The electrical load serviced by this source is not constant: modal timelines have been generated for the various surface operations which take into account estimated demands from each on-board system as it is activated. For example, a typical power profile during surface operations for the AREAL rover is shown in Fig. 2 [4]. This profile can be characterized as a base load with intermittent peaks superimposed on it. The peak value is roughly three times the baseload power level, but due to its relatively low repetition rate and duty cycle, the total integrated value is close to the baseload requirement. A steady state generator combined with secondary battery storage system is most appropriate to service this load. Based on power profile information for all operating modes a conservative estimate of 350 W/h of battery storage has been established to accommodate the peaking requirement. Normally the battery discharge depth will be less than 10% of rated capacity, so that a moderate cycle life, high energy density system such as silver/zinc can be used. The battery should weigh less than 20 kilograms. The steady-state power system must continuously supply the time-averaged power demand from all users, plus extra energy over time to recharge and maintain the battery. Even at idle, power consumption aboard the vehicle is an estimated 240 watts [5]. In the aggregate, this translates to a steady state demand of roughly half a kilowatt. Given the requirement for this amount of continuous primary power, the low levels of sunlight experienced on the surface, and the wind and dust environment (see Table II), solar arrays are very large and cumbersome. Therefore, a nuclear heat source is ideally suited to this mission.
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