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The Tanto is a 10-furnace, single-thruster, 8-tile-wide Factorio spaceship design. It can be built in 13 launches.
Huge thanks to reddit user Symbol_1 for their tweaks!
Unfortunately, its speed needs to be limited. When doing laps between Nauvis and Fulgora, it will lose a forward solar panel about once every four hours when hitting 144km/s in a dense asteroid field.