Galileo's great contemporary was Johannes Kepler, who made vast strides in revealing the true nature of the universe. He came up with the theory that Earth's tides were caused by the Moon - a theory which was rejected by Galileo but which turned out to be correct. His laws of planetary motion explained how the planets moved under Copernicus's theory - something which Copernicus himself had not done. He also theorised that there must be a "Solar Wind" which could, in theory, be utilised to propel objects.
His 1634 work "Somnium", relating a trip to the Moon, was one of the earliest versions of what would become SF and in which Kepler was careful not to move beyond what was known at the time.
A key development was the foundation of the Royal Society of England on July 15 1662, whose motto may be translated as "Take No-one's Word For it." One of its founders was John Wilkins (1619 - 1655) and in 1638 he published his non-fiction work "The Discovery of a World in the Moon". In this, he proposed that the Moon must be a world like Earth with its own climate, seasons and life. He believed that intelligent life might be possible there and that one day we might travel there and meet them, setting up interplanetary commerce.
He is even credited with the proposal that hibernation might be necessary for long journeys in space!