A vehicle is disclosed that includes a propellant tank, an optical absorber operable to transform optical energy into thermal energy, a quantity of solid lithium within the propellant tank, a heat exchanger, and an engine. The heat exchanger is operable to transfer thermal energy from the optical absorber to the quantity of solid lithium to liquefy at least a portion of the solid lithium, and further operable to boil the liquefied portion of the solid lithium. The engine is operable to utilize lithium vapor from the boiled lithium to propel the vehicle.