A solar powered spacecraft power system including a solar photovoltaic array, an electric propulsion system connected directly to the solar photovoltaic array in parallel with the spacecraft power system; the electric propulsion system including a Hall effect thruster, a thruster power supply for driving the thruster; a sensor for sensing the power output of the solar array and a controller responsive to the power output of the solar array and configured to periodically adjust an operating parameter of the thruster to operate the thruster at the maximum available output power of the solar array including comparing a previous solar array output power level with a later solar array output power level, and incrementing the operating parameter with a positive value if the later is greater and with a negative value if the later is lesser; a solar powered spacecraft power system including a solar photovoltaic array, an electric propulsion system connected directly to the solar photovoltaic array, and a power management and distribution system connected to the solar photovoltaic array for distributing power to one or more bus loads and payloads.