STRATOSPHERIC PHOTOGRAPHY — SCHWARZCHILD 325 



earth's atmosphere. For this reason we decided to study the possi- 

 bility of sending a telescope up on a balloon with the specific purpose 

 of obtaining high-definition photographs of sample areas on the solar 

 surface. "Wlien these studies indicated that such an undertaking 

 appeared technically feasible we decided to go ahead with it — elated 

 and filled with awe at the same time. 



The instrument built for this specific research, Stratoscope I, had 

 to fulfill two central conditions : First, it had to contain optics capable 

 of producing a highly enlarged image of the solar surface on the 

 photographic emulsion ; for this purpose a parabolic mirror 12 inches 

 in diameter was used as the primary optical element followed by an 

 enlarging lens which produced an image of part of the solar surface 

 with a scale equivalent to a telescope with a 200-foot focal length. 

 Second, this telescope had to be pointed toward the sun by electrical 

 motors steered by electronic devices so steadily that the telescope would 

 not turn by more than about a fifth of a second of arc in the required 

 exposure time of about two-thousandths of a second of time, an 

 extremely exacting condition on pointing steadiness indeed. 



We flew this instrument for the first time in the summer of 1957. 

 After a preliminary test flight with a dunmiy telescope to determine 

 whether the balloons and launching techniques then employed were 

 capable of safely carrying a delicate optical instrument into the strato- 

 sphere and whether the return of the instrument by parachute was 

 practicable, two flights were carried out with Stratoscope I, itself. 

 These two flights brought down 16,000 photographs of parts of the 

 solar surface. Nearly all of these photographs were of poor quality 

 because of a number of instrumental inadequacies disclosed by sub- 

 sequent analysis. Among this vast number of photographs, however, 

 we found about half a dozen superb ones, which for the first time 

 showed the detailed structure of the convective elements in the solar 

 granulation well. We returned home from that first flight season 

 jubilant — and still filled with a sense of awe. 



The next 2 years we were strenuously occupied by measuring and 

 analyzing the fundamental characteristics of the solar convection 

 shown on our best photographs and deducing from these data tentative 

 conclusions regarding convective energy transport in stars relevant 

 for the theory of stellar evolution. At the same time we concentrated 

 hard to eliminate the instrumental faults shown up in the first flights 

 of Stratoscope I. Also, we made one major modification of the instru- 

 ment which increased greatly the effectiveness of this telescope as a 

 research tool. This was the addition of a radio-command link from 

 a ground station to the unmanned balloon telescope by which the 

 focus of the telescope could be regulated and by which the telescope 

 could be pointed at will to any portion of the solar disk. To make 

 this command link effective we also added a small television link 



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