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Smart Executive

              <img src="/m/project/remote-agent/images/psbig.png" alt="Cartoon" style="float: left;" height="172" width="200">
                Throughout your day, you are executing plans to achieve your daily goals.  In the 
                Planner/Scheduler section, we described a plan designed to accomplish the goal of 
                buying milk.  However, creating a plan is not enough to accomplish the goal; the 
                plan must also be carried out. For example, one  task in the plan was to find keys 
                and wallet.  In order to do this, your eyes have to be told to be looking for these 
                two objects, your hands must be told to move any obstacles that might be covering 
                the objects, and your legs must be told to carry you from room to room.  Your 
                brain is actually sending signals to your eyes, arms, legs to work together to 
                accomplish the task; it happens so quickly and autonomously that you are not even 
                aware of it.
                In addition to coordinating different parts of your body to do different things at the 
                appropriate times, you must also make sure the plan is carried out successfully.  If 
                the car doesn't start at first, you might try to turn the key in the ignition again.  
                If it takes you too long to find the milk in the store, you may want to ask someone 
                where the milk is located.  If your car starts smoking during the drive to the store, 
                you may have to pull over and stop the car and scrap the plan of going to the store 
                until someone can help fix your car.
                Smart Executive (EXEC) is the part of Remote Agent that is responsible for executing the 
                plans created by Planner/Scheduler (PS).  EXEC must command different parts of the 
                spacecraft to act at the appropriate times, make sure each part's task is accomplished 
                successfully, and must decide what to do if something is not going as planned.
              <h2>Benefits of Remote Agent's Smart Executive</h2>
                EXEC's ability to carry out <strong>flexible</strong> plans is one of its most unique and 
                significant qualities.  In the past, plans created for spacecraft activities were made up 
                of specific tasks that were to be done at specific times.  The flexible plans generated by
                PS do not always have specific times that actions must take place; instead, many actions 
                are given windows of time within which an activity can take place.  EXEC uses information 
                about the spacecraft's position and status to determine the best time within the window 
                to accomplish the task.  This increases the chance that the plan can be carried out 
                successfully.  For example, it is difficult to predict how long things will take and 
                the effects of unexpected variables in space.  If a plan dictates that a picture be 
                taken of an asteroid at a particular time, it is possible that the asteroid will not be 
                in front of the camera at that time.  On DS1, however, EXEC can determine on its own the 
                ideal time to take the picture based on up-to-date information on the position of the 
                asteroid relative to the spacecraft.  This flexibility, along with EXEC's ability to 
                recover from faults, significantly increases mission <strong>reliability</strong>.
                Another advantage of EXEC's ability to carry out flexible plans is it enables a spacecraft 
                <strong>to take advantage of unexpected science opportunities</strong>.  Sometimes, 
                significant science discoveries are made unexpectedly, like the discovery of pennicillin 
                on moldy bread. EXEC's flexibility opens up the future possibility of spacecraft being 
                able to take advantage of unexpected science opportunities.  The hope is that if the 
                spacecraft detects something unusual, like a unique type of radiation coming from an 
                asteroid, the EXEC will be able to make scientific observations of it, while still 
                continuing with the original plan.
              <h2>How Smart Executive Works</h2>

EXEC has two main roles: executing the plan and recovering from failures that prevent proper execution of it. To execute a plan the EXEC:

  • obtains the plan for some time period from PS.
  • breaks the plan tasks into smaller steps that must be carried out to accomplish those tasks.
  • commands the necessary spacecraft components to perform the necessary actions to accomplish each task in the plan.
  • monitors the execution of each task and begins the next task as soon as possible.

To detect and recover from failures, EXEC:

  • receives information regarding task completion from spacecraft systems and retries tasks, or commands an alternative method to carry out tasks, if they are at first not completed.
  • receives information regarding the failure of spacecraft components from MIR.
  • in the case of a failure, requests a recovery action from MIR and executes recovery action.
  • in the case of a serious failure, like lack of power, commands the spacecraft to enter standby mode, shutting down all activities but the ones necessary for survival of the spacecraft, and waits for instructions from ground control.
  • if there is no recovery action available to continue the plan execution, then there will be a replanning period
More details about EXEC in action

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