How Lost Hikers Can Send an SOS to Space

The Sarsat satellite system is a kind of celestial lifeguard for explorers, boaters, and aviators who might be in need of search and rescue.

JUN 14, 2022

distress beacon

LAST JULY, TWO hikers were on a backpacking trip in California’s Shasta-Trinity National Forest. Just northeast of Granite Lake—a small body of water edged by deadfall and a rocky mountainside—one of them fell and was too badly hurt to continue.

From their supplies, they pulled out a personal locator beacon. They extended the device’s antenna and pressed the button beneath. Immediately, a radio signal began beaming out at 406 megahertz, eventually hitting detectors on orbiting satellites. These instruments, part of the National Oceanic and Atmospheric Administration’s Search and Rescue Satellite-Aided Tracking program (Sarsat), picked up the signal and immediately pinged alerts to Earth.

Someone’s in trouble near Covington Mill, California, the alerts told the Air Force Rescue Coordination Center, along with details about who owned the device and how to get in touch with them. Soon, a helicopter was en route to the distressed trekkers’ latitude and longitude. After hoisting both hikers, the aircraft flew them to the hospital.

As far as wilderness distress calls go, that was not only a happy ending, but an easy one. (This incident, along with thousands of others, lives in the Sarsat program’s Incident History Database.) Locating the hikers required no scouring of trailhead sign-in sheets, nor deciphering notes taped to cars left at the starting spot. That’s by design: Sarsat’s catchphrase is “to take the ‘search’ out of search and rescue.” Sarsat is a little-known US program that aims to save lost or hurt hikers and climbers, overturned ATV and snowmobile drivers, sailors aboard sinking ships, and passengers in crashed planes. It is part of an international collaboration called Cospas-Sarsat, involving 45 countries and two independent organizations. The system relies on simple devices that have one job—send a location-revealing distress signal, anywhere, in any weather—and a system of satellites that listen for those calls. “If you really need your life saved, this is, in my view, going to be the one that is there for you,” says Sarsat ground systems engineer Jesse Reich.

As of 2022, NOAA’s database has more than 723,000 registered rescue devices, mostly owned by those who hope they’ll never have to use them. There are, though, more than 50,000 people worldwide who have been rescued because they activated their 406 beacons, sending an SOS signal to space.

SARSAT BEGAN AFTER an incident that could have benefited from its technology: In 1972, two members of Congress, Hale Boggs and Nick Begich, were flying in a twin-engine Cessna 310 across Alaska. Their plane disappeared in a remote region in ill-tempered weather. A 325,000-square-mile search that took 39 days and 90 aircraft found nothing. The search was called off, and the politicians and their plane remain missing to this day.

Afterward, Congress declared that aircraft had to carry emergency beacons that would automatically broadcast in the event of a crash. But the plan had a technological limitation: Another aircraft would have to be flying nearby to pick up the call. NASA, perhaps unsurprisingly, realized that satellites would have a much wider view and could also survey the vast swaths of the planet that are, in fact, ocean. A group of space agency scientists researched what was possible, and by 1979 the US, Canada, France, and the former Soviet Union had signed papers in Leningrad. The international collaboration, which would later be made more official as Cospas-Sarsat, launched its first satellite in June 1982.

distress beacon

That September, the initial search-and-rescue satellite, called COSPAS-1, was beckoned by its first emergency call. It came from a plane that had fallen from the skies over British Columbia while trying to look for another downed aircraft. It took rescuers only one day to find it, thanks to its beacon. The second plane—the one it had been searching for, and which had no such beacon—was never found.

NOAA and its partner agencies abroad keep databases of all the emergency incidents they have responded to, dating all the way back to 1982. The US database includes calls from three different kinds of devices: Personal Locator Beacons for people on land, Emergency Position Indicating Radio Beacons for boats, and Emergency Locator Transmitters for aircraft. The latter two get activated automatically, while the former requires a button push.

The spacecraft listening in on these calls live in multiple orbits. The Sarsat constellations include GPS spacecraft in medium-Earth orbit, NOAA satellites below them in low-Earth orbit, and GOES satellites above them in geostationary orbit. All keep watch for the 406.

Once they hear the call, that information is relayed to a ground station, which independently computes the beacon’s location. (Many modern beacons broadcast a location based on GPS coordinates too.) In the US, the information sluices into computers at the US Mission Control Center in Maryland, operated by NOAA. The center then farms out the request to the Air Force if the call comes from a contiguous state; the Coast Guard if it’s an offshore activation or one from Guam, Hawaii, Puerto Rico, or the Virgin Islands; and the Alaska Air National Guard if they’re on land in the last frontier. The US satellites work together with those from Russia, India, and Europe to detect and locate come-get-me signals. And if an American beacon goes off but shows the person atop a peak in Thailand, the US military will coordinate with officials in that country to get the rescue going.

Those authorities can then contact local search-and-rescue groups. “Every single one of these alerts that come in, it’s just a bunch of words on paper,” says Layne Carter, a Coast Guard liaison for Sarsat. “But in our heads, we’re thinking, ‘Somebody’s doggy-paddling out there, and they’re just waiting for us to come get them.’” (Paper, here, is more of a metaphor: The 406 alerts are actually digital. While all these operations have humans in seats 24/7/365, most of the data gets distributed automatically.)

distress beacon

In low-Earth orbit, the satellites don’t have a big-picture view of the planet because they see only about 6 percent of its surface at any given time. But the much higher GOES satellites each catch around 42 percent of the world. Both sets of satellites have their pros and cons: The low-flying spacecraft have to pass almost directly over a distressed person to catch their cry—and they only orbit over the same spot every 102 minutes—but they can tell precisely where that person is. The higher-flying spacecraft watch a wider area but can’t pinpoint an exact location.

That’s why in 2016 the Sarsat program started using a third set of satellites, which orbit at an altitude in between the others. These are GPS satellites with search-and-rescue payloads plugged into them. There are currently 21 such SAR payloads aboard GPS satellites, 24 aboard Galileo navigation satellites, and four on Glonass satellites. The Galileo and Glonass navigation satellites are operated by the European Space Agency and Russia, respectively.

“The third system combines the best of both worlds,” says Marisa Gedney, a Sarsat operations and outreach officer with NOAA. They each see a third of the globe and together cover its whole span. At any given time, at least four satellites would have eyes on any given earthly location, enabling better pin drops. Popular

That’s especially true if an activated beacon is on the move. If, say, the owner is drifting in a life raft, these spacecraft should be able to narrow down their location, enabling rescuers like Matt Carlton, a Coast Guard Sarsat officer who has spent years flying search-and-rescue copters, to spend less time scouring the sea. “Ideally,” he says, “I don’t need a big lunch.”

THE SYSTEM ISN’T perfect: The data whisked down from a satellite sometimes has errors. If your beacon doesn’t have a GPS position embedded in its broadcast, your spot on this vast and terrible planet can remain imprecise for a while—and those hours could mean the difference between fatal hypothermia and hot chocolate in a helicopter. Waves, signal-blocking cliffs, and other terrain can make the location more difficult to decipher. “When you start getting into some mountainous areas and things like that, the signal can bounce around,” says Carlton.

There is also an awful lot of user error: 98 percent of 406 distress calls are false alerts. Most of these are accidental. Maybe a backpacker bends exactly the wrong way and their belt presses “broadcast.” Maybe an airplane has a hard landing and sets off the sensor. Maybe a skiff owner is scraping some algae off the side of the boat and the device drops into the water. Maybe the owner throws their beacon away, and the call goes out from the middle of a landfill. (It’s happened.) Or maybe—as in the case of one Colorado user—someone keeps activating it every time they go skiing because they think it’s an avalanche beacon that’s supposed to transmit all of the time. (Search and rescue personnel scrambled to locate that man eight times, only to find the beacon turned off when they arrived at the signal’s origin point. They finally found him on the ninth try—not in the wilderness, but in the city of Boulder, because he left the device on accidentally while driving to a doctor’s appointment.)

There is a delicate balance between making an SOS call too easy to trigger and making it too hard. For example, the land-based beacons require you to push a button with your finger or toe or nose—but what if you’re immobilized, or the beacon is in your pack and you fell gearless off a cliff? (That’s why experts suggest keeping the beacon on your person, so you’re at least not accidentally separated from it.)

One solution to the accidental-push problem could be, as a backcountry-skiing blogger suggested after the Colorado debacle, to have the beacons blare an audio message every time they spool up, warning the user that they have triggered it, kind of like how modern carbon monoxide detectors bossily say “Warning! Evacuate!” There are more passive measures already in place: The personal locator beacons all have some sort of two-step activation method, like hinged covers over their help button, which you have to lift.

Given the number and nature of false alarms, Sarsat personnel are always begging people to register their 406 beacons. When registered, they don’t just broadcast calls for help; they also send personal information embedded in a Hex ID, a unique digital code that gives the name and contact information of the owner, as well as their emergency contacts and the locations of places they usually visit. That helps operators figure out what to do. The people who coordinate search and rescue operations are, says Carter, “really like detectives. They’ll call your mom, your sister, your uncle, your cousin, your third cousin, your neighbors. We’ll do whatever we can to try and find the owner and figure out what’s happening. Is this person actually in distress?

If the person’s just fine and say, washing their boat, the search personnel can cancel the distress call. But if nobody answers, and if the beacon’s not registered, they have to treat the situation like an emergency.

Partly because of those issues, the Sarsat program is currently upgrading to what Gedney calls “very uniquely named second-generation” beacons. Their digital signal will be more information-rich, and transmitted more frequently, which will cut down on errors. The signal will be more homed-in on the owner’s position, and with the addition of the middle-altitude satellites, that calculation should also be better.

NOAA is also working to make position-determination better in unstable conditions. Reich, for instance, just finished putting reference beacons out to sea on buoys to study how the ocean’s waves, swells, and currents affect the accuracy of their perceived location. He recently got the first picture back of the buoy in the middle of the ocean—alone, in its own way, but not lost.

Officials are also considering adding “return link service.” Right now, if a beacon deploys, there’s no way to know if anyone has heard the call. You can imagine the kind of extra distress that might cause a missing hiker or boater—even if they believe in both the power of satellites and the competency of government agencies, their minds will have plenty of time to spin out in anxious spirals. “Right now, there is some discussion in the works—it has not been finalized—of including, perhaps, just a confirmation light, saying that your distress has been received and somebody’s coming out to try and find you,” says Gedney.

The pace of upgrades can be frustrating because they involve so many different agencies and countries. “It sometimes moves so slowly,” Reich says. “It’s painful getting this technology out there. It’s just too hard and it takes too long to get everyone to agree.”

There are, though, alternative satellite-based search-and-rescue systems that capitalism—not the feds—hath wrought. Satellite phones can usually send an SOS. Garmin, the famed GPS device maker, has a private SAR system called InReach, which uses satellites in the Iridium communications constellation to send get-me-out messages. A company called Spot offers distress-call services through the Globalstar satellite constellation, which is owned by its parent company.

These systems have definite advantages. For instance, they usually allow two-way communication. You can text, or sometimes talk to, your rescuers. And once help is on the way, you can let your mom know that your leg is broken, and could she make up the sofa bed for you? Having that sort of capability could save NOAA and the military some heartache and resources, and give adventurers more peace of mind.

But these commercial services require an active paid subscription to work. The government-run alternative requires only that a user buy the device itself. There’s no subscription, and the rescue itself is free (or, at least, covered by the taxes everyone is already paying.) All you need to do is make sure your beacon’s battery isn’t dead. “As long as you don’t put it in a hot environment for 10 years and expect it to work,” says Reich, “it’ll be there and ready to go.”

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