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## 5.6 The Satellite Domain

In the Satellite domain a number of satellites orbit the Earth, each equipped with a set of scientific imaging instruments. The satellites turn in space, targeting stars, planets and interesting phenomena to capture images of them using different instrument operation modes.

These modes can include regular or infrared imaging and spectrographic or thermographic readings but are different for each problem. The planner's task is to schedule a series of observations so that the satellites are used efficiently. Figure 7 shows a small example problem instance, with arrows showing the directions in which the satellites are pointing.

Directions are not represented as explicit coordinates. Instead, satellites can turn to a new direction by giving the turn to **operator an argument specifying the star, planet or** phenomenon that the satellite should point to. Instruments **first need to be activated using**
switch on**, then calibrated at a calibration target with the** calibrate **operator before they** can capture images using take image**. Each satellite has only enough power to operate one**
instrument at a time, so switching active instruments is always initiated by the switch off operator to deactivate the first instrument.

## 5.6.1 Satellite: Strips

Since the task consists of collecting a number of images, we begin by restricting the use of take image **to images that are mentioned in the goal.**

#control :name "**only-take-pictures-of-goals**" [t] ¬have image(direction, mode) ∧ [t+1] have image(direction, mode) → goal(have image(direction, mode))
The next step is to restrict the directions in which satellites turn to those that may actually help in collecting the images. The task is split into a **control rule,** only-point-ingoal-directions**, and a definition of goal directions. A satellite is allowed to turn towards a**
direction to take a picture, to calibrate an instrument or if **a goal specifies that the satellite**
should point in the direction and there is no more work left to do.