The objective of the flight was to obtain atmospheric air samples during a stratospheric balloon in the stratosphere. The instrument -a whole air sampler- was developed in the decade of 1960 by the National Center for Atmospheric Research in Boulder, Colorado. It flew in several balloon missions between 1965 and 1973.
The whole air sampling technique involves taking an air sample into a suitable container (ideally without fractionation of its constituents). This can be accomplished in several ways, the simplest being to expose a previously evacuated container to ambient air, and after pressure equilibration, to close it. In this way a so-called "grab sample" is obtained for which the sample pressure is that of ambient air at sampling altitude. Because of its simplicity grab sampling can be carried out on any vehicle, aircraft, balloon, or rocket and the method has been used widely.
To obtain the vertical profiles a grab sampler was carried by balloon to an altitude of 30 km and opened at different altitudes during descent. The balloon sampling train is shown in the figure at left. The gas sampling device, consisted of eight evacuated bottles which could be connected in turn to a sampling manifold by a rotary valve. Prior to opening the bottles to the atmosphere, the manifold was flushed about 20 times with ambient air by a small pump, and the residual pressure (if any) in the bottles was measured by thermocouple gauges. The bottles were constructed by welding the mouths of two 2 liter stainless steel beakers together. An inlet to this bottle was provided by a 0.63 cm outer diameter spigot and a small instrument type valve was used to isolate the bottles from the sampler. The material used was stainless steel.
The payload was suspended about 150 m below the balloon to prevent contamination with the helium vented by the balloon. To reduce contamination from the gondola itself, the sample intake was located about 6 m below and the inlet line was flushed about 20 times prior to sampling using a liquid Nitrogen cooled adsorption pump. As an additional precaution sampling was done during descent only. This virtually eliminated any external contamination.
Balloon launched on: 2/25/1974
Launch site: Columbia Scientific Balloon Facility, Palestine, Texas, US
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen - 102.409 m3 (19.05 microns - Stratofilm)
Flight identification number: 811P
End of flight (L for landing time, W for last contact, otherwise termination time): 2/25/1974
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 3 h 45 m
Payload weight: 386 kgs
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