For a 500-day crewed Mars mission NASA has studied using solar power and nuclear power for its base, as well as power storage systems (e.g. batteries).[45] Some of the challenges for solar power include a reduction in solar intensity because Mars is farther from the sun, dust accumulation, and periodic dust storms, in addition to the usual challenges of solar power such as storing power for the night-time.[45] One of the difficulties is enduring the global Mars dust storms, which cause lower temperatures and reduce sunlight reaching the surface.[45] Two ideas for overcoming this are to use an additional array deployed during a dust storm and to use some nuclear power to provide base-line power that is not affected by the storms.[45] NASA has studied nuclear-power fission systems in the 2010s for Mars surface missions.[46] One design was planned for an output of 40 kilowatts, and its more independent of the sunlight reaching the surface of Mars which can be affected by dust storms.[46][47]