– The development of Search and Rescue Satellite-aided Tracking (SARSAT) is commonly traced to October 1972, when a plane carrying U.S. Reps. Hale Boggs of Louisiana and Nick Begich of Alaska disappeared during a campaign trip while flying from Anchorage to Juneau. If their aircraft only had been equipped with a beacon capable of emitting a signal to a satellite, rescuers might have at least located the wreckage, if not actually found survivors at the site. It did not. Boggs and Begich were never found.
Indeed, emergency locator transmitters had been in existence for several years by then. NASA records show that scientists at Goddard Space Flight Center, Greenbelt, Md., were working on prototypes in 1967. But the loss of two Democrat political leaders – Boggs was House Majority leader at the time – led regulators to require most planes and vessels to carry the devices, and register them with the U.S. government as well.
As the U.S. SARSAT system marks its 25th anniversary, evidence is strong that the regulation has paid off. The program, managed by the National Oceanographic and Atmospheric Administration (NOAA) in Suitland, Md., has helped rescuers save the lives of more than 8,000 people
in distress within the United States, and more than 23,000 worldwide since its introduction.
In less than a decade, SARSAT will likely disappear and be replaced by a new generation of more powerful, rapid and accurate locator systems under development by the United States,
and China. Although the name SARSAT will go away, it will leave behind a legacy of technological advances and lessons learned.
COSPAS-SARSAT was born as a joint goodwill enterprise among the United States
, Canada, France
and the former Soviet Union when the
launched the first satellite in the system in 1982. The first U.S. SARSAT satellite was launched the following year into a low polar orbit, circumnavigating the Earth once every 100 minutes. Since its inception COSPAS-SARSAT – COSPAS is the Russian acronym for the Space System for the Search of Vessels in Distress, the Soviet-Russian parallel program to SARSAT – has evolved to the point where it serves anything and anyone from large commercial airborne and seaborne freight carriers or the armed forces to individual hikers who seek adventure in remote corners of the globe.
Technological advances during the past quarter-century have made the ground equipment affordable enough so that recreational enthusiasts can buy hand-held devices for a few hundred dollars at retail stores.
Accuracy and timeliness, too, has progressed to the point where search-and-rescue teams can be en route to the precise location of an incident within minutes. Only a few years ago, Coast Guard, Air Force and Alaska State Police rescue crews considered a 90-minute gap between notification of a lost vessel, plane or person, and pinpointing it, as state-of-the-art. With new technology now under development by NASA
, notification and precise location likely will be virtually instantaneous.
SARSAT became much more effective in 1998, when the first geostationary satellites came into service.
When the earlier, low orbit (called LEOSAR, which stands for Low Earth Orbit Search and Rescue) satellites received a signal from a distress beacon, they used the Doppler effect to determine where that signal
originated. As a satellite that received transmission from a beacon got nearer to the site of its origin, the beacon’s signal became more intense. As the satellite moved away again, the beacon’s signal diminished. Because of the way the Doppler Effect works, it provided two possible locations of the beacon’s origin, on either side of the satellite’s track line.
To better identify the beacon’s location, the satellite had to make a second 100-minute orbit, which provided two more possible sites of origin. NOAA satellite-monitoring crews would mark the area that was overlapped during the two orbits, dismiss extraneous information, and then notify rescue authorities near the site that they had a search-and-rescue situation on their hands. The process, from start to finish, could take three to four hours.
“The geostationary satellite was an improvement because it’s always overhead and looking for beacons going off at 406 megahertz,” said
Lt. Jeffrey Shoup of the NOAA Commissioned Corps, the SARSAT operation support officer, who works in the agency’s Suitland facility.
But geostationary (called GEOSAR, for Geosynchronous Earth Orbit Search and Rescue) satellites alone still cannot pinpoint a beacon’s location,
because it cannot take advantage of the Doppler effect. The solution: “Use the two systems together,” Shoup said
With the exception of a few older devices still in use on some aircraft and ships, all beacons emit signals at a radio frequency of 406 MHz. Beginning Feb. 1, 2009, NOAA will no longer monitor the older devices, which transmit at 121.5 MHz or 243 MHz. Shoup says such devices are harder for satellites to detect anyway, because they transmit at a power level of 0.5 watt; newer 406-megahertz devices transmit at 5 watts. Persons still using these older units will have to hope someone with similar equipment on their plane or ship picks up their distress call.
Four different types of devices emit 406-MHz beacons that can be picked up by SARSAT satellites and relayed to NOAA:
– Emergency position indicating radio beacon (EPIRB)
for maritime distress situations. “They’re on any major vessel and even a lot of private boats,” Shoup says. “At a certain level, they become mandatory.” Designed to float and work well in water, some units are designed to release from sinking vessels and begin transmitting beacons automatically;
Emergency locator transmitters for any aircraft with more than one seat.
– Personal locator beacons used by military pilots, who can decide whether or not they want to activate it. After a 10-year trial in Alaska, where rescues of bush pilots, snowmobilers and hunters are frequent, they became available everywhere in the United States
in 2003. Recreation supply retailers sell units for anywhere from $400 to $600. The higher priced units are equipped with
capability. “We recommend getting GPS,” Shoup said
. SARSAT satellites pick up both beacons and GPS signals, he said
. “We see you right away,” instead of waiting for satellites to pass, he said
Then there is the ship security alerting system, which is similar to EPIRB, but will not float free if a vessel sinks. “It’s more of an anti-piracy beacon,” Shoup said. “If someone takes over a ship, a crew member flips a switch.” Upon receiving the beacon, NOAA notifies the Coast Guard, who knows that the emergency involves a hostile situation rather than a search-and-rescue operation.
signals from any of these devices, NOAA distributes the data to the U.S. Coast Guard for maritime operations
to the Air Force Rescue Coordination Center at Tyndall Air Force Base, Fla., for situations that occur within the continental United States
, or to the Alaska Air National Guard in Anchorage for events there.
“This is for ‘fallen and can’t get up,’” Shoup said
. “You’re completely lost, or the boat is sinking from underneath you.”
In 2007, 353 persons were rescued in the United States
thanks to SARSAT. So far this year, SARSAT has helped save the lives of 113 persons. Twenty-three people were rescued from a ship in the Atlantic Ocean; another 11 from a freighter off the coast of Puerto Rico in the Caribbean Sea
after high waves caused its cargo to shift. “The boat started to roll and went down pretty quick,” Shoup said
While SARSAT continues to serve as an essential life saving tool, NASA technicians in cooperation with the Air Force and U.S. Department of Energy have put together a concept for the next generation system that has been proven in tests.
“It will offer the benefits of both [existing] satellite systems, only more robust,” Shoup said
Called the Distress Alert Satellite System (DASS), it would involve moving the service from NOAA’s aging satellites to a constellation of 21 GPS satellites owned by the Air Force. Nine are already in orbit
; the rest likely will be launched, probably from either Kennedy Space Center, Fla., or Vandenberg Air Force Base, Calif., in sequence, as present GPS satellites wear out.
Because they will use existing Department of Energy hardware, NASA does not have to spend money developing something new, said
David Affens, who manages NASA’s Goddard-based search-and-rescue mission. “We just have to modify their package,” he said
“For years, we’ve been looking at some of the deficiencies in the original LEOSAR system, most important of which are the significant delay times at the
equator because of polar-orbiting satellites,”
All too often, Affens said
, beacons on imperiled aircraft and vessels could only emit one or two bursts before burning or sinking. Also, particularly in the tropics, the time it took for satellites to make polar orbits hindered rescue efforts. Delays could be as long as one or two hours, or double that if satellites had to make a second pass. The chances of both saving a life and minimizing injury are much slimmer after one hour, Affens said
“If I were bobbing around in the ocean, I’d want to be rescued as quickly as possible,” Affens said
DASS distress beacons would hit four of these mid-Earth orbiting (called MEOSAR, for Mid-Earth Orbit Search and Rescue) satellites at any given time. Rather than relying upon the Doppler effect to determine a beacon’s point of origin, DASS analyzes the difference in times the beacon hits each satellite and uses reverse triangulation.
Each new satellite will carry a repeater device that will pick up signals differently from each other satellite.
“That allows you to do many different Doppler and triangular calculations,”
Affens said. “You can do it in a single [beacon] burst, as opposed to LEOSAR, which required multiple bursts.”
NASA officials say the agencies involved will benefit from the improved technology.
“From a national policy perspective, adding DASS capabilities to the next generation of GPS enables the system to be the best that it can be, in terms of serving the needs of all users,” said
James J. Miller, NASA’s senior GPS technologist. “[It] optimizes the functionality of a MEO system for all properly equipped civil and military users.”
If funding comes through and the system passes muster with the Defense Department, DASS should become available on the first GPS 3
Block B satellites, which now are scheduled for launch around 2016.
Around that time, in about 2015, existing SARSAT satellites will start degrading and eventually fade forever.
Meanwhile, the European Space Agency intends to put up something similar in its Galileo global navigation system; the Russian Federal Space Agency has a similar timetable for its Glonass program as well.