There are two distinct power requirements of limited time probe operation and long term relay operation. The probes will have their power devices maintained by the satellite until they are launched. The satellite will have to have a power source that provides baseline levels of power during transit to Neptune and then provides power for the mission.
The probes have a limited life cycle requirement of 50 hours. Space qualified lithium ion batteries will be used to provide the power required during its operation. A reference for the power and weight performance of a lithium ion battery can be found
here
. The probes will have a maximum transmission power of 5W and an assumption of an additional 5W will be made for additional subsystem consumption.
Watt hour requirement for probes:
From the reference above a 3.3kg (7.3lb) lithium ion battery can provide the Watt hours required for probe operation.
Neptune is
away from the sun and radiates more energy in the local vicinity than is received from the sun
2
. If a solar array was used to power the satellite the panel area would be undesirably large and expensive to manufacture and launch.
Radioisotope Thermoelectric Generators (RTG)
will be used to power the relay satellite given the limitations of solar cells in this situation. An RTG system will need to be developed that can handle the power requirements of the satellite during transit to Neptune and then for the remainder of its mission. Any excess power developed by the rtg unit would be used to rebroadcast probe data. During the mission the satellite will utilize 20W for broadcasting. Without knowing more specific details of the satellite subsystems it is impossible to approximate the total power required. In general, several redundant RTGs would be installed to ensure a low failure probability due to loss of power.
.
