Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight.Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scientific instruments or experiments, or other equipment.Extra fuel, when optionally carried, is also considered part of the payload.hen the weight of the payload and fuel are considered together, it is known as the  useful load fraction . In spacecraft, mass fraction is normally used, which is the ratio of payload to everything else, including the rocket structure.