You would want to make it bimodal
Back in '91, INEL came up with a noval approach to SP100 which not only provided 100KW electric to the satellite but also propulsion by running hydogen through the core. Doing this gave the reactor a decoupling problem but since it was a fast reactor, it was inherently safe. For example, the moderating effects of water would shut it down. Still, I wouldn't run it within the Earth's ionosphere.
Dave M