The CSEL system is composed of three segments: OTH, Ground, and User. Two way line-of-sight (LOS) voice communications between the evader and recovery forces or between evaders will be provided by a UHF and/or VHF radio capability in the CSEL hand-held radio. The radio will be capable of geo-location using the GPS precise positioning service (PPS) under dual frequency (Y Code) operation. The CSEL multifunction hand-held radio is specially designed for easy, intuitive use. Unique communication and message encryption prevents signals from being intercepted, and 21-day battery life provides crucial contact for extended periods. To meet geo-positioning security requirements, employs a Selective-Availability Anti-Spoofing Module (SAASM). CSEL will be the initial SAASM-equipped receiver, however production of CSEL radios is not to be delayed by the development of SAASM.The hand-held receivers are only one segment of the overall CSEL command and control system. The satellite-relay base station, Joint Search and Rescue Center software suite and radio set adapter units all have been previously delivered. These components interface with the ultra-high frequency satellite communications network to provide two-way communication for a worldwide search and rescue capability. When Serbian missile fire shot down Capt. Scott O'Grady's F-16 from the skies over Bosnia June 2, 1995 his survival equipment, helped bring the pilot home safely. He was carrying a Flight Mate Global Positioning System (GPS) receiver. By using both his standard AN/PRC-112 and the GPS receiver, O'Grady was able to transmit his nearly exact location to his rescuers. The Vietnam-era AN/PRC-90 and its successor, the AN/PRC-112, are the basic survival radios American military pilots have carried for years. With these older PRC-90s and 112s, the lack of geopositioning information made recovery mission planning very difficult. The ability of enemy forces to detect the homing beacon and voice transmissions caused many recovery missions to fail, because the evaders had been captured by the time recovery forces arrived in the area. Hook 112, the system developed to support operations in Bosnia, is a AN/PRC-112 with an added GPS receiver. Based on the Talon Hook demonstration project, which proved the Hook 112 would work as advertised, Hook 112 is an interim solution to an immediate need. The Hook 112 radio transmits data messages from the survivor to rescue forces along with its associated interrogator unit. From aboard an airborne platform such as a helicopter, an E-2C, C-130, or a ground site, the interrogator can receive preprogrammed or free-form transmissions from downed aircrew containing the serviceman's location, identification and status. The interrogator unit also provides the capability for rescue forces to interrogate the Hook 112 radio without the operator having to physically send the message. If the pilot is incapacitated and has a Hook 112, the rescuers can still receive a message, one with a location more accurate than in the past because of the interrogation capabilities added as part of the radio modification. While the Hook 112 provides an interim solution for an immediate combat need, the more far-reaching solution to the problem of outdated equipment for America's military flyers is the Combat Survivor Evader Locator. The future of Developmental Planning's CSEL program plan looked bleak when it was denied funding for fiscal 1997. But that was before Capt. Scott O'Grady. When the story of his rescue finally became public, the world took a closer look at the power and versatility of GPS. Thus, the CSEL was given another look. CSEL is similar to the Hook 112, but takes that unit's advances one step further. The biggest difference is the CSEL's ability not only to communicate messages over the horizon, but also to transmit them worldwide. Canned messages such as "Capture is imminent," or "Injured but can move," along with GPS-derived location, can be sent to rescue response cells anywhere in the world via communication satellites. Also planned is the ability of these rescue response cells to communicate a message back to the downed aircrew member, something the Hook 112 can't do. In addition, Hook 112's GPS receivers are less accurate and more vulnerable, because they only incorporate the GPS Standard Positioning Service and not the more precise military GPS capabilities, which would be part of CSEL. The latest in Global Positioning System technology is being used to modify the existing survival radio into a state-of-the-art locator, which will help rescue downed pilots. The Department of Defense's plan is a dual one in which two different systems, the Hook 112 and the Combat Survivor Evader Locator (CSEL), are being developed simultaneously. The CSEL, which is co-managed by the Electronic Systems Center at Hanscom Air Force Base, MA, provides the worldwide identification, location, and communications required between military rescue teams and people in need of assistance. The goal is to remove the 'search' from search and rescue missions. The key feature of these new survival radios is their ability to provide search and rescue forces with the capability to locate, authenticate and communicate with downed aircrew at any range. This is accomplished through the use of an imbedded GPS receiver and satellites for relay of the survivor location, authentication and status messages to rescue forces.
GPS is a space-based radio-positioning system consisting of a constellation of 24 orbiting satellites, which provide navigation and timing information to military and civilian users worldwide. The system also consists of a worldwide satellite control network and GPS receiver units. The network can pick up signals from the satellites and translate them into position information.