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Launch preparations begin for Gaia galaxy-mapper

Posted: 22 August 2013

Europe’s new eye on the galaxy arrived in French Guiana on Friday, beginning three months of flight preparations before liftoff on a Soyuz rocket in November to commence a survey of a billion stars and chart their chaotic motion in the Milky Way galaxy.

Artist's concept of the Gaia spacecraft. Credit: ESA/ATG medialab; background image: ESO/S. Brunier
The Gaia observatory will be stationed a million miles from Earth, its dual telescopes sweeping across the sky with the sensitivity to plot the exact locations and movements of stars, detect the signatures of alien worlds, and spot icy dwarf planets on the outer frontier of the solar system.

The breadth of Gaia’s scientific promise ranges from scanning the Milky Way to create a three-dimensional map of the galaxy to the discovery of asteroids in Earth's neighborhood. Scientists say Gaia could return data leading to the discovery of up to 2,000 planets around other stars – mostly Jupiter-sized gas giants. And the European space mission has the precision to test tenets of Albert Einstein’s theory of general relativity by observing how the pull of the sun and planets bend starlight before it reaches Gaia’s apertures.

In five years, Gaia will collect a petabyte of data, enough to fill 1.5 million compact discs. It will see a billion stars, more than ever observed by any other mission, and use information about those objects to study the origin and evolution of the Milky Way.

“The estimate of the number of stars in the Milky Way is between 100 and 200 billion stars, so we observe between one-half and one percent of these stars,” said Timo Prusti, Gaia’s project scientist at the European Space Agency. “Because of the completeness of Gaia to a limiting magnitude, this proving of 1 percent of these objects will help us reconstruct the remaining part. We’re not going to take a full census of the Milky Way, but we are going to look at a billion stars and we’ll have enough statistical power to deduce the structure of the Milky Way.”

A team of scientists and engineers has worked on Gaia since the mission was approved by the European Space Agency in 2000. The mission’s cost is 740 million euros, or approximately $990 million.

After of 13 years of development, design reviews, construction and testing, Gaia is one step closer to the launch pad.

Liftoff is scheduled for Nov. 20 at 0857 GMT (3:57 a.m. EST; 5:57 a.m. local time) aboard a Europeanized version of Russia’s Soyuz rocket. The mission will mark the seventh flight of a Soyuz booster from French Guiana, and a Fregat upper stage will propel Gaia on a trajectory toward the L2 Lagrange point about a million miles from the night side of Earth, where gravity from the Earth and sun balance a satellite’s motion.

The Gaia spacecraft traveled from its factory in Toulouse, France, to French Guiana this week, arriving in the predawn hours Friday at the territory’s only international airport in the capital of Cayenne. Technicians unloaded Gaia from its Antonov An-124 transport plane and delivered the spacecraft to the European-run Guiana Space Center in nearby Kourou via local highways.

“The most exciting moment is the work toward the launch itself, and the fact that it’s shipped to Kourou makes it very real,” Prusti said.

Giuseppe Sarri, Gaia’s project manager, said the An-124 cargo jet landed about 3:50 a.m. local time (0650 GMT) Friday in Cayenne after an overnight flight from Toulouse.

It is the first of two Gaia shipments from Toulouse to French Guiana. Friday’s flight carried the Gaia spacecraft, including its service module and science instruments. Another An-124 flight Aug. 28 will deliver the sunshield, designed to keep Gaia’s instruments and dual telescopes in shadow during the mission.

The Antonov An-124 cargo plane with Gaia sits on the tarmac at Cayenne - Felix Eboue Airport after arriving in French Guiana. Credit: ESA/Giuseppe Sarri
Built by an industrial team led by Astrium Satellites, Gaia needs the sunshield to control temperatures inside the probe’s dual telescopes, focal plane and instrumentation. Gaia’s payload module will be maintained at a constant minus 166 degrees Fahrenheit, according to ESA.

“This is the start of the launch campaign,” Sarri said. “In the first month, we will do plenty of checks on the spacecraft. Once we have the spacecraft in the clean room, we will do inspections, and we will do some basic functional testing to check that everything is still fully functional after the transport. Then we will integrate the sunshield on the spacecraft.”

Engineers will test the deployment of the sunshield inside the clean room in Kourou, extending it to a diameter of 10 meters, or 33 feet. The sunshield will be folded against the body of the spacecraft for launch.

“This is the first big chunk of activity, which takes place in one dedicated clean room in French Guiana,” Sarri said. “Then we move the spacecraft to another place called the hazardous payload facility because we need to fuel the spacecraft and put the propellant in the tanks.”

Gaia will launch with about 296 kilograms, or 652 pounds, of propellant. The bulk of the fuel will be consumed about a month after launch, when the probe maneuvers into orbit around the L2 Lagrange point. Some of the propellant will feed Gaia’s cold gas micro-propulsion system, which will keep the telescope in a stable spin at a rate of four rotations per day.

"When [fueling] is done, we go to another place where we integrate the spacecraft on the adapter, which is an interface cone to adapt the spacecraft to the launcher,” Sarri said. “Then we integrate the spacecraft, plus the adapter, on the Fregat, which is the fourth stage of the launcher. Then we close the composite with the two fairing halves and we have the upper part of the rocket ready. At that point in time we go to the launch pad, and there we will integrate this upper composite cylinder on top of the Soyuz three-stage rocket.”

Gaia and the Fregat upper stage will be attached to the Soyuz launcher four days before the Nov. 20 liftoff.