The Standoff Observation of Enemy Ground Forces: From Project PEEK to JointSTARS
Charles A. "Bert" Fowler
C.A. Fowler Associates
March 11, 1998
"I've spent most of my career wondering what was on the other side of the hill." This oft-quoted observation of the Duke of Wellington emphasizes a critical problem for battle commanders that dates back to the beginning of warfare and continued up to this decade.
In January 1991, two prototype JointSTARS aircraft and their associated ground stations were deployed to the Gulf. This system makes use of moving target indicator (MTI) radar to provide a picture of all the moving ground vehicles and helicopters throughout most of the theater and present the information in such a way that enemy force size, makeup, disposition, actions, and in some cases, intentions are evident. This capability covers the range from small unit actions to major force movements. Furthermore, the timeliness and accuracy of the information is of targeting quality.
JointSTARS permitted our theater commander and his air and ground component commanders to see not only what was on the other side of the hill but what was going on throughout the entire theater and to select and attack specific targets and target sets. Thus a totally new and unique kind of information, whose military value and significance was equal to that of overhead imagery and signals intelligence, was made available to US and coalition forces. It was a long time coming -- a very long time.
I was involved in and followed this subject for a long time, and this talk is my version of the evolution of JointSTARS. There were three series of events that led up to JointSTARS -- an Army one, an Air Force one, and a joint one. In 1958 I was first exposed to this area in an Army-sponsored Summer Study as a member in the radar sensor group. One member, Dr. Jim Wolf, pronounced that "motion was the Achilles heel of the modern ground army" because such motion was detectable by an airborne MTI radar. This set our group to inventing. We came up with a system where a small MTI radar would be elevated above the tree and hill level to take a couple of looks at the battle area and then would be quickly lowered. The reason it stayed up for only a short time was that the postulated Soviet threat included large numbers of omnipotent, ubiquitous surface-to-air missiles (SAMs), so that anything that stuck its head up above the horizon for more than a few minutes was "dog meat." To the everlasting shame of everyone who participated in the study, no one challenged this greatly overstated threat.
We even came up with a name for our little radar: "PEEK" which derived from, naturally, "Periodically Elevated Electronic Kibitzer." The Army was sufficiently interested in PEEK to look into it, but the two ideas proposed for raising and lowering the radar were not practical so Project PEEK was dropped.
Chal Sherwin took Jim Wolf's thought back to the University of Illinois' Control Systems Laboratory and developed an X-band MTI Side-Looking Airborne Radar (SLAR). The US Army adopted the idea and selected Grumman to develop a system consisting of the OV-1 or Mohawk aircraft, the Motorola-produced AN/APS-94 SLAR radar, a scope display and film processor to produce a strip map, and a data link to relay the information to a ground station. The Mohawk SLAR system was used in Europe to look over the borders from a stand-off distance into Czechoslovakia and East Germany and in Vietnam to look at movements along roads in North Vietnam.
Chal Sherwin took Jim Wolf's thought back to the University of Illinois' Control Systems Laboratory and developed an X-band MTI Side-Looking Airborne Radar (SLAR). The US Army adopted the idea and selected Grumman to develop a system consisting of the OV-1 or Mohawk aircraft, the Motorola-produced AN/APS-94 SLAR radar, a scope display and film processor to produce a strip map, and a data link to relay the information to a ground station. The Mohawk SLAR system was used in Europe to look over the borders from a stand-off distance into Czechoslovakia and East Germany and in Vietnam to look at movements along roads in North Vietnam.
From late 1966 to late 1970, I was a "tourist" in the Department of Defense’s Research & Engineering tactical warfare area. In late 1968, I accompanied my boss, Dr. John Foster, on a trip to Southeast Asia. At that time, there had been nighttime movements on roads of small groups of Vietcong forces all around South Vietnam. The Army had set up AN/TPS-21 combat surveillance radars on four tall buildings on the outskirts of Saigon to monitor approaches to the city, but there was no coverage of the rest of South Vietnam. On the way home I came up with the idea of mounting a rotating APS-94 SLAR radar on a UH-1 helicopter. The continual scanning of the covered area would, unlike the Mohawk single pass, allow us to track targets and direct counteractions against them. A memo directing the Army to "build and deploy within a year ten such systems to South Vietnam" was never acted upon.
But the real concerns of the US Army were in the NATO-Pact conflict and it was realized that information from continual MTI coverage would be interpretable to provide a picture of where enemy forces were and what they were up to. The Army eventually agreed to build and test an experimental system. They came up with the name Airborne Long-range Alerting Radar for MTI or ALARM. I shamelessly proposed the motto: "We view the Warsaw Pact with ALARM!" A contract to develop the system was awarded in 1970, and the system was tested in 1972 with great success. The name got changed to SOTAS (Stand Off Target Acquisition System) and was successfully tested during the seventies several times, but SOTAS was canceled in 1981.
As early as 1969 the Air Force, in the person of Harry Davis, began investigating MTI, such as the Army ALARM system, and what the Air Force role might be. Harry quickly invented the Multi-Lateration Radar Surveillance and Strike System or MLRS3. The system used precision range measurements from two airborne L-band MTI radars to locate ground and airborne targets and to provide weapons guidance to attack those targets. MLRS3 never went far but the basic concept was successfully demonstrated. The principle outgrowth from this program was the MIT Lincoln Laboratory development of a MTI radar on a fast moving platform. The Multiple Antenna Surveillance Radar, or MASR, program developed a precision, low sidelobe, electronically-scanned Displaced Phase Center Antenna (DPCA) system to provide the necessary degree of ground clutter cancellation from the aircraft platform. The system also made important advances in programmable signal processors and Surface Acoustic Wave (SAW) devices for achieving large pulse-compression ratios.
In 1975 the Grumman and Norden Corporations started a company-sponsored effort to develop a Radar Guided Weapon System which included a forward looking electronically scanned X-band MTI radar. The radar featured a three port antenna to permit DPCA processing followed by monopulse measurements for accurate azimuth determination. The three-port antenna and associated processing developments became a key part of the Grumman/Norden Pave Mover Radar Program (in the late 70s and early 80s -- part of the Assault Breaker program) and eventually of the JointSTARS system.
In the early 80s it became clear that neither OSD nor the Congress would go for two programs, so the Chiefs of the Army and the Air Force agreed upon a single joint program, Joint Surveillance Target Attack Radar System or JointSTARS. JointSTARS would be a theater asset that provided information for attacking the second and third echelons (a la Pave Mover) but would also provide the detailed, continually updated MTI information on the battle areas of interest to the Army (a la SOTAS). Because the aircraft would be operated by the Air Force, this decision caused great consternation in many Army quarters. Despite many disagreements and a fair amount of distrust the two services worked hard and effectively together to build a big complicated system consisting of an electronically-scanned, three-port antenna, multiple transmitters and receivers, advanced digital signal processing, a million lines of code, multiple operator and maintenance displays, air-to-air and air-to-ground communications and data links, and ground support modules.
By November 1990 most of the significant performance capabilities of the system had been confirmed in tests and demonstrations. On January 12, 1991, JointSTARS was deployed to the Persian Gulf. The aircraft flew every day during the war, flying 49 combat sorties and logging over 535 hours between the two aircraft. The ten to fourteen hour missions were conducted primarily at night, denying the enemy its ability to reposition, resupply, or employ under cover of darkness. At the conclusion of the war, General Schwarzkopf and his staff described JointSTARS as an "unqualified success." Unfortunately, after the war, JointSTARS went back into our standard acquisition system from which it is only emerging now so we have still not developed the database from observing and recording patterns of motion needed to create algorithms which can help capitalize on the data produced by JointSTARS. The system has a lot of potential that needs to be developed.
Charles A. "Bert" Fowler of C.A. Fowler Associates has been a consultant to industry and government since 1986. His major field is electronics, with specialties in radar, command, control, and communications (C3), counter-C3, intelligence and military systems. He has held a wide range of industrial positions, most recently as Senior Vice-President of MITRE Corporation. He is a member of the Defense Science Board (Chair 1984-88), the Defense Intelligence Agency Science and Technology Advisory Board (Chair 1976-82), and the National Academy of Engineering.
Jane Kellett Cramer -- Rapporteur