Purpose of the flight and payload description
The Upper Atmosphere Monitoring Program (nicknamed Project Ashcan because of the classical shape of the first sampling unit used) was initiated in 1956 as an answer for the pressing need for information concerning the nature, concentration and distribution of radioactive debris injected into the stratosphere during nuclear weapons tests. The main instrument of the project was an impactor collector that was carried out by a stratospheric balloon to obtain samples at preset altitudes between 50.000 and 90.000 feet.
General Mills engineers designed the first "Ashcan" filter sampler which utilized a Torrington 403 blower. A critical re-examination of the system led to several improvements over the following months, but still it most serious deficiency was the low filtering efficiency of the unit. To overcome this, in 1958 was introduced the Direct Flow Filter Sampler shown at left. This unit utilized one square foot of IPC filter paper instead of the five square feet used by the Ashcan sampler. Flow rates of 500 to 800 cubic feet per minute were achieved through use of a Torrington 704 blower, powered by a 0.52 hp Westinghouse aircraft motor. This unit presented a number of advantages with respect to weight, ease of handling, etc, but most important was the higher efficiency achieved. The Direct Flow Sampler replaced the Ashcan filter sampler at San Angelo, Texas since early 1960. Units initially flown from that base were powered by surplus Torrington 403 blowers at some sacrifice in performance, but all units flown after April 1, that year used the larger Torrington 704 blower. Years later the program suffered new improvements and modifications in the equipment used.
ASHCAN program was run in a monthly basis, with regular flights from Alaska, Australia, Brazil, Panama, and in several sites of the United States. Also special missions were performed to analize certain events like the debris left by the reentry of soviet satellites carrying small nuclear reactors, or after volcanic eruptions. The program was terminated in 1983.
Details of the balloon flight
Balloon launched on: 5/4/1961 at 7:10 EST
Launch site: HIBAL - Balloon Launching Station, Mildura, Victoria, Australia
Balloon launched by: ABLS Mildura
Balloon manufacturer/size/composition: Zero Pressure Balloon
Flight identification number: HIBAL-23
End of flight (L for landing time, W for last contact, otherwise termination time): 5/4/1961
This flight carried onboard two units of the Direct Flow Sampler, both powered by the Torrington 704 blower