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To scan space and see nearby intersteller destinations a Telescope must first be built on the surface of a Planetoid. Orbital Data Collection Lab in orbit around a Planetoid, and Cartographic Module attached to a rocket can also reveal places on a Starmap.
Always check engine fuel to determine if your rocket can reach its destination, keeping in mind rockets can only land on Planetoids with a Rocket Platform on it although some modules like Rover's Modules and Trailblazer Modules can be sent to the surface of a Planetoid from a rocket in orbit.