such a colony would be Earth's first act of self-replication. Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and tools. Population size In 2002, the anthropologist John H. Moore estimated that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years. Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin and the particle physicist Camille Beluffi calculated that the minimum viable population for a generation ship to reach Proxima Centauri would be 98 settlers at the beginning of the mission (then the crew will breed until reaching a stable population of several hundred settlers within the ship) . In 2020, Jean-Marc Salotti proposed a method to determine the minimum number of settlers to survive on an extraterrestrial world. It is based on the comparison between the required time to perform all activities and the working time of all human resources. For Mars, 110 individuals would be required. Advocacy Several private companies have announced plans toward the colonization of Mars. Among entrepreneurs leading the call for space colonization are Elon Musk, Dennis Tito and Bas Lansdorp. Involved organizations Organizations that contribute to space colonization include: The National Space Society is an organization with the vision of people living and working in thriving communities beyond the Earth. The NSS also maintains an extensive library of full-text articles and books on space settlement. The Space Frontier Foundation performs space advocacy including strong free market, capitalist views about space development. The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars. The Space Settlement Institute is searching for ways to make space colonization happen within a lifetime. SpaceX is developing extensive spaceflight transportation infrastructure with the express purpose of enabling long-term human settlement of Mars. The Space Studies Institute funds the study of outer space settlements, especially O'Neill cylinders. The Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth. The Artemis Project plans to set up a private lunar surface station. The British Interplanetary Society promotes ideas for the exploration and utilization of space, including a Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds. In June 2013 the BIS began the