One of the first devices to successfully employ the principles essential to rocket flight was a wooden bird. Somewhere around the year 400 B.C., Archytas mystified and amused the citizens of Tarentum by flying a pigeon made of wood. Escaping steam propelled the bird suspended on wires. The pigeon used the action-reaction principle, which was not to be stated as a scientific law until the 17th century. During the latter part of the 17th century, the great English scientist Sir Isaac Newton laid the scientific foundations for modern rocketry. In 1926, an American, Robert H Goddard, launched the first liquid propellant rocket, and discussed the possibility of a rocket reaching the moon. On October 1957, the Soviet Union stunned the world by launching an Earth-orbiting artificial satellite. Physiological studies in microgravity are young. It is clearly essential to have long-term studies of physiology in microgravity if further space exploration is to take place. For example, a Mars mission will take of the order of 1,000 days, which is about three times longer than anybody has been in space so far.