The requirement that the propellants used in launch vehicle systems must also provide the thermal energy to be converted to kinetic energy in the rocket nozzle has plagued rocket designers since the dawn of the space age. Beamed propulsion systems, however, avoid this constraint by placing the energy source on the ground and transmitting the energy to the spacecraft via microwaves. This computational work evaluates three different heat exchanger channel designs for use in a beam propulsion spacecraft. The working fluid was hydrogen and the input energy was 1.3 kW. The increase in axial temperature along the 0.1 m long channel was as high as 2000 K. In addition, it was found that despite the very small diameter of the minichannels, 1 mm, each design produced extreme temperature gradients across the channel cross section. These temperature gradients affected the velocity profile; the maximum velocity was not located at the channel center.