Article by: Joe Sorroche and Riley Rainey (joe.sorroche@kirtland.af.mil)
IEEE 1278.1a, the Distributed Interactive Simulation (DIS) protocol, is currently being updated by the Simulation Interoperability Standards Organization (SISO) DIS Product Development Group (PDG). The DIS PDG is creating new Protocol Data Units (PDUs), and further defining existing PDUs. The Directed Energy (DE) Tiger team, part of the DIS PDG, has designed two new DIS Protocol Data Units (PDUs) for high fidelity DE modeling and simulation: DE Fire and DE Damage Status. These PDUs include many DE specific parameters necessary for high fidelity DE weapons and associated effects modeling. The Air Force Research Laboratory (AFRL) provided funding to develop and experiment with these new PDUs during the Advanced Concept Event (ACE) 06. This event provided a proper venue to test the new DE PDUs, with interactions between shooters and targets. This experiment also tested the interoperability of higher fidelity DE PDUs with legacy simulations that model DE weapons using the existing DIS standard. The experiment was conducted at the USAF Distributed Mission Operations Center (DMOC).
The DE high fidelity model design was first documented in the DIS PDG Problem Change Requests (PCR) 152, July 2006 [Ref (1)]. PCR 152 (Ref [1]) describes the DE Fire and Damage Status PDU structures, records, issuance rules, and all required modeling algorithms. In November of 2006, an experiment was conducted to test the initial design, PDU exchange algorithms, fidelity/interoperability with legacy simulations, and recommend changes if required. The experiment results showed that some changes were required to the original DE PDU structures. PCR 174 (Ref [5]) documents these required changes. Since then, additional PCRs have been written to further expand the DE weapon fidelity.
Models for DE weapons and target damage models are described in the following paragraphs.
Directed Energy Weapons Models
DE weapons range from precision High Energy Lasers (HEL) to High Powered Microwave (HPM) weapons. Each has different weapons characteristics and the damage they cause on targets. These weapons are modeled as either DE Precision or DE Area weapons. All DE weapons are modeled as being attached to an entity. The DE Fire PDU models both as virtually the same because each is modeled as a DE weapon fired from a platform. The weapons parameters modeled are: 1. Shot Start Time
2. Cumulative Duration
3. Aperture/Emitter Location in Firing Entity Coordinates
4. Aperture Diameter
5. Wavelength
6. Peak Irradiance
7. Pulse Repetition Frequency
8. Pulse Width and Shape
DE weapons can be directed at a specific point or general area, so there are different target models: Precision Aim Point and Area Aim Point. The Aim Point records models differentiate between how energy is deposited on a specific target or area, and how the target is affected.
Directed Energy Precision Weapons Modeling
DE precision weapons are essentially lasers. The typical laser weapon design includes some sort of active beam control system designed to concentrate the arriving energy on a particular spot on the target. Modeling this type of active tracking system poses a challenge in the distributed simulation environment. In the real world, a DE shot emerges from the aperture of a weapon - a well-known location - and arrives at the target spot. One way to model the current state of a shot would be a simple line segment in a DE Fire PDU record. But typical DIS network latencies (Ref[6]) combined with fast maneuvering targets or terrain database differences between simulations make it unreasonable to model the origin and destination of a laser using DIS world coordinate records. Latencies and these additional effects would result in the shooter as well as other observers "seeing" completely different resulting shots. A higher fidelity model is required to characterize the beam spot tracking in the DE Fire PDU that is insensitive to these degrading effects. A DE Fire PDU record addresses this by identifying the target entity and then providing beam spot location, velocity, and acceleration information relative to the origin of that entity. This allows dead reckoning of the target spot motion based on each simulation application's notion of the current target entity state, thus canceling these accuracy-degrading effects. However, note that problems may arise if the firing and target simulations use different geometric models for the target. This is resolved by incorporating the Damage Status PDU parameters, which are described later.
The DE spot profile on the target can be many shapes due to several variables, such as atmospheric effects, and the instantaneous velocity, acceleration, and distance of the shooter and the target. For distributed modeling purposes, an elliptical beam spot size model was chosen as the best that would represent all possible shapes, and can be used for first order real time lethality damage model calculations.
The irradiance profile can be modeled as a Gaussian shape whose peak is given in the Peak Irradiance field. Details of this Gaussian model can be found in Annex X.4 of PCR 152. The beam spot model (Ref [1]) is shown in Figure 1.
Figure 1: Beam Spot Model The Beam Spot model parameters are defined as:
a = Beam Spot Cross Section Semi-Major Size
b = Beam Spot Cross Section Semi-Minor Size
f = Beam Spot Cross Section Orientation Angle
The irradiance at a point on the YZ plane is then given by:
Where:
DE Area Weapons Modeling
DE Area weapons modeling are accomplished by using the Area Aim Point records. The energy deposited in an area is modeled as affecting one or many targets in a given area. Separate weapons effects can be modeled for each target by the Beam Antenna Parameter record and the Target Energy Deposition record. The Beam Antenna Record specifies the direction, pattern, and polarization of the DE Area weapon, and is described in detail in Reference 3. The Target Energy Deposition record contains the target ID and the peak irradiance in watts per square meter.
Directed Energy Damage Effects Models
In DIS version 6, the damage caused by conventional weapons is modeled in the Entity State PDU. DE weapons damage models required additional parameters, so the Damage Status PDU was created. The Damage Status PDU models structural damage and temperature effects, complementing the Entity State PDU appearance bits. Issuance rules are also defined for the DE Fire, Damage Status, and legacy Fire and Detonate PDUs. The DE PDU structures are shown in Appendix A. The DE PDU Exchange diagram is shown in Appendix B.
DE PDU Engagement Model A high-fidelity DE engagement is modeled as follows. First, a DE simulation sends a DE Fire PDU indicating weapon on or fired and immediately followed by a Fire PDU. Then, additional DE Fire PDUs may be sent depending on weapon and engagement type, and then terminates with a final DE Fire PDU, followed immediately by a Detonation PDU. A simulation that transmits the DE Fire PDU is also required to transmit the legacy Fire and Detonation PDUs. Pulsed DE weapons, where the laser is turned on and off in rapid succession, is modeled as a continuation of a single engagement, and no additional Fire or Detonation PDUs are issued. The DE Fire PDU may be sent multiple times while a shot is in progress to allow the receiving simulation to continuously assess damage, provide immediate feedback by transmitting Entity State and Entity Damage Status PDUs. The target is also required to dead reckon the weapon impact point.
Directed Energy PDU Experiment
The DE Experiment was a unique opportunity because tests could be conducted on the proposed high fidelity weapons models before incorporation into a distributed simulation standard. The experiment had three phases: Software development and unit test; integration test, and conduct specific experiments. Each phase provided valuable feedback for standards development and design. Additional details can be found in the Directed Energy Experiment Test Plan and Results for the Advanced Concept Event 06 (Ref[2]).
Directed Energy Experiment Resources
The Directed Energy resources used were the DMOC F-16 HEL Fighter, the Scenario Toolkit And Generation Environment (STAGE) simulations, and the Distributed Interactive Simulation Network Analysis Tool (DISNAT) data logger. These systems were modified to send, receive, process, and record the DE PDUs. Other resources used but not modified were the DMOC DIS Filter and the Joint Conflict and Tactical Simulation (JCATS).
Directed Energy Experiment Results
The experiments were categorized into 3 different tests: Test 1: HEL Fighter engaging a fixed ground targets, in this case, a stationary tank; Test 2: HEL Fighter engaging ground and air moving targets, in this case, an F-15C fighter; and Test 3: High Fidelity DE weapon engaging a low fidelity target. The DIS experiment initial conditions are as follows:
1. Exercise ID: 2
2. UDP Port: 2000
3. DIS Entity State Update rate:
a. Air: 5 Seconds Straight and Level
b. Ground: 55 Seconds
4. Dead Reckoning Algorithm:
a. STAGE: 5
b. F-16 HEL: 5
For each test, the JCATS simulation was also run to observe how non DE modified simulations responded to DE specific PDUs.
Test 1: Air to Ground Engagement Test 1 experiment parameters are as follows:
1. F-16 HEL Fighter Weapon configuration
a. Site ID: 48.16.1
b. Aperture Diameter: 0.3 Meters
c. Wavelength: 1.03E-06 Meters
d. Peak Irradiance: 2000 Watts/Meter
e. Pulse Rep. Frequency: 97100 Hz
f. Pulse Width: 10 Seconds
g. Status Flag: 0
h. Pulse Shape: Other
i. DE Aim point record type: DE Precision
2. Target: Non Moving Tank.
a. Site ID: 48.8.27
The stationary tank broadcasted Entity State PDUs every 55 seconds. The F-16 HEL proceeded with an air to ground engagement, acquiring the target, and fired the HEL once the target was acquired. Both DE Fire and Fire PDUs were transmitted. The DE Fire PDU status flag was set to 3, for weapon on and state change. The Fire PDU showed the correct event ID, target ID, world coordinate location, warhead type and quantity was set to 1. After 1 second, another DE Fire PDU was transmitted, and STAGE transmitted a Damage Status PDU, showing minor damage, fire present, and white smoke. After 2 seconds, another DE Fire PDU was transmitted showing the cumulative duration of 2 seconds, and the status flag set to 3 for weapon on and state change. After 3 seconds, another DE Fire PDU was transmitted incrementing the duration correctly. STAGE then transmitted an Entity State PDU with the appearance bits set to Slight Damage and still active. After 3 seconds, the F-16 HEL transmitted a DE Fire with the status flag set to 2 for weapon off and state change. The F-16 HEL also transmitted a Detonate PDU with the correct event ID, weapon type, and detonation result. STAGE then transmitted a Damage Status PDU showing medium damage, moderate smoke, and grey smoke. Five seconds later, STAGE transmitted an Entity State PDU with the appearance bits set for moderate damage and smoke plume, but still active.
The F-16 HEL - STAGE PDU exchanges were consistent with algorithms defined in PCR 152 (Ref [1]), and the unclassified DE damage tables provided.
Test 2: Air to Air Engagement Test 2 experiment parameters are as follows: 1. F-16 HEL Fighter Weapon configuration
a. Site ID: 48.16.1
b. Aperture Diameter: 0.3 Meters
c. Wavelength: 1.03E-06 Meters
d. Peak Irradiance: 2000 Watts/Meter
e. Pulse Rep. Frequency: 97100 Hz
f. Pulse Width: 10 Seconds
g. Status Flag: 0
h. Pulse Shape: Other
i. DE Aim point record type: DE Precision
2. Target: STAGE F-15C.
a. Site ID: 48.8.11
The F-16 HEL proceeded with an air to air engagement, flying behind the F-15C, acquired the target, and fired the HEL. Both DE Fire and Fire PDUs were transmitted. The DE Fire PDU status flag was set to 3, for weapon on and state change. DE Fire PDUs were transmitted every second. The DE weapon duration was 7 seconds, resulting in a destroyed F-15C.
The F-16 HEL - STAGE PDU exchanges were consistent with Ref 1 and the unclassified damage tables provided. Although the DE weapon dwell time could not be controlled manually, the engagement was adequate for complete destruction of the F-15C.
Test 3: Air to Ground Mixed Fidelity Test 3 Parameters are as follows:
3. F-16 HEL Fighter Weapon configuration
a. Site ID: 48.16.1
b. Aperture Diameter: 0.3 Meters
c. Wavelength: 1.03E-06 Meters
d. Peak Irradiance: 2000 Watts/Meter
e. Pulse Rep. Frequency: 97100 Hz
f. Pulse Width: 10 Seconds
g. Status Flag: 3
h. Pulse Shape: Other
i. DE Aim point record type: DE Precision
4. Target: Non Moving Tank.
a. Site ID: 48.55.14016
The F-16 HEL - JCATS PDU exchanges were consistent with Ref 1. The JCATS did not process any DE Fire PDUs, only the Fire and Detonate PDUs. JCATS responded to the standard Fire and Detonate PDUs.
Another experiment was run using the F-16 HEL and STAGE, with the STAGE DE Fire and Damage Status PDU user modules disabled. Results similar to the F-16 HEL - JCATS PDU exchanges were observed. The fidelity - interoperability experiment proved that the proposed DE PDU exchange model worked for these two legacy CGFs only. Other legacy simulations should be tested because they may read and process PDUs differently, and the simulation may crash.
Detailed PDU Log files have been saved on the DISNAT logger for further analysis.
Conclusions
The DE Experiment was extremely successful because proposed DE models and algorithms were tested before incorporation into a standard. Because of this, three design flaws were discovered. First, the Site, Application, and Entity Id of the target in the Damage Status PDU were not provided, so there was no way to track who the Damage Status PDU came from. This was added to the PDU. Second, the DE Fire PDU Aim Point Record was not properly byte aligned as required by Reference 3. An additional 32 bits were added, thus meeting the DIS standard for byte alignment. And third, the description and enumerations for the pulse shape field were not provided in PCR 152 (Ref [1]). This was also added.
Another significant discovery was that mixed fidelity engagements were possible with non DE simulations. This is important because non DE simulations can participate in DE events and not require modification.
Once the test results were analyzed, PCR 174 (Ref [6]) was created and submitted that corrected the deficiencies and omissions in PCR 152 (Ref[1]). PCR 174 (Ref [6]) also added a capability to the Damage Status PDU that allows for damage records from multiple engagements in one PDU.
Additional PCRs have been written that expand the DE modeling capabilities. PCRs 183 and 184 add variable record parameters, and PCRs 195 and 196 modify the variable record parameters so that they are consistent with other DIS version 7 variable records. These modifications, along with other tests will be part of the ACE 07 DE PDU Experiment, scheduled for 24 - 27 September 2007. The results will be documented in subsequent SISO papers.
Acknowledgements
The DMOC thanks the DE Tiger Team for providing the DE models and algorithms. The DMOC also thanks Mr. Rudy Martinez, AFRL, for approving and sponsoring the Directed Energy PDU Experiment. We also thank the DE Tiger Team Lead, Mr. Riley Rainey, DE Tiger Team members, and 1Lt Brian Spanbauer for providing unclassified DE damage tables.
We also thank the DMOC ACE 06 Team:
1. Project Officer, Lt. Eric Charest, Assistant Project Officer, Jim Teak, Systems Engineer, Dwight Drager, Network Engineer Jason Atkinson, System Administrator Steve Binyon, and Scenario Developers Susan March-Thomas and Scott Defrates.
2. DE PDU Software Developers: Glen Michealson, Ed Colunga, Kevin Cottage, Craig Goodyear, Joel Castellanos, and Desiree Marquez.
3. F-16 HEL Pilot, Jono Tyson.
References
[1] PCR 152B, Directed Energy Weapons Upgrade , SISO DE Tiger Team, Mr. Riley Rainey DE Tiger Team Lead.
[2] DMOC Document 13-0455, "Directed Energy Experiment Test Plan and Results for the Advanced Concept Event 06", Joe Sorroche.
[3] IEEE 1278.1, 1995, "Standard for Distributed Interactive Simulation - Application Protocols".
[4] 05F-SIW-105, "Bandwidth Reduction Techniques: An Update", Joe Sorroche, Jerry Szulinski.
[5] PCR 174, "Directed Energy PCR 152 Update", SISO DE Tiger Team, Mr. Riley Rainey DE Tiger Team Lead.
[6] 05F-SIW-086, "Latency Testing in the USAF Distributed Missions Operations Environment," Jerry Szulinski, Chad Simpkins.
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