Purpose of the flight and payload description

This flight was part of the Joint Indo-U.S. Balloon Flight Program - 1961 a cooperative scientific launch campaign carried out between February and April 1961 by scientists from India and the United States in Hyderabad, India. The objective of the extended series of high-altitude balloon flights was to probe the tropical stratosphere using a wide variety of scientific instruments.

This particular flight was part of a series to mesure the vertical distribution of submicron particles in the stratosphere over India by means of a balloon-borne inertial impactor device known as the AFCRL Large Impactor which was basically a scaled-up version of the impactor air sampler developed by General Mills for the Air Force Cambridge Research Lab. modified by the addition of a backup filter. At left we can see an scheme of the flight train along with an image of the impactor at launch (click to enlarge).

The air-sampling apparatus consisted essentially of a motor-driven rotary air pump which drawed air through a series of jet impactors, thereby removing the solid particles from the air stream. In the large unit, four separate barrels were manifolded to the one pumping system and individually programmed during the ascent to provide a four-point vertical profile on a single balloon flight. Each barrel had a two-stage impactor and a third-stage polystyrene microfiber filter as a backup collector for the very small particles. The four sets of impactor jets for each altitude interval were individually designed and adjusted so that their first and second stages had a 50 percent collection efficiency at about 0.15 microns and 0.02 microns particle radius, respectively, for particles of 2 g/cm3 density, at mid-altitude for the sampling interval. These cutoffs were kept fairly uniform regardless of altitude by increasing the jet dimensions with altitude to compensate for the decrease in air density. A separate battery pack of silver peroxide-zinc cells supplieed electrical power to the various components of the air sampler.

The population of particles was determined after the flight by visually counting the particles under a microscope, and the numerical concentration was then known from the accurately measured volume of air sampled.

A series of four identical flights were performed during the India campaign with the following profile: ascent to 100,000 ft altitude, at or near a 500 fpm rate of rise; air sampling programmed to collect four samples during ascent from 30.000 to 50.000 ft, 50.000 to 70.000 ft, 70.000 to 90.000 ft, and 90.000 to 100.000 ft. The total time flight duration was 150 min from initiation at 30,000 ft. to the descent in parachute.

Details of the balloon flight

Balloon launched on: 4/11/1961 at 7:35 IST
Launch site: Begumpet Airport, Secunderabad, India  
Balloon launched by: General Mills Inc.
Balloon manufacturer/size/composition: Zero Pressure Balloon General Mills 189-1-1 (2.0 mil)
Balloon serial number: 458-1
Flight identification number: GMI Nº 2538
End of flight (L for landing time, W for last contact, otherwise termination time): 4/11/1961 at  
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 10 m
Landing site: Uncommanded flight termination at 3000 ft. Payload landed inside the launch base

Balloon was launched on April 11, 1961 at 7:35 local time from Begumpet Airport, near Secunderabad using dynamic method. The system was ascending in a normal fashion when, at approximately 2000 ft, the ballast used to assure safe launch with low percentage of free lift was suddenly released. The flight continued to ascend and at approximately 3000 ft the payload was suddenly released from the balloon and descended to the ground by parachute. Impact occurred only a few hundred yards from the launch site, on the Indian Air Force Station parade ground.

The reason for payload release was apparently radio-command malfunction. The reason for this malfunction is not known except that the position in the flight train was hazardous for the unit at launch . The radio - command unit was positioned between the parachute and balloon and was therefore subjected to severe shocks at launch. The unit could not be repositioned on the gondola below the parachute because of the lack of adequate cabling required to reach to the top of the parachute from that position for payload release purposes.

External references

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