When a Lightcraft is in the atmosphere, air is used as the propellant material (reaction mass). In space, it would need to provide the propellant material from onboard tanks or from an ablative solid. By leaving the vehicle's power source on the ground and by using ambient atmosphere as a reaction mass for much of its ascent, a Lightcraft could potentially be capable of delivering a very large percentage of its launch mass to orbit as an SSTO, an impossible task for chemical rockets. As such, a Lightcraft is distinct from a solar sail because it is dependent on the expansion of reaction mass to accelerate rather than being accelerated by light pressure alone. Within the atmosphere, the Lightcraft propulsion is dependent on the external laser power only, so propulsive power is not limited to that generated by usual on-board machinery (i.e. rockets).