Purpose of the flight and payload description
The purpose of the high altitude solar cell calibration program was to produce air mass zero (AM0) standard solar cells that could be used for accurately setting solar simulator intensities. The program was started in 1962 by the Jet Propulsion Laboratory, of the California Institute of Technology in Pasadena.
Since the output of solar cells is spectrally selective, the electrical power derived from solar cells depends on the total intensity and the spectral distribution of the light source: the Sun. Attempts were made to procure a laboratory light source which has the same spectral character and intensity as the Sun. However, such attempts have been complicated as different types of radiation sensing devices, such as pyrheliometers and thermopiles, have been used which can not be accurately calibrated on either a total intensity or spectral intensity basis. To overcome this was introduced the concept of flying cells on a balloon, to measure their output at altitudes, to recover the cells and to use them as reference standards. The calibrated standard solar cell is placed in the solar simulator beam, and the beam intensity is adjusted until the standard solar cell reads the same as it reads on the balloon.
Althought, some modifications were introduced over time, the main components of the balloon flight system were maintained along the entire program: a sun tracker, a helium-filled balloon, a telemetry system, and a battery power supply, as shown in the scheme at left (click for more detail). The sun tracker was mounted on the balloon apex, which is the most stable position of the balloon system. The telemetry transmitter and battery power supply, along with several instruments for measuring altitude, were suspended in a second gondola beneath the balloon. An electrical cable, incorporated into the balloon during manufacture, connected the top and bottom payloads.
The solar tracker was used to position the solar cell payload toward the sun, independent of balloon movements. The tracker was capable of movement in both elevation and azimuth to maintain an "on-sun" condition within +2 deg. A reflection shield attached to the solar tracker was used to prevent unwanted reflected light from reaching the solar cell payload. The tracker and associated electronics boxes were mounted on a plywood disk 6 ft in diameter, which, in turn, was bolted to the balloon top end fitting. The plywood disk permited the tracker to "float" on top of the helium bubble. Total weight of the upper payload was approximately 23 kg.
This was the first balloon flight for the solar cell calibration program. It was the starting kick of an initiative that would endure more than 40 years and spanned through more than 80 flights.
Details of the balloon flight
Balloon launched on: 3/21/1962
Launch site: University of Minnesota Airport, New Brighton, US
Balloon launched by: General Mills Inc.
Balloon manufacturer/size/composition: Zero Pressure Balloon General Mills - 130.000 cuft
End of flight (L for landing time, W for last contact, otherwise termination time): 3/21/1962 at
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 2 h
Landing site: Premature termination at 50.000 ft
The balloon was launched March 21, 1962 from the General Mills Balloon Flight Center in New Brighton, Minnesota. It was meant to be the first flight of the program, however due to noise generated in the telemetry system, the automatic aborting system was fired at an altitude of 50,000 ft. Since the balloon was to have reached an altitude of 80,000 feet, the first flight was unsuccessful and no useful data were obtained.
- Balloon flight calibration of solar cell standards in JPL Space Programs Summary Nº 37-17,
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