A method of launching a powered unmanned aerial vehicle at an altitude of at least 13,000 m, the method comprising lifting the vehicle by attachment to a lighter-than-air carrier from a substantially ground-level location to an elevated altitude, causing the vehicle to detach from the carrier while the velocity of the vehicle relative to the carrier is substantially zero, the vehicle thereafter decreasing in altitude as it accelerates to a velocity where it is capable of preventing any further descent and can begin independent sustained flight.