MAGNETIC SPECTROMETER

Developed by NASA - Goddard Space Flight Center (GSFC)

Balloon launched on 8/3/1974, from Fort Churchill Airport, Manitoba, Canada

Purpose of the flight and payload description

Objective of the flight was to measure separate spectra of positrons and negatrons using a balloon-borne SPARK CHAMBER MAGNETIC SPECTROMETER. The detector system employed magnetic core digital spark chambers to determine the trajectories of charged particles through the instrument, both before and after they passed through the gap of a permanent magnet. The direction and magnitude of the magnetic deflection provided the sign and rigidity of each particle traversing the detector. The instrument was developed by NASA at the Goddard Space Flight Center.

The apparatus -which can be seen in the scheme at left- was triggered by a counter telescope consisting of a directional gas Cerenkov counter and two plastic scintillation counters. Two anti-coincidence scintillation counters were used to veto events in which a particle failed to pass through the magnet gap. The Cerenkov counter contained Freon-12 at 1 atmosphere pressure, which provided an energy threshold of about 21 mc² for a particle of mass m. The gas Cerenkov counter was insensitive to all protons and heavier nuclei with rigidities in the range of interest as well as all upward moving particles within the telescope aperture.

Two plastic scintillation counters D1 and D2 were positioned at depths of 1 and 3 radiation lengths of lead. For rigidities below 450 MV they served primarily as range counters for nuclei. A proton required a rigidity of at least 340 MV to reach D1, and at least 440 MV to reach D2. The two coincidence counters S1 and S2 were also pulse height analyzed and were important in eliminating nucleon background above about 200 MV.

The permanent magnet had pole faces 15x15 cm2 and a gap of 8 cm. Its central field was about 1 kilogauss, and it had a vertical line integral of about 25 kilogauss/cm. The data, along with the spark chamber data, were telemetered to the ground in PCM format and recorded on magnetic tape.

The experiment was mounted in a flat plywood panel that served to house the balloon control instrumentation, batteries for operation and ballast hopper. Strong tubing structure around the chamber and crush pads below the platform served to protect the instrument at landing.

Details of the balloon flight

Balloon launched on: 8/3/1974 at 20:30 cst
Launch site: Fort Churchill Airport, Manitoba, Canada  
Balloon launched by: Raven Industries Inc.
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen 50.300.000 cuft (Natural Shape - 0.5 mil. Stratofilm + 2 0.7 mil. Caps)
End of flight (L for landing time, W for last contact, otherwise termination time): 8/4/1974 at ~ 12:00 cst
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 16 h 20 m
Landing site: In the Athabasca River area, Alberta Canada
Campaign: SKYHOOK CHURCHILL 74  
Payload weight: 800 lbs

The ballon was launched on August 3, 1974 from Fort Churchill, Manitoba, Canada and beacme the world's largest unmanned balloon succesfully flown to that date, carrying an 800-pound scientific payload to 155,000 feet altitude. The balloon was fabricated by Winzen Research, Inc. from half-mil polyethylene film, measured 703 feet long, and weighed 1,5 tons. When fully inflated, it had a volume of 50.3 million cubic feet and a diameter of 512 feet. The complete flight train was 835 feet long and weighed 4,300 pounds.

Once released, the balloon rose over Hudson Bay to its float altitude of 155,000 feet and drifted westward approximately 500 miles toward Lake Athabasca. It was tracked by the Project SKYHOOK DC-3 aircraft. After 18 hours at float altitude, helium was released to bring the balloon to 100,000 feet, where the scientific package and parachute were separated by radio command. The balloon then split from top to bottom, allowing remaining helium to escape and the balloon material to descend.

External references

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