Misty Castle VII: Minor Uncle (1993)
Date: 10 June 1993
Location: Permanent High-Explosive Test Site (PHETS), White Sands Missile Range
Explosive Charge: 2,431 tons, ANFO
Primary Objective: Provide a testbed for airblast, ground shock, dust loading, and thermal radiation effects for DoD-sponsored experiments. These experiments were designed to determine the response of tactical and strategic weapon systems, communications equipment, vehicles, and a variety of structures to a simulated nuclear environment.
Secondary Objective: Provide a thermal environment (in addition to airblast) for several experiments.
By the Numbers
- 101 experiments conducted
- 1,629 digital recording channels
- 6 hardened bunkers
- 20 rawinsondes meteorological balloons
- 42 smoke puff launchers
- 50 “Time-of-Arrival” high pressure airblast gauges
- 117 diagnostic airblast measurement gauges
Planning for the Minor Uncle test event began in mid-1991 following the completion of the Distant Image event in June. Like the previous tests, a Technical Review Board from the Defense Nuclear Agency reviewed and approved experiment proposals submitted by different agencies and organizations. In March 1992, project officers formally submitted the Minor Uncle test proposal to Defense Nuclear Agency headquarters, which then made its Test Execution Decision to officially start the program.
Experiment setup began in March 1993. This mostly consisted of grading the testbed around ground zero and preparing the support facilities on the Permanent High Explosive Test Site in the northern area of White Sands Missile Range. The container used to hold the 2,431 tons of ANFO was similar to the one used in Distant Image and had a diameter of 71 feet. It took 88 truckloads to completely fill the container. Producing the ANFO at the ANFO mixing plant began on 1 June 1993. Also on that day, personnel placed the 275-pound main booster assembly inside of the container.
While the Distant Image event only fielded one aircraft in support of the test, Minor Uncle included four aircraft: one Cessna 180 to monitor and document fireball, shockwave, ejecta, and cloud development; one WB-57 bomber collected dust samples in the dust cloud several minutes after detonation; one B-2 bomber evaluated its avionic systems; one King Air aircraft from the National Center for Atmospheric Research collected dust samples just before the cloud had dissipated.
Sensors around the charge container measured an average detonation velocity of 4,836 meters per second on the 10-degree radial and 5,524 meters per second on the 60-degree radial. Peak overpressures from the explosion exceeded 70 megapascals (10,000 psi). In addition to the sensors around ground zero, a total of 17 other sensors were erected as a part of the far field blast experiment at distances exceeding 1.5 kilometers. The closest was Station 1, located 1,500 meters along the north radial, which measured the overpressure at 10,307 pascals (1.495 psi). The farthest sensor was located in Socorro at a distance of 60 kilometers. Of the 17 far field airblast sensors, only one, located at Long Station roughly 50 kilometers away in the northern range extension, did not function properly for the test.
The direct-induced ground motion was very similar to that on Distant Image. Both were markedly higher than Misers Gold. Indications are that in the reconstituted Misers Gold and Distant Image crater region, the ground motion acceleration and velocities were almost a factor of 2 greater than for in-situ soil. It is postulated that the compaction process produces a much more homogeneous soil condition that enhanced the ground motion propagation in and around ground zero. Measurements beyond the recompacted ground zero area indicate that airblast-induced ground motion was about the same as observed on Misers Gold.
The crater left by the explosion measured in at approximately 276 feet in diameter and 74.2 feet in depth. The explosive yield was similar to Distant Image and came in at approximately 4 kilotons. One possible explanation for anomalies detected during the explosion could be that the density and distribution of ANFO was different from the other events in the Misty Castle series. Minor Uncle was the only test to use a top-down feeding method. Some of the previous tests had personnel inside the charge container to distribute the ANFO pillets. The top-down feeding method allowed the ANFO to distribute naturally, falling into container and then spreading out to the sides. This may have lead to a higher density of pillets in the center of the charge.