Nearly six years after the Sago mine disaster that killed 12, an innovative mine communication system rolls off the assembly line for the first time next week.
Lockheed Martin's MagneLink Magnetic Communication System is the only wireless, through-the-earth communication technology approved so far by the federal Mine Safety and Health Administration.
Wireless emergency communications were mandated by the Mine Improvement and New Emergency Response Act, or MINER Act, passed by Congress after the Sago explosion in 2006.
The lone Sago survivor described a situation in which he and 12 fellow miners survived together for a time but could not communicate with the surface.
The technology just hadn't been developed.
"Since the act was passed, there's been all kinds of development throughout the industry trying to meet the requirements," said Warren Gross, MagneLink program manager for Lockheed Martin in Syracuse, N.Y.
"A number of approaches were taken that are not what we would define as truly ‘wireless.' They're subject to catastrophic failure in the case of an event," Gross said. "Our approach is a self-contained system that is truly wireless, that does not rely on infrastructure like connections running throughout the system — we actually transmit (a magnetic field) through the earth."
MagneLink provides two-way wireless voice and text communication between the coal mine and the surface, at tested depths of about 1,500 feet and distances within a mine of about 2,500 feet.
It doesn't use radio waves as the wireless devices most people are accustomed to, Gross said. Rather, it uses a magnetic field — just like Earth's magnetic field, only much smaller, like the ones generated by motors.
Principal research engineer David LeVan described the process in a video on Lockheed Martin's website.
"When a miner sends a message with MagneLink, the transmit antenna is energized and a bubble of magnetic energy is generated around it," he said. "As the message is sent, the bubble essentially bubbles up through the earth and creates a dome of magnetic energy at the surface. If another MagneLink system is anywhere within that magnetic dome, whether within the mine or up on the surface, it can receive the message."
Magnetic field communication is not a new idea, Gross said, but the "noise" of the Earth's and other magnetic fields has been a challenge. Lockheed's innovation is in signal processing that cuts through that noise.
"We have a lot of experience in dealing in high-noise environments and very small signals," he said. "We developed a triaxial antenna that we then do correlative processing on to look through the noise and just look at the signal."
The system consists of an in-mine transceiver with a keyboard and handset housed in a waist-high, explosion-proof enclosure, and, at the surface, a smaller, portable transceiver.
The underground device would sit at a refuge shelter so that miners who experienced an accident could communicate with the surface from a safe location. Even if the miners weren't able to get to shelter, the unit could relay messages from their radios.
Gross notes that the communication ability is low-bandwidth — it can send a short text message in a few seconds, he said. But that's better than attempts that might send one letter per minute and a world of difference over the Sago victims' complete inability to communicate with the surface.
Lockheed Martin has a pre-production unit under evaluation at CONSOL Energy's Robinson Run mine in Mannington.
And the first units will come off the production line in early December, Gross said. Sub-assembly of key components is taking place in Clearwater, Fla., with final assembly in Palm Beach, Fla.
Those units will be distributed by Lockheed's reseller, Carroll Technologies Group, through its subsidiaries Carroll Engineering Co. and Delta Electric.
The first units will be placed in working mines as demonstration units for potential customers, according to Carroll spokesman John Burkhart.
A retail price has not yet been set, Burkhart said, but he expects the unit to be available for retail in January.