ELSA (European Leadership in Space Astrometry) is a four-year, EU-funded ResearchTraining Network ending in September 2010. It has employed 10 postgraduate students and 5postdocs for 2–3 years and financed a number of workshops, training events and topicalmeetings, culminating in the present symposium. The primary goal of ELSA is to train youngscientists in the context of the Gaia project while contributing to the scientificpreparations for the mission. The organization, aims and history of ELSA are outlined.

Gaia is an ESA mission to build a census of our Milky Way Galaxy. This is done with a suite of three instruments combining two fields of view into a single focal plane. On-board detection of all sources will ensure a bias free survey down to the 20th magnitude. In addition to astrometry also photometry is done down to the 20th magnitude. The third, spectroscopic instrument will provide radial velocities down to the 17th magnitude of the Galactic stellar population. Currently the scientific requirements on Gaia are largely met except for bright stars for which in astrometry additional efforts are needed to squeeze the remaining μarcsecs out of the positional information error budgets. In the mid-magnitude range (15 mag) the end of mission parallax errors are from 10 to 25 μarcsec and photometry errors are between 5 and 16 mmag. Radial velocities are better than 1 km s-1 for the bright stars with errors increasing to 15 km s-1 for the faintest ones. At the moment there are no unsolvable technical challenges on the table and Gaia is progressing toward the launch in 2012.

Gaia is the sixth cornerstone of the ESA Scientific Programme. Beginning 2006, the programme implementation phase was kicked off at Astrium Satellites. At summer 2010 all Critical Design Reviews of the modules have been passed successfully, which enables to give a good snapshot of the development progress. This presentation summarizes the history of the satellite programme. The status of the current development will be presented with a focus of the main challenging equipment, with a particular insight on the payload.

For more than ten years, a collaboration of European scientists has been producingsimulations of the Gaia mission. These simulations range from detailed realistic simulatedCCD images to large volume simulations of the Gaia telemetry.

The data of this decade of simulations has been used for many purposes: instrumentdesign, data processing software testing and validation, prediction of missionperformances, etc. Today the launch date is getting closer and the task of the simulatorin the mission preparation will be wrapped up in a couple of years.

However, this is not the end of the story since the Gaia simulator can also be used forthe preparation of the scientific exploitation of the Gaia data. In this talk we willpresent the simulator and its components, the data it can produce and the perspectives forthe utilisation of this data during the mission, both for data evaluation and scientificexploitation.

Testing instrument capabilities is a crucial issue for Gaia, where high levelperformances are expected. This activity involves many aspects: simulation of theinstrument through suitable modelling, comparison of the models with the actualinstrument, as well as producing evaluation methods, which are strictly related to the waydata will be processed and calibrated. In this paper I discuss the interconnections amongthese aspects, and provide some example from the current testing activities.

Algorithms aimed at the evaluation of critical quantities are based on models with manyparameters, which values are estimated from data. The knowledge, with high accuracy, ofthese values and the control of their temporal evolution are important features. In thiswork, we focus on the latter subject, and we show a proposed pipeline for the BAM (BasicAngle Monitoring) Long Term Analysis, aimed at the study of the calibration parameters ofthe BAM device and of the Basic Angle variation, searching for unwanted trends, cyclicfeatures, or other potential unexpected behaviours.

A detailed study of the Hipparcos attitude exposed events in the satellite’s motion (micro-meteorite hits and clanks) that require special adaptations in the attitude reconstruction modelling. Identifying these events in the data stream, and incorporating them in a specially designed dynamical attitude modelling, has led to an overall reduction in the attitude reconstruction noise from 3 mas down to 0.6 mas. Considering that the main noise contribution on the astrometric data for stars brighter than magnitude 8 in the Hipparcos catalogue originated from the attitude reconstruction, and that this noise led to correlated parallax errors for neighbouring stars, it was decided to redo the astrometric reductions of the Hipparcos data. This was completed in 2007, and resulted in the publication of a new catalogue. The lesson to be learnt for Gaia is, that incorporating a detailed understanding of the satellite’s motions in the attitude modelling can have a significant impact on the overall reliability of the final astrometric data produced by the mission.

The Gaia Attitude Model (GAM) is a simulation package that is developed to achieve adetailed understanding of the Gaia spacecraft attitude. It takes into account externalphysical effects and considers internal hardware components controlling the satellite. Themain goal of the Gaia mission is to obtain extremely accurate astrometry, and thisrequires a good knowledge of Gaia’s behaviour as a spinning rigid body under the influenceof various disturbances.

This paper describes the damage occurring in CCDs exposed to solar radiation and explainsits implications for the Gaia measurements by focusing on the astrometric instrument. Itintroduces the strategy that will be used in the Gaia data processing to mitigate theradiation induced effects, and presents CEMGA (CTI effects Models for Gaia) amulti-purpose platform which hosts different models that simulate radiation effects onCCDs.

To fulfil its numerous science objectives, the Gaia mission needs to account for theimpact of the radiations at CCD level. Through the defects generated in the silicon, theradiations will not only degrade the overall signal-to-noise ratio of the measurements,but also corrupt them with a bias to be corrected on ground. In order to characterize thiseffect, and help deriving a proper calibration strategy, an extensive radiation testcampaign has been carried out in EADS Astrium since 2006, covering the differentinstruments and CCD variants. We present an overview of this radiation test bench, and thedifferent investigations performed so far and associated findings.

The Gaia pixel-level data simulator GIBIS (Gaia Instrument and Basic Image Simulator,Babusiaux (2005)) provides detailed artificial data for all three instruments on-board theGaia spacecraft. This data is used for the preparation of procedures required for theanalysis of real Gaia data to come during the mission. Among the effects that stronglyaffect all Gaia data, that therefore have to be modelled with GIBIS, is charge transferinefficiency (CTI). CTI, caused by radiation-induced microscopic defects in the CCDdetectors, becomes manifest in a distortion of the line spread functions of observedobjects, as well as in a loss of photo-generated charges inside the window allocated toeach observed source. It affects the astrometric, photometric, and spectroscopic accuracyof the data. The CTI effects on a particular observation depend on observations donebefore, on CCD operations such as gate activity and charge injections, and on physicaleffects such as the sky background brightness and cosmic ray events in the detectors. Inthis paper, an approach for the simulation of CTI with GIBIS is presented and theinfluence of the sky background brightness and cosmic ray events of CTI is discussed inmore detail.

The paper summarizes the current status of light detectors in astronomy with focus on space science missions. Due to the effort and time needed for the necessary space qualifications, new technologies potentially interesting for space applications are commonly developed and tested for use at on-ground observatories and flown once the technology has matured. But the space environment also requires the development of special detectors for spectral ranges only detectable beyond earth’s atmosphere or the development of features and technological enhancements, for example to mitigate space radiation effects. An overview of detector technologies from the visible to short wavelength infrared (SWIR) band together with an outlook to the challenges of a next generation of light detectors for space astronomy missions.

A considerable amount of computing power is needed for Gaia data processing during the mission. A pan European system of six data centres are working together to perform different parts of the processing and combine the results. Data processing estimates suggest around 1020 FLOP total processing is required. Data will be transferred daily around Europe and with a final raw data volume approaching 100 TB. With these needs in mind the centres are already gearing up for Gaia. We present the status and plans of the Gaia Data Processing Centres.

This paper is a summary of a presentation done during the ELSA conference in Sèvres, onJune 7th 2010 to describe the actions of the French space agency for space astronomy.

It starts by remembering what was done for Hipparcos, then on more recent astronomyprograms. It describes the supporting role of CNES for the French astronomy laboratories,and the acting role in the DPAC consortium for the Gaia data processing: CNES isintegrating the scientific chains of object processing (CU4), spectroscopic processing(CU6) and astrophysical parameters (CU8) in one processing centre. It will be operated inCNES during the whole Gaia mission.

Life science researches have been profoundly impacted by technological advances allowingfaster and cheaper DNA sequencing. Opening a wide range of applications in medical andbiology, the last generation sequencing platforms raised new challenges, in particular inprocessing, analysing and interpreting massive data. In this talk, the growing role ofbioinformatics will be illustrated by providing some figures about genome sequencing andothers applications aimed at unravelling biological mechanisms. Methods to gather insightsfrom massive amount of data will be illustrated by the genome annotation process, by whichgenes are identified in the genome sequence.

In this paper we discuss a few aspects of the data volume to be generated by the ESA space astrometry mission Gaia. This volume is assessed first from the on-board point of view in the form of the instantaneous number of sources in the combined astrometric fields of view as a function of time. Then one focuses on the data flow for the data processing itself measured by the number of objects entering the pipeline every day. Finally the combination of the on-board acquisition scheme with the number of stars per day gives the actual telemetry volume to be transferred to the ground and its variation during the mission.

Java is one of the most widely used computer programming languages, however its use in High Performance Computing (HPC) is relatively low. A typical HPC environment consists of a number of multi-core computing nodes, while a typical application running in such an environment will normally contain CPU intensive code that can be executed in parallel. Such an application may require inter-node as well as intra-node communication. Message Passing Interface (MPI) is a language independent specification of an API to allow such communication. MPJExpress (Baker et al. 2006) and F-MPJ (Taboada et al. 2009) are Java-based implementations of MPI, designed with the efficient performance of data transfers as a main objective. In this paper we discuss the scalability of one approach of distributing data to compute nodes in HPC and we propose the design of an alternative data transfer system, building upon MPI.

We outline the basic principles of scanning space astrometry, such as represented byHipparcos, Gaia, and some other astrometric satellites planned or proposed. We explain theneed for large-angle measurements, why these are essentially one-dimensional, how it ispossible to determine absolute parallaxes, and why a Hipparcos-type scanning law isfavourable. We discuss the choice of the basic angle between the two viewing directions,the principle of self-calibration, and why the resulting numerical problem must bedifficult to solve.

The astrometric global solution is a principal component of the final star catalogue. Itis the solution of a relatively complex least-squares problem related to Gaia’s designthat can only be solved using an iterative process. Hopefully we found an efficientconverging algorithm with a robust stopping criterion. Nonetheless the usage of aniterative algorithm imposes some limitations on our knowledge of the statisticalproperties of the solution such as the variance which need to be investigated furtherthrough simulation techniques.