astronomical and aeronomical observations. The magnitude of the effects is determined by the apparent brightness of the satellites and the properties of the atmosphere. In turn, the brightness of the satellites is determined by their size and reflectivity. The satellites will be exceeded in brightness by only the sun and the moon. Each one will in fact be bright enough to cast a shadow. Parametric Characterization of the Effect of the SPS on Diffuse Sky Brightness In order to meaningfully assess the SPS effects on diffuse sky brightness, the computations presented in the Briefing Document and the limitations of the Briefing Document as discussed in the invited presentation of G. M. Stokes were carefully considered. While the working group agreed that the SPS effects can all be described in terms of the apparent brightness of the satellites, the useful numbers for designers of the power satellites are the collecting area and the reflectivity of the various parts of the satellites. The problem of a large collecting area is not solved simply by reducing satellite size. The important number is the total collecting area for the 2 system, which for the Reference System is 3300 km , about the size of the state of Rhode Island. A reduction in total surface area would require an increase in the overall efficiency of the System, which is now about 7%. Analysis in the Reference System documentation does not suggest that the overall efficiency of the SPS will change much. If this is the case, then the most important parameter in determining the apparent brightness of the satellite is its albedo, which is the ratio of the radiation reflected from an object to the total incident radiation. As noted in the preceding section, the albedo consists of a specular component, a measure of the extent to which the object acts like a mirror, and a diffuse component, which is a measure of one's ability to see the object in any aspect. The working group's deliberations on the diffuse albedo of the SPS solar blankets led to two conclusions. First, the diffuse albedo of 4%, as described in the Briefing Document, is an optimistic estimate. As such, the effects predicted on the basis of the 4% albedo were taken as lower limits of the possible effects of the SPS on optical astronomy. A second, related
RkJQdWJsaXNoZXIy MTU5NjU0Mg==