This paper discusses the dilemma of increasing GPS requirements from the current requirement for 24-satellites to a larger, more stringent requirement of 30 satellites. The paper will first discuss the existing GPS Standard Positioning Service (SPS) Performance Standard (PS) requirement and analyze the currently provided GPS level of service. The current GPS SPS PS was last approved in Sep 2008, yet improvements to the GPS command and control system and an increased constellation size (currently 35 GPS satellites on orbit) since that time have allowed the currently provided GPS level of service to far exceed the requirement. This paper then discusses how a commitment to increase the required GPS constellation size and placements within the orbits would benefit both military and civilian users worldwide. For example, "sky-impaired" warriors, such as those on the slopes of mountains in Afghanistan or the urban streets of a Middle East city, have degraded availability with only 24 satellites due to obstruction of 45 to 60 degrees from mountain slopes. Updating and increasing the constellation size to 30 satellites would increase the number of satellites in view (increased availability due to the increased number of satellites available to obtain a GPS solution) to horizon line of sight disadvantaged users. The USAF is committed to maintaining only 24 GPS satellites, and is obtaining suboptimal performance since it is currently flying them in a constellation optimized for only 24 primary slots.
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