Remote Laser-Evaporative Molecular Absorption (R-LEMA) spectroscopy is a NASA Innovative Advanced Concepts (NIAC) initiative to develop a sensor capable of remotely probing the molecular composition (as opposed to atomic composition) of cold solar system targets such as asteroids, comets and moons without significant atmospheres from a distant vantage. A continuous-wave laser heats a spot on the distant target; the heated spot forms a “backlighted” source through which the ejected plume is illuminated and target composition is determined from infrared molecular absorption lines. Theory and ongoing laboratory experiments indicate that the sensor concept is valid. To advance the system Technology Readiness Level (TRL), the concept must be demonstrated in the space environment. A formation-flying CubeSat experiment is proposed to demonstrate R-LEMA spectroscopy in the space environment. The main craft is equipped with a high-power laser, spectrometer and auxiliary subsystems necessary for executing the experiment. A second craft serves as target material, flying in formation at a specified distance from the main craft. This paper describes experimental objectives for a CubeSat experiment, including a 6U main craft and 3U target. In-orbit experiments are specified, and a supporting system architecture is derived from experimental objectives. A mechanical design is presented for both crafts, including all subsystem components required for the experiments. An execution sequence for in-orbit experiments is described.