range of today's spacecraft, as the most important "cargo" would not need much space or weigh very much. Sleeper ship proposals call for freezing adult humans. While there is research into hibernation, the complexity of a living fully developed human body may make the sleeper ship proposals much more difficult. While sleeper ships and generation ships would deliver to a prospective colony world a population that has undergone some degree of education, training, and socialization in areas reconcilable with those of the sponsor culture (e.g. historical, scientific, and technical education, language acquisition, an understanding of the original mission and broader cultural norms), individuals who are born into colony worlds through embryo space colonization would initially lack this education. Difficulties in implementing the concept Like every proposal for interstellar colonization, embryo space colonization depends on solutions to still-unsolved technological problems. Some of these are: Robotics: Whether it will be possible to develop fully autonomous robots that can build the first settlement on the target planet and raise the first humans, is unclear. Because the initial probe must be maximally compact, the industrial robots that build the habitat would themselves have to be built autonomously from local materials. Though such technology does not yet exist, there are strong economic incentives to develop it, which are unrelated to space colonization. Artificial Intelligence: It would be challenging to create an artificial intelligence that could serve as an adequate artificial parent and successfully raise human children who have no contact with other human beings. Its design would have to include strategies for the transmission of terrestrial culture and language, as well as the prerequisites for healthy psychological functioning, to persons who cannot interact with Earth. Artificial Uterus: Artificial wombs exist today but they are not available for full-term development of fetuses. Human embryos have been successfully grown in artificial uteri for 13 days. There is a 14-day rule, codified into law in twelve countries, preventing human embryos from being kept in artificial uteri past 14 days. Long-duration computers: Computer hardware would need to function reliably over long periods of time, in the range of several thousands of years. Propulsion: Furthermore, a propulsion system would be required that could accelerate the EIS to a high speed and slow it down again upon nearing the destination. Even assuming a speed one hundred times faster than any of today's space probes and a target planet within a couple