You fly a survey satellite in low orbit. Below you is Earth. The real one, built from NASA imagery, with real terrain, real city lights, and a day/night terminator crossing it as the planet turns.

Somewhere down there are 35 Points of Interest: Everest, the Amazon, the Mariana Trench, Angkor Wat, the volcano buried under Antarctic ice. You cannot see them. You have to find them.

Fire the sonar and it answers with a distance, not a location. The rest is yours to narrow down, sweep by sweep, battleship played on a globe. Hold the beam on a contact and the instrument resolves it into a real place, with the real science attached: what it is, how it formed, what lives there.

Every identification pays research data, spent at the ISS. A wider sonar. Faster analysis. Infrared, for the dark half of the planet. A polar orbit, for latitudes you currently cannot fly over. Better instruments don't just make the work faster, they reveal sites the old ones could not read at all.

• A real satellite in a real orbit around a real Earth, from NASA, ESA and USGS data

• Discovery, not collection: sonar tells you how close you are, never where to go

• 35 Points of Interest, each with its own geology, fauna and flora: researched, not invented

• Upgrade at the ISS: three survey levels, and sites you literally cannot detect until you earn them

• Day and night matter: the unlit half needs infrared, or patience