On 10 June 1993 Exercise MINOR UNCLE at White Sands Missile Range NM, was a large scale synergistic test on military clothing and equipment. MINOR UNCLE (MU) was planned by the US Defence Nuclear Agency (DNA) to be the last of the large scale conventional explosive events. It was conducted at the White Sands Missile Range in New Mexico. It had participants from US, UK, Canada, Norway, Sweden, Switzerland and Australia. The explosive charge had a yield approximately equivalent to a 4kt nuclear explosion or 2kt of TNT. MU was particulary timely in that regard and allowed extensive discussions with users of a variety of instruments all on the one site.
The MINOR UNCLE test was executed on 10th June, 1993, at 0910 hrs Mountain Daylight Time at the Permanent High Explosive Test Site (PHETS) site , White Sands New Mexico. The event simulated a 4 kt nuclear detonation (the simulation was most accurate in the 7 kPa overpressure region) by detonating a hemispherical charge of 2472 tonnes of ammonium nitrate and fuel oil (ANFO) mixture initiated by a 125 kg octol booster. The charge which was detonated at its center, was contained by a fibreglass hemispherical shell which was located at ground zero. The average charge density was 0.85g/cm3 and the average fuel oil content was 6.1 % by weight. MU brought together scientists and engineers from seven countries. It was planned to be the final, large scale, conventional explosive airblast to be held in the USA by DNA. That US agency has conducted many similar tests at its permanent high explosive test site on the White Sands Missile Range.
One of the main claims to fame for White Sands, or as it was formerly called, the Alamogordo Bombing and Gunnery Range, is that it was the site of the world's first atomic explosion, the Trinity test, on 16 July, 1945. Indeed the Trinity test, carried out under the Manhattan Project, occurred with the bomb placed atop a 30m tower which was located only a few kilometres from where the MU site is. Likewise, the MacDonald ranch house (still standing), where the plutonium core was assembled prior to being transported to the Trinity site for insertion into the bomb casing, was also very close to the site. At ground zero at the Trinity site, there are still some memorabilia from that momentous event in the world's history.
Projects in MU included the exposure of blast resistant structures both above ground level and buried. Norway, Sweden Canada and Switzerland had specific interests in this work. Various items of military hardware and vehicles were exposed to the airblast; so too were manikins representing military personnel dressed and equipped for combat. It became apparent during the on site preparation period on MU that the real "drive" came from Norway for the various forms of passive airblast instrumentation to be deployed on the same radial at the test site. The north radial of the test site contained passive gauges of various types from Australia, Canada and the US. This arrangement was designed to enable a comparison of results from the various measurement methods. Such a comprehensive comparison of gauges had not been carried out before, so MU provided this unique opportunity.
In addition to airblast exposure, some items were also exposed to thermal radiation from installed gas burners, to simulate the dual energy from a nuclear event of similar yield. The thermal radiation sources were activated just prior to the detonation, so that the heat was experienced by the targets prior to the arrival of the airblast, as in a nuclear attack.
Although there have been major changes in measurement instrumentation, principally due to developments in electronic technology, passive instrumentation still fulfills a function, particularly in large scale testing requiring a large number of measurements and generally over a large area. This is especially applicable if the prime requirements are for comparative measurements or those not requiring high levels of accuracy. Recording field data with passive instrumentation is often fraught with difficulties and limitations but nonetheless there are distinct applications where its use can fill in large data gaps and maybe even surpass more sophisticated methods of measurement. Passive methods should not be too readily dismissed in favour of more sophisticated methods, or even no measurement at all, as they have much to offer; such methods are usually simple in design, inexpensive to manufacture and easy to install. For the past thirty years of so, the author has observed the use of passive methods in the measurement of airblast data and MU was a good showcase of how the simple application of sound physical principles and engineering initiatives has not totally been replaced by higher technology. In a complementary way, MU also displayed state of the art instrumentation which is usually essential for best achievable accuracy in field data measurement. Australia was requested to participate in MU by carrying out the measurement of DPI for comparison with other measurements of the same parameter. For the purposes of MU participation, this project was designated as Defence Nuclear Agency (DNA) Project #6705.
The Defense Nuclear Agency (DNA) Field Command at White Sands Missile Range conducted a Thermal Radiation Simulator (TRS) test for the Naval Surface Warfare Center (NSWC) during project MINOR UNCLE. The NSWC was interested in measuring the radiant thermal energy absorbed by a fiberglass panel during a simulated nuclear weapon event. The resultant thermocouple data showed an unusual initial high-temperature rise and fall, followed by the expected conductive heating. The initial transient was theorized to be the result of thermal radiation transmitted through the panel. To investigate this theory, NSWC prepared several more panels of different thicknesses, preinstrumented with thermocouples and strain gages for testing with a U.S. Army Research Laboratory (ARL) TRS. ARL also provided additional instrumentation to measure thermal radiation on the front surface as well as behind the panel. The results showed that there was direct heating of the rear of the composite panel by thermal radiation. The quantity of heat transmission through the panel and the point of ignition of the front surface of the panel were determined. Smoke and charring of the front surface protected the panel from further heating and possible destruction.
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