Earth to satellite: When will you hit — and where?

MARCIA DUNN

AP Aero­space Writer

CAPE CANAVERAL, Florida — NASA sci­en­tists are doing their best to tell us where a plum­met­ing six-ton satel­lite will fall later this week. It’s just that if they’re off a lit­tle bit, it could mean the dif­fer­ence between hit­ting Florida or land­ing on New York. Or, say, Iran or India.

Pin­point­ing where and when hurtling space debris will strike is an impre­cise sci­ence. For now, sci­en­tists pre­dict the ear­li­est it will hit is Thurs­day U.S. time, the lat­est Sat­ur­day. The strike zone cov­ers most of Earth.

Not that cit­i­zens need to take cover. The satel­lite will break into pieces, and NASA put the chances that some­body some­where will get hurt at just 1-in-3,200.

As far as any­one knows, falling space debris has never injured any­one. Nor has sig­nif­i­cant prop­erty dam­age been reported. That’s because most of the planet is cov­ered in water and there are vast regions of empty land.

If you do come across what you sus­pect is a satel­lite piece, NASA doesn’t want you to pick it up. The space agency says there are no toxic chem­i­cals present, but there could be sharp edges. Also, it’s gov­ern­ment prop­erty. It’s against the law to keep it as a sou­venir or sell it on eBay. NASA’s advice is to report it to the police.

The 20-year-old research satel­lite is expected to break into more than 100 pieces as it enters the atmos­phere, most of it burn­ing up. Twenty-six of the heav­i­est metal parts are expected to reach Earth, the biggest chunk weigh­ing about 300 pounds (136 kilo­grams). The debris could be scat­tered over an area about 500 miles (800 kilo­me­ters) long.

Jonathan McDow­ell, for one, isn’t wor­ried. He is in the poten­tial strike zone — along with most of the world’s 7 bil­lion cit­i­zens. McDow­ell is with the Harvard-Smithsonian Cen­ter for Astro­physics in Cam­bridge, Massachusetts.

“There’s stuff that’s heavy that falls out of the sky almost every year,” McDow­ell says. So far this year, he noted, two mas­sive Russ­ian rocket stages have taken the plunge.

As for the odds of the satel­lite hit­ting some­one, “it’s a small chance. We take much big­ger chances all the time in our lives,” McDow­ell says. “So I’m not putting my tin hel­met on or hid­ing under a rock.”

All told, 1,200 pounds (544 kilo­grams) of wreck­age is expected to smack down — the heav­i­est pieces made of tita­nium, stain­less steel or beryl­lium. That rep­re­sents just one-tenth the mass of the satel­lite, which stretches 35 feet (10.7 meters) long and 15 feet (4.6 meters) in diameter.

The strike zone strad­dles all points between lat­i­tudes 57 degrees north and 57 degrees south. That’s as far north as Edmon­ton and Alberta, Canada, and Aberdeen, Scot­land, and as far south as Cape Horn, the south­ern­most tip of South Amer­ica. Every con­ti­nent but Antarc­tica is in the crosshairs.

Back when UARS, the Upper Atmos­phere Research Satel­lite, was launched to study the ozone layer in 1991, NASA didn’t always pay atten­tion to the “what goes up must come down” rule. Nowa­days, satel­lites must be designed either to burn up on re-entering the atmos­phere or to have enough fuel to be steered into a watery grave or up into a higher, long-term orbit.

The Inter­na­tional Space Sta­tion — the largest man­made struc­ture ever to orbit the planet — is no excep­tion. NASA has a plan to bring it down safely some­time after 2020.

Russia’s old Mir sta­tion came down over the Pacific, in a con­trolled re-entry, in 2001. But one of its pre­de­ces­sors, Salyut 7, fell uncon­trolled through the atmos­phere in 1991. The most recent uncon­trolled return of a large NASA satel­lite was in 2002.

The most sen­sa­tional case of all was Sky­lab, the early U.S. space sta­tion whose impend­ing demise three decades ago alarmed peo­ple around the world and touched off a guess­ing game as to where it might land. It plum­meted harm­lessly into the Indian Ocean and onto remote parts of Aus­tralia in July 1979.

The $740 mil­lion UARS was decom­mis­sioned in 2005, after NASA low­ered its orbit with the lit­tle remain­ing fuel on board. NASA didn’t want to keep it up longer than nec­es­sary, for fear of a col­li­sion or an explod­ing fuel tank, either of which would have left a lot of space litter.

Pre­dict­ing where the satel­lite will strike is a lit­tle like pre­dict­ing the weather sev­eral days out, says NASA orbital debris sci­en­tist Mark Matney.

Experts expect to have a good idea by Thurs­day of when and where UARS might fall, Mat­ney says. They won’t be able to pin­point the exact time, but they should be able to nar­row it to a few hours.

Given the spacecraft’s orbital speed of 17,500 mph (28,162 kph), or 5 miles (8 kilo­me­ters) per sec­ond, a pre­dic­tion that is off by just a few min­utes could mean a 1,000-mile (1,609-kilometer) error. It prob­a­bly won’t be clear where it fell until after­ward, Mat­ney says.

If it hap­pens in dark­ness, it should be visible.

“If some­one is lucky enough to be near the re-entry at night­time, they’ll get quite a show,” says Mat­ney, who works at John­son Space Cen­ter in Hous­ton, also in the poten­tial strike zone.

Space junk in gen­eral is on the rise, much of it destroyed or bro­ken satel­lites and chunks of used rock­ets. More than 20,000 man­made objects at least 4 inches (10.2 cen­time­ters) in diam­e­ter are being tracked in orbit.

It’s mostly a threat to astro­nauts in space, rather than peo­ple on Earth. In June, the six res­i­dents of the Inter­na­tional Space Sta­tion took shel­ter in their docked Soyuz lifeboats because of pass­ing debris. The uniden­ti­fied object came within 1,100 feet (335.2 meters) of the com­plex, the clos­est call yet.

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