PLEIADES was the name of a multi-balloon manned mission carried out in 1937 by Jean Piccard from Rochester, Minnesota.
All started in 1935, when Piccard, working along with Dr. Thomas Johnson of the Bartol Research Foundation, developed and constructed the first non-rubber balloon. It was made of cellophane and was succesfuly flight tested that same year in Swarthmore, Pennsylvania. After moving to the University of Minnesota in 1936, Piccard pursued his developmental work and at the same time envisioned a new system to reach extreme altitudes: the use of a cluster of a large number of such balloons to carry a manned capsule.
Piccard named the project Pleiades, after the seven-star constellation. The goal he impossed himself was to reach 100,000 feet, but first, as a demonstration of the validity of his idea, he would perform a small-scale flight.
That first demonstrative mission was supported by the Kiwanis Club of Rochester, Minnesota. The balloon train was composed of a cluster of 98 rubber weather balloons, grouped in two tiers while Piccard was sit in a brand new box-shaped gondola he made from aluminum and magnesium.
The top group of balloons reached about 100 feet above the ground; while the lower group about 50 feet. Piccard placed a small explosive charge around the lines between the two clusters so he could release the top group when he was close to the ground. He also had the option of cutting balloon cords with a knife or shooting them with a pistol.
The flight took place in July 19, 1937, from the Soldiers' Field in Rochester, Minnesota. He reached more than 10,000 feet, and then began his descent. No experiments were carried on the flight because Piccard did it solely to demonstrate the technique of using balloon clusters. When he was about to touch down, Piccard released the top group of balloons, but the severed end of the rope -still smoldering from the explosives- landed in the gondola. Immediately a celluloid cover caught fire and ignited the magnesium components in the gondola. Piccard jumped from it but could only stand by helplessly as the Pleiades gondola burned.
The war stopped the continuation of the effort but in late 1945, after returning to Minnesota, Piccard met Otto Winzen who caught his enthusiasm for the stratospheric balloon project. The two agreed to work together and approached the United States Navy with a proposal called PLEIADES II which would use a spherical capsule carried to an altitude of 100,000 feet by a cluster of cellophane balloons. Initially the Navy accepted to study the idea, created a Technical Committee under the leadership of Commander George Hoover and throught the Office of Naval Research (ONR) provided limited funding to pursue the project, which became known as Helios.
However HELIOS never materialized, due basically to the limitations of the balloon technology of those times.