Friday, October 28, 2011

'Bat signal' pinpoints castaways from space

Tom Hanks contemplates "Wilson" the volleyball, his sole companion after being stranded on a desert island in the movie "Cast Away."
The European Space Agency, using its expertise probing deep space to pierce the darkness of the seas, has developed a wearable antenna -- essentially a bat signal designed to enable search and rescue at sea.
Move over, Wilson the volleyball: this is the castaway's new best friend

From DiscoveryNews

  • a new antenna communicates with satellites to pinpoint the coordinates of those lost at sea.
  • the cloth antenna can be sewn onto lifejackets or uniforms of military personel.
The European Space Agency, using its expertise probing deep space to pierce the darkness of the seas, has developed a wearable antenna -- essentially a bat signal designed to enable search and rescue at sea.

Finnish defense company Patria and Tampere University of Technology worked with ESA to apply its space know-how to dramatically reduce the time it takes for a distress signal to be picked up, for rescue authorities to be alerted, and for help to reach a man overboard, shipwrecked or otherwise lost at sea.

So how does this new bat signal work?
Emergency radio beacons can be carried not only by ships and aircraft but also by people (where they become known in the business as "personal location beacons").
But unlike other transmitters and their long floppy antennas, the ESA's new invention resembles a small square of washcloth.
There's a reason for that: This antenna can be handily sewn into a life vest.

When someone is lost at sea, the distress transmitter connects with the Cospas-Sarsat Search and Rescue system -- satellites in space that listen around the clock for activated beacons in the 406 – 406.1 MHz frequency band.
The beacon transmits a distress signal with the exact coordinates of the person in distress to these satellites, and they notify mission control and coordination centers that a rescue is needed.

In a great example of international cooperation, four countries -- the U.S., Canada, Russia and France -- came together to sponsor this satellite system. Cospas-Sarsat provides worldwide coverage for search and rescue; it's been instrumental in rescuing at least 26,000 since it was established in 1979.

Traditionally, life vests equipped with Cospas-Sarsat transmitters relied on cumbersome and unwieldy whip antennas that restricted a wearer's movement -- which is hardly ideal when you're trying to stay alive out at sea.

The lower the frequency, the larger an antenna tends to be.
And the operating frequency bands for the Cospas-Sarsat are very, very low, making the challenge of creating a small, wearable antenna fit for search-and-rescue a difficult task.

Since it operates at VHF/UHF band, free space wavelengths are approximately 2.3 to 8.2 feet.
To fit in a life vest, the antenna needed to be miniaturized while keeping gain, bandwidth and effectiveness to make sure the satellite system could "hear" the call for help.

There's an additional problem: Closeness to the human body can cause antenna effectiveness to be eroded and the radiation pattern to be disrupted.
That's clearly a challenge if you're trying to design a wearable antenna, but it's one that this international team has managed to crack.

Capable of withstanding the rough conditions at sea and direct contact with salt, this lightweight, flexible, water-resistant antenna is integrated into the life vest.
When the vest is deflated, the wearable antenna can be fitted inside the cover fabric and the small Cospas-Sarsat transmitter into the cover pouch.

But one challenge remains: If the sewn-in antenna is submerged, the connection to the Cospas-Sarsat satellite is lost.
And when someone is battling to stay alive in rough seas, the life vest may end up in all sorts of positions, whether floating or swimming, that may arrest the beacon's effectiveness.

Fortunately, there's an easy solution: sew several wearable antennae into different positions in the life vest to ensure the distress call gets out to the satellite system.

While a wearable antenna designed for 243 MHz (the military frequency band) wasn't part of this project, a larger one for local homing targeting 121.5 MHz and one smaller for the 406-406.1 MHz were able to reach those satellites.

Also very cool, the ESA has developed an attachable one for the Suunto diving vest, specifically for divers lost at sea.

Davy Jones' locker might get a lot emptier in the future.

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