Description of the payload

The purpose of the high altitude solar cell calibration program is to produce air mass zero (AM0) standard solar cell that can be used for accurately setting solar simulator intensities. The program was started in 1962 by the Jet Propulsion Laboratory.

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 read on the balloon.

The balloon system layout is shown in the scheme at left. The solar cells are mounted on the face of the solar tracker, which is mounted on the top side of the balloon. The cells are located on the top of the balloon in order to prevent their illumination by reflections of both direct sunlight and Earth albedo from the balloon. During a flight, data are transmitted from the balloon via an FM-FM telemetry system.

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 and scientific outcome

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

The balloon was launched at 09:19 CDT on June 13, 1962 from the General Mills Balloon Flight Center in New Brighton, Minnesota. The balloon reached a maximum altitude of 77,000 ft at about 11:15 CDT and remained at this altitude for approximately 3 hr around solar noon. During this time, the short-circuit currents of the 14 solar cells flown were measured. Also measured were the temperatures of both the front and back sides of control cells mounted on the same heat sink as the other cells. The balloon began its descent at 14:25 CDT and made Earth impact at 16:00 CDT, about 80 mi south of the launching site. The solar-cell payload did not suffer any damage from either the flight or impact.

External references and bibliographical sources

Images of the mission