Starfish Prime was a high-altitude nuclear test conducted by the United States, a joint effort of the Atomic Energy Commission (AEC) and the Defense Atomic Support Agency. It was launched from Johnston Atoll on July 9, 1962, and was the largest nuclear test conducted in outer space, and one of five conducted by the US in space.
A Thor rocket carrying a W49 thermonuclear warhead (designed at Los Alamos Scientific Laboratory) and a Mk. 2 reentry vehicle was launched from Johnston Atoll in the Pacific Ocean, about west-southwest of Hawaii. The explosion took place at an altitude of , above a point southwest of Johnston Atoll. It had a yield of . The explosion was about 10° above the horizon as seen from Hawaii, at 11 pm Hawaii time.
Operation Fishbowl
The Starfish test was one of five high-altitude tests grouped together as Operation Fishbowl within the larger Operation Dominic, a series of tests in 1962 begun in response to the Soviet announcement on August 30, 1961, that they would end a three-year moratorium on testing.
In 1958, the United States had completed six high-altitude nuclear tests that produced many unexpected results and raised many new questions. According to the U.S. Government Project Officer's Interim Report on the Starfish Prime project: Previous high-altitude nuclear tests: YUCCA, TEAK, and ORANGE, plus the three ARGUS shots were poorly instrumented and hastily executed. Despite thorough studies of the meager data, present models of these bursts are sketchy and tentative. These models are too uncertain to permit extrapolation to other altitudes and yields with any confidence. Thus there is a strong need, not only for better instrumentation, but for further tests covering a range of altitudes and yields.
The Starfish test was originally planned as the second in the Fishbowl series, but the first launch (Bluegill) was lost by the radar tracking equipment and had to be destroyed in flight.
The initial Starfish launch attempt on June 20 was also aborted in flight, this time due to failure of the Thor launch vehicle. The Thor missile flew a normal trajectory for 59 seconds; then the rocket engine stopped, and the missile began to break apart. The range safety officer ordered the destruction of the missile and warhead. The missile was between in altitude when it was destroyed. Parts of the missile and some radioactive contamination fell upon Johnston Atoll and nearby Sand Island and the surrounding ocean.
Explosion
On July 9, 1962, at 09:00:09 Coordinated Universal Time (11:00:09 pm on July 8, 1962, Honolulu time), the Starfish Prime test was detonated at an altitude of . The coordinates of the detonation were . The actual weapon yield came very close to the design yield, which various sources have set at different values in the range of . The nuclear warhead detonated 13 minutes 41 seconds after liftoff of the Thor missile from Johnston Atoll.Starfish Prime caused an electromagnetic pulse (EMP) that was far larger than expected, so much larger that it drove much of the instrumentation off scale, causing great difficulty in getting accurate measurements. The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about away from the detonation point, knocking out about 300 streetlights, setting off numerous burglar alarms, and damaging a telephone company microwave link. The EMP damage to the microwave link shut down telephone calls from Kauai to the other Hawaiian islands.
A total of 27 small rockets were launched from Johnston Atoll to obtain experimental data from the Starfish Prime detonation. In addition, a large number of rocket-borne instruments were launched from Barking Sands, Kauai, in the Hawaiian Islands.
A large number of United States military ships and aircraft were operating in support of Starfish Prime in the Johnston Atoll area and across the nearby North Pacific region.
A few military ships and aircraft were also positioned in the region of the South Pacific Ocean near the Samoan Islands. This location was at the southern end of the magnetic field line of the Earth's magnetic field from the position of the nuclear detonation, an area known as the "southern conjugate region" for the test. An uninvited scientific expeditionary ship from the Soviet Union was stationed near Johnston Atoll for the test, and another Soviet scientific expeditionary ship was in the southern conjugate region near the Samoan Islands.