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Both spacecraft have on-board consumables that are adequate to support spacecraft operation until at least 2020. Electrical power is the major consumable which limits the spacecraft lifetime. Power should be adequate to support science data acquisition until at least 2020 and possibly beyond. Both spacecraft have about 30 kg of hydrazine that provides about 50 years of operation at current usage rates.
Electrical power is supplied by three Radioisotope Thermoelectric Generators (RTGs) that are performing nominally. The current power levels are about 275 watts, with power margins of about 30 watts and an average degradation rate of about 4.3 watts per year. As the electrical power decreases, power loads on the spacecraft will have to be turned off, reducing space-craft capabilities and operational flexibility. Power margins are adequate to operate the complement of science instruments, save the UVS, until after 2020. For power management, the UVS must be turned off in late 2010.