced imaging concepts and to anchor system simulation and modeling tools in reality. It is important to use a rigorous system engineering approach to the design of laboratory test beds so that the objectives of the test bed will be achieved. This paper will discuss some of the common mistakes that can be avoided by using a system engineering approach to the design. Specific examples will be presented.

The presentation illustrates the standard life cycles and project phases of a typical large scale astronomical facility acqui-sition and development project and explains the role of Systems Engineering (SE) during the entire project life cycle. The basic SE philosophy and systematic SE approach are described and a road map identifying the main activities of SE during the individual project phases - from the requirement definition to the eventual validation of the erected system- is developed. In addition the presentation describes the methodologies and processes SE can offer to analyse the risks asso-ciated with the definition, development and implementation of large complex scientific infrastructure projects. Risk control methods and approaches which are necessary to systematically reduce the technical, financial and schedule risks to a level acceptable to the scientific / technical project management and to the funding agencies are explained.

Systems Engineering (SE) is the discipline in a project management team, which transfers the user's operational needs and justifications for an Extremely Large Telescope (ELT) -or any other telescope-- into a set of validated required system performance characteristics. Subsequently transferring these validated required system performance characteris-tics into a validated system configuration, and eventually into the assembled, integrated telescope system with verified performance characteristics and provided it with "objective evidence that the particular requirements for the specified intended use are fulfilled". The latter is the ISO Standard 8402 definition for "Validation". This presentation describes the verification and validation processes of an ELT Project and outlines the key role System Engineering plays in these processes throughout all project phases. If these processes are implemented correctly into the project execution and are started at the proper time, namely at the very beginning of the project, and if all capabilities of experienced system engineers are used, the project costs and the life-cycle costs of the telescope system can be reduced between 25 and 50 %. The intention of this article is, to motivate and encourage project managers of astronomical telescopes and scientific instruments to involve the entire spectrum of Systems Engineering capabilities performed by trained and experienced SYSTEM engineers for the benefit of the project by explaining them the importance of Systems Engineering in the AIV and validation processes.

The international environment of the astronomical research and the world wide distribution of astronomical institutes and observatories create a high demand of flexibility from the designers and engineers developing and building the scientific instruments for use in astronomical research programs. In particular, with respect to the safety performance characteristics of the scientific instruments, a harmonization process among the various safety requirements could lead to more safety awareness and understanding of these requirements. Additionally, some kind of standardization in the methods and means used during the acquisition of the instruments would reduce safety risks to an acceptable level

We present a quality criterion for telescopes based on the fulfillment of observation needs as defined by a client. It is intended for the pre-conception and broad control level. The criterion is built from the fidelity measure by limiting the spatial scales taken into account to the scales useful to the proper imaging of the detail of interest. By construction this mono-dimensional criterion allows trade-off between spatial and radiometric resolution. The comparison of different design strategies is also possible, for example between undersampled large aperture telescopes and well sampled smaller telescopes. It can also be used to predict the usefulness of each available telescope for a given observational purpose. Being global, the criterion requires only high-level specifications, thus allowing the client to exercise a greater degree of control over the instrument definition. We present here a pre-calibration of the mission quality criteria enabling to give an absolute quality value for the telescope and to determine whether the observation mission is fulfilled. A comparison of test-case telescopes is then made by varying several design parameters.

The high-performance nature of VISTA, the Visible & Infra-Red Survey Telescope for Astronomy, with its wide-field high-throughput f/1 optical design coupled with the multi-organisation, multi-disciplinary nature of the VISTA collaboration places significant demands on the project's Systems Engineering function. The project has relied heavily on a Systems Engineering approach, which has been vigorously applied throughout the conception, specification, and tendering stages of the project lifecycle, and is in place to be continued through the remaining phases of design & development, manufacture, assembly, commissioning, verification and acceptance. As the project matures from the Requirements/Design phase towards the Development and Manufacturing phase, the current status of the VISTA project is illustrated in terms of its Systems Engineering aspects, along with examples of how a formal Systems Engineering approach has resulted in benefits to the important project parameters of performance, cost and schedule. Key tools such as engineering budgets, configuration control procedures and the approach to risk management will be discussed in terms of their value to the project.

AMOS S.A. is a small company specialised in the fields of opto-mechanical, thermal and vacuum technology. To develop, manufacture and test the ESO VLTI Auxiliary Telescope System (ATS) was considered internally as a big challenge. ATS is a large-sized project and difficult to manage for a small company (since ATS, AMOS has hired about 25 people and now employs about 60 people). ATS is also technically a very complex system because of the following reasons: • Unusual telescope (mobile telescope) • Very tight system performances (e.g. Image quality, OPD, Pointing) • Severe design constraints because of existing site interfaces (e.g. volume, mass) and environment (including wind and earthquake) • Multidisciplinary engineering system (mechanical, optical, electrical, thermal, pneumatic, hydraulic) This paper describes how this project has been managed in practice by AMOS and also the important role of the system engineering. The last paragraph will be dedicated to the main lessons learned.

In this paper, we consider the design of minimum time maneuvers for multi-spacecraft interferometric imaging systems. We show that the process of image formation in a multi-spacecraft interferometric imaging system is analogous to painting a "large disk" with smaller "paintbrushes", while maintaining a minimum thickness of paint. We show that spiral maneuvers form the dominant set for the painting problem. Further, we frame the minimum time problem in the space of spiral maneuvers and obtain the Double Pantograph Problem. We show that the solution of the Double Pantograph Problem is given by the solution to two associated linear programming problems. We illustrate our results through an imaging example where the image of a fictitious exo-solar planet is formed using the maneuver prescribed by the Double Pantograph Problem.

The Terrestrial Planet Finder (TPF) project aims to detect and characterize extra-solar Earth-like planets. The coronagraph telescope is one of the two mission concepts being studied. To reject the star flux and detect the planet flux in the visible light range, the coronagraph telescope must achieve a rejection ratio on the order of a billion to one. Dynamic jitter, introduced by environmental and on-board mechanical disturbances, degrades the optical performance, as characterized primarily by contrast ratio. The feasibility of using passive vibration isolation combined with active attitude and line-of-sight (LOS) control systems to stabilize the spacecraft and the optical components to the requisite level is being studied. The telescope is also required to slew between targets or rotate around the LOS. The slew mode control law must be designed to balance the need for efficient large-angle maneuvers while simultaneously avoiding the excitation of flexible modes in order to minimize settling time. This paper provides an overview of the current control design concept and sensor/actuator topology for TPF Coronagraph and illustrates the fine pointing performance of the telescope. This performance is primarily a function of the rejection of high-frequency dynamic disturbances, in this case due to reaction wheel disturbance forces/torques transmitted through the passive isolation stage. Trade studies between isolator force rejection and disturbance level reduction via wheel redesign are also presented to illustrate the requirements imposed on current technologies. Finally, the paper summarizes preliminary results on the slew/settle performance of the telescope.

We present a method for simulating CCD focal plane array (FPA) images of extended deep sky objects using Data Modeling. Data Modeling is a process of deriving functional equations from measured data. These tools are used to model FPA fixed pattern noise, shot noise, non-uniformity, and the extended objects themselves. The mathematical model of the extended object is useful for correlation analysis and other image understanding algorithms used in Virtual Observatory Data Mining. We apply these tools to the objects in the Messier list and build a classifier that achieves 100% correct classification.

We describe a software tool developed to simulate the behaviour of the angle between two lines of sight in a dual view telescope assembly (usually referred to as basic angle) due to optical misalignments induced by thermo-mechanical fluctuations. The tool applies to a variety of reflective optical designs. In principle, not only the basic angle behaviour can be simulated, but also other optical parameters. As a practical example, we present and discuss results obtained from application of our software to the case of the Gaia baseline optical design. We show that the final error can be severely degraded by fluctuations of the basic angle due to thermo-mechanical effects.

The support system of the primary mirror of 2.1m telescope at SPM allows correction of some optical aberrations. A low cost Active Optics System (AOS) can be developed based on this property of the support system. Within the preliminary development of this system, computer simulations were being performed. The general propose of simulations was to find the optimal scheme for the wavefront control of the primary mirror. This paper presents results for the wavefront sensor of the AOS proposed for the 2.1m telescope at San Pedro Martir.

The wavefront sensor is an important part of active control for an Active Optics System (AOS). The wavefront sensibility of a beam compressor is experimentally tested on the 2.1m telescope at SPM. This is a simple wavefront sensor based on the wave propagation equation. A qualitative analysis of the experimental data is presented. It is concluded that the beam compressor has enough sensibility to be used as a wavefront sensor for the AOS.

Telescope mount models use a mathematical model to introduce commanded position adjustments to compensate for predictable pointing errors. The parameters of the model are estimated from observed pointing deviations on a set of calibration stars. These calibration measurements generally contain random noise and other features that limit the precision of the parameter estimates and ultimately degrade pointing. This paper compares the ability of various statistical solution methods to improve the precision of the parameter estimates and improve pointing

The requirements for position, orientation and performance of the primary mirror active support system have been optimised through extensive FEA to minimise the wavefront slope error. The output of this optimisation has been a detailed performance specification which also takes into account telescope control and wind rejection requirements. The FE model has also been used to calculate the active force eigenmodes based on the static actuator patterns rather than approximations to the vibration modes. In addition significant development and prototyping has been undertaken in the actuator and definer design including control. Interesting aspects of this development include use of flexures in the mirror definers in order to meet the stiffness requirements and control of a pneumatic astatic system. This paper describes the process of requirement optimisation for mirror performance and also the development and design of the support system.

The enclosure for the Advanced Technology Solar Telescope (ATST) is both a wind shield and a source of seeing. Its design must minimize self-induced seeing while remaining within cost constraints and balancing with other error budget items. We report the methods used to quantify seeing performance, including thermal modeling, seeing estimation, and systems engineering error budgets. Thermal modeling is performed using a commercial software package that applies measured site weather data to a CAD-generated enclosure model. Seeing estimation is performed using a simple aerodynamic treatment. The results, along with measured site wind and temperature distributions, are combined into a "bottom-up" performance prediction using Monte Carlo techniques.

The infrared camera for the Visible and Infrared Survey Telescope for Astronomy (VISTA) sets many technical challenges for mechanical and thermal design. The flexion between optical subsystems must be minimised to maintain alignment in various camera orientations and meet performance requirements. Thermally induced stresses, atmospheric pressure and earthquake loads place high demands on structural components, some of which must also thermally isolate the cold (~70 K) detectors and optics. The success of the design hinges on the optimisation of heat flow to minimise thermal loads on the detectors whilst holding external temperatures very close to ambient to reduce misting and convective disturbances in the field of view. This paper describes the mechanical and thermal components of the design and discusses the analyses in detail.

The integrated modeling tools for Canada's 20-meter telescope model, VLOT, have advanced significantly in the last year. Specifically, the flexibility of the tool and the pre-processing and post-processing functions have been enhanced. Also, closed loop control of the primary mirror and feeding the optical displacements through an adaptive optics tool, have been developed. This paper details the enhancements made to the tool and discusses the future challenges of the integrated modeling team.

In this paper, we report on extending a theoretical framework based on Gaussian Beam Mode Analysis for modelling standing waves in receiver systems coupled to submillimetre wave telescopes. This analytical technique includes a full electromagnetic description of corrugated detector horns, used as a standard feed horn in the THz frequency range. In previous papers we reported on the underlining theory and described some important examples including reflections between a feed horn and telescope secondary mirror and also reflections between a horn and a plano-convex lens. As the theory uses a full multi-moded scattering matrix description within the horn, which can then be transformed to equivalent free space modes, mulitple reflections between the detector, located at the back of the horn, and any arbitrary surface in the optical path can be accurately analysed. We present an experimental validation of the model, comparing predicted standing wave patterns occuring between two corrugated horns to laboratory measurements, owrking in a frequency range around 0.1THz.

The Fourier-Kelvin Stellar Interferometer (FKSI) has been proposed to detect and characterize extra solar giant planets. The baseline configuration for FKSI is a two-aperture, structurally connected nulling interferometer, capable of providing null depth less than 10-4 in the infrared. The objective of this paper is to summarize the process for setting the top level requirements and the jitter analysis performed on FKSI to date. The first part of the paper discusses the derivation of dynamic stability requirements, necessary for meeting the FKSI nulling demands. An integrated model including structures, optics, and control systems has been developed to support dynamic jitter analysis and requirements verification. The second part of the paper describes how the integrated model is used to investigate the effects of reaction wheel disturbances on pointing and optical path difference stabilities.

This paper presents an application of the neuro-fuzzy modeling to analyze the time series of solar activity, as measured through the relative Wolf number. The neuro-fuzzy structure will be optimized based on the linear adapted genetic algorithm with controlling population size (LAGA-POP). First, the dimension of the time series characteristic attractor is obtained based on the smallest Regularity Criterion (RC) and the neuro-fuzzy modeling. Second, after describing the neuro-fuzzy structure and optimizing its parameters based on LAGA-POP, the performance of the present approach in forecasting yearly sunspot numbers is favorably compared to that of other published methods. Finally, the comparison predictions for the remaining part of the 22nd and the whole 23rd cycle of solar activity are presented.

HIFI is one of the three instruments for the Herschel Space Observatory, an ESA cornerstone mission. HIFI is a high resolution spectrometer operating at wavelengths between 157 and 625 μm. The need for a compact layout reducing the volume and mass as much as possible has important consequences for the optical design. Many mirrors are located in the near-field of the propagating beam. Especially in the long wavelength limit diffraction effects might therefore introduce significant amplitude and phase distortions. A classical geometrical optical approach is consequently inadequate. In this paper we present a rigorous quasi-optical analysis of the entire optical system including the signal path, local oscillator path and onboard calibration source optical layout. In order to verify the results of the front-to-end coherent propagation of the detector beams, near-field measurement facilities capable of measuring both amplitude and phase have beam developed. A remarkable feature of these facilities is that the absolute coordinates of the measured field components are known to within fractions of a wavelength. Both measured and simulated fields can therefore compared directly since they are referenced to one single absolute position. We present a comparison of experimental data with software predictions obtained from the following packages: GRASP (Physical Optics Analysis) and GLAD (Plane Wave Decomposition). We also present preliminary results for a method to correct for phase aberrations and optimize the mirror surfaces without changing the predesigned mechanical layout of the optical system.

In this paper we discuss the use of an innovative SIM simulator, called SIMsim, to perform end-to-end simulations of the SIM mission. The inputs to the simulator are a physically-based parameterization of the major SIM error sources and the output is the mission astrometric accuracy for various observing scenarios such as narrow-angle (NA) and wide-angle (WA) observations. The primary role of SIMsim is to validate the SIM astrometric error budget (AEB), but it is also being used to study a variety of mission performance issues as well as being a test-bed for prototype data reduction algorithms. SIMsim is giving us confidence that the SIM AEB is a valid estimate of mission performance. It also is illustrating where analytical formulas for estimating certain effects breakdown and a numerical approach has to be adopted.

The Heterodyne Instrument (HIFI) is part of the ESA Herschel Space Observatory Project. The instrument is intended for high-resolution spectroscopy and has a frequency coverage from 480 to 1250 GHz band in five receiver bands and 1410 to 1910 GHz in two additional bands. HIFI is built based on a modular principle: the mixers together with their respective optics are integrated into Mixer Sub-Assemblies (MSA). Each frequency band has two MSAs allocated for horizontal and vertical polarization. In this paper, we present the work done on the design and construction of a Gaussian beam measurement range. One of the unique features of the developed method is a possibility to measure the beam parameters of the MSAs in the absolute coordinate system referred to the device under test. This along with other methods should allow integration of the entire HIFI with the best possible coupling of the antenna beam to the receivers and achieving ultimate performance in such a complicated optical system. The range houses the measured MSA, which is at 4 K ambient temperature, and a continuous wave source placed on a precise scanner entirely under vacuum. Developed triangulation system provides mechanical reference data on the MSA, in-situ, after the entire system is evacuated and the cooling is finished. We adopted a scalar measurement approach where the test source scans the receiver input beam and the mixer IF power is measured. The data collected from 3-4 planar scans are used to calculate the orientation and position of the optical axis. We present results from the first beam measurements for MSA HIFI bands 1 and 2 (480 and 640 GHz), the measurement system performance and accuracy analysis.

This paper depicts the general analysis before designing optics for an APS based star sensor. The high accuracy requirement and low sensitivity of APS make the optics overcritical. To avoid the extreme difficulty in optics, we abstract the PSF models in sub-pixel scale as the compensation for the distortion error. Both centroid and correlation algorithm are used to determine the spot center. The result of the simulation is presented in the text.

MATLAB and its companion product Simulink are commonly used tools in systems modelling and other scientific disciplines. A cross-disciplinary integrated MATLAB model is used to study the overall performance of the proposed 50m optical and infrared telescope, Euro50. However the computational requirements of this kind of end-to-end simulation of the telescope's behaviour, exceeds the capability of an individual contemporary Personal Computer. By parallelizing the model, primarily on a functional basis, it can be implemented across a Beowulf cluster of generic PCs. This requires MATLAB to distribute in some way data and calculations to the cluster nodes and combine completed results. There have been a number of attempts to produce toolkits to allow MATLAB to be used in a parallel fashion. They have used a variety of techniques. Here we present findings from using some of these toolkits and proposed advances.

Integrated modeling has become a standard tool for evaluating performance of optical telescopes for design optimization and controller development. The integrated model combines structural dynamics, optics and control systems into a single simulation which outputs optical metrics of the telescope under the action of disturbances. The latter include external loads on the telescope, such as wind, seismic or temperature loads, as well as control inputs, which are provided by the actuators of the telescope system. Structural dynamics is a central part of the integrated model and its accurate representation is essential for high fidelity simulation. Traditionally, a structural dynamics model is derived from finite element analysis of the telescope and it is prohibitively large in size for practical simulation. In this paper, we investigate the use of model order reduction (MOR) techniques to resolve this problem for a Very Large Optical Telescope (VLOT). We propose a practical two-step procedure for obtaining a reduced model of the telescope. The finite element model is first reduced by truncating modes above a certain eigenfrequency. Subsequently, this truncated model is further reduced by a suitable MOR method to retain the more relevant lower frequency modes. In this paper, we compare several MOR methods both in frequency and time domain. The reduced models’ dynamic characteristics are compared with the truncated model of the telescope system. Finally, delivered image quality predictions are compared for the reduced systems of VLOT subject to wind loading.

Next generation giant telescopes are under study around the world, with great variety in size and pupil segmentation scheme. We present performance calculations for different pupil segmentation geometries, in the presence of segment surface errors and residual atmospheric phase errors after Adaptive Optics correction. Optical performance is evaluated through point-spread function (PSF) calculation. Pupil segmentation parameters include segment size and shape, gap diffraction, and segment surface errors. We consider large, 8m-class, circular or polygonal segments, and small, 2m-class, hexagonal segments. These options represent the choices of the different telescopes design groups. Our segmentation scheme consists of eight polygonal petals forming a filled octagonal pupil. All segment and pupil edges are along four unique directions, minimizing the number of diffraction spikes in the PSF, creating large areas of low levels of scattered light close to the core. This is important for high-dynamic range imaging. Comparison between polygonal and circular petals shows that, in addition to the presence of low-scatter areas, the encircled energy is higher. One of the most challenging goal for these future ground-based telescopes is the exo-planet detection and observation. The integration in a single model of the telescope pupil shape, aberrations on the mirrors, AO residual wavefront errors provides an evaluation of the capacity of future extremely large telescopes in the key domain of high dynamical range imaging.

ESO will measure pressure fluctations on the surface of the 76m radio telescope at Jodrell bank and on a scaled down model of this telescope in a wind tunnel. The data will be used to calculate the effect of pressure variations on the overall deformation of the mirror and in particular the effect on segment to segment misalignments taking into account the correction capabilities of the segment supports.

ESA's DARWIN mission is to accomplish the unprecedented challenge of finding Earth-like planets orbiting nearby stars. To tell apart the planet from its blinding 'sun', the system relies upon nulling interferometry: the light collected by six free-flying telescopes is recombined inside a central 'hub', in a way that the beams from the star are 'nulled', while those from the planet interfere constructively. The diameter (50 to 500m) of the free-flying interferometer is determined by the need for angular resolution. In contrast, the differences in optical pathlength between the incoming beams must be kept below 5 nm. It is the purpose of the ongoing "Interferometer Constellation Control" Research & Development study for the European Space Agency (ESA) to propose a design and validate the performances for the GNC system adapted to such a high-precision formation-flying application. The requirements & detailed design of this GNC system are addressed first, including the close connection with the parallel ESA study called "High Precision Optical Metrology" used to verify the feasibility of the critical DARWIN optical metrology system. Then, the modelling & performance assessment of the GNC system is presented, together with the way forward to build a high precision coupled optical/GNC simulator.

Most imaging systems today include a mosaic detector array in the focal plane. Optical designers of astronomical telescopes typically produce a design that yields a superb on-axis aerial image in the focal plane, and detector effects are included only in the analysis of the final system performance. Aplanatic optical designs (corrected for spherical aberration and coma) are widely considered to be superior to non-aplanatic designs. However, there is little merit in an aplanatic design for wide field applications because one needs to optimize some field weighted average measure of resolution over the desired operational field of-view (OFOV). Furthermore, when used with a mosaic detector array in the focal plane, detector effects eliminate the advantage of the aplanatic design even at small field angles. For wide fields of view, the focal plane is frequently despaced to balance field curvature with defocus thus obtaining better overall performance. We will demonstrate that including detector effects in the design process results in a different optimal (non-aplanatic) design for each OFOV that is even superior to an optimally despaced aplanatic design.