Mounted Perpindicular Arcjet RCS. Engine starts with Is Powered: true, but as soon as I fire the RCS, it reverts to Is Powered: false. Toggling the Power button causes the Is Powered to flash to true, but immediately reverts to false. The ship has enough MegaJoules.

By enough MegaJoules do you mean access to a reactor or only stored megajoules?

After reading the source code, I now understand how the supply and demand behaves. And I was off by factor of 100.

Yes they require a lot of power