Basically the fission material substitutes for the jet burn canister and the rocket chamber. It’s product is intense heat that heats a compressed gas. Fission temperature rises in proximity of fission material below critical mass. Very dangerous stuff as neutrons can penetrate a cement block a yard wide. The special rods prevent fission material exposure to oxygen so radioactive rust won’t get blown out.
By potting the Bell thrusters at opposite extremes. Plasma rockets still needed for fine positioning in desired orbit and to keep ship on course. The plasma rockets for causing and Stopping spin not shown. In the delicate situation of docking and releasing shuttle craft easier Done by stopping ship spin.
The energy is better put to use blasting ice balls because of astronomical higher
Exhaust speed fission heating cannot compete with. The static thrust higher than
Ionic motors but well below one G. More than sufficient for orbital to interplanetary
And back to orbital. The biggest problem is food supply. The Astronauts need food
At their destination hence bases to go to.