Skyhook balloons were high-altitude balloons developed by Otto C. Winzen and General Mills, Inc. They were used by the United States Navy Office of Naval Research (ONR) in the late 1940s and 1950s for atmospheric research, especially for constant-level meteorological observations at very high altitudes. Instruments like the Cherenkov detector were first used on Skyhook balloons.
In the late 1940s, Project Skyhook was conceived of as a means by which plastic balloons could be used to transmit or send instruments into the stratosphere to conduct research. This project carried forward work from an earlier project, Helios, that General Mills and Jean Piccard initiated to use arrays of giant plastic balloons to carry humans aloft.[1]
Balloons, long used for collecting meteorological data, now offered the opportunity of collecting highly specialized information and photographs. The first Skyhook balloon was launched on September 25, 1947. The balloon was developed by the Aeronautical Division of General Mills.[2] [3] It carried a payload of nuclear emulsion to over 100000feet. At low level immediately after launch, the lifting gas (hydrogen or helium) in the balloons formed a small bubble at the top of the envelope, resulting in the balloon having a "limp" look. At the lower air pressure at higher altitudes, the gas expanded and eventually filled the whole envelope forming a sphere or ovoid. In some models the balloons could reach diameters of more than 30 m.[4]
In the succeeding 10 years, over 1,500 Skyhook flights were made for investigations supported by the ONR and for European scientists. These flights were made from locations in the United States, Canada, and naval vessels in the Atlantic, Pacific, Caribbean, and Arctic waters. Both Winzen Research and General Mills participated in these launchings, and in later years, the Atomic Energy Commission joined ONR in support of Project Skyhook.[5]
Among significant flights, Project Skyhook launched the first successful three-balloon cluster in 1948. Then in 1949 the first shipboard Skyhook launch took place. It was followed by nearly 300 shipboard launchings over the next 10 years.
The first manned plastic balloon flight under ONR contract took place in 1949. Project Rockoon, in 1952, featured a Skyhook balloon that released small Deacon rockets at about above arctic waters.
One of the first known attempts to carry out an astrophysical measurement from a plastic balloon occurred under the Skyhook program on June 30, 1954. During the solar eclipse on that date two Skyhook balloons were launched by Winzen Research with camera gondolas employing simple orientating systems.[6] The objective was to photograph the eclipse from high altitude. Varied photographic equipment was carried and aimed at the Sun to obtain full coverage for the total period of totality.[7]
On September 7, 1956, the University of Minnesota launched a giant Mylar balloon (developed by the G. T. Schejeldahl Corporation of Northfield, MN) to set an unofficial balloon altitude record of for unmanned balloons. In 1957 the US Navy began an operational aerology system known as Transosonde (trans-ocean sounding), consisting of almost daily balloon flights across the Pacific Ocean from Japan.[5]
On August 19, 1957, an unmanned Skyhook balloon lifted the first Project Stratoscope telescope. Project Stratoscope I was a program developed to research the Sun. Instruments included a 12-inch (30-centimeter) telescope with a special light-sensitive pointing system and a closed circuit television camera that was guided by the scientists on the ground. This was the first balloon-borne telescope. The telescope took more than 400 photographs of sunspots. These were the sharpest photographs taken of the Sun up to that time. The photographs increased scientists' understanding of the motions observed in the strong magnetic fields of the sunspots.[8] [9]
In 1948, Skyhook balloons were used to show that in addition to protons and electrons, cosmic rays also include high energy atomic nuclei that are stripped of their electrons. Thirteen stratospheric plastic Skyhook balloons were launched in September 1953 as part of Project Churchy,[10] an Office of Naval Research funded cosmic ray expedition at the geomagnetic equator. Project Churchy was conducted at the Galápagos because high-energy cosmic-ray particles can only be collected at the geomagnetic equator without accompanying low-energy particles found at higher latitudes. Balloons carrying scientific instruments rose to between 90000feet and 105000feet and encountered temperatures as low as -80 °C (-112 °F). Aircraft from Patrol Squadron (VP) 45 ‘Pelicans’ took off an hour after the launch of each balloon and visually tracked the balloon until it released its cargo and deflated. The instruments were observed until splashdown, and marked for destroyers to retrieve.[11]
Skyhook balloons may have been the origin of some UFO observations. The most famous case possibly involving a Skyhook mis-sighting was the Mantell UFO incident.[12] (The script of the film Earth vs. the Flying Saucers (1956) mentions "Project Skyhook").