Purpose of the flight and payload description
The cryogenic sampler was designed following the line of a similar instrument developed by NCAR in early 1970's. It is composed by eight evacuated sampling tubes of 300-ml volume made of stainless steel which are immersed in liquified neon as can be seen in the scheme at left. The neon is kept under a constant pressure of 1.5 bar at a temperature of 28.6 degrees Kelvin. Through motor-driven valves activated by telecommand, the tubes are connected to a manifold and air intake. When a valve is opened, the outside air is immediately sucked in and sublimates on the cold walls of the sampling tube. Hence the opening time determines the quantity of air sampled at a given ambient pressure.
During the flights of the instrument, samples of 101 STP were collected, requiring about 20 min at an altitude of 35 km, and this time decreased with increasing pressure to 1 min at 15 km altitude. A ninth tube was used as a pump to flush the manifold and air intake tube prior to each sampling. To eliminate or at least minimize the effect of outgassing and wall reactions (interior contamination), all interior surfaces of the sampler were electropolished. The complete system of air intake tube, manifold, and sampling tubes was baked out at 380º C for 2 weeks, 1 week under high vacuum and then 1 week with the system filled with synthetic air.
Exterior contamination from the balloon system was eliminated during the flights by taking air samples only during the slow descent of the helium-filled balloon, at a rate of about 50-100 m/min. This was achieved by releasing gas through a remotely controlled valve on top of the balloon (apex valve). The distance between the balloon and the sampler was about 200 meters. Care was taken to avoid contamination from the cryosampler itself by sealing it in a vacuum-proof stainless steel container. The neon refrigerant was vented through a pressure valve and a black tank that absorbed sufficient solar energy to heat it to at least ambient temperatures. Two beams, each 6 m in length, were attached to the gondola, one for the neon exhaust and one on the opposite side for the sample intake. Such an arrangement prevented the exhausted neon from being collected with the samples.
For reasons of undisturbed data transmission the telemetry/telecommand unit, supplied by the balloon sector of CNES, had to be suspended immediately below the gondola. It was sealed in a polyethylene bag so that outgassing freons from this unit, which was insulated with polystyrene, did not effect the samples.
Details of the balloon flight
Balloon launched on: 9/12/1977
Launch site: Centre de Lancement de Ballons CLBA, Aire Sur L'Adour, Landes, France
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 100z Zodiac - 100.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 9/12/1977