ESA Struggles with “the Ferrari of Gravity Missions”

TURIN, Italy —


Europe’s Goce gravity-field and ocean-circulation observation satellite is two years behind schedule following what designers agree were overly ambitious performance and schedule demands but is now on track for a March 2008 launch, Goce managers said.

The satellite, expected to weigh 1,100 kilograms at launch, is designed to operate from about 250 kilometers in altitude – the lowest orbit ever intentionally used by a European satellite – following its launch aboard a Russian




Rockot
launch vehicle operated by the German-Russian firm Eurockot Launch Vehicles GmbH.

Keeping the satellite still to permit sensitive gravity-field measurements while compensating for the considerable atmospheric drag at that altitude are part of a host




of design challenges that Goce had to meet. The satellite has no moving parts, and will be powered by small xenon-ion electric motors whose continuous pulses will correct for drag.

In another concession to atmospheric drag, the satellite was designed to look more like a crude design for a space shuttle than a satellite. It is 5 meters long, just 1 meter in diameter, with rigid solar panels and tail fins that will help stabilize flight.

Goce
is scheduled to leave prime contractor ThalesAlenia Space Italy’s production site here




Aug. 20 for several months of testing at the Estec technology center in Noordwijk, Netherlands, operated by the satellite’s owner, the European Space Agency (ESA).

Originally slated for a 2006 launch, Goce fell further and further behind schedule following steep design hurdles, notably for its accelerometers, designed by Onera, the French aerospace-research institute.

“We knew from the outset that the technical hurdles for this program were not benign,” said Reinhold Zobl, head of ESA’s Earth observation projects department. “But it’s true we didn’t expect this much of a delay. These accelerometers are beyond state of the art.”

Mark Drinkwater, ESA’sGoce project scientist, said Goce is “the Ferrari of gravity missions.” The instruments, he said, have a sensitivity equivalent to being able to detect the force generated by a 200-milligram snowflake as it lands onto an oil tanker weighing 1 million metric tons.

Goce’s gradiometer gravity-field instrument will rely on three pairs of accelerometers. ESA officials said the accelerometers are up to 100 times more sensitive than any previously flown in space.

Goce’s
contracting team was selected in early 2001. But as managers confronted successive scientific requirements, the program was slowed and the critical design review was not completed until July 2005.

In a series of




presentations here at Goce prime contractor ThalesAlenia Space Italy




July 19, Goce program managers said that despite the delays, the




total cost – satellite, launch and 20 months of operations in orbit – will be no more than 10 percent over the original budget of about 270 million euros ($372




million).

Zobl said the satellite itself will end up costing 200 million euros, with another 100 million euros needed for the Rockot launch, ESA’s program management charges and operations over its 20-month life.

There is no fixed launch date that Goce must meet, but ThalesAlenia Space Italy engineers have nonetheless been working two shifts a day, six days a week for the past nine months, according to Andrea Allasio, the company’s Goce program manager.

Danilo
Muzi, ESA’sGoce project manager, said program managers want the satellite launched as soon as possible to take advantage of the current relative quiet in the 11-year solar cycle. The more solar activity, the more atmospheric drag and the higher the orbit needed to assure that Goce can contend with it. “We want to fly as low as possible to take measurements as precise as possible,” Muzi said.

Goce
will carry 40 kilograms of xenon fuel for its ion-electric thrusters, an amount that is viewed as sufficient to permit the satellite to remain operational for 20 months, including a 4.5-month hibernation period to sit out the solar eclipse. Officials said they are hopeful of having enough fuel left over for an additional 10 months.