The increasing urgency of climate change mitigation necessitates innovative solutions beyond terrestrial efforts. Space-based solar geoengineering – particularly a Planetary Sunshade System (PSS) positioned near the photo-gravitational equilibrium point L<inf>1</inf>^∗, which lies closer to the Sun than the classical L<inf>1</inf> due to the effect of solar radiation pressure – has been proposed as a potential method to reduce incoming solar radiation and stabilize global temperatures. This paper presents the preliminary design of a precursor mission aimed at demonstrating key technologies essential for the deployment of a full-scale PSS. The proposed mission features a 12U CubeSat equipped with a 400 [m²] solar sail, which will be used for propulsion, attitude control, and station-keeping at L<inf>1</inf>^∗. The mission objectives focus on validating the long-term performance of optical shielding materials, demonstrating solar sailing as a sustainable propulsion method, and assessing the feasibility of autonomous orbit and attitude control systems. The technical and economic feasibility of the precursor mission, with an estimated budget of 10M USD is examined. By addressing key uncertainties in spacecraft formation flying, material degradation, and long-term solar sailing operations, this mission represents a crucial step toward the realization of a scalable PSS for climate intervention.