Early days: NASA's International Sun-Earth Explorer C (also known as ISEE-3 and ICE) was undergoing testing and evaluation inside the Goddard Space Flight Center's dynamic test chamber when this photo was snapped in 1976. NASA hide caption

itoggle caption NASA

In 1986, the European spacecraft Giotto looked into the heart of Halley's Comet as it approached the sun. Data from Giotto's camera were used to generate this enhanced image of the comet's potato-shaped nucleus, measuring roughly 15 kilometers across. Halley Multicolor Camera Team/Giotto Project/ESA/NASA hide caption

itoggle caption Halley Multicolor Camera Team/Giotto Project/ESA/NASA