however, 1s a major consideration for low orbit construction. Fortunately, a gravity-gradient orientation (which 1s required to eliminate enormous torques) can also be a low-drag orientation. Drag force at 500 km is on the order of 400 N for a 10 GW output station oriented horizontally with solar concentrators "into the wind." There are several induced loads on the structure, most of which are caused by the following: Control system inputs to thrusters are required for attitude control and orbit correction. TFrust loads of 100 to 300 N are expected to be maximum, depending upon how the satellite is oriented for operation. Current loop/magnetic field interaction is a function of current conductor configuration with torque proportional to the loop area and current. With particular conductor path design, this torque can be made zero. However, it may be possible to use these forces to advantage by integrating them, with proper switching, into the control system as a partial substitute for some of the required control forces. If the total system current was routed around the exterior of the configuration, torques could be obtained about an east-west or about a radial axis of approximately 10-mil1 ion N-m. In low earth orbit, the magnetic field is around 200 times as high as it is in geosynchronous orbit. Therefore, for construction and initial operation for transfer from 500 km, the current loop/magnetic interaction is proportionately more significant. Interaction between conductors is also configuration dependent. The resulting forces are proportional to the square of the current and inversely proportional to the distance separating the conductors. These forces can be held to reasonable levels with proper power distribution design; i.e., by a large number of conductors spaced as far apart as possible and/or by a high voltage low current power distribution system. Antenna recoil is the reaction force due to microwave transmission from the antenna. Force is proportional to power transmittal and is about 22 N for each antenna. Due to the solar radiation pressure, antenna motion will not be a uniform one rev/day since the orbit is not circular. Peak torque from this motion will be about 240 N-m for an expected eccentricity of 0.04. Transient thermal gradients will occur during occultation by the earth for up to 1 1/4 hours daily for six weeks around the spring and fall equinoxes. In addition, when these satellites are deployed in numbers large enough to place them as close as a degree apart, the satellites will partially shadow each other for 10 to 15 minutes twice each day near the equinoxes and these occultations will not be uniform over the array (as discussed in IV-A-3). The environment of the solar array consists of a hard vacuum with thermal radiation, primarily from the sun, the solar wind, and the earth's magnetic field. The sun emits thermal radiation with a spectra! distribution characteristic of a black body at about 6000°K with a peak flux in the visible range. Due to the large distance between the sun and the earth, the magnitude of this thermal flux is about 1.4 GW/km2. This energy flux is characteristic of a local black body at about 400°K. In this environment with the reference array configuration exhibiting a concentration factor of two solar fluxes to the solar cells, the solar cells will operate at about 100°C to 125°C. The reflectors on the other hand will operate at about -40°C to 0°C depending on whether
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