ASTRONOMICAL TECHNOLOGY — MEINEL 299 



interest now exists in the pending operation of the first space tele- 

 scopes. Telescopes as developed for use in the early rocket veliicles 

 have been severely limited by the space available in the nose cone of 

 the rocket. The accompanying photograph shows the instrument 

 flown by Stecher and Milligan to illustrate this point. Their instru- 

 ment was designed very compactly. A 10-inch telescope and diffrac- 

 tion grating was fitted into a space 14 inches in diameter and 12 

 inches in length. 



The success of the rocket experiments and the great promise for 

 the exploration of the miiverse m the far ultraviolet has led to the 

 initiation by NASA (U.S.A.) of a spacecraft system capable of carry- 

 ing a 36-inch telescope and all its related instrumentation. The 

 program plans tliree such systems at an expected cost of $100 million. 

 This is a large amount of money on any monetary scale and is justified 

 by the fact that in no other way is it possible to learn what such an 

 instrument will be able to tell us. The payload for the OAO telescope 

 will be in excess of 4,000 pounds, the largest unmanned scientific pay- 

 load to be launched to date by the U.S.A. 



The most obvious gain to be had from a space telescope is, of course, 

 the accessibility of the ultraviolet. Tliis region of wavelengths is 

 of great interest to the astrophysicist since the resonance absorption 

 and emissions from atoms occur m this region. A less obvious ad- 

 vantage, and one that will require more teclinological development, 

 is that an orbital telescope can work at the theoretical resolving power 

 of the optical system, since no "seeing" disturbance is present. Given 

 sufficient guiding accuracy, possible in free space, one could use dia- 

 phragms of very small angular size and increase the star-to-sky signal 

 by 5 magnitudes over the same telescope on earth. If T.V. devices of 

 sufficient information handling capability become available then high 

 resolution studies on a fulltime basis will be possible. This possi- 

 bility is of special interest for the observation of time- variable phe- 

 nomena at a predetermined time or for long periods of time since 

 neither weather nor daylight will interfere with the work of a space 

 telescope. 



Space telescopes pose engineering problems that are not encountered 

 in terrestrial telescopes and whose solution is required before successful 

 missions can be made. The launching g-forces are an example. 

 During the launching phase the telescope will be subject to thrust 

 and vibration forces up to the order of 10 g's. As a consequence, either 

 the engineer must find a structural design that will preserve optical 

 collimation or the astronomer will have to have controls to permit liim 

 to realign his optical systems after the telescope arrives in orbit. The 

 lack of proper collimation could seriously degrade the performance 

 of a space telescope. 



