EVALUATING SHiELD AS A COST-EFFECTIVE SURVIVABILITY ENHANCEMENT FOR LATE-GENERATION AIRCRAFT
By Wen Xiang Ong and Christopher Adams
Air Force Research Laboratory Image
When operating in a man-made hostile environment, a fourth-generation fighter aircraft (such as an F-15 Eagle or F-16 Fighting Falcon) would likely be more susceptible to adversarial air-to-air and surface-to-air missile threats when compared against the more modern and stealthier fifth-generation counterparts (such as an F-22 Raptor or F-35 Joint Strike Fighter) [1]. Expendable countermeasures such as chaff and flares are currently deployed to defend the aircraft against such threats. However, the effectiveness of these countermeasures is highly dependent on the aircrew’s judgement regarding when to deploy them to achieve the highest probability of survivability and whether the incoming missiles are “smart” enough to distinguish the countermeasures vs. the actual target [2]. Such countermeasures are also limited in quantities—once they are expended, the aircraft would have no other tools to defend itself against incoming threats. Accordingly, against a backdrop of increasingly complex air-to-air missiles, increasingly accurate and lethal air defense capabilities, and ongoing developments in hypersonic missiles, enhanced combat survivability of late-generation fighter aircraft is needed.
This article presents a fundamental evaluation of enhancement to a fourth- and fifth-generation fighter aircraft’s combat survivability through the deployment of a tactical airborne laser system—such as the Self-Protect High Energy Laser Demonstrator (SHiELD)—as a survivability enhancement feature (SEF). A system-level study applying the concepts of aircraft combat survivability to a notional combat scenario was designed and modelled using Monte Carlo simulations to analyze the enhancement to combat survivability. Subsequently, a cost effectiveness analysis of the tactical airborne laser pod was performed to understand whether its deployment on the current and next-generation fighter aircraft might make it a worthwhile, cost-effective aircraft combat SEF in the future.
[Authors’ Note: The names of specific fighter platforms in this article are included for illustrative purposes only and do not reflect actual platform-specific test/analysis data. In addition, the potential system characteristics described herein are taken from information available in open literature, and the modeling and simulation of systems are for conceptual analysis only.]
SHiELD: A NEW LIGHT IN THE FIGHT
The Air Force Research Laboratory—in collaboration with Lockheed Martin, Northrup Grumman, and Boeing—has developed the SHiELD tactical airborne laser pod to be installed on fighter aircraft and potentially defeat incoming surface-to-air and air-to-air missile threats [3]. With SHiELD’s wide field of regard, it can “see” incoming threats, maintain direct line of sight, and direct its laser beam to engage threats without needing the pilot to execute evasive maneuvers. The system’s beam control and turret were also designed to compensate for the turbulent effects of transonic flight regime. In addition, the host aircraft can recharge SHiELD’s battery without the need to replace its entire power generation system [4].
As a pod-mounted weapon system, SHiELD would be compatible with many fighter aircraft platforms, including fourth- and fifth-generation platforms. Lockheed has conducted a significant number of flight tests and hopes to improve the power output of directed energy systems in the coming years [5, 6]. It should be noted, however, that adding an external pod to a fifth-generation fighter could significantly increase the radar signature to an unacceptable level depending on the threats encountered on the mission.
SHiELD comprises three key subsystems: (1) the Laser Advancements for Next-generation Compact Environments (LANCE) high-energy laser (HEL), an electrically powered fiber laser by Lockheed Martin; (2) the SHiELD Turret Research in Aero Effects (STRAFE) beam control subsystem by Northrop Grumman; and (3) the Laser Pod Research and Development (LPRD) subsystem for the external aircraft pod, from which the HEL would be powered and cooled, by Boeing [7, 8].
By early 2021, SHiELD’s key subsystems had achieved significant project milestones. The Air Force successfully flew test flights using an F-15 mounted with Boeing’s test pod and shot down air-launched missiles from a ground-based version of the LANCE HEL [9].
MODELING AIRCRAFT COMBAT SURVIVABILITY
The concept of aircraft combat survivability, as developed by the Naval Postgraduate School’s Dr. Robert Ball, revolves around two keywords: susceptibility and vulnerability [2]. In an engagement scenario, the probabilistic kill chain is defined by the susceptibility and the vulnerability probabilities, where susceptibility refers to the inability to avoid threats and is represented by a P(Hit)—or P(H)—while vulnerability is defined as the inability for the aircraft to withstand damage inflicted and is represented by P(Kill|Hit)—or P(K|H).
As shown in Figure 1, susceptibility has been described by the probabilities of the first five phases of the engagement scenario, as seen from the perspective of the enemy’s air defense system. These phases include:
- P(Active)—or P(A);
- P(Detect|Active)—or P(D|A);
- P(Launch|Detect)—or P(L|D);
- P(Intercept|Launch)—or P(I|L);
- P(Hit|Intercept)—or P(H|I).
Figure 1. Single-Shot One-on-One Probabilistic Kill Chain Between Aircraft and Air Defense System [10].
ENGAGEMENT SCENARIOS
Two sets of single-shot one-on-one engagement scenarios were modeled for a fourth-generation fighter (such as the F-16) and a fifth-generation fighter (such as the F-35) to be individually engaged by a notional foreign surface-to-air missile system. In the first scenario, the fourth- and fifth-generation fighters were equipped with their respective baseline SEFs, such as an electronic countermeasure suite. However, in the second scenario, the fighters were additionally equipped with the SHiELD pod on their centerline station. During the engagement, each fighter aircraft was modeled to fly individually through an area of operations defended by the notional missile system. A total of 100,000 Monte Carlo simulation runs were performed to calculate the probabilistic outcomes and evaluate the enhancement in probability of survival P(S) for a SHiELD-equipped fighter aircraft vs. a baseline aircraft.
[Authors’ Note: Other than estimated cost, the numbers shown or derived in this article are notional and not representative of any specific system or aircraft, as the intent of this article is simply to provoke discussion on the cost benefit of certain SEFs to combat effectiveness.]
Due to atmospheric attenuation, we could expect SHiELD’s laser beam to have greater effect on the incoming missile during its mid-course intercept phase compared to its initial launch phase. As such, for engagement scenarios involving SHiELD-equipped fighter aircraft, the P(I|L) and P(H|I) values were arbitrarily reduced by mean values of 20% and 50%, respectively, with a 5% standard deviation. For example, as shown in the “Final Percent Reduction” column of Table 1, the P(I|L) was reduced by 17% while the P(H|I) was reduced by 48% in one of the simulations. A standard deviation value of 5% was arbitrarily chosen to represent the differences in the SHiELD pod’s effectiveness due to various factors, such as manufacturing tolerances.
The input parameters used in the Monte Carlo modeling of the single-shot one-on-one engagement scenario for the fourth-generation fighter vs. the notional missile system are shown in Table 2. The parameters were adapted from Kim et al. [11], which attempted to evaluate the susceptibility of a representative fighter aircraft against a surface-to-air missile threat using the Analytic Hierarchy Process’s (AHP) weighted score algorithm. (Once again, these parameters do not reflect actual test data values and instead serve simply to provide an illustration of the model for readers to better understand.) Also, while external carriage of SHiELD pods on the aircraft will adversely affect the P(D|A) and P(L|D), these effects were largely ignored in the model so as to reduce the variables and instead focus solely on the enhancements to survivability due to the SHiELD pods.
For the fifth-generation fighter vs. missile system engagements, the input parameters are as shown in Table 3. As the notional fifth-generation fighter was designed with stealth capabilities and has a significantly reduced radar cross section compared to the fourth-generation fighter, the input parameters for the baseline fifth-generation fighter vs. missile system were arbitrarily determined by assuming that the fifth-generation fighter P(D|A) was 30% lesser than that of the fourth-generation fighter. Similarly, the conditional probabilities P(L|D), P(I|L), and P(H|I) were arbitrarily reduced by 15% when compared to the fourth-generation fighter, as it was assumed that once the fifth-generation fighter was detected and a launch solution calculated, the remaining probabilities of intercept from the engagement would change slightly.
Table 4 shows the results from the Monte Carlo simulations. Note that the average P(S) for the baseline fourth-generation fighter is 0.796, while the SHiELD-equipped fourth-generation fighter yielded significantly better average P(S), at 0.918, which represents a 12.2% survivability enhancement, as shown in Figure 2. For the fifth-generation fighter, the baseline aircraft has an average P(S) of 0.912, and the SHiELD-equipped fifth-generation fighter is 0.965. The fifth-generation fighter, being a stealthier aircraft, already has high P(S) even for its baseline configuration, and SHiELD only marginally enhanced its survivability by 5.3%, as shown in Figure 3. Note also that the SHiELD-equipped fourth-generation fighter was marginally more survivable than the baseline fifth-generation fighter.
Figure 3. P(S) for Fifth-Generation Fighter in Single-Shot One-on-One Engagement Scenario.
Furthermore, when the single-shot one-on-one engagements were extended to 10 engagements, it became clear that as the number of engagements increases, the P(S) decreases. The results from the engagements are shown in Table 5.
For a typical fighter squadron with 24 aircraft, the P(S) values obtained meant that only 0.109×24≈2 baseline fourth-generation fighters would be expected to survive 10 engagements with the missile system. In contrast, 0.434×24≈10 SHiELD-equipped fourth-generation fighters would be expected to survive after the 10 engagements. In that regard, it is evident that the 12.2% susceptibility reduction—or enhancement in P(S)—has a significant impact on the aircraft availability.
For the fifth-generation fighter, the survivability results were considerably better than the fourth-generation fighter, as would be expected for the latest-generation fighter aircraft. The baseline fifth-generation fighter was expected to have 0.405×24≈9 aircraft surviving after 10 engagements. In contrast, the SHiELD-equipped fifth-generation fighter was expected to have 0.702×24≈16 aircraft surviving after 10 engagements due to the 5.3% enhancement in P(S).
COST-EFFECTIVENESS OF SHIELD FOR FOURTH- VS. FIFTH-GENERATION FIGHTERS
Table 6 shows the cost of replacing fighter aircraft when encountering multiple one-on-one engagements with the missile system. Assuming each SHiELD pod costs $2 million (in U.S. dollars), a simple estimation for the total acquisition cost of equipping a squadron of 24 fighter aircraft would be $48 million (using the F-16 as an example). In terms of aircraft, each F-16 costs approximately $30 million, while the conventional F-35A variant costs approximately $80 million, and the short takeoff and vertical landing (STOVL) F-35B variant costs approximately $115 million [12–14].
Based on the model’s assumptions, SHiELD-equipped fighter aircraft achieved significant total cost savings when compared against their baseline configuration. This savings is because the replacement cost for each fighter aircraft was much higher compared to the price of a SHiELD pod.
Now if we use cost figures for some current fighters (such as the F-16, F-35A, and F-35B) as stand-ins for the cost of the notional fourth- and fifth-generation fighters and then apply the output data from the preceding model, we can get a rough idea of the cost benefit of SHiELD. For example, the total cost of replacing 22 attritted baseline F-16’s after 10 engagements would be $660 million, but it costs only $496 million to replace 14 SHiELD-equipped F-16’s. This fact translates to a cost savings of $164 million due to SHiELD. The highest cost savings applying the notional survivability model was achieved when comparing baseline F-35B’s against SHiELD-equipped F-35B’s after 10 engagements, at $741 million. Overall, it thus appears more cost-effective to equip these expensive fighter aircraft with SHiELD.
A sensitivity analysis for the cost price of the SHiELD pod and the total cost savings for the fighter aircraft types after 10 engagements was also performed, and the results are given in Table 7. The analysis showed that when the SHiELD pod was priced at $7 million per unit, it incurred a loss of $26 million between the baseline F-16 and the SHiELD-equipped F-16. Thus, it would be more cost-effective not to equip the SHiELD pods on the F-16. However, due to the significantly higher price tag of an F-35, it was still more cost-effective to equip them with SHiELD. For the F-35A and F-35B, the decision-making would only lean toward not equipping them if a SHiELD pod was to cost $18 million and $26 million, respectively, in 10 engagements.
CONCLUSIONS
Based on the modeling, assumptions, and evaluations presented herein, the subject fourth- and fifth-generation fighter aircraft equipped with the SHiELD system have been shown to achieve better combat survivability than equivalent baseline fighter aircraft. In addition, a fully effective SHiELD-equipped fourth-generation fighter could achieve similar survivability to a baseline fifth-generation fighter. Finally, from a cost-effectiveness perspective, the deciding factor on whether to equip fighter squadrons with the SHiELD pod will ultimately depend on factors such as the cost of the SHiELD pod and its true capabilities.
ABOUT THE AUTHORS
Military Expert 5 (ME5) Wen Xiang Ong has been an Airforce Engineer with the Republic of Singapore Airforce (RSAF) since 2011 and is currently serving as the Depot Commander of 5 Ammunition Depot, Singapore Armed Forces Ammunition Command. He has held various appointments related to maintenance of weapon and armament systems for the F-15SG and F-16 fighter aircraft, including serving as Officer Commanding of the Aircraft Weapon Operations Flight in 805 SQN, Air Power Generation Command. ME5 Ong holds a bachelor’s degree and a master’s degree in mechanical engineering from the Nanyang Technological University and the Naval Postgraduate School (NPS), respectively, and was most recently conferred a master’s degree in defense technology and systems from the National University of Singapore.
Mr. Christopher Adams is a Senior Lecturer at the Naval Postgraduate School (NPS) Department of Mechanical and Astronautical Engineering and is a former Associate Dean of NPS’s Graduate School of Engineering and Applied Sciences. A retired Navy Commander and aviator with multiple tours in Iraq and Afghanistan, he is a widely recognized subject-matter expert and educator on combat survivability. Mr. Adams holds a bachelor’s degree and master’s degree in aerospace engineering from Boston University and NPS, respectively.
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