Current topics:

(2009-01-26) New ODAS description issued:

Stefan Jordan has completed a technical document (GAIA-C3-TN-ARI-SJ-009-01) giving the first reasonably complete technical description of the mathematical algorithms and processing scheme for the operational One-Day Astrometric Solution (ODAS) software to be used in the First Look processing. The ODAS software implements the so-called Ring Solution method to get a quick astrometric calibration and assesssment of the Gaia data from just one day of mission each.
The ongoing transformation of earlier ODAS software prototypes into a largely operational configuration had originally been planned to be complete in the fall of 2008. It was significantly delayed, firstly by the departure of its main developer (Dirk Dorsch) early last year, and secondly by the realization that more functionality had been lacking from the prototype - and in fact had not even been sufficiently specified for a software developer to work on - than previously thought. The former gap was closed by hiring new developers in the course of 2008, the latter gap is now closed by the new document. A quasi-operational ODAS software configuration is planned to be completed by mid 2009.

(2009-01-16) DPAC Project Coordinator starting up:

Today, Emmanuel Mercier is officially starting up work as DPAC Project Coordinator at ESAC Villafranca. He is the head of the growing DPAC Project Office, ultimately to consist of 4 people and to be responsible for several central, europe-wide DPAC functions. The Project Office will care for the practical project administration, project scheduling and reporting for the Gaia consortium DPAC, and be the main point of contact between DPAC and the Gaia Project team of ESA. Emmanuel is formally employed at ARI, through DLR funding.
One of his group members, Gonzalo Gracia, also started up at ESAC this month. He is the DPAC Project Scheduler, formally employed by the University of Barcelona. Start-up of the third Project Office member, the DPAC/ESA Interface Engineer, is to follow soon.

(2009-01-15) New light on the "Pleiades problem" of Hipparcos:

Alex Bombrun, using his experimental implementation of the conjugate gradients method for Gaia (see current topic of 2008-12-05) has shed new light on the "Pleiades problem" of Hipparcos. In 1997 the Hipparcos mission had given a somewhat surprising measurement for the distance of the Pleiades star cluster. Quickly thereafter, F. v. Leeuwen had conjectured that a problem of the data reduction procedure might be (part of) the cause. Alex now has convincingly demonstrated two things: Firstly, the problem suspected by van Leeuwen indeed exists. Secondly, it is not a fundamental problem but due to insufficient numerical convergence. Thus it can be avoided by more iterations, or by using a better iterative method (such as conjugate gradients, maybe). A technical note and publication is in preparation.

(2008-12-10) GaiaTools Committee:

Wolfgang Löffler, chief software engineer of Gaia@ARI, was appointed new member and CU3 representative of the GaiaTools Committee. GaiaTools is the name of DPAC's overarching Java toolbox, containing Gaia-specific astronomical, technical, numerical, mathematical, ... software modules which are used in more than just one DPAC software system. The Committee has the task of controlling and steering the development of the toolbox - to keep it consistent, concise and easily useable.

(2008-12-05) Conjugate gradient method for AGIS:

The Astrometric Global Iterative Solution (AGIS) is the core step in the astrometric data reduction for Gaia. It is being developed in the framework of DPAC's Coordination Unit 3, under the leadership of L. Lindegren (Univ. Lund, Sweden) on the science side, and U. Lammers (ESAC, Villafranca, Spain) on the software development side, with contributions from ARI and TU Dresden. Up to now, a block-iterative scheme has been implemented - and its feasibility and convergence been demonstrated - for the solution of the vast system of equations posed by Gaia's astrometric data reduction task.
The somewhat slow convergence of that scheme has provoked thinking into alternative solution methods. A joint effort of L. Lindegren and Alex Bombrun (ELSA fellow at ARI) has now demonstrated that the method of conjugate gradients (CG) is a viable and promising way to improve the convergence. Today, on a dedicated AGIS meeting at Dresden, Alex presented first results of his implementation of the CG method for the AGIS problem. His software runs in a special development setup called AGISLab which is meant to provide a framework for small-scale scientific experiments on the AGIS problem before moving them to the "full-scale" software trunk.

(2008-11-30) Software release:

A new version of the Detailed First Look Monitor (DFLM) software (see current topic of 2008-05-31) was released for test integration at the Gaia Science Operations Center at ESAC Villafranca. The new version, released according to the 6-monthly cyclical development philosophy of DPAC, features and extended and improved design, and for the first time incorporates the major part of those diagnostics that are deemed launch-critical.

(2008-10-01) ARI's software developer group completed:

With the advent of Shilpa Aguduri, a freshly graduated master of engineering from Halle University, the Gaia software developer group at ARI has for the first time reached its full, planned size of 3.5 FTE. During the last few months of her studies she had already worked as an intern at SAP Walldorf (near Heidelberg), where the vacancy notice of ARI caught her attention.

(2008-09-30) DPAC Project Coordinator selected:

The selection committee (see current issue of 2008-07-31) has selected Emmanuel Mercier to become the DPAC Project Coordinator, i.e. the head of the DPAC Project Office. For about ten years, Emmanuel has done project management for - among others - the French space agency CNES. Formally he will be an addition to the German Gaia contribution (through ARI), but factually he will work at ESAC, Villafranca, Spain.

(2008-08-13) Two new team members:

Early this month, two additional software developers started up in the Gaia@ARI group. Nina Hernitschek is a student who joined us for a few months to do Java programming on the First-Look Monitor (see also current topic of 2008-05-31). Thomas Bruesemeister is a software engineer who on a longer term will work on all aspects of First Look and Gaia Core Processing for which ARI has taken responsibility. His first duties lie within the ongoing ODAS design revision.

(2008-07-31) DPAC Project Office being set up:

June 30 was the deadline of the vacancy notice(s) for the DPAC Project Office positions (see also current topics of 2008-03-05 and 2008-05-06). During July shortlists of candidates were set up by an international selection committee comprising three national representatives (for the funding) and three DPAC Executive members (the actual future collaborators of the persons to be selected). The interviews will take place in September. The DPAC Project Office will hopefully start working in November.

(2008-05-31) "Detailed First Look Monitor" released:

The latest version of the so-called Detailed First Look Monitor (DFLM), one of the software products for the First-Look task to be prepared by the ARI group, was formally delivered today. The DFLM is the part of the First-Look software which "condenses" the First-Look's input data into diagnostics, i.e. extracts characteristic statistical information from the giant heap(s) of data that the First-Look task will daily receive from Gaia's Initial Data Treatment (IDT) and One-Day Astrometric Solution (ODAS) processing steps. The new version features a revised, flexible infrastructure. This is the "skeleton". The "flesh" will be large numbers of specific diagnostics, successively to be added to the skeleton from now on.

(2008-05-16) "WMAP poses for Gaia" made it to ESA Science News:

Martin Altmann's composite photo of WMAP (see "current topic" of 2008-04-18), and Ulrich Bastian's little story explaining it, made it from a Gaia Picture of the Week to the official ESA Science News, and from there to a lot of other media. Apparently, the "human touch" associated with the NASA-ESA connection - along with the pretty representation of the moving object - created this significant media reaction, although the picture itself is not a big achievement scientifically and technically. From the point of view of the scientists preparing Gaia there would be much more exciting things to report. But that's how the media are working. The more exciting things usually are more difficult to convey.

(2008-05-06) DPAC Project Office position(s) announced:

The vacancy notice for the German DPAC Project Office position was released (see also current topic of 2008-03-05). This announcement will shortly be followed by a Spanish one; while Italy has already selected one specific candidate without a general vacancy notice.

(2008-04-18) NASA's WMAP photographed to "simulate" ESA's Gaia:

Sebastien Bouquillon (SYRTE/Obs. de Paris) and Alexandre Andrei (Observatorio National, Rio de Janeiro) have photographed NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite in orbit, located at the Earth-Sun Lagrange point L2, about 1.5 million kilometers from Earth in the antisolar direction. The images were taken on April 5 using the WFI camera at the 2.2m telescope of the European Southern Observatory at La Silla, Chile. This signals the start-up of a test campaign to investigate the feasibility of the so-called ground-based optical tracking of Gaia. The latter will be necessary during the whole of Gaia's scientific mission in order to improve the knowledge of Gaia's orbit - unless a method can be found to improve Gaia's orbit from Gaia's own observations of the stars. The tremendous requirement of 2.5 mm/s and 150 meters for the absolute position and velocity of the spacecraft with respect to the solar-system barycentre cannot be reached by traditional radio ranging and orbit reconstruction techniques. Martin Altmann of ZAH/ARI is in charge of organizing and coordinating the ground-based optical tracking of Gaia.

(2008-04-11) CU3 and CU5 meeting(s) at Barcelona:

This week saw (partly joint) meetings of two of DPAC's Coordination Units at Barcelona: CU3 ("Core Processing", led by Ulrich Bastian of ARI) and CU5 ("Photometry Processing", led by Floor van Leeuwen of IoA, Cambridge). About 60 scientists and software engineers met at Barcelona to discuss the status and planning of the ongoing development work. One of the four days was specifically devoted to common topics and the interface between the two CUs.
The meeting(s) placed a strong focus on the CCD radiation damage effects. New laboratory measurements on irradiated CCDs are emerging from industry, and a heavy effort has been launched within DPAC (under the leadership of Floor van Leeuwen) to develop concepts for the treatment of the effect in the data reduction. There is still a long way to go until we will know exactly how and precisely to which extent the damage can be remedied to conserve the full astrometric and photometric capabilities of Gaia. The radiation damage issue also makes the interface between CU3 and CU5 more complicated. The present concept intends to create an empirical model for the radiation effects on the image profiles. That model is foreseen to be calibrated by CU5 (as part of the overall CCD and PSF calibrations) and to be applied to the raw data by CU3 (in the IDT and IDU processes).

(2008-04-01) Two departures, one addition to the Gaia group at ARI:

At the end of February astronomer Sonja Hirte, and one month later software developer Dirk Dorsch left our group. Both will be replaced by still-to-be-found software developers. Meanwhile Ulrike Stampa started up as half-time software developer. The two departures will lead to a few months of delay in the development of the One-Day Astrometric Solution (ODAS) software, which we hope to catch up by adding one more software developer to the team than we had before.

(2008-03-05) German contribution to the DPAC Project Office:

The German Space Agency DLR has agreed to fund one of the four positions (which are: Project Coordinator, Project Scheduler, DPAC/ESA Interface Engineer, Quality Assurance Engineer) of the DPAC Project Office. The members of that office will be located at the Gaia Science Operations Centre at ESAC, Villafranca. Its formation was suggested by ESA and the leading national funding agencies. Its task will be support the two DPAC chairmen in the day-to-day practical management of DPAC's scheduling, information flow, documentation, reporting, configuration control, quality assurance etc. The German member will be funded and employed through ARI/ZAH.

(2008-02-21) Preliminary Design Review (PDR) on the Gaia Video Processing Unit (VPU):

Mid February Astrium delivered the VPU documentation package. It consisted of 17 documents with a total of 1300 pages. These documents were reviewed for the VPU PDR by ESA's Project Team and by several DPAC representatives. Finally, a total of 31 RIDs (Review Item Discrepancy reports) were submitted from DPAC, 3/4 of which had been generated by Michael Biermann of ARI/ZAH.

(2008-02-08) Structure of the Gaia least-squares problem reveiled:

Alex Bombrun has finished an in-depth investigation (the report is here ) into the feasibility of a direct solution method for the global astrometric least-squares adjustment problem posed by Gaia. For this purpose he studied the sparseness structure of the relevant normal-equation matrix. He found that even a strongly simplified problem yields a minimum-fill-in Cholesky factor that is beyond reasonable treatment. These findings make it very unlikely that any direct method to solve the real Gaia astrometric adjustment problem will be feasible.
The positive side of the results is that the Gaia Nominal Scanning Law has once again been shown to provide an extremely dense and tight geodetic network on the sphere - prerequisite for the self-calibrating nature of the mission and for the internal "rigidity" (i.e. absence of zonal systematic errors) of the final Gaia celestial sphere solution.

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