By Bob Fosbury

With this post I want to point out a new website that contains an important collection of interviews and essays from Michael Perryman. These provide a unique inside view of the development of space astrometry from before 1980 to the present spectacular success of ESA’s Gaia spacecraft currently operating from the second Lagrangian Point orbit one and a half million kilometres from Earth.

His website also hosts an updated second edition of his Exoplanet Handbook published by Cambridge University Press in 2018 along with a number of fascinating essays on mathematics.

I provide a brief introduction to the story in the text below this URL for Michael’s website:

Michael Perryman worked for the European Space Agency (ESA) and was appointed project scientist for the Hipparcos space astrometry satellite at the early age of 26. Its task was to measure unprecedentedly precise positions of over 100,000 stars out to distances of several hundred light years using methods that were around 200 times more accurate than previous catalogues.



The satellite was launched in August 1989 into a highly eccentric Earth orbit, ready for transfer to its intended Geostationary position. However, the rocket motor designed to achieve this orbit change failed to ignite, leaving the satellite to plunge regularly into the damaging Van Allen radiation belts. When all attempts to ignite the rocket had failed, Michael and the ESA operations engineers worked tirelessly to understand how to keep the satellite operating for as long as possible in its current orbit and how to redesign the entire programme of measurements to recover as much of the science programme as was possible.

With this heroic effort, the satellite lasted somewhat longer than its design goal of three years and the entire science programme was completed to levels of accuracy greater than expectations. The final Hipparcos Catalogue was published in 1997 along with a larger list of 2.5 million stars with somewhat reduced acciracy.

This catalogue represented a huge leap in our knowledge of the three dimensional positions of stars in our Galactic neighbourhood and it carried many profound implications for physics well beyond the field of stellar astrometry. Given the success of the mapping methodology, it was natural to think of a successor that would both greatly increase the precision of measurement and extend its reach throughout and beyond our Milky Way galaxy.

In collaboration with the prominent astrometrist Lennart Lindegren from Lund University, Michael pursued this idea which led to a proposal for funding being made to ESA in 1993. This was to construct a larger, more complex spacecraft that would become known as GAIA (Global Astrometric Interferometer for Astrophysics). This was eventually selected as a ‘Cornerstone’ of the agency’s Horizon 2000 Plus long-term scientific plan in October 2000. Although the final design of the spacecraft was not actually an interferometer, the name Gaia was kept for project continuity. Michael subsequently led the project though its detailed design, technology development, and data analysis preparation through to his retirement from ESA in 2009.


Gaia was successfully launched from Kourou in French Guiana in 2013 and is currently scanning the sky from a position some 1.5 million kilometres from Earth to produce a revolutionary 3D star map containing positions of around 2 billion stars, varying fractions of which will include other data such as colours, spectra, radial velocities etc.

Data collection is expected to continue until the end of 2023.

The story of the Hipparcos Mission is told by Michael in his book: “The Making of History’s Greatest Star Map”, Michael Perryman, Springer-Verlag, 2010.

Michael is currently producing a number of audio interviews with the scientists and engineers responsible for the realisation of both Hipparcos and Gaia. These provide a priceless documentary record of these two very major scientific space missions. He is also recording interviews with scientists who wrote some of the thousands of scientific papers already published based on the Gaia results.

Along with other material, including an updated version of the 2nd edition of the Exoplanet Handbook and a fascinating set of around 50 short (2 page) essays on relevant science topics, this material is now available on Michael’s website:

The next Gaia public data release by ESA, Gaia Data Release 3, expected in June 2022, will take place within the 200th anniversary year of the death of William Herschel, marking a period that spans a remarkable developments in the history of mapping the sky.

(Original post November 2021; updated to 22 March 2022)