In Measuring the Universe I described the ESA Hipparcos mission in detail. Hipparcos was the first space-based mission dedicated to astrometry: it mapped the precise position of 100000 stars, and by doing so helped firm one of the first steps on the cosmological distance ladder. In the book I wrote that:
“the success of Hipparcos has led ESA … to consider further space astrometry missions. A proposed ESA mission, cclled the Global Astrometric Interferometer for Astrophysics (GAIA), would measure the parallaxes of one billion stars down to magnitude 20, with a precision 100 times better than that of Hipparcos.”
I gave two possible launch dates for GAIA: 2009 or 2014. When I wrote the book, both dates seemed impossibly distant. But time passes, and GAIA is on track for launch on board a Soyuz rocket in 2013.
In September 2011, the mission team took receipt of the last of ten state-of-the-art mirrors. These mirrors will form the heart of a system that will study a billion stars in our Galaxy, observing each star 70 times in order to pinpoint its location. The GAIA catalogue, which will be finalised some time in 2021, will provide us with a superb three-dimensional map of the Galaxy. The value of this map won’t be so much in developing our understanding of the distance ladder; rather, it will tell us volumes about how the Milky Way formed and subsequently evolved.
Keep an eye out for GAIA.