Introduction to Space Exploration - Enlightened Observations

Centuries later the great Italian painter and engineer Leonardo da Vinci (1452–1519) foresaw the day that humans would fly. He wrote "There shall be wings! If the accomplishment be not for me, 'tis for some other." Leonardo made several sketches of human-powered flying machines and gliders with bird-like wings.

At the time astronomical knowledge was limited, and it was widely believed that the Earth was the center of the universe and everything else revolved around it. The Polish astronomer Nicolaus Copernicus (1473–1543) studied the motion of the heavens and drew different conclusions. In 1543 he published the famous book De revolutionibus orbium coelestium (On the Revolutions of the Celestial Orbs). Copernicus insisted that Earth and the other planets orbit the Sun. He said "At the middle of all things lies the sun."

During the early 1600s the first telescopes appeared in Europe. Although historians are not sure who invented the telescope, they know that Italian astronomer Galileo Galilei (1564–1642) popularized their use. Galileo also improved the design and power of the telescope. He used several to study the cosmos and published his findings in the 1610 book Sidereus Nuncius (Starry Messenger).

At about the same time the German astronomer Johannes Kepler (1571–1630) was also studying the solar system. He discovered that planets move according to mathematical rhythms, and he derived laws of planetary motion from these rhythms that are still studied today. In 1593 Kepler wrote Galileo a letter in which he said "Provide ships or sails adapted to the heavenly breezes, and there will be some who will not fear even that void."

The mechanics of spaceflight were explored by English physicist Sir Isaac Newton (1642–1727). Newton first unraveled the mysteries of gravity on Earth and then extended his findings into space. He was the first to explain how a satellite (an orbiting body) could be put into orbit around Earth.

Newton's thought experiment, as it was called, proposed a cannon atop a tall mountain as a theoretical means for putting an object into orbit around Earth. The cannon shoots out projectiles one after another, using more gunpowder with each successive firing. Newton said each projectile would travel farther horizontally than the previous one before falling. Finally, there would be a projectile shot with enough gunpowder that it would travel very far horizontally and when it began to fall toward Earth, its path would have the same curvature as the Earth's surface. The projectile would not fall to Earth's surface but continue to circle around the planet. It would be another two centuries before humans could prove Newton's theory.

It was only a few decades after Newton's death that humans began to fly upon earthly breezes. During the late 1700s two French brothers named Joseph and Etienne Montgolfier built the first hot-air balloons. On November 21, 1783, two noblemen from the French court ascended to 500 feet and sailed across the city of Paris. They landed safely miles from the city and offered champagne to the terrified villagers there. The age of flight had begun.