Europe’s Star-mapping Gaia Satellite Finally Launch Pad-bound


TOULOUSE, France — Europe’s Gaia satellite, designed to provide a 3-D map of 1 billion stars in the Milky Way and plot their movement, mass, composition and age, is set to leave its manufacturing site here Aug. 2 to prepare for a late-October launch on a Europeanized version of Russia’s Soyuz rocket.

Seven years in development and 13 years after it was formally approved by European space scientists, Gaia will provide an order-of-magnitude improvement over the performance of Europe’s Hipparcos satellite, which was launched in 1989 and produced a map of 100,000 stars.

The Gaia industrial contracting team, led by Astrium Satellites, wrapped up final satellite tests June 26 and will now prepare it for shipment to Europe’s Guiana Space Center on the northeast coast of South America.

Giuseppe Sarri, Gaia project manager at the 20-nation European Space Agency (ESA), said Gaia will be shipped to the spaceport even if there are more tests to be done, in part to secure the launch date, tentatively set for Oct. 25.

Europe’s Soyuz manifest has been the subject of a competition among payloads this year as originally six missions were planning liftoffs when only four Soyuz rockets were available in 2013.

While the Gaia satellite is of modest size, just 2,030 kilograms at launch, it is an example of Big Science enabled by Big Data.

Mapping a billion stars, each from 70 separate observations made over Gaia’s 4.5-year observing life from the L2 Lagrangian point around the sun 1.5 million kilometers from Earth, means 40 million observations per day.

To handle the data flow estimated at 40 gigabytes per day, or more than 1 petabyte, or 1 million gigabytes, over the mission’s life, a multination Data Processing and Analysis Consortium (DPAC) has been created. Six data-processing centers have been established in Europe.

It will need massive parallel computing power. Francois Mignard of DPAC said during a Gaia preshipment press briefing here at Astrium Satellites’ facility that spending only one second to process the data on each star swept up in Gaia’s view would take 30 years to process.

Gaia’s current budget is estimated at about 940 million euros, or $1.24 billion. ESA is paying 740 million euros to build and launch the satellite and operate it for five years in orbit. Another 200 million euros has been spent over six years by the DPAC consortium, Mignard said, with more to come as Gaia reaches orbit and begins sending down data.

The mission originally was scheduled for launch in late 2011. But despite being nearly two years late, it is only over budget by about 16 percent, according to Sarri.

Even that figure is exaggerated since nearly half of the budget overrun was caused by the increased cost of the Europeanized Soyuz medium-lift rocket. Sarri said ESA had penciled in a 40 million-euro cost for the Soyuz when Gaia was approved, using the price ESA paid for a Soyuz launch of the agency’s Mars Express satellite in 2003.

But that launch was from Soyuz’s traditional launch site, the Russian-run Baikonur Cosmodrome in Kazakhstan. Launching from the European spaceport is more expensive. Sarri said the agency’s originally forecast cost of 40 million euros swelled to around 65 million euros by the time the contract was signed in late 2009.

The remaining overruns were due to the payload module of Gaia. Sarri said ESA was able to limit the financial costs of the two-year delay by waiting until the last minute to ramp up ESA’s own Gaia team. When it became clear that Gaia would miss its 2011 launch date by a wide margin, the agency maintained its limited-size Gaia team. That way, he said, ESA’s program management charges did not swell over the two-year period.

The Gaia payload module required three years of work by Astrium engineers to assemble, integrate and test to assure that the optical alignment to within a few microns of precision was up to specifications, said Vincent Poinsignon, Astrium’s Gaia project manager. 

The satellite has a giga-pixel focal plane assembly and 106 CCD chips arranged in a half-meter-square mosaic.

Gaia’s precision is made possible not only by its orbit — the stability of the L2 Lagrangian point is well-known — but also by a micropropulsion cold-gas system that took nearly eight years to develop. The thrusters expel 1.5 micrograms of nitrogen per second to provide satellite attitude control.

If it works as planned, Gaia’s focus will be sharp enough to be able to view a human hair at a distance of 1,000 kilometers.