The sampling program begun as HASP was extended into Projects Stardust, Airstream, and Ashcan. All shared common objectives:
- The determination of the quantities of various radionuclides in the stratospheric reservoir and the distribution of this debris as a function of latitude, altitude and time
- The estimation of the residence times of these radionuclides in the stratospheric reservoir, and
- The determination of the mechanisms and rates of mixing and transfer of this debris within the stratosphere and into and through the troposphere.
Programs and Database Organization
All of the data presented here has been published previously. Much of it was made available in computerized form as the TRACDAB and RANDAB databases. However, EML has substantially improved the organization of the data in conjunction with conducting a comprehensive inventory and creating an accurate archival database.
Stardust
The Stardust program is divided into two domains: individual ID numbers and composite ID numbers. The individual ID numbers were those numbers assigned to the actual samples as they were received. They are sequential five-digit numbers running from 00001 through 24484, with occasional gaps.
Pieces from one or more samples were combined to form composite samples for analysis. The analysis samples were assigned a composite ID - two letters followed by a number, such as ST-104. The letters generally indicate which isotopes were analyzed for that composite:
- SF - fission products (90Sr, 144Ce, 89Sr, 95Zr, others)
- SQ - plutonium and 137Cs
- SR - 90Sr, 210Pb and 210Po
- ST - products of cosmic ray activity and tracer nuclides
- SX - 90Sr, 54Mn, 109Cd, 238Pu, 239Pu
- SZ - products of neutron activation produced during 1961 and 1962
There were many variations during the program with regard to exactly which isotopes were analyzed at a given time, based on the expected usefulness of certain analyses at that time. Most composite samples produced were analyzed for Sr-90, both as a consistency check and because measuring the atmospheric burden of 90Sr was a major aim of the program. For further information about the sampling program, analysis procedures, etc., please see DASA-2166.
In this database's previously published form, the individual samples were not crosslinked with the composites, which has now been done. One can now find any analyses performed on composites which included a part of a given individual sample, or find which individual samples made up a given composite. Some weeding out of typographical errors which crept into the computerized data has also been performed.
The Stardust program employed a number of different aircraft: the WU-2, RB-57F/C, RB-52, WB-50 and C-130. On most sampling flights the filters were exposed for an average of 45 minutes. Generally, for an exposure time of 45 minutes, samples collected at 12-13 km came from 2-2.5 kscm of air. Samples collected at 17 km came from .6-.7 kscm, and samples collected at 19-20 km came from .3-.4 kscm.
Airstream
Project Airstream was a continuation of Stardust/HASP except that RB-57F/WB-57F aircraft were employed and sampling missions were limited to one per season, 3 or 4 missions per year. The aircraft were flown by the National Aeronautics and Space Administration under the direction of the Johnson Space Center, Houston, Texas.
Initially samples were collected in a track from 75° N to 51° S. Missions were flown from Eielson AFB (64° 40'N, 147° 06'W); Kirtland AFB (35° 03'N, 106° 36'W); Albrook AFB (08° 57'N); and Mendoza AFB (32° 49'S, 68° 47'W). In July 1977, flights in the southern hemisphere were ceased and missions were flown from Elmendorf AFB (61° 15'N, 149° 48'W); McChord AFB (47° 09'N, 122° 29'W); Ellington AFB (29° 37'N, 95° 10'W); and Howard AFB (08° 55'N, 79° 36'W).
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| Scope of the Airstream/Ashcan programs as of 1977 (northern hemisphere only). |
Up to twelve samples are collected per flight using IPC 1478 filter paper (16.375" dia.). A typical filter was cut into sixths under clean room conditions. Opposite sixths were combined into composite thirds, and typically one third was analyzed by Los Alamos National Laboratory for water-soluble inorganic ions; one third was analyzed by EML; and one third was retained for the EML archive of stratospheric samples. Generally multiple filter thirds were combined for EML's analysis, and were given a new sample ID number. The sample ID's for both composite and individual samples run from 00001 to 15261.
Ashcan
The Upper Atmosphere Monitoring Program (nicknamed Project Ashcan because of the cylindrical shape of the first sampling unit used) was begun in 1956. The sampling program began a crash effort to obtain data on concerning the nature, concentration, and distribution of radioactive debris injected into the stratosphere during nuclear weapons tests.
It became evident in the early planning stages of the program that large-volume filter samplers, suitable for use with high-altitude balloon vehicles, were non-existent. General Mills engineers designed the original "Ashcan" filter sampler which was flown operationally from five sites until December 1959. This sampler utilized a Torrington 403 blower to pull air through five square feet of low background, low pressure drop filter paper, manufactured by the Institute of Paper Chemistry. Sampling rate depending upon altitude and voltage applied, but averaged between 500 and 600 cfm. Because there was no means for measuring air flow directly, volumes were extracted from a table in which sampling rate was related to telemetered blower rpm and altitude. This table was derived from the experimentally determined pressure drop characteristics of an average filter mat, and from performance curves furnished by the blower manufacturer.
In 1957, a re-examination of the Ashcan system was undertaken by General Mills, Inc. in a research program supported by the Atomic Energy Commission. One outcome of this was the introduction of 40-foot exhaust ducts with the intent of preventing re-sampling of sampled air. Comparative flight tests were conducted in 1958, and duts were subsequently added to all flights starting in 1959. Comparative flight tests, however, did not reveal any conclusive evidence of a significant difference in sample activities between ducted and unducted systems.
The most serious deficiency of the Ashcan system was revealed through laboratory tests which revealed that the filtering efficiency of the unit was quite low (30-70%) and dependent upon the air velocity through the filter, air density, particle size, and particle density. To remedy this problem, it was decided to move to a system which used a more powerful blower, and a smaller exposed area of filter paper, to achieve a large increase in face velocity at the filter surface. This increased sampling efficiency to 90-97%. A flight test program showed that two to three times as much activity per thousand standard cubic feet was obtained by the new Direct Flow Samplers than was obtained by the standard Ashcan units flown on the same balloon.
The next problem encountered during the program was the inability to measure the true volume of air passed through the filter. This problem was remedied with the use of low-drag anemometers to measure the true volume of air, as opposing to making calculations based upon the blower speed.
To make collections at extremely high altitudes, two other samplers were developed. The Air Ejector Pump (AE) used two square feet of I.P.C. 1478 filter paper. Air was drawn through the filter by the aspirator action of escaping nitrogen gas released downstream of the filter. A larger Air Ejector known as the HV3K allowed even greater volumes to be sampled at higher altitudes.
Filters were forwarded to EML for analysis where they were assigned a sample number. Sample numbers from ~07400 to ~14100 were assigned during the early years of the program up through September 1960. Starting in October 1960, the sample number sequence was begun again at 00001 and continued through ~4000 at the program's end in 1983. Two types of analyses were made: a non-destructive gamma measurement at EML, and an individual radionuclide assay at a contractor laboratory.
All samples were compressed and sealed into 6 cm diameter by 3.5 cm depth aluminum cans. The samples were then analyzed spectrometrically for 7Be, 95Zr, 137Cs and 144Ce by lithium drifted germanium diode systems.
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| The U2 aircraft. Note the sampling ducts in the nose and fuselage (just above the front wheels). |
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| Portions being cut from a HASP filter for analysis. |
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| The U2 from above. Capable of high-altitude, long endurance flights, it is well suited to both spying and sampling. |
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| Filters being loaded into a nose sampler. |
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| WB-57 used in the Airstream program. |
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| The Direct Flow Sampler. |
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| Sampling system used in gaseous collections. |
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| Filling a balloon in preparation for an Ashcan flight. |
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