Purpose of the flight and payload description

The flight was the first mission of a Indo-German collaborative research program for measuring vertical profiles of source gases at tropical latitudes and the first attempt to document such gas profiles in the region. It was performed through a collaborative German-Indian initiative supported by the Indian Space Research Organisation (ISRO), the Tata Institute of Fundamental Research (TIFR) and the Deutsches Zentrum für Luftund Raumfahrt (DFVLR) from Germany.

The balloon train was composed by two instruments: a CRYOGENIC SAMPLER provided by the Max-Planck-Institut für Aeronomie (MPAE), Lindau, Germany and a MULTICHANNEL RADIOMETER provided by the Physical Research Laboratory (PRL), Ahmedabad, India.


In the image above left is a drawing of the sampler (click to enlarge). It was composed by 15 evacuated sampling tubes of 300-ml volume made of stainless steel which were immersed in liquified neon. The neon was 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 were connected to a manifold and an air intake. When a valve was opened, the outside air was immediately sucked in and sublimated on the cold walls of the sampling tube. Hence the opening time determined the quantity of air sampled at a given ambient pressure. A 16th 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.

During each flight, several samples were obtained at different altitudes up to a capacity of about 30 liters of air (at standard temperature and pressure). The collecting procedure required about 20 min at an altitude of 35 km (due to the low atmospheric pressure) while the time at a lower altitude of 15 km (and increased ambient pressure) was about 1 minute. Exterior contamination from the balloon system was eliminated during the flights by taking air samples only during the slow descent of 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.

Extreme 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, 6 meters length each, 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.


In the image above right can be seen the radiometer and its main constitutive elements: (1) tracking platform; (2) detector assembly and elevation sensor; (3) azimuthal sensor; (4) electronic package I; (5) slipring assembly; (6) electronic package II; and (7) azimuthal motor and gear-box.

The instrument was designed to measure the attenuation profile of solar radiation in six wavelength bands. Each photometer consisted of an entrance baffle, an interference filter and a photodiode. The interference filters used in this experiment had centre wavelengths at 210, 214, 230, 290, 450 and 800 nm, respectively, with a full-width half-maximum of 10 nm. The 450 and 800 nm channels were meant for aerosol measurements, the 290 nm channel for ozone measurements and the other three channels for measuring the altitude distribution of solar UV radiation and for studying their relationships with the trace constituents' concentrations at different altitude levels. The entire detector assembly was mounted on a two-axes sun-tracking platform which tracked the sun both in azimuth as well as in elevation and kept the detectors looking at the sun within 1º.

Details of the balloon flight

Balloon launched on: 3/27/1985 at 6:08 IST
Launch site: TIFR National Balloon Facility, Hyderabad, India  
Balloon launched by: National Balloon Facility, Tata Institute of Fundamental Research
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen StratoFilm - 143.300 m3
Flight identification number: 380
End of flight (L for landing time, W for last contact, otherwise termination time): 3/27/1985 at 11:51 IST
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): ~ 6 h
Payload weight: 468 kgs
Overall weight: 886 kgs

The balloon was launched from the TIFR balloon launch facility in Hyderabad on March 27, 1985 at 6:08 hrs IST, reaching a ceiling altitude of 35.2 km at 8:50 hrs IST. Ballast had to be dropped at several stages during the balloon ascent, twice around 7:30 hrs IST when the balloon was in the 20 km region and then around 7:50 hrs IST near 24 km altitude and again at 8:25 hrs when passed the 32 km mark to keep the ascent rate within acceptable limits. The balloon was kept floating at ceiling altitude for about half an hour before it was allowed to descend controlled by an apex valve to keep its descent rate low to facilitate the collection of gas samples by the MPAE instrument. During the ascent, the MPAE instrument collected 10 samples between 10 and 27 km while 5 more samples were collected between 35 and 28 km during the valve-controlled descent. The payload was finally released from the balloon at 11:51 hrs at about 29 km altitude after all the gas bottles were filled. The parachute landing was satisfactory and the instruments could be recovered in good condition.

External references

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