Missions to small bodies have become increasingly attractive in recent years, firstly, due to their scientific value, but also because of their potential risk to Earth and prospective economic return. A variety of missions have been proposed, ranging from manned exploration to commercial mining missions. There have already been missions to asteroids (e.g. Hayabusa) which brought samples and scientific data, while successor spacecraft are on their way to new targets. For such and future missions, it is essential to perform in-situ observations by landers in order to enhance scientific return. Simple, reliable and low-cost lander modules would satisfy the desired observational capability by exploiting the natural dynamics of these bodies. Therefore, CubeSat systems are good candidates to fulfil the aforementioned exploration demands. This research considers a mission that is targeted to binary asteroid system, which constitute 15% of NEA population. The mission architecture includes a mothership carrying one or several CubeSats. CubeSat deployment is performed by a spring mechanism which is limited for maximum velocity. Natural landing trajectories are investigated after deployment for an unpowered CubeSat within the dynamics of binary system by using the frame of Circular Restricted Three Body Problem (CR3BP). Landing is envisaged in local vertical direction in order to avoid damage to the CubeSat. Dynamical model is propagated backwards from the surface in a novel bisection algorithm to obtain lowest energy trajectories. CR3BP only considers point mass gravity in the model, therefore a perturbation analysis is carried to find out when solar radiation pressure would dominate the evolution of trajectories. The research provides new insights into the regions and sizes of binary systems that could potentially be explored by a simple, underactuated lander with very little control. Suggestions are also made for a CubeSat that could possibly be employed as a lander for small body exploration.