Krafft Arnold Ehricke

German American rocket scientist and engineer and space colonization advocate
He worked at Peenemünde as a propulsion engineer from 1942 to 1945 with Walter Thiel, then went to the United States with other German rocket scientists and technicians under "Operation Paperclip" in 1947. He worked for a short time with the Von Braun Rocket Team at Huntsville. In the same year he wrote a book with Wernher von Braun, The Mars Project, which detailed how man could travel to Mars using a ferry system. Upon leaving government service in 1952, Ehricke worked at Bell Aircraft, and then moved to Convair in 1954. He also created an early space station design, based on launch by Convair's Atlas rocket. The NEXUS reusable rocket was a 1960s concept designed by a group at General Dynamics led by Ehricke. Also, during his stay at General Dynamics, he participated in Project Orion (nuclear propulsion). In 1966, Ehricke was inducted into the International Aerospace Hall of Fame for his engineering achievements and his influential ideas on the purpose of space exploration. Ehricke undertook a major, multi decade study of the industrial development of the Moon, which he described as Earth's "seventh continent." His lunar industrialization concept was based on the most advanced technologies, such as nuclear powered freight transporters, and using fusion energy to power his city, Selenopolis, on the Moon. He married Ingeborg Ehricke (born 12 September 1922). Ehricke received a space burial on April 21, 1997, when a rocket sent a small amount of his cremated remains into Earth orbit.

Ehricke was an accomplished practitioner in the field of astrodynamics and its applications. His two volume work entitled Space Flight is probably the most complete and surely the most useful introduction to this complex subject ever written. It focuses on methods for exploration of the solar system. Although he was not the first, he clearly demonstrated the so called "gravity assist" method for utilizing hyperbolic encounters with an intermediate planet to increase (or decrease) the velocity and orbital elements of a space vehicle. This technique opened the entire solar system to robotic exploration by using what he called "Instrumented Comets." Examples include the Voyager missions to the outer planets and the recent successful New Horizons mission to Pluto. His contribution to this important field of exploration has been neglected for many decades and incorrect claims of the "invention" of what is now called gravity assist were made by Minovitch.

Ehricke promoted a philosophical concept called the "Extraterrestrial Imperative." This idea refers to Ehricke's belief that it was the responsibility of humanity to explore space and exploit the resources of the Solar System, in order to sustain the development of the species. There are no external "limits to growth," Ehricke insisted, because while the Earth is a "closed system," the exploration of space opens the universe to humanity. For Ehricke, human creativity has no limits.