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While Titan is too distant to explore efficiently using traditional methods it is still near enough to monitor the performance of automated functions and to take intervening action should the need arise. As exploration distances extend farther out into the Solar System, such intervention becomes increasingly difficult so the demand for greater mission autonomy and higher-level machine intelligence rapidly intensifies. An outline of operational mission stages integral to the full range of exploratory activity, from the Titan demonstration to interstellar exploration, is presented below. Each phase underscores a variety of machine capabilities, some unique and some overlapping, required if full autonomy is to be achieved. These capabilities represent the primary technology drivers for machine intelligence in future space exploration.

3.2.1 Titan Mission Operational Stages

A fully automated mission to Titan (and beyond) requires a very advanced machine intelligence as well as a system which is highly adaptive in its interactions with its surroundings. This latter aspect is even more significant in extrasolar missions because a sufficient operational knowledge base might not be available prior to an encounter with new planetary environments. The explorer must generate and use its own information regarding initially unspecified terrain, and this knowledge must evolve through the updating of databases and by the continual construction and revision of models. Such a machine system should be capable of considerably higher-order intelligent activities than can be implemented with state-of-the-art techniques in artificial intelligence and robotics.

The short-term mission objective is to encompass the tripartite staging of NASA missions within a single, fully automatic system capable of performing scientific investigation and analysis, the immediate objective being a complete and methodical account of Titan. Later, and as a longer- term goal, given the successful achievement of the short- term objective, a similar exploration of the outermost planets and bodies of the Solar System could be conducted with improved equipment, building on the systems operations knowledge gained at Titan.

The proposed exploration system must be capable of the following basic functions: (1) Select interesting problems and sites.

(2) Plan and sequence mission stages, including deployment strategies for landers and probes.

(3) Navigate in space and on the ground by planning trajectories and categorizing regions of traversibility.

(4) Autonomously maintain precision pointing, thermal control, and communications links.

(5) Budget the energy requirements of onboard instrumentation.

(6) Diagnose malfunctions, correct detected faults, and service and maintain all systems.

(7) Determine data-taking tasks, set priorities, and sequence and coordinate sensor tasks. (8) Control sensor deployment at all times. (9) Handle and analyze all physical samples.

(10) Selectively organize and reduce data, correlate results from different sensors, and extract useful information.

(11) Generate and test scientific and operational hypotheses.

(12) Use, and possibly generate, criteria for discarding or adopting hypotheses with confidence.

One way to formalize the precise characteristics of a proposed mission is in terms of a series of prerequisite steps or stages which, in aggregate, capture the nature of the mission as a whole. The operational mission stages selected for the Titan demonstration analysis are: configuration, launch, interplanetary flight, search, encounter, orbit, site selection, descent, surface, and build. Each is discussed briefly below.

Configuration. This initial phase addresses considerations of size, weight, instrument specifications and other launch vehicle parameters, and usually depends on the equipment and tasks required for a specific mission. Questions concerning the precise nature of the investigation and experimentation traditionally are taken up at this point.

For deep-space exploration, spacecraft configurations must be general and flexible enough to handle a wide range of environments. Hardware and software impervious to extreme pressure, temperature, and chemical conditions and with long lifespans are required. Also, a diverse assortment of onboard sensors with broad capabilities is necessary to produce basic information via complementary and selective sensing to be used in scientific investigation and planning.

Launch. The focus of this stage depends to some extent on the perceived configuration of the mission vehicle. Issues related to propulsion and energy needs and appropriate launch sites (e.g., Low Earth Orbit vs vicinity of extraterrestrial resources utilized for the mission) are decided. The launch phase is conducted largely by Earth-based humans, but could benefit from machine intelligence capabilities (e.g., CAD/CAM/CAT) for testing, checkout, flight preparation, and launch support.

Interplanetary flight. Prior to Viking and Voyager, unmanned flyby and orbiter spacecraft were totally dependent upon Earth-based remote observation and direct human intervention to accomplish accurate navigation, stationkeeping, and rendezvous and docking maneuvers (Schappell, 1979). This underscores the control and communication time delay problem that limits efficient investigation of distant bodies such as Titan and even more dramatically constrains exploration of the interstellar realm. Some ground-based support for the initial Titan