Internal Power Milestone—EarthX Battery for the F1 Rocket Project

“The ship is now on internal power!”

That’s always great to hear when launching a spacecraft—it means you’ve cleared the preflight checklist and are nearly free of all ground support equipment. We got the same thrill yesterday as we installed two batteries in the F1 Rocket project and disconnected the ground power supplies for the first time—and all the lights stayed on!

Of course, we’ll return to external power during the remaining build process, but the fact that the aircraft electrical system can now support itself on the primary and backup EarthX batteries is a major milestone. Everything works as intended, and the wiring is correct—magic achieved.

We’re using an aft-mounted EarthX ETX900 as the primary battery, with the master and starter contactors mounted in the baggage area. This setup ensures the big starter cable is only energized during engine cranking, minimizing the risk of a short circuit. For backup power, we’ve installed the more compact EarthX ETX680C forward in the cockpit under the panel. While this battery has enough power to crank the engine in a pinch, that would be a ground-only operation. To do so, you’d have to move it to the primary position, as the backup wiring doesn’t connect to the starter circuit.

In the bad old days of lead-acid and AGM batteries, builders typically used a smaller backup battery to save weight. But with today’s lightweight LiFePO4 technology, there’s no reason not to carry extra amps. Keeping both batteries within the same chemistry also simplifies charging and maintenance—just one voltage to manage.

Now that we’ve celebrated this milestone—watching the electrical and avionics systems operate independently—we’ll reconnect to shop power to keep the batteries fresh until that big 540 cranks over for the first time.