Size a spacecraft power system consisting of a solar array and NiCd batteries to supply 1.5kW of power using 12% efficient silicon cells (at 28 C) with sun-tracking flat panels. The orbit is 500 km circular at 28.5 degree inclination. Assume a five-year life, with a minimum of 28Vdc required during eclipse. Determine:

a) Battery capacity (amp-hours) and weight to support the power load during eclipse, and b) Size of the solar array to re-charge the battery and to provide the s/c power load during the sunlit portion of the orbit.

There are lots of design choices and no unique answer.

First, approximate the eclipse time. For the battery, assume an energy density of 15 W-hr/1b and an average cell voltage of 1.5 Vdc. Note that the DOD of 70% for the GEO example is not valid for this LEO problem, due to the relatively short period of time in sunlight per orbit available for re-charging the battery - a good rule of thumb for LEO Spacecraft is to allow 20% DOD.

For the solar array, use all of the given variables as the example problem except the battery capacity which you have calculated in part a) of this homework. Assume a solar cell area of 2 cm X 4 cm; solar cell current is 0.2274 A; solar cell voltage is 0.3646 V.