The more you delve into Europe's space agenda, the more you realise we're onto some pretty special stuff. The Gaia mission - launched in December 2013 - is no exception. It's one of those missions you could easily overlook, but at the same time one of such huge significance - and imagination.

Gaia: a five year mission to map a billion stars from the depths of space - far beyond the Moon's orbit. It is measuring motion, luminosity, temperature and composition of the stars. The data will tell unknown stories about the evolution of our galaxy.

And the first of that data is released on September 14, 2016. Gaia mission manager, Dr Fred Jansen, told DW why we should care.

Fred Jansen: Well, basically, it is the biggest star catalogue in our Milky Way ever. We've never before achieved this level of accuracy. And what you can do with that is look back into the history of our galaxy - but that's just one example. [People are saying] Gaia will revolutionize science. There are people who have already planned what they call "sprints" as soon as the Gaia data is released - to look at the data in a team and immediately think about publishing. Some even say that within a month of the data release, there will probably be one 100 papers submitted using Gaia data.

They will use Gaia data to supplement their own research?

Yes.

And in what areas can we expect this research?

In galactic dynamics - the history of the environment of our solar system - and where we are going, quite literally. There is the period luminosity relationship, which is used to build the cosmic distance ladder.

The cosmic distance ladder is made up of a few basic principles, starting with the relationship between period and luminosity of objects. And if we can now calibrate the luminosity of those objects, because we know the distance accurately, we can do the same for identical objects at much farther distances, or even in other galaxies. It's the first step in building a cosmic distance ladder to our known horizon.

Gaia has been dubbed a "cornerstone" mission for Europe. Has no other space agency attempted to map the galaxy in this way - the Americans, or others?

Strangely enough, astrometry [the science of measuring the positions and movements of stars] is almost exclusively a European thing. Although the Japanese do have something planned, but it's rather small. Europe had a precursor mission, too, called Hipparcos in the late 1980s.

So is this an area of expertise that Europe has over other space agencies?

Yes, but I wouldn't tie it necessarily to the European Space Agency. We do serve the European community, but scientifically, there's always been a lot of interest for astrometry in Europe. And if you look historically, it was people like Tycho Brahe, the Danish astronomer, who charted the sky to levels of accuracy that had never been achieved before. So it's always been a European type of activity. But why? That I find very hard to analyze!

What have the first two years been like for Gaia? We know about some early technical difficulties, but has it been a smooth ride?

No, I wouldn't call it a smooth ride, but on the other hand I wouldn't exaggerate it either. We've had our share of difficulties. I've worked on five or six spacecraft in orbit, and almost every mission has had its challenges once in space.

With Gaia, we observed a number of problems, and first we had to find out what they were. Then we had to adapt either software on the spacecraft or software on the ground. And that means using resources for things we didn't originally plan to use them for, which causes delays here and there - and that's why I'm extremely pleased this data release is here. It's actually earlier than we thought, despite some of the setbacks and challenges we've met on the way.

Looking at one of those setbacks in detail, we know you've had issues with water freezing on some of the optics, and that reduced the sensitivity of the telescopes. What did you do there? Could you just adapt the software to fix the problem?

The system - that is the spacecraft - has a built-in capability to heat itself and the [telescope] mirrors. That's been done a few times to drive off contamination, and it works very efficiently. In the beginning, the contamination returned rather quickly, but at the moment the rate of return is such that we don't have to decontaminate more than once a year. We just decontaminated at the end of August and the one before that was in June 2015 - so the rate of re-contamination is decreasing.

We adjust the software to correct for any potential effects. There may be wavelength dependant issues in the photometers. That will be the challenge for the next data release, but not this first one, because we're not including photometer data.

And the full data will be ready by the early 2020s. That's sometime after the mission ends...

We plan to have three more data releases, and then a final data release in 2022. There will be data from the photometer, the radial velocity spectrometer. We're currently using a parallax for two million objects - a distance derived using prior data from the Tycho catalogue, which is based on that earlier Hipparcos mission. But the next data release will be a Gaia-only solution. We're going to see more and more detail, and more and more scientific content with the data over the next few years.

Dr Fred Jansen is the Gaia Mission Manager. He was also a mission manager on the Rosetta mission, which landed the Philae probe on Comet 67P/Churyumov-Gerasimenko.