These requirements will engage numerous disciplines and thus create challenging instrumentation and design engineering problems for mission planners.
6.1.4 Data Storage The terrestrial world model will require satellite storage of from 101° to as much as 5.10 _I bits and perhaps 10 _4 bits on the ground. Forecasts (Whitney, 1976) give estimates of 1014 bits of in-space memory and >1016 bits of a typical on-ground memory by the year 2000. The data storage should be structured in a manner compatible with build-up of an image and extraction of image processing during orbital overpass. Optical disc, electron beam, and bubble memories are possible candidates in addition to more conventional alterable memories. The technology requirements include a high density, erasable memory suitable for use in the space environment, optimum memory architecture for readout of the world model during orbit overpass, and error-correcting memory design.
6.1.5 Automatic Mapphzg Terrestrial automatic mapping by IESIS can be accomplished using geographical data already obtained from Earth or front satellite data alone. The Defense Mapping Agency has developed digital mapping techniques for regions of the globe (Williams, 1980). By contrast, the mapping of Titan must be accomplished almost exclusively from orbit. In either case, information in the form of niche identification, basic modeling equations, and known planetary parameters will be supplied from Earth both initially and during operations. Automatic mapping from space requires state-of-theart AI techniques including boundary and shape determination, optinmm sensor choice, niche identification, and learning techniques. Full autonomous learning by abduction and inference to build new knowledge is presently beyond the capability of AI (see section 6.2). Though use of such advanced AI techniques would tremendously enhance the utility of a satellite world-model-based information system, they are not considered essential in this application. Mapping technology ultimately must prove sensor independent since the map produced should reflect a reality existing in the absence of the sensor data. ttowever, specific sensor combinations will produce a completed map more rapidly and reliably depending upon the niche environment to be mapped. Orbits which repeat over fixed portions of the planet are especially advantageous in assisting automatic mapping and memory structuring. Technology requirements, summarized briefly, are: • Rapid autonomous mapping techniques from orbital data • Optimum sensor combinations for reliable and rapid mapping . Determination of relative advantage of radar, optical, IR mapping • Optimum orbit height and orbit type for automatic mapping • Techniques to rapidly, reliably, and autolnatically update world model components in satellites and on ground directly from orbital image data • Digital mapping techniques • Autonomous hypothesis formation techniques.
6.1.6 Image Processhzg via Worm Model The satellite memory component of the world model is used for image processing. The actual image data from one or several sensors nmst be cross-correlated with a pass map (retrieved from memory) in strips along the orbit to produce an optimum match of imaged niches with their mapped locations. This process rectifies the sensed image and produces geometrical corrections necessary to adjust the sensed image to the reality reflected in the stored map. This process also will help determine the precise satellite location (Kalush. 1980). Boundaries must then be identified from the actual imagery and compared to the nominal boundaries of the map. The boundary area is an important and simply determined characteristic of the niche. Other characteristics such as anomalies are determined by new boundaries, altered location of boundaries, or changes in the determined sensor readings from their expected values. Temporal, sensorial, and solar corrections must be applied to the sensor readings and defining labels supplied for all niche characteristics for complete referencing purposes (Schlienn, 1979). The satellite location can be combined with velocity and navigation information from a global positioning system to prepare for the next image in the sequence. This preparation allows minimum processing in the subsequent image rectification and permits determination of the optimum sensor combination for the next imagery. Instructions from Earth ground control or a central satellite autonomous manager must be incorporated into the preparation and image processing procedures. Very sophisticated computer technology is required aboard the satellite to accomplish the image processing. Such processing is not found on any present-day satellites, and is done on-ground only in very limited form today. Fully parallel processing techniques are anticipated as a possible alternative to serial processing (Gilmore et al., 1979: Matsushilna et al., 1979; Schappell, 1980). Optical processing methods should also be investigated since these techniques
