More than a ton of advanced electronics, including an ion engine and sensors that help detect variations in gravity, crashed into Earth's atmosphere Sunday night, when the European GOCE satellite ended its four-year mission. Most of the 2,425-pound craft disintegrated when it re-entered the atmosphere over the South Atlantic Ocean; about 25 percent did not.
The European Space Agency says that GOCE — the Gravity Field and Steady-State Ocean Circulation Explorer — experienced "atmospheric interface" at 7:16 p.m. ET Sunday. The satellite re-entered Earth's atmosphere less than 300 nautical miles south of the Falkland Islands, the agency said, citing data that were confirmed by NASA.
"While most of the 1100 kg satellite disintegrated in the atmosphere, an estimated 25 percent reached Earth's surface," the agency says.
GOCE ran out of fuel last month, beginning a countdown to its eventual destruction. It continued sending data to ESA through its final days and hours, yielding its observations about ocean currents as well as air density and wind speeds in the upper atmosphere.
"The central computer temperature is at 80ºC [176 degrees Fahrenheit] and the battery is at 84ºC," ESA reported less than two hours from the craft's destruction. "At an altitude of less than 120 km, the spacecraft is — against expectations — still functional."
Because its orbit crossed Earth's poles, scientists were uncertain of where GOCE would come down, as NPR reported Saturday. That uncertainty lasted into the final hours of the satellite's re-entry — an update from ESA on Sunday stated, "The most probable reentry area lies on a descending orbit pass that mainly runs across the Pacific and the Indian Oceans."
The final track of its orbit took GOCE over Siberia, parts of the Pacific and Indian Oceans, and Antarctica. Its re-entry occurred east-southeast of the tip of South America.
"As expected, the satellite disintegrated in the high atmosphere and no damage to property has been reported," ESA said Monday.
The satellite was nicknamed a "space Ferrari" owing to its sleek and aerodynamic shape, meant to help it maintain a stable orbit at very low altitude. It relied on a steady stream of thrust from an electric ion engine to compensate for any drag it encountered.
And in a bit of serendipity, as we looked around for an object to put the satellite's weight of 2,425 pounds into perspective, we found a story from last year predicting that an actual Ferrari was being built that might weigh "just 2,425 pounds." For further comparison, a Smart ForTwo model weighs around 1,800 pounds.
One of GOCE's lasting achievements is likely to be the mapping of a new "geoid," showing deviations in the Earth's surface. The European agency explains why that's important:
"A precise model of Earth's geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics. The geoid is also used as a reference surface from which to map the topographical features on the planet. In addition, a better understanding of variations in the gravity field will lead to a deeper understanding of Earth's interior, such as the physics and dynamics associated with volcanic activity and earthquakes."
As for its uncontrolled descent, European officials had downplayed concerns raised by people who were alarmed by the thought of a car-size orbiter crashing to Earth at random.
"Statistically speaking, it is 250,000 times more probable to win the jackpot in the German Lotto than to get hit by a GOCE fragment," says the head of ESA's Space Debris Office, Heiner Klinkrad.
"The 1-ton GOCE satellite is only a small fraction of the 100–150 tons of man-made space objects that re-enter Earth's atmosphere annually," Klinkrad says. "In the 56 years of spaceflight, some 15,000 tons of man-made space objects have re-entered the atmosphere without causing a single human injury to date."