Mitigating potential hazards for planetary rovers posed by soft soils requires testing in representative environments such as with Martian soil simulants in reduced gravity. However, constraints imposed by testing aboard an aircraft performing parabolic flights make critical elements of the test procedure, such as soil preparation, challenging. This work describes the design, development, and operation of a novel rover-soil testing system that includes rapid automated soil preparation. The repeatability of the prepared soil condition is demonstrated by cone penetrometer tests in the laboratory as well as in a Falcon 20 aircraft during a parabolic flight campaign.