posted 12-19-2013 03:00 PM               

Liftoff for ESA’s billion-star surveyor

ESA's Gaia mission blasted off this morning on a Soyuz rocket from Europe's Spaceport in Kourou, French Guiana, on its exciting mission to study a billion suns.

Gaia is destined to create the most accurate map yet of the Milky Way. By making accurate measurements of the positions and motions of 1% of the total population of roughly 100 billion stars, it will answer questions about the origin and evolution of our home Galaxy.

The Soyuz launcher, operated by Arianespace, lifted off at 09:12 GMT (10:12 CET). About ten minutes later, after separation of the first three stages, the Fregat upper stage ignited, delivering Gaia into a temporary parking orbit at an altitude of 175 km.

A second firing of the Fregat 11 minutes later took Gaia into its transfer orbit, followed by separation from the upper stage 42 minutes after liftoff. Ground telemetry and attitude control were established by controllers at ESA's operations centre in Darmstadt, Germany, and the spacecraft began activating its systems.

The sunshield, which keeps Gaia at its working temperature and carries solar cells to power the satellite, was deployed in a 10-minute automatic sequence, completed around 88 minutes after launch.

Gaia is now en route towards an orbit around a gravitationally-stable virtual point in space called L2, some 1.5 million kilometres beyond Earth as seen from the Sun.

Tomorrow, engineers will command Gaia to perform the first of two critical thruster firings to ensure it is on the right trajectory towards its L2 home orbit. About 20 days after launch, the second critical burn will take place, inserting it into its operational orbit around L2.

A four-month commissioning phase will start on the way to L2, during which all of the systems and instruments will be turned on, checked and calibrated. Then Gaia will be ready to begin its five-year science mission.

Gaia's sunshield will block heat and light from the Sun and Earth, providing the stable environment needed by its sophisticated instruments to make an extraordinarily sensitive and precise census of the Milky Way's stars.

"Gaia promises to build on the legacy of ESA's first star-mapping mission, Hipparcos, launched in 1989, to reveal the history of the galaxy in which we live," says Jean-Jacques Dordain, ESA's Director General.

"It is down to the expertise of Europe's space industry and scientific community that this next-generation mission is now well and truly on its way to making ground-breaking discoveries about our Milky Way."

Repeatedly scanning the sky, Gaia will observe each of the billion stars an average of 70 times each over the five years. It will measure the position and key physical properties of each star, including its brightness, temperature and chemical composition.

By taking advantage of the slight change in perspective that occurs as Gaia orbits the Sun during a year, it will measure the stars' distances and, by watching them patiently over the whole mission, their motions across the sky.

The position, motion and properties of each star provide clues about its history, and Gaia's huge census will allow scientists to piece together a 'family tree' for our home Galaxy.

The motions of the stars can be put into 'rewind' to learn more about where they came from and how the Milky Way was assembled over billions of years from the merging of smaller galaxies, and into 'fast forward' to learn more about its ultimate fate.

"Gaia represents a dream of astronomers throughout history, right back to the pioneering observations of the ancient Greek astronomer Hipparchus, who catalogued the relative positions of around a thousand stars with only naked-eye observations and simple geometry," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"Over 2000 years later, Gaia will not only produce an unrivalled stellar census, but along the way has the potential to uncover new asteroids, planets and dying stars."

By comparing its repeated scans of the sky, Gaia will also discover tens of thousands of supernovas, the death cries of stars as they reach the end of their lives and explode. And slight periodic wobbles in the positions of some stars should reveal the presence of planets in orbit around them, as they tug the stars from side to side.

Gaia will also uncover new asteroids in our Solar System and refine the orbits of those already known, and will make precise tests of Einstein's famous theory of General Relativity.

After five years, the data archive will exceed 1 Petabyte or 1 million Gigabytes, equivalent to about 200 000 DVD's worth of data. The task of processing and analysing this mountain of data will fall to the Gaia Data Processing and Analysis Consortium, comprising more than 400 individuals at scientific institutes across Europe.

"Where Hipparcos catalogued 120 000 stars, Gaia will survey almost 10 000 times as many and at roughly 40 times higher precision," says Timo Prusti, ESA's Gaia project scientist.

"Along with tens of thousands of other celestial and planetary objects, this vast treasure trove will give us a new view of our cosmic neighbourhood and its history, allowing us to explore the fundamental properties of our Solar System and the Milky Way, and our place in the wider Universe."

"After years of hard work and determination of everyone involved in the mission, we are delighted to see our Gaia discovery machine on the road to L2, where we will continue the noble European tradition of star charting to decipher the history of the Milky Way," adds Giuseppe Sarri, ESA's Gaia project manager.

The spacecraft was designed and built by Astrium, with a core team composed out of Astrium France, Germany and the United Kingdom.

posted 04-02-2025 11:26 AM               

Farewell, Gaia! Spacecraft operations come to an end

The European Space Agency (ESA) has powered down its Gaia spacecraft after more than a decade spent gathering data that are now being used to unravel the secrets of our home galaxy.

On 27 March 2025, Gaia's control team at ESA's European Space Operations Centre carefully switched off the spacecraft's subsystems and sent it into a 'retirement orbit' around the Sun.

Though the spacecraft's operations are now over, the scientific exploitation of Gaia's data has just begun.

Gaia's stellar contributions

Launched in 2013, Gaia has transformed our understanding of the cosmos by precisely mapping the positions, distances, motions, and properties of nearly two billion stars and other celestial objects. It has provided the largest, most precise multi-dimensional map of our galaxy ever created, revealing its structure and evolution in unprecedented detail.

The mission uncovered evidence of past galactic mergers, identified new star clusters, contributed to the discovery of exoplanets and black holes, mapped millions of quasars and galaxies, and tracked hundreds of thousands of asteroids and comets. It also enabled the creation of the best visualisation of how our galaxy might look to an outside observer.

"Gaia's extensive data releases are a unique treasure trove for astrophysical research, and influence almost all disciplines in astronomy," says Gaia Project Scientist Johannes Sahlmann.

"Data release 4, planned for 2026, and the final Gaia legacy catalogues, planned for release no earlier than the end of 2030, will continue shaping our scientific understanding of the cosmos for decades to come."

Saying goodbye is never easy

Gaia far exceeded its planned lifetime of five years, and its fuel reserves are dwindling. The Gaia team carefully considered how best to dispose of the spacecraft in line with ESA's efforts to responsibly dispose of its missions.

They wanted to find a way to prevent Gaia from drifting back towards its former home near the scientifically valuable second Lagrange point (L2) of the Sun-Earth system and minimise any potential interference with other missions in the region.

"Switching off a spacecraft at the end of its mission sounds like a simple enough job," says Gaia Spacecraft Operator Tiago Nogueira. "But spacecraft really don't want to be switched off."

"Gaia was designed to withstand failures such as radiation storms, micrometeorite impacts or a loss of communication with Earth. It has multiple redundant systems that ensured it could always reboot and resume operations in the event of disruption."

"We had to design a decommissioning strategy that involved systematically picking apart and disabling the layers of redundancy that have safeguarded Gaia for so long, because we don't want it to reactivate in the future and begin transmitting again if its solar panels find sunlight."

On 27 March 2025, the Gaia control team ran through this series of passivation activities. One final use of Gaia's thrusters moved the spacecraft away from L2 and into a stable retirement orbit around the Sun that will minimise the chance that it comes within 10 million km Earth for at least the next century.

The team then safely deactivated and switched off the spacecraft's instruments and subsystems one by one, before deliberately corrupting its onboard software. The communication subsystem and the central computer were the last to be deactivated.

"Today, I was in charge of corrupting Gaia's processor modules to make sure that the onboard software will never restart again once we have switched off the spacecraft," says Spacecraft Operations Engineer, Julia Fortuno.

"I have mixed feelings between the excitement for these important end-of-life operations and the sadness of saying goodbye to a spacecraft I have worked on for more than five years. I am very happy to have been part of this incredible mission."

Gaia's final transmission to ESOC mission control marked the conclusion of an intentional and carefully orchestrated farewell to a spacecraft that has tirelessly mapped the sky for over a decade.

A lasting legacy

Though Gaia itself has now gone silent, its contributions to astronomy will continue to shape research for decades. Its vast and expanding data archive remains a treasure trove for scientists, refining knowledge of galactic archaeology, stellar evolution, exoplanets and much more.

A workhorse of galactic exploration, Gaia has charted the maps that future explorers will rely on to make new discoveries. The star trackers on ESA's Euclid spacecraft uses Gaia data to precisely orient the spacecraft. ESA's upcoming Plato mission will explore exoplanets around stars characterised by Gaia and may follow up on new exoplanetary systems discovered by Gaia.

The Gaia control team also used the spacecraft's final weeks to run through a series of technology tests. The team tested Gaia's micro propulsion system under different challenging conditions to examine how it had aged over more than ten years in the harsh environment of space. The results may benefit the development of future ESA missions relying on similar propulsion systems, such as the LISA mission.

Forever in Gaia's memory

The Gaia spacecraft holds a deep emotional significance for those who worked on it. As part of its decommissioning, the names of around 1500 team members who contributed to its mission were used to overwrite some of the back-up software stored in Gaia's onboard memory.

Personal farewell messages were also written into the spacecraft's memory, ensuring that Gaia will forever carry a piece of its team with it as it drifts through space.

As Gaia Mission Manager Uwe Lammers put it: "We will never forget Gaia, and Gaia will never forget us."