Planning and scheduling is a complicated part of spacecraft control. Planning, for our purposes, can be thought of as determining all the small tasks that must be carried out in order to accomplish a goal. Let's say your goal is to buy a gallon of milk. It may sound like a simple task, but if you break it down, there are many small tasks involved: obtain keys, obtain wallet, start car, drive to store, find and obtain milk, purchase milk, etc.
Planning also takes into account rules, called constraints, which control when certain tasks can or cannot happen. Two of the many constraints in this example are, you must obtain your keys and wallet before driving to the store and you must obtain the milk before purchasing it.
Scheduling can be thought of as determining whether adequate resources are available to carry out the plan. Two resources which scheduling would have to take into account for in our example above are fuel and time. If it takes two gallons of gas to get to the store and back and your car only has one gallon, you must develop a plan which includes a stop at the gas station. If it takes 15 minutes to drive to the store, the store closes at 10:00, and it is currently 9:30, you must take that time constraint into account also when scheduling your tasks.
Throughout your day, you are executing plans that your brain comes up with to achieve your daily goals. Creating the plan is not enough to accomplish the goal; the plan must also be carried out, which can be more complex than it seems. 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 act, working together to accomplish the task; it happens so quickly 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.
What exactly can Remote Agent do?
How are remote agents used?
How does PS work?
How does the Smart Executive work?
How does the Mode Identification and Recovery system work?
How will Remote Agent be tested?
How does PS really work?