Thruster-only rocket still requires fuel tank

If you build a rocket that relies entirely on thruster power to travel, it won't launch, because it "needs a fuel tank". Even though it's perfectly possible to use a few Solid Fuel Thrusters to get enough distance to visit the nearby planets!

I'm between steam and petroleum right now, and I wanted to use thrusters and a cargo bay to collect some niobium from the 10000km planets while my other dupes worked on building a petroleum pipe along the entire length of the map). I made a spaceship with a petroleum engine, a cargo bay, 2 solid fuel thrusters, 3 research modules, and a command module. The starmap says that it has 15873km range, and I got a dupe into it, but it refuses to launch.

Save is attached; rocket is at the top left.

Invisible Dystopia.sav