Simulating a satellite imaging scenario for cities

As satellite imaging companies are becoming popular by the day, some big names like Planet Labs, BlackSky, etc and the use cases of decentralized imaging is growing, I have decided to simulate a scenario where this can be some from a technical point of view. In this scenario, we investigate a situation where our satellite is required to point at different cities when it passes over them. In the image below, one can find the cities simulated here.

So our satellite is located near Central America and is approaching the USA from the southern tip of Florida. The first point of interest is Cape Canaveral, followed by Charleston, then Washington, and so on. Our satellite is shown below with its “sensor footprint” shown in white. This “footprint” allows us to see what part of the ground is actively being imaged.

Now, AGI STK allows us to add our points of interest to its simulation and automatically command the satellite point towards our area of interest as it is passing over it. This can be seen in the video below:

As the satellite traverses, the one can see the footprint width to get an idea of how long of a time the satellite is spending pointing at a certain location, this can be seen when it actually points at a point of interest. If observed carefully, when the satellite transitions between two points, one can see that the footprint in white instantaneously moves from point A to point B.

Of course, this is not the case in real life. Since the satellite attitude is controlled by momentum wheels, the motion of changing pointing is controlled and designed to be stable. This can be achieved through some sort of controller (PD, PID, LQR), etc. For simplicity, a PD controlled is implemented here. This is done through a VB script and the Attitude Control Option in STK (not diving into details here.) As seen below, now the red footprint shows our “controlled satellite” which represents a near-realistic motion. Watch the video carefully and compare how the white footprint and the red footprint behaves.

As can be noted, the red footprint swings back and forth when it is transitioning to a point of interest as it is now controlled by a controller which applies forces according to the error offset from the desired pointing strategy. This example shows and simulates how satellites actually carry out specific pointing attitude maneuvers.

More info can be found here. Credits to the AGI STK for this tutorial.