Gaia/Hipparcos: project interviews

The Gaia Data Processing and Analysis Consortium, DPAC, works with ESA to convert the raw satellite data into the catalogues used by the world-wide scientific community. The Consortium is divided into nine “coordination units” with various responsibilities. Joining me today are the two scientists who have been leading the work of the classification effort: Coryn Bailer-Jones of the MPIA, Heidelberg (Ithaca, 1972) and Orlagh Creevey of the Observatoire de la Côte d'Azur, Nice (Dublin, 1977).

Ulrich Bastian (Haardt, Palatinate, Germany, 1951) started his long career in astrometry with his involvement in the ground-based activities of the Astronomisches Rechen-Institut (ARI, Heidelberg) in the early 1980s. He made leading contributions to the Hipparcos-Tycho project in the 1980s and 1990s and, since the earliest days of the Gaia mission 30 years ago, has played a central role in a number of critical activities, which continue to this day. We look back over this period of major advances in astrometry.

Frédéric Faye (Dijon, 1963) joins me for a second time. In an earlier conversation we talked about the earliest phases of the Gaia project in industry, 10 years or so before launch, and looked at the complexities that were lying ahead when he took over responsibility for the systems engineering in 2005. In this second part, Frédéric describes the organisation of his system engineering group, and some of the management and organisational challenges that his team had to deal with.

Frédéric Faye (Dijon, 1963) was the System Engineering Manager for the Gaia satellite. Within the industrial prime contractor team, Airbus Defence & Space, he was in charge of the satellite design, integration and verification, from 2005, all the way through to the in-orbit commissioning review that took place a few months after the successful spacecraft insertion around L2 in 2014. Today, we're talking about his central role in the design, manufacture, assembly, testing, and launch of Gaia.

Lennart Lindegren (Svalöv, Sweden, 1950) joins me for a second time. In an earlier conversation we talked about the period leading up to the adoption of Hipparcos in 1980. Today (as in my second conversation with Erik Høg), we discuss the Hipparcos mission, from its acceptance in 1980 to its completion in 1997. We talk about his role in the mission development, and in the preparation for - and the analysis of - the data sent down from the satellite. We also talk about his memories of the satellite launch in 1989, and of finalising the Hipparcos Catalogue.

In the second of our two-part interview, Claus Fabricius talks about his activities after Hipparcos. With astrometry no longer supported financially in Denmark, Claus moved to the University of Barcelona in 2005, joining the active Gaia team there to work on the initial data treatment and on the photometry. Later, he took over responsibility for the validation of the successive versions of the Gaia Data Releases, and here he talks about the many tests that are made, pre-publication, on the astrometric and photometric results.

Claus Fabricius (Copenhagen, 1954) spent the first part of his career at the Copenhagen University Observatory in Denmark, where he worked on one of the main instruments contributing to ground-based astrometry in the years preceding Hipparcos. In the first of this two-part interview, Claus talks about his involvement in the development and operation of the Brorfelde transit circle, later as the Carlsberg Automatic Meridian Circle in La Palma, and in the creation of the Tycho Catalogue and its associated initiatives.

In the second of our two-part interview, David Milligan, Spacecraft Operations Manager for Gaia, describes the challenges involved in the spacecraft commissioning, including the problems of 'icing' and 'straylight'. And he talks about keeping the satellite operational and optimised over almost a decade, including optimisation to allow the downlink of significantly more data, and the various tiny effects that can be detected, including bubbles in the propulsion system, micro-meteorites, and the effects of sunspots.

David Milligan (Blackpool, UK, 1971) joined ESA, at its operations centre, ESOC in Germany, in 2000. There, from 2008 to the end of 2020, he was the Spacecraft Operations Manager for Gaia, the leader of the team responsible for its operation, health, and safety. In the first of this two-part interview, David talks about the preparations for the satellite operations in the years leading up to launch, and the major tasks involved in sending it on its way to its intended L2 orbit, 1.5 million km from Earth.

Carme Jordi (Barcelona, 1958) is a senior research scientist at the University of Barcelona. She played a key part in designing the photometric measurements that could - and should - be made with Gaia, and played a key role in the preparation for the photometric data analysis. We talk about the scientific rationale for making photometric observations from the satellite itself, the considerations underlying the design of the photometric system, and how the photometric measurements compare with the original plans.