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  Use of SOFAR bombs to track Mercury spacecraft

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Author Topic:   Use of SOFAR bombs to track Mercury spacecraft

Posts: 1623
From: Worcestershire, England, UK.
Registered: Apr 2008

posted 06-05-2013 10:41 AM     Click Here to See the Profile for Tykeanaut   Click Here to Email Tykeanaut     Edit/Delete Message   Reply w/Quote
I just watched a re-run of "The Search for Liberty Bell 7" on QUEST in the UK.

Why were SOFAR bombs used as tracking devices when it was stated they were the equivalent of 16 hand grenades in explosive power. Surely they would have destroyed the capsule?


Posts: 216
From: Dublin, Ireland
Registered: Mar 2011

posted 06-05-2013 01:53 PM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
The SOFAR (Sound Fixing And Ranging) Channel is a horizontal ocean layer where the speed of sound approaches a minimum.

Acoustic pulses, particularly sound at low frequencies i.e. less than a few hundred Hz, are conducted very efficiently and can travel great distances in the ocean if they are trapped in this acoustic "wave guide" channel. This principle is exploited by submariners and marine animals.

During World War II Dr. Maurice Ewing, a pioneer of oceanography and geophysics, suggested that dropping into the ocean a small metal sphere (called a SOFAR bomb or SOFAR disc), specifically designed to implode in the depths of the SOFAR channel, could be used as a secret distress signal by downed allied pilots. A position could be determined from the differences in signal arrival times at receiving stations with known geographic locations.

Liberty Bell 7 carried two SOFAR bombs made by the Bermite Corporation in Santa Clarita, CA. The two barometrically fired explosive signaling devices were meant to alert recovery vessels in the area through their sonar. Each SOFAR bomb would arm as it sank through ~3,500 feet of sea water, and fire at ~4,000 feet. There were two on the capsule: one in a pocket on the main parachute risers and one behind the instrument bulkhead. The first SOFAR device would be ejected as the main parachute deployed, fall to the ocean surface, sink, arm and detonate thus alerting the recovery ships to what bearing the capsule would soon land. The second SOFAR device was intended to detonate if the capsule sank giving its approximate location and destroying the instrument bulkhead thus scuttling it so no unfriendly nation could recover it. Liberty Bell 7's second SOFAR bomb failed to detonate as planned and Curt Newport said he dropped it overboard after the capsule's recovery.


Posts: 216
From: Dublin, Ireland
Registered: Mar 2011

posted 06-05-2013 03:22 PM     Click Here to See the Profile for YankeeClipper   Click Here to Email YankeeClipper     Edit/Delete Message   Reply w/Quote
Curt Newport provided additional information in a 2006 cS post.

Originally posted by CNewport 01-21-2006:

"SOFAR stands for Sound Fixing and Ranging; they were small explosive devices attached to the Mercury spacecraft to indicate the splashdown location. They did this by detonating at a specific water depth in what was called "the SOFAR listening channel" which acted like a waveguide allowing the sound to be heard for long distances, possibly several thousand miles if I remember correctly.

Each device was both armed and detonated by water pressure and contained 11 ounces of HBX, a military explosive similar to TNT. The device attached to Liberty Bell 7 was located and removed by UXB International and fortunately was a dud.

From what I recall, about 10% of these devices did not explode. I find it especially ironic that the one capsule that did sink to a "nonrecoverable depth" had a SOFAR bomb that was a dud. If it had gone off, it would not have destroyed the capsule; however, it certainly would have made a mess of things."

All times are CT (US)

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