By Benjamin Vroman


The Enhanced Surface-to-Air Missile Simulation (ESAMS) is a computer program used to model the interaction between airborne platforms and a radio frequency (RF) surface-to-air missile (SAM) air defense system. As an engineering-level model, ESAMS simulates many pieces of a SAM engagement, including radar performance, missile aerodynamics, countermeasure algorithms, environmental factors, tactics, and endgame. Each of these SAM engagement factors is dependent on the type of threat and the availability of intelligence data. An extensive amount of time and effort is applied in consuming detailed data abstracted from intelligence information and incorporating the data into the individual models to provide comprehensive representatives of land-based and naval RF SAM systems. ESAMS includes a family of more than 30 threat models, all similar in function, but each unique to the SAM system it simulates.

ESAMS is a constructive-level model written in Fortran and operated from a command line. It is developed, tested, and operated on Linux operating systems with GFortran compliers. There is limited support for Windows operating systems as well. ESAMS development efforts are heavily driven and funded by acquisition programs at the Air Force Life Cycle Management Center (AFLCMC), with significant contributions from the joint community. ESAMS is owned, developed, maintained, and used at AFLCMC’s Engineering Directorate, Analysis and Training Systems Division, Combat Effectiveness & Vulnerability Analysis Branch (AFLCMC/EZJA) at Wright-Patterson Air Force Base in Dayton, OH.


ESAMS has had significant exposure at high levels of the Department of Defense (DoD) and has been used by Government and industry analysts since its inception in the early 1970s. It has been highly valued because of its ability to realistically simulate the numerous components of a SAM system and its interaction with air vehicles. ESAMS is a proven engagement-level tool routinely used to support aircraft studies exploring air vehicle survivability and effectiveness assessments against current and emerging RF threat systems.

The use of ESAMS critically impacts numerous DoD efforts in three major areas: acquisition program analysis of alternative (AoA) studies, platform modernization studies, and development test (DT) and operational test (OT) activities. For AoA support, ESAMS is used to assess weapon alternatives and assist decision-makers on future force structures. In platform modernization efforts, the tool is used by analysts to conduct blue system gap analyses, assess requirements, and flush out solutions to blue platform capability gaps. For DT and OT efforts, analysts use ESAMS to provide pre-test and post-test insight, allowing for extrapolation of performance against threats unavailable in software or hardware labs or open-air test ranges.

As shown in Figure 1, ESAMS covers a large portion of the kill chain in a typical real-world engagement. In general, ESAMS provides an engagement-level framework, allowing analysts to evaluate air platform survivability, estimate effectiveness, set requirements, and optimize tactics.

Figure 1. ESAMS Overview Graphic.

For example, ESAMS can simulate the operational performance of a SAM defense system against an intruding aircraft approaching a defended area. An acquisition radar (which may or may not be collocated with a SAM site) may detect the aircraft and then cue a SAM site with the aircraft’s range, azimuth, and elevation data. The SAM may have a fire control radar or engagement radar. The fire control radar receives its cue from the acquisition radar and then attempts to acquire and track the aircraft with greater accuracy, which is usually needed to formulate a missile launch solution for the SAM to launch its missile(s) at the intruding aircraft. One or more launchers with one or more missiles per launcher launch the missile(s). The fire control radar and/or the missile seeker then provides guidance commands to the missile during the engagement. When the missile approaches its target, the fuze detects the target and activates the warhead detonation.

Three kill mechanisms can be evaluated: direct hit, blast overpressure, and fragment damage. In addition to the aircraft, the radars may interact with other entities in the simulation, including munition/bombs, decoys, and jamming vehicles. ESAMS can simulate, in detail, the chronological events of the entire engagement process.

The general release of ESAMS has been made possible with the support of the Joint Aircraft Survivability Program Office (JASPO). The current release of the tool—ESAMS version 5.6—has been available from the Defense Systems Information Analysis Center (DSIAC) since June 2020. The next release of ESAMS, version 5.7, is tentatively scheduled for April 2021.

ESAMS version 5.7 will contain the 30 threat systems that are common to ESAMS users, with some notable improvements to threat systems from the “Advanced RF Counter Measure” and “Vertical Lift Capability for ESAMS” JASP projects (project numbers S-16-04 and S-18-02, respectively). In addition to these threat improvements, ESAMS versions 5.6 and 5.7 will also contain a number of threat missile updates supported by the “Missile Models for ESAMS” JASP Project (project number S-20-03). The “Missile Models for ESAMS” project updates a set of kinematic missile flyout simulations from the Missile and Space Intelligence Center (MSIC) and Operational Navy Intelligence (ONI) into the ESAMS environment. The kinematic missile flyout models are then integrated with ESAMS ground radars and missile radar seekers. It should be noted that because these models are in fact modified from the originals, they are not endorsed by the intelligence agencies as being authoritative.

The biggest addition to ESAMS version 5.7 will be the capability to assess rotorcraft survivability. In addition to the threat improvements mentioned previously, two large enhancements have been driven by the JASP “Vertical Lift Capability for ESAMS” project. The first enhancement is to provide several threat systems with the ability to accept and process dynamic, spectrally spread returns from rotating blades. ESAMS will be able to accept direct in-phase and quadrature (I&Q) measurements from rotating blades. However, this measured I&Q data can be difficult to process into ESAMS and may require pre-processing. An application was added to ESAMS to enable the user to generate a spectrally spread signature through defining scattering points on the body and blade rotation parameters through the ESAMS input file; this application can also be used if appropriate measured I&Q data are not available. The rotorcraft capabilities have been developed alongside ESAMS pedigree documentation that are released with ESAMS.

The second large improvement for rotorcraft capabilities enhances the propagation methodology in ESAMS. This enhancement includes four main highlights. First, ESAMS now has extended the atmospheric loss calculations to 40 GHz. Second, the atmospheric loss calculations no longer assume the transmitter or receiver is at sea level. Third, refraction can now be characterized more explicitly than the 4/3rds earth simplification and can also include measurement error and anomalous propagation. Finally, clutter effects and radar modes to mitigate clutter have been addressed. In total, these propagation enhancements allow for better low-altitude engagements operating in clutter and multipath environments.


ESAMS version 5.7 is scheduled to be the last general DoD release of the package through DSIAC. This last general release is due to the increasing complexity of emerging threats and modern blue countermeasure systems, as well as the increased availability of other tools. As such, it is recommended that intelligence agency modeling and simulation (M&S) capabilities be fully explored for JASP analysis community requirements.

Intelligence agencies such as MSIC, ONI, the National Ground Intelligence Center (NGIC), the National Air and Space Intelligence Center (NASIC), and the Test and Evaluation Threat Resource Activity (TETRA) have made significant progress in  developing authoritative stand-alone threat system models. In addition, the Joint Technical Coordinating Group (JTCG) and JASP are rapidly working toward next-generation M&S applications—such as the Joint Anti-Air Model (JAAM), Air Combat Effects Library (ACEL), and Survivability and Lethality of Aircraft in Tactical Environments (SLATE)—which are expected to fulfill much of the JASP analysis community requirements.

These applications directly integrate intelligence center models/simulations and have accomplished much work in producing tools available to the JASP analysis community. These applications are also migrating key new capabilities, such as processing dynamic spectrally spread returns, additional atmospheric losses in propagation methodology, explicit refraction modeling, and clutter effects from ESAMS to enable greater use across simulations. A subset of ESAMS capabilities will remain under these applications until suitable replacements are available. These initial simulations should be made available in 2022, within a year of the ESAMS version 5.7 release.


In summary, ESAMS is a powerful and complex engagement-level analysis tool used by AFLCMC/EZJA to support aircraft studies exploring air vehicle survivability and effectiveness assessments against current and emerging RF threat systems. EZJA will continue to assist its customers individually with studies and analyses. The ongoing growth and development of ESAMS will provide critical competencies to assess emerging technologies supporting war-winning capabilities now and into the future. For further information concerning the ESAMS tool, please contact AFLCMC/EZJA.


Mr. Benjamin Vroman is an engagement-level technical expert for the Air Force Life Cycle Management Center. He has served the Air Force for more than 16 years. Mr. Vroman has also served as the ESAMS Model Manager for approximately 12 years. He has a B.S. in mechanical engineering from Cedarville University and an M.S. in engineering management from the University of Dayton.