Having traversed the Asteroid Belt and given scientists their first good look at Jupiter and its satellites, the vehicle now rushes toward the edge of the Solar System at a speed of about 3 AU/yr. The exact moment of penetration into extrasolar space is unpredictable because the boundary of our System is not precisely known, and because the spacecraft's ability to transmit useful data will likely degrade by the time of passage (circa 1986) that it will be unable to report transit of the heliosphere when this occurs. Several other unmanned vehicles will also eventually exit the Solar System. Astronomers and geologists have participated since they represent the sciences traditionally most involved in the observation and classification of planetologi- cal and celestial phenomena. During the last two decades researchers from other physical sciences and the biological sciences have become interested in investigating how the laws of nature operate in the cosmos, using the techniques of radio astronomy and space exploration including direct biological samplings of other planets. Interest in the outer Solar System and deep space will likely remain high among natural scientists. (7) A partial knowledge of the Titan environment permits equipment and experiment economies over later missions wherein many more contingencies and hypotheses must be anticipated. A Titan Demonstration Mission in the year 2000 AD would benefit from two types of heritage (fig. 3.2). The first, knowledge heritage, allows the use of spacecraft com ​ ponents which need not be designed to cope with wholly unknown alien environments. The experience gained during the Pioneer 11 and Voyager encounters with Saturn and its moons has provided essential prior scientific and engineering data on Titan and its surroundings. Mars, of course, is one of Earth's closest neighbors. Time delays in data transmission and control functions reach a maximum of 21 min in each direction, and travel time from Earth to Mars is approximately 1 year. In the outer Solar System the delay for one-way data transmission and control is measured in hours or days, while at interstellar distances, delay is measured in years with travel times of decades or more. As exploration goals are extended into the farthest reaches of space, development of nontraditional techniques and systems requiring a lesser dependency on Earth-based operations and possessing far greater autonomy become increasingly desirable and necessary. To the extent that new developments in machine intelligence technology move in the appropriate directions, the Titan mission might include demonstrations of autonomous onboard processing of mechanically acquired data in at least one sample of scientific investigation. This results in great compression of return information because only the "important" or "interesting" hypotheses about the target planet are transmitted back to Earth. Such a function presupposes a machine capacity both for hypothesis formation and for learning, neither of which is inherent in state-of- the-art AI technology (see section 3.3). Self- modification of advanced expert systems also prepares the exploration system to make autonomous decisions and corrections regarding its relationship with the environment. An additional essential task en route to an unknown planetary system around another star is the determination of gross parameters such as sizes, masses, densities, orbital periods, rotational periods, axial tilts, and solar distances for each member planet and moon. A fully autonomous spacecraft would utilize these characteristics, determined by early data collection, in making onboard selections of appropriate bodies to explore. Hazards hidden from view along the intended itinerary must be identified en route, and the path ahead continually re-scanned and updated as in the case of a human walking through a rocky area. An alternative (and more difficult) approach places greater reliance on autonomous lander processing systems. A planet model provides an apparently traversible path from the landing site to another location observable from the landing site (based on low-resolution data). Atmospheric modeling should begin early in the approach to an unknown planet since many mode-of- exploration decisions require information on the nature of the atmosphere. During the course of the mission the atmospheric model accumulates greater detail with continuous updating as higher sensor resolution is achieved and probes are deployed for direct measurements. The investigation of an atmosphere differs from studies of surface characteristics in that it involves the complex integration of many interrelated subhypotheses and measurements of numerous allied parameters. - Scientific investigation.  ​ Hypothesis formation and learning have emerged as central problems in machine intelligence, representing perhaps the primary technological prerequisites for automated deep space exploration. The Titan, outer planet, and interstellar missions discussed by the Space Exploration Team require a machine intelligence system able to autonomously conduct intensive studies of extraterrestrial objects. The artificial intelligence capacity supporting these missions must be adequate to the goal of producing scientific knowledge regarding previously unknown objects. An automated system that performs only this type of inference could probably undertake reconnaissance missions successfully. Next is inductive inference. A machine system able to perform this type as well as analytic inference could successfully undertake missions combining reconnaissance and exploration, provided the planet explored is represented well enough by the fundamental models with which the system would be preprogrammed. But if the processes underlying the