A missions payload is essentially the mission itself. The payload contains every mechanism that the mission is going to use to achieve its goal. Payloads break away from earths orbit and travel across our solar system in order to deliver these mechanisms and thus accomplish the mission as a whole.
Payload Diagram
The payload capsule will be connected to the launch vehicle, and will later break off from this vehicle as it leaves earths orbit. It will then use a nuclear propulsion system to carry it into a transfer orbit between Earth and Enceladus. The payload capsule itself will contain the Orbiter and Lander, and every instrument on those two mechanisms. On the payload capsule there will be condition monitors to ensure that temperature, and radiation levels remain normal. There will also be information gathering sensors, such as the CoDICE device, to collect data on solar radiation and deep space particles.
The Payload capsule will then enter Enceladus' atmosphere and break apart to release the landing and orbital mechanisms. The timing of this will be conducted with the use of remote sensors connected to latches on the payload capsule.
Payload Mechanisms
The payload will accomplish the missions main goal through the use of mechanisms that have been introduced earlier. An Emission spectrometer is an example of one of these mechanisms, and technically all of them fall under the payload subsystem.
Specifications
The payload will be: 15 meters in height, 20 meters in length, and 20 meters in width. This will be to ensure that there is enough space within the capsule for the scientific instruments to be protected accordingly.