Guiding Weapons, Finding Soldiers

July 31, 2002 By: Matteo Luccio GPS World

Designed, funded, and operated by the military and, originally, for the military, GPS continues to develop in a wide range of demanding warfighting applications. On the cutting edge are guidance for weapons — ranging from artillery shells to cruise missiles — and search and rescue of downed air crews.

Weapons Guidance

With the increased miniaturization and hardening of GPS receivers, smaller and smaller munitions are becoming candidates for in-flight guidance, blurring the lines between shells, rockets, and missiles. This is why Defense Secretary Donald H. Rumsfeld wants to kill the Crusader artillery program — designed to rain 155-millimeter shells on enemy forces more than 25 miles away — and shift $9 billion to accelerating the development of precision-guided artillery shells and rockets.

In the October 2001 issue of GPS World, Lawrence Wells listed the following requirements for GPS guidance of army artillery shells and projectiles fired from Navy deck guns: gun-hardening, to survive the gunfire shock; fast signal acquisition, to maximize the guidance interval; tight coupling with an Inertial Measurement Unit (IMU), for resistance to jamming; SAASM, for battlefield security; interfaces and operating modes to support initialization of the GPS receiver; small size, to fit the allocated space; low power consumption; and low recurring cost.

Artillery. The U.S. Army’s Excalibur 155-millimeter projectile was designed specifically to be guided in-flight. Its nosecone contains an ASIC (Application-Specific Integrated Circuit) GPS chip, a data processor chipset, and an IMU incorporating a Micro Electro-Mechanical System (MEMS). Once in flight, it deploys canards controlled by a drive guidance unit which makes use of the navigation data derived by the GPS/IMU. Compared to current 155- millimeter shells, which typically land more than 370 yards from their target, Excalibur shells could hit within 10 yards of their targets and have a much greater range (more than 35 miles).

Recently an industry team achieved a milestone in the development of long-range precision-guided projectiles in support of ground maneuver warfare. During a test, an Autonomous Naval Support Round (ANSR) fired from a 5”, 62-caliber gun flew 62 miles. The test was part of a program to develop a ballistic trajectory, GPS-guided solution to U.S. Navy, Marine Corps, and Army requirements for affordable, long-range, precise artillery. According to the team, the technology is applicable to other precision projectile systems, such as the U.S. Navy’s 155 Advanced Gun System (AGS) and the U.S. Army’s Excalibur and Multi-Role Armament and Ammunition Systems (MRAAS) programs.

ERGM Test. On June 25, the Naval Surface Warfare Center, Dahlgreen Division, and a large military contractor conducted a guided flight of the Extended Range Guided Munition (ERGM) at White Sands Missile Range, in New Mexico. They launched the ERGM from a representative Mk45 Mod 4 gun system, using a tactical propellant charge, and successfully executed navigation and guidance after GPS acquisition. This guided flight test completed the subsystem- and system-level design validation tests of the ERGM guidance, control, and propulsion systems. The final validation tests are planned for next year after introduction of the new unitary warhead. This marks the start of ground environmental and flight performance qualification testing phase, which is the precursor to fleet deployment.

Smart Shell. The British Defence Evaluation and Research Agency (DERA) has also tested a GPS-guided “smart shell” containing a Course Corrected Fuse (CCF), which sits in the front of the round and calculates a navigation solution to the target. It includes a tiny and very rugged computer and GPS receiver. Within a few seconds of launch, the guidance system establishes the shell’s height, trajectory, and distance to the target and determines whether any course correction is needed. Between firing and reaching the end of the barrel, the shell undergoes an acceleration of 13,500 g. Long-range shooting also requires the round to be stabilized by spinning, just like an ordinary bullet. A typical howitzer shell will revolve at 300 RPM, which greatly complicates GPS signal acquisition and trajectory calculations. The rounds are expected to be in military service by about 2005 and cost a few thousand dollars each.

From Laser to GPS. The EDGE (Exploitation of Differential GPS for Guidance Enhance-ment) program is a follow-on to the Paveway program, which developed clip-on laser guidance kits providing cheap precision targeting capabilities to air-dropped bombs. EDGE develops similar capabilities but with GPS rather than laser guidance. In one test at Eglin AFB a U.S. Air Force F-16 dropped a GBU-15, 2000-pound glide bomb equipped with a combined INS/GPS guidance unit from 25,000 feet and it hit within 6 feet of a target 11 miles from its drop point. Four DGPS base stations, located approximately 1,000 nautical miles from Eglin AFB provided corrections to the bomb. The EDGE program has since transitioned to the Joint Direct Attack Munition (JDAM) program.

MLRS Rocket.Recently, the U.S. Army and a contractor tested the new GPS-guided version of the Multiple Launch Rocket System (MLRS) rocket at White Sands Missile Range, New Mexico. The Army launched the rocket from an MLRS M270 Improved Position Determining System launcher. It flew more than 43 miles to the target area and dispensed its sub- munition payloads. Guided MLRS initial operational capability is scheduled for CY ’05. The rocket will have a range of more than 37 miles.

Combat Survivor/Evader Locator

After being neglected for years by the Pentagon’s leadership, Combat Search & Rescue (CSAR) is undergoing a renaissance. It is on the cutting edge of “network-centric” warfare, which is the core of Secretary Rumsfeld’s vision for a transformation of the U.S. military. At the heart of CSAR is the Combat Survivor/Evader Locator radio (CSEL) — a communication system which provides a survivor/evader, such as a downed pilot, with precision GPS-based geoposition and navigation data, two-way over-the-horizon (OTH) secure data communication to Joint Search and Rescue Centers (JSRC), OTH beacon operation, and Line-of-Sight (LOS) voice communication and swept tone beacon capabilites.

Worldwide. The new units will be used by combat personnel of all services to transmit secure, digital GPS-derived location information and both keyed-in and scanned messages. This capability will allow rescue forces to receive the message from anywhere in the world via OTH communication satellites and to locate, authenticate, and communicate with those who they are assisting.

Complex Web. Besides using GPS, CSEL also relies on support from several other sytems, including UHF Satellite Communications (UHF SATCOM), Search and Rescue Satellite Aided Tracking System (SARSAT), and Secret Internet Protocol Network (SIPRNET).

The Hand Held Radio (HHR) uses UHF/VHF LOS voice, beacon, precise GPS, and three OTH data communications modes to provide worldwide coverage. GPS position is included in all OTH transmissions. The radio support equipment consists of the unit-level CSEL planning computer and radio set adapter. The OTH segment includes four unattended UHF Base Stations (UBSs) that control SATCOM communications with the HHRs and interface with National Assets, SARSAT, and JSRC via the SIPRNET. The ground segment displays and prepares messages for transmission to/from the HHR through the UBS.

The planning computer is used to load HHRs with communication frequencies, GPS data and waypoints, passwords, and other mission-related data.

Four in One. A CSEL unit combines into a 32-ounce package the capability which previously required four devices, with a combined weight of nearly 300 ounces: a SARSAT beacon, a P(Y) GPS receiver, a SATCOM transceiver, and a LOS SAR radio.

CSEL will use SAASM, which will give its users a greater confidence in their exact location despite any enemy attempts to spoof them with a false signal. The CSEL radio was designed to take advantage of SAASM and will likely be the first fielded receiver system to employ it. However, production of CSEL radios is not to be delayed by the development of SAASM.

History. CSEL will replace the AN/PRC-112/112B survivor radio. This successor to the Vietnam-era AN/PRC-90 is the basic survival radio American military pilots have carried for years. With these older units, 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 an AN/PRC-112 with an added GPS receiver. CSEL is similar to the Hook 112, but takes that unit’s advances one step further by adding the ability to communicate worldwide and send canned messages such as “Capture is imminent,” or “Injured but can move,” along with GPS-derived location. Also planned is the ability of 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 Precise Positioning Service, which would be part of CSEL. The Department of Defense plans to simultaneously develop both the Hook 112 and the CSEL.

Production Decision. CSEL is a joint services program, with the Air Force as lead agency. According to Major David Micheletti, CSEL deputy program manager, “The CSEL program is currently in its final phases of operational test for the Block I system. Between March and May 2002 the program office completed a series of developmental and operational tests at Fort Huachuca, Arizona, at Eielson, AFB, Alaska, and onboard the aircraft carrier USS Lincoln. Recently, CSEL underwent operational testing at Desert Rescue, Fallon NAS, Nevada. All this is leading to a multiservice operational test and evaluation, sheduled for October and November.” Results of this test will support a decision to enter CSEL into full-rate production.

Manufacturers

The Excalibur projectile uses the Tracker GPS ASIC and the Key Data Processor II chipset from L3-Interstate Electronics Corporation, Anaheim, California. The IMU incorporates a Micro Electro-Mechanical System (MEMS) produced by L3-IEC’s Micro Sciras group in Redmond, Washington. ATK Tactical Systems, headquartered at the Alleghany Ballistics Laboratory (ABL) in Rocket Center, West Virginia, is the lead contractor on the ANSR program. Other members of the ANSR team are Custom Analytical Engineering Systems (CAES), Cumberland, Maryland and Draper Laboratory, Cambridge, Massachusetts. The choice of GPS receiver for the ANSR has not yet been made. The ERGM industry team is led by Raytheon Missile Systems, Tucson, Arizona. The ERGM’s GPS receiver is manufactured by L3 Communications and is a derivative of their TruTrack receiver. The DERA “smart shell” team worked in conjunction with Thomson-Thorn Missile Electronics, Basingstoke, Hampshire, United Kingdom and British Aerospace Royal Ordnance, Westcott, Buckinghamshire, United Kingdom. It contains a custom-built Rockwell Collins 12-channel, P(Y) code GPS receiver. The MLRS is manufactured by Lockheed Martin Missiles and Fire Control, Dallas, Texas. The CSEL is co-managed by the Electronic Systems Center at Hanscom Air Force Base, Massachusetts and by the prime contractor for the program, The Boeing Company, Seal Beach, California. It contains a Rockwell Collins GEMIII, P(Y) code embedded GPS module.