The Department of Defense (DoD) has depended on different space-based assets as critical components to battlefield operations. As technology has evolved, space-based assets have become the eyes and ears of the military. Unfortunately, these assets have become one of the most vulnerable U.S. infrastructures. In 1995, the U.S. Global Positioning System (GPS), a complex and sophisticated space-based asset, became fully operational, providing accurate, reliable, and secure information on position, navigation, and timing to the joint force. The joint force uses GPS navigation to locate objectives and coordinate movement of ground forces and supplies. In addition, cruise missiles, smart bombs, and artillery projectiles currently use GPS to guide them to enemy target coordinates. GPS also provides a timing element that has become critical for the military in communications, computer networks, combat planes, and Unmanned Aerial Vehicles. Space-based technologies reach down into everyday military activity, so interrupting service immediately degrades operations. GPS capabilities are great and adversaries may be quick to deny or degrade them. Currently, there is not an alternative to GPS for ground, air, sea, or space operations. The methods of operating with a degradation or loss of GPS are contingent on the type of operation, whether it is land, sea, air, or space; as the current backup alternatives to GPS can only support one operation at the time. For this reason, it is critical for the joint force to have at least one backup alternative. At this time, the only alternative appears to be space-based, as a space-based alternative can provide simultaneous global coverage more affordably and accurately on PNT to the entire joint force. The most feasible potential space-based alternative to GPS is the existing commercial Iridium system, a sixty-six satellite communication constellation in low-earth orbit, under a program known as the high integrity GPS or iGPS. This constella