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 mission concepts addressed in this chapter. Of particular interest is the question, "How soon after the Titan mission will extraterrestrial materials be utilized to facilitate interstellar exploration missions?" A Delphi poll was conducted using all Study participants (considered the best sample of experts immediately available to consider the question) and the results were: Median year 2028 AD, with the 14 estimates ranging from 1995 AD through 2100 AD.

3.2 Titan Demonstration Mission Definition

The Titan Demonstration Mission as envisaged by the Space Exploration Team encompasses a continuum of scientific investigative activities culminating in a fully autonomous extrasolar exploratory capability. The primary focus is on condensing into a single extended mission NASA's present sequential approach of reconnaissance, exploration and intensive study. In the past, interplanetary discovery has required Earth-launch of consecutive exploratory devices designed on the basis of data gathered by precursor craft. This approach assumes a broad range of sophisticated sensing equipment but little capability for onboard processing. Analysis of acquired data typically has been relegated to earthbound scientists who make judgments to determine the best next course of action, a procedure which incurs considerable time delays in return transmission of data as well as in ground-based control of distant spacecraft. An even more dramatic delay problem emerges with respect to the deployment of subsequent exploratory devices. In the case of Mars, for example, an initial reconnaissance vehicle (Mariner 4) was dispatched in 1964 but it was more than 10 years later (in 1975) before Viking 1 could be launched to attempt a Martian landing and a more intensive planetary investigation.

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. It is in this spirit that the Titan Demonstration Mission is proposed - anticipation of the potential for advanced machine intelligence eventually to permit fully autonomous exploration of the interstellar domain, a capability born of earlier demonstrations within the closer context of the Solar System.

In order to maintain linkages with current and future NASA activities (e.g., Voyager, Saturn Orbiter Dual Probe) and between short- and long-term objectives, the initial Titan demonstration relies upon extensions of current arti- ficial intelligence (AI) techniques where these are appropriate. For example, by the year 2000 a considerable amount of information about Titan's characteristics, including a basic atmospheric model, already may have been compiled. Assuming research and development progresses in both interacting simulation models and rule-based automated decisionmaking, then extensions of current AI knowledge-based systems will have the potential to contribute to the automatic maintenance of mission integrity to insure the survival of mission functions and components.

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). Significant new research in machine intelligence is a clear prerequisite to successful completion of the proposed Titan Demonstration Mission (see table 3.2). TABLE 3.2.-TITAN EXPLORATION MISSION DRIVERS Technology ? A coordinated surrogate scientific community on and around Titan ? Long system life - 10 years or more reliable/redundant propulsion/energy ? Distributed decision and expert systems ? Self-monitor and repair ability ? Semi-autonomous subsystems Probes, Landers, Rovers, Satellites ? Data storage and reduction; information communication to Earth ? Integrated multisensor capability Intelligence ? Overcome the intelligence barrier. Current AI capabili ties and research will not achieve autonomous MI needs for space exploration ? MI for space exploration must be able to learn from and adapt to environment. To be able to formulate and verify hypotheses is essential, but may not be sufficient. Goal: Full autonomic exploration system with human intervention option.