The Direct Fusion Drive (DFD) is a small fusion reactor that has the potential to revolutionize space power and propulsion. Direct Fusion Drive is based on the Princeton Field-Reversed Configuration reactor concept from Princeton Plasma Physics Laboratory. We have been using our NASA funding to explore the balance of plant for this unique engine, which can provide both megawatts of electric power and multi-Newtons of thrust in a single integrated device. The engine has an array of field shaping coils with two smaller but higher field mirror coils. Coolant lines running along the fusion chambeer collect thermal energy from the neutrons, bremsstrahlung radiation, and synchrotron radiation for producing electricity. A ∼1 kW neutral beam injects the fusion fuel into the center of the engine, while propellant enters from the ionizing gas box on the end opposite the nozzle. This paper will present the latest work on sizing a Brayton engine for DFD and compare a typical Xenon-Helium coolant engine to a supercritical carbon dioxide engine. The coolant lines for the thermal engine will need to run through the engine’s shielding, which must absorb sufficient heat and neutrons to protect the superconductors and their cooling systems. This is a complex and interesting engineering problem, which we are addressing in parallel with development of the core fusion physics. The paper will begin with a short summary of the DFD technology. We will then present the latest work on sizing the Brayton engine, and comparing the Xenon-Helium option to supercritical carbon dioxide. We will then briefly review the preliminary design for the space radiators and provide a mass breakdown showing the estimated specific power achievable. Results on the RF generation system and on the power generators are also presented.