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Micro Ship
Seems to work. Uses a bunch of circuits and cruises about 100km/s.
It will need to be bootstrapped once pasted in. Once some asteroids have been collected, in the fuel/oxidizer chemplant, briefly uncheck the "enable/disable" checkbox, until the thruster is about halfway full of fuel and oxidizer. This enables the ship to actually depart. Don't leave it unchecked too long, or it will deadlock.
Was a challenge getting the fluid switcher working. Have to produce exactly the right amount of oxidizer and fuel to not clog the pipe, so it toggles between those recipes on completion of a recipe. Also have to wait for the fluid to drain from the pipe before attempting to push more into it, so adding more speed modules doesn't work - the output contents of the chem plant will simply be deleted if less than 100, and it will pack more into the pipe until it deadlocks. The switcher uses XOR with the "finished" signal to toggle the fuel signal, and another constant combinator just outputs the oxidizer signal - the chem plant prioritizes the fuel recipe. Also has a circuit to detect if "moving to" a planet, and activates the plant only when moving. The inserter into the chem plant is disabled when the plant is working, and has a stack limit of 2 so it will not attempt to craft another during the 1 tick while it switches recipes. It's a big headache to save a few tiles.
The front end uses filters on the asteroid collector and uses it as the buffer. The crusher recipes are actually set by signals like iron ore, carbon, ice, which is convenient and avoided more circuitry.