If all goes according to Plan B, the actual rescue could be underway on Tuesday, pulling the men 2,070 feet to the surface of the Copiapó mine. The crew now dubbed "Los 33" has been down there since the mine collapse on August 5.
Almost at the finish line is the Schramm T130XD Rotadrill, a tire-mounted machine used for drilling wells down to 7,000 feet. The drill operates by a diesel-driven air compressor mounted on the rig and uses a combination of hammering and rotation. Schramm Inc. is a privately held company based in West Chester, PA.
In a manner of speaking, the Schramm rig's bit (manufactured by fellow PA company Center Rock) already reached the miners on August 22, but with a small pilot hole. There are three drill rigs in all (literally, a "three deep" rescue plan): the others are the Xtrata 950 and the RIG-422. The latter is a bigger machine than the other two and doesn't rely on a pilot hole.
Now the Schramm crew is in the last stages of reaming the borehole to a final diameter of 28 inches. Why not more? This is the size of the table opening on the rig, so the bit can't be bigger than that.
There are other jobs to finish besides drilling, and risks to manage. No borehole can be perfectly straight, and rocks can come loose from the side, which breeds concern about the 21-inch-wide rescue capsule jamming on the way up or down. A video camera will be lowered to inspect the sides for trouble spots. The uppermost section of the borehole -- a few hundred feet, and maybe more -- will have to be lined with steel casing since this is where rock is likely to come loose. And the miners will probably have to help out by blasting out the bottom of the borehole. Otherwise the bit could jam, given the angle in which it's entering the mine.
So ... kudos to the organizers, drillers, and particularly the team that will be heading down to organize the rescue from below: they have to make this perilous trip twice. Not a job for the claustrophobic, but as a West-Point-trained IBM manager told me once, "You have to know the point of crisis. That's where a leader needs to be."
Of course, if the owners of the mine had laid it out with two well-separated access shafts all this wouldn't have been necessary.
I wrote about the history of really big boreholes at this post, including the Fenix & Scisson work to drill a 90-inch wide, 6,000-foot-deep shaft for the 1971 Cannikin H-bomb test on Amchitka Island, Alaska.