When studying the solar system, it's hard to beat Solar Walk ($2.99) from Vito Technology. You begin with an image of the earth with many light blue lines circling it. Tap one and the app provides a close-up view of a satellite. All the satellites are rendered in 3D, and a clickable info button reveals information and images associated with the satellite. Solar Walk provides enough satellite detail to have good conversations about orbits, satellite construction, and observation. Combine this app with Google Earth and you can have a good dialog about public and private surveillance. There also is information on the International Space Station.