Ernst Öpik, an Estonian astronomer whose wide-ranging work on meteors led to the development of heat shields for spacecraft, was born on 23 October 1893. Öpik studied the erosion of meteors as they plunge through an atmosphere. His calculations led to the design of heat shields and other protective devices that enable spacecraft to survive the friction and heat upon reentering Earth's atmosphere.
Earlier in his career, Öpik originated the practice of the "double-count," in which two astronomers simultaneously scan the heavens for meteors to gain a more accurate count. He also proved that stars depend on nuclear reactions for their energy.
[Source: Roy Porter, Ed., The Biographical Dictionary of Scientists (Oxford University Press, ed. 2, 1994).]