Satellite falling: What you need to know about GOCE's descent

A 1-ton satellite is falling toward Earth's surface. Experts estimate that the European satellite will break into 25 to 45 pieces that will crash to Earth Sunday or Monday, Nov. 10-11.

|
AOES Medialab/ESA
The Gravity field and steady-state Ocean Circulation Explorer (GOCE), a 16-foot-long satellite with no moving parts, has completed its mission and is now gliding down toward a collision course with Earth.

The European Space Agency's 2,425-pound satellite is in the process of falling to Earth. Should you worry? Probably not.

This is a planned fall, not an accident or catastrophe. The Gravity field and steady-state Ocean Circulation Explorer (GOCE) has completed its mission, and now that it has run out of fuel, it has reached what ESA calls the "natural end" for the sleek satellite. 

"We have obtained the most accurate gravity data ever available to scientists. This alone proves that GOCE was worth the effort – and new scientific results are emerging constantly,” said Volker Liebig, ESA’s Director of Earth Observation Programmes.

Where and when will it hit?

ESA scientists are trying to constrain this further, but for now, they've estimated that the satellite will fracture into 25 to 45 pieces that will make impact on Sunday or Monday, Nov. 10-11. A day before entry, they hope to have that pinned down to a 4-5 hour window. They'll have help from the Inter-Agency Space Debris Coordination Committee, the Defense Department's Space Control and Space Surveillance (SCSS), ESA's Space Debris Office, and NASA's Orbital Debris Program Office.

During its mission, GOCE (pronounced go-chay) orbited Earth every 88 minutes. (You can track the satellite's location here.) Since running out of fuel on Oct. 21, it has fallen like a hang glider, slowly coasting downward.

“Quite literally GOCE is now nearly flying like an airplane without an engine," mission manager Rune Floberghagen told the New York Times,"with the upper layer of the atmosphere providing aerodynamic stabilization."

It is picking up speed as it falls; it initially lost about a mile of altitude per day, but is now falling several miles per day, ESA scientists report.

How common is this?

More than 21,000 objects the size of your hand or larger are currently in orbit, NASA reports. Currently, the SCSS is monitoring the trajectories of more than 16,000 of them, of which 5 percent are still functioning. The rest are rocket bodies, inactive satellites, or other debris. Objects smaller than your hand are harder to count, but NASA estimates that about half a million objects between half an inch and 4 inches across are currently tumbling through Earth orbit, along with more than 100 million particles smaller than a dime. If they fall toward Earth, the smallest objects would burn up in the atmosphere, but the larger chunks have better odds of survival.

"During the past 50 years an average of one cataloged piece of debris fell back to Earth each day," NASA reports, but "no serious injury or significant property damage caused by reentering debris has been confirmed." Most debris doesn't survive the trip through the atmosphere, just like meteors, and the bigger chunks usually fall into the ocean. Despite what you may have learned from Jerry Bruckheimer films, natural disasters do not preferentially target New York, Los Angeles, or other population centers.

About 70 percent of Earth's surface is covered in water, so there's a roughly 2 in 3 chance that anything entering from space will hit water, not land. If falling debris does hit land, odds are fairly good that it will land in Canada, Siberia, the Sahara, Antarctica, or another barely-inhabited corner of the world.  Less than a quarter of Earth's landmass is inhabited, so statistically speaking, there's only about a 7 percent chance that the debris will land near people. If GOCE beats the odds and is forecast to make landfall in North America, SCSS will notify the Federal Emergency Management Agency and/or Public Safety Canada.

What was GOCE doing up there? 

GOCE measured subtle variations in Earth's gravity field, using three pairs of highly sensitive accelerometers, observing gravitational gradients along three different axes. The measurements detected hidden volcanoes, ocean currents, ice sheets, and more. 

Gravity isn't uniform across Earth's surface. The biggest effect comes from Earth's rotation: as Earth whirls around its north-south axis, it bulges slightly around the middle. This extra distance from the center of the planet means that gravity is slightly weaker at the equator than at the poles. In addition, Earth's surface is far from smooth, ranging from deep ocean trenches to massive mountains. The third factor is Earth's inner variability. Magma chambers, groundwater reservoirs, oil deposits, underground caves, even massive buildings – they all impact the shape of Earth's gravity field. 

Originally designed to fly for just 20 months, GOCE lasted more than 4.5 years before running out of the xenon it uses for its ionic propulsion. In that time, GOCE mapped many of Earth's hidden structures, including the core-mantle boundary and ocean currents. To allow for maximum sensitivity, GOCE had a very low orbit, only about 150 miles up. It launched March 17, 2009, and ran out of fuel October 21, 2013, at which point it began gliding downward, on an inexorable course toward Earth's surface – a fitting end for a mission devoted to understanding gravity.

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Satellite falling: What you need to know about GOCE's descent
Read this article in
https://www.csmonitor.com/Science/2013/1107/Satellite-falling-What-you-need-to-know-about-GOCE-s-descent
QR Code to Subscription page
Start your subscription today
https://www.csmonitor.com/subscribe