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1987-An Intelligent Tutoring System for Interpreting Ground Tracks

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1987-An Intelligent Tutoring System for Interpreting Ground Tracks From: AAAI-87 Proceedings. Copyright ©1987, AAAI (www.aaai.org). All rights reserved. AN INTELLIGENT TUTORING SYSTEM FOR INTERPRETING GROUND TRACKS DT. Kathleen Swigger* Lt. Cal. Hugh Burns Harry Loveland Capt. Terresa Jackson Air Force Human Resources Laboratory Intelligent Systems Branch Brooks Air Force Base, Brooks Texas 78235 Abstract loops, direction, etc., and then use this information to This paper describes an intelligent tutor- “estimate” the orbital elements. In order to duplicate ing system for the space domain. The system this nrocess. we decided to build a qualitative model of was developed on a Xerox 1108 using LOOPS how *the exbert nredicts orbital elements, and then use and provides an environment for discovering this model Awitgn a microworld, or simulated environ- principles of ground tracks as a direct function ment, that allows the student to manipulate various of the orbital elements. The system was orbital elements and observe how each of the parame- designed to teach students how to “deduce” a ters affects the shape of the ground track. satellite’s orbital elements by looking at a graphic display of a satellite’s ground track. B. Student/Computer Interaction The system also teaches students how to use As nreviouslv mentioned. the microworld for the more systematic behaviors to explore this Ground Track problem offers a number of online tools domain. Since the system is equipped with a that permit students to discover relationships between number of online tools that were specially orbital parameters and ground tracks. This environ- designed to help students better understand ment consists of an elaborate ground track display (Fig- facts, principles and relationships, the student ure 1) and a number of interactive tools designed to is free to investigate different options and encourage systematic behaviors for investigating-ground learn at his own pace. track related problems. The student initiates a I. Introduction discovery activity by changing one or more orbital A. General Introduction parameters or changing the injection parameters. This One of the nine basic operational missions for the Air task is accomnlished bv nositionine: the cursor over the Force is the continuous monitoring of the exoatmos- individual Da&meters and messin; the left mouse but- pheric arena through ground and space surveillance. ton to in&ease the value& or th\ middle button to NORAD, through its Space Defense Center, maintains decrease the value. The injection point is changed by a worldwide network that senses, tracks, and analyzes positioning the cursor over a particular point on the map and pressing the left mouse button, which the characteristics of orbiting systems. automatically sets both the longitude and latitude. A In order to monitor and plan for satellite missions, student can- observe the results of these changes by the Air Force crew must be able to read and under- selecting Generate a Ground Trace from the- main stand ground tracks. Ground tracks are two- menu. After investigating the effects of changing dif- dimensional displays that show the portion of the earth ferent narameter values for different ground tracks. the that a satellite covers in one orbit. If you can imagine student can advance to the Prediction window where being placed inside a satellite and being able to look he can make a hypothesis regarding the particular directly down on the earth, then the “ground track” is shape of a ground track. that portion of the earth that you would see as you travelled through space. The ground track is a direct In the Prediction portion of the program, the sys- function of the orbital elements, so proper understand- tem displays a list of words that describe various ing of these functions and of the interactions between features -about ground tracks such as shape, size, and orbital elements is critical for anyone interested in symmetry Figure 2). From this list of descriptors, the satellite operations. student seI ects the words that “best” describe the current ground track under discussion. The student One way to teach students how to deduce orbital then tes& his prediction bv selecting this option from elements from a satellite’s ground track is to present the menu and* comnarine: -his innuts to the Expert’s the various mathematical formulas that are used to conclusions. The &deGt can then interrogate the compute the orbital elements and then show how to Expert System by placing the cursor over aflvy of the apply these formulas to situation- specific tracks [Bates descriptors and pressing the left mouse button. A et al., 1971; Astronautics, 19851. In contrast to this “Why” pop-up menu appears on the screen which the approach, we discovered that experts store ground student can mouse and receive an exulanation of the tracks as graphical representations, indexed by feature expert’s reason for the correct descripior. The student and shape. Based on previous experience, experts learn can continue this iterative process of changing parame- how to detect specific features such as size, number of ters, making predictions, and asking why until he understand the various relationships between After *The research reported herein was supported, in part, with funds making several successful predictions, the student from the Air Force Office of Scientific Research (AFOSR), and enters-a Test environment which is designed to check sponsored by the Air Force Human Resources Laboratory, Brooks the student’s predictive powers by &king him to AFB, Texas. 72 Al & Education perform a task in the reverse order of the one described Model, and (6) .the Coach. The Expert Module includes above. The student is shown a specific type of ground the rules and inference procedures used to deduce track and asked to enter a “guess-estimate” of the shape descriptors from a set of orbital parameters. The corresponding orbital parameters. If the student is suc- Curriculum Module contains the major concepts associ- cessful, then he can continue to explore different types ated with the ground track domain. The State Module of ground tracks. If the student is unsuccessful, then he contains a list of appropriate behaviors for exploring receives information about why his answers are the microworld. The Diagnostician is a set of software incorrect. procedures which evaluates the student’s answer, analyzes student errors, and updates the Student and C. Tool Description Curriculum Models. The Student Model stores the student’s current state of knowledge of both ground There are three major online tools that can be used by tracks and effective tool use. The Coach contains the the student to gather information and to understand instructional rules that tell the system when to inter- concepts and principles about ground tracks. These vene. The Coach makes this decision based on informa- tools are a) a History Tool that allows the students to tion it receives from the Student, Curriculum, and overlay previously generated ground tracks and note ‘State Models regarding the student’s current state of relationships between parameters b) an Orbit Window knowledge. A more detailed description of each module that displays a two-dimensional representation of the is presented below. orbit (Figure 1); and c) a Definition/Example tool which displays factual information about different orbi- B. The Expert Module tal parameters (Figure 1). This Module contains the rules and procedures used to The History tool is specifically designed to help deduce shape descriptors (e.g., closed-body, symmetri- students recognize relevant patterns between and cal, vertical; compressed, lean-right, hinge-symmetry, among previously generated ground tracks. As the stu- with loops) from a set of orbital parameters (eccentri- dent generates various ground tracks, the system col- city, period, semi-major axis, argument of periapsis, lects and stores each transaction. The student can inclination). The Expert Module is invoked only when retrieve any of thii data by selecting the History option the student is making a prediction or is in the Testing from the main menu. A lit of the past twenty ground mode. The Expert Module works by posting a series of tracks appears on the screen from which the student goals which determine the various shape descriptors. can select one or more related ground tracks. The sys- The general problem solving strategy employed by the tem then overlays the selected ground tracks onto a Expert Module is to determine a shape descriptor by single map. Again, the student observes the results of examining a specific orbital element. If this fails, then this exercise. the system looks at another shape descriptor and For any given set of orbital parameters, the stu- attempts to find its value, or looks at a combination of dent can obtain a two-dimensional display which shows two or more orbital elements to see if the system can the position of the satellite in relationship to the earth. deduce a shape descriptor. For example, the Expert The student selects the option labelled Orbit Window Module determines the symmetry shape goal by asking and gains immediate access to this particular display. whether this is a circular orbit. If the orbit is classified The Orbit Window is especially useful for demonstrat- as a circular orbit, then its eccentricity must be equal ing the relationship between the ground track and the to zero. If the orbit is elliptical then its eccentricity is actual orbit and for illustrating the effect of perigee on not equal to zero and the Expert Module must look at elliptical orbits. the orientation descriptor, which in turn must look at The Definition/Example tool provides the student the argument of periapsis. In thii manner, the Expert with the factual knowledge about various parameters. Module can determine a set of shape descriptors for a A student can obtain definitions and examples for both given set of ‘orbital parameters (and vice versa).
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