‘Divine Strake’ is about ‘bunker busting’

Sunday, Nov. 19, 2006 | 7:19 a.m.

The basic idea is simple: Take 700 tons of a mixture of fertilizer and fuel oil - the same stuff that leveled the federal building in Oklahoma City in 1995, killing 168 people - pour it into a large, bowl-shaped depression in the ground above some underground tunnels.

Set it off and see what happens.

The test dubbed "Divine Strake" will be the culmination of five years of research into "bunker busting," or how to destroy or at least disrupt underground facilities. The issue has come into the forefront of military thinking as planners continue to perceive threats from emerging nuclear powers North Korea and Iran. Both countries reportedly have buried their potential military targets.

The name Divine Strake means nothing, federal officials have said, merely code words derived from "d" for Defense Department and "s" stands for the particular event in the test series for the bunker-busting program.

Robert Nelson, a physicist with the national nonprofit Union of Concerned Scientists, said the test is a simulation of an incredibly powerful, probably nuclear, explosion. But with an explosive power of about 600 tons of TNT, the blast is smaller than the "bunker buster" previously identified by defense contractors, he said.

The B-61-11 nuclear weapon, identified by various groups as the main nuclear bunker buster in the U.S. arsenal, has an explosive yield almost a hundred times bigger than the planned Nevada Test Site blast.

"There's no way you can do a full-scale mock-up with conventional explosives," Nelson said. "But you can learn how shock waves travel through rock. You can scale it up to answer the questions What they are really trying to do is understand in a buried explosion, how the shock wave travels through the rock, crushes the rocks, rattles around the buried machinery and so on."

A tunnel runs about 100 feet below a 40-foot-deep pit where the explosive slurry will be dumped. The tunnel is lined with cables to transmit information on the intensity of the ground shock.

The pit and tunnel are ready for the test. All that remains are the legal and policy questions to be answered.

Nelson's analysis of the effort is consistent with explanations from the Defense Department on the need for the test. The effort, officials have said previously, is needed to generate basic information on how to destroy underground structures.

The blast itself will send a dust cloud two miles into the air, and will generate a ground shock equivalent to a small but perceptible 3.0 magnitude earthquake.

Four miles from the site, the shock will produce 5 mph winds maximum, according to Defense Department documents.

According to those documents, the test "improves our ability to hold deeply buried targets at risk - providing leaders operational flexibility."