1 American Institute of Aeronautics and Astronautics

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1 AEROGELS FOR RETROFITTED INCREASES IN AIRCRAFT SURVIVABILITY An Improved Approach to Reduce MANPADS Threats against Aircraft Kang P. Lee, Ph.D Chairman and Chief Technology Officer Aspen Aerogels, Inc. 188 Cedar Hill Street Marlborough, MA (508) , ext Abstract Most military and civilian aircraft flying at altitudes below 15,000 feet are susceptible to infrared (IR) based weapons systems due to persistent heat signatures emanating from hot structural components. An improved approach to reduce threats posed by Man-Portable Air Defense Systems (MANPADS) against aircraft is being investigated. Use of aerogel based superinsulation panels passively shields aircraft skin components from internally generated heat and significantly reduces the IR signatures of aircraft with a very small weight penalty compared to other approaches. Aerogel insulation parts can be readily designed for retrofitting to existing aircraft or for new production vehicles for maximum signature reduction. Serious MANPADS Threats Most aircraft not specifically designed to have small IR signatures are especially susceptible to IR seeking MANPADS at altitudes below 15,000 ft. In this section of important air space, current IRCM s (Infra Red Counter Measures) are not very effective against MANPADS because persistent, intense IR signatures from hot external structures provide a ready lock-on target. It is estimated (1) that 90 percent of all the aircraft lost in combat around the world during the past 15 years are attributable to MANPADS. For instance, many of the 250 Soviet aircraft lost in Afghanistan, were victims to Stingers supplied to Mujahideen by the US. Despite being equipped with IRCM s during the 1991 Persian Gulf War, 12 of the 29 American aircraft lost in combat were presumed shot down by Iraqi SA-16 Iglas (1). Apaches that carry MAWS (Missile Approach Warning System) and IRCMflares flying at low altitudes were such easy preys to MANPADS as to be pejoratively called MANPADS Magnets. It is estimated that approximately 50,000 MANPADS are scattered around the world. Because of the lethality and ready availability of MANPADS, low altitude ground support operations by helicopters and fixed wing aircraft have become risky and logistically problematic. A solution to this problem is urgently needed. Current Protection Measures To protect aircraft against MANPADS, several active IRCM approaches have been implemented such as plume suppressors (e.g., HIRSS), diffusers, flares, lamp and mirror systems, laser DIRCM s, and MAWS (Missile Attack Warning Systems). Although these IRCM systems have proven effective in certain situations, they are still considered inadequate. IRCM s can be, costly, bulky, heavy, or can degrade aircraft performance. Sometimes the complexity or hypersensitivity of an IRCM system can negatively impact acceptance by the user community. For instance, MAWS has too many false alarms at the higher sensitivities needed for missile detection. Currently, not all aircraft come equipped with IRCM s, and even when equipped, they do not provide an adequate and acceptable level of protection once the aircraft comes below 15,000 ft. To make matters worse, the MANPADS themselves have become increasingly sophisticated, to counter specific IRCM systems often at a fraction of the cost of the IRCM s. In general, not all aircraft are fitted with the MAWS to due to considerations of cost, weight, performance penalty, etc. Even with 1

2 MAWS, the aircraft pilots have, a few precious seconds, if at all, to deploy expendable IRCM s in order to avoid the missile hitting the plane once the missile approach signal is detected by MAWS. At this critical moment, the pilot has to make the split second decision as to which of the protective flare cocktails to deploy. So, the natural tendency is to fire them all indiscriminately, and quickly run Figure 1. IR signatures of the OH-58, Kiowa Warrior out of flare cocktails. It is unlikely that in the foreseeable future any new advanced active system(s) will resolve the problem to everyone s satisfaction. The fact that none (?) of the aircraft have not been shot down by MANPADS over Afghanistan during the ongoing Operation Enduring Freedom might also give a false sense of security or invincibility to some people further hampering the implementation of reliable corrective measures. A major underlying cause for this historically untenable and seemingly no-win situation in the battle of the aircraft vs. MANPADS is that there are simply too Intense IR signatures emitted by the aircraft skin. This is true even if one can somehow reduce the signatures from the exhaust plume and the hot tail pipe to the extent possible. The image of the OH-58D (Kiowa Warrior) shown at the bottom of Figure 1 presents the IR signature a helicopter can emit in flight. The brightly lit areas of the upper pylon fairing and tail boom of the OH-58D present easy lock-on targets for IR MANPADS seekers. The upper pylon fairing gets hot due to the heat coming from the engine and the exhaust pipe whereas the tail boom signature comes from the hot exhaust downdraft washing over the tail boom. Fortunately, IR signatures from both sections can be effectively reduced using a retrofit approach combining an exhaust plume suppressor that redirects the plume away from the tail section and high temperature aerogel insulation attached to the inside of the upper pylon fairing and engine bay doors. For the latter, the limited volume of insulating space available in the Kiowa cowling structures, and the undesirability of taking on any parasitic weight into the aircraft, make ultra-light, flexible aerogel composite blankets the insulating material of choice. Aerogels are the best solid insulation materials known in the ambient temperature ranges typically found in an aircraft engine bay. It is desirable to passively and inexpensively reduce the IR signatures emanating from aircraft to a level that prevents and/or delays detection by the MANPADS seekers. If this can be done, it will significantly reduce mission risk and increase the safer/available battle space to the aircraft. The benefits of reduced IR signatures have been known to the military for a long time. However, the necessary technology to passively mask the IR signatures effectively using insulation with very low areal densities has not been available until recently. Therefore, by default, main emphasis had been placed on developing clever systems such as multi-spectrum cocktail flares, reactive suppressors, exhaust mixing devices, etc. to defeat or mitigate the threat. The result has been less than satisfactory so far. Potential Solution Arrives via Aerogels Even though complete protection of any given aircraft against MANPADS threats in all circumstances is all but impossible, there is a strong potential for a relatively quick, inexpensive and comprehensive approach to this long-standing goal. Recently, Aspen Systems, Inc. made aerogel technology breakthroughs in the 70 year old aerogel technology i.e., lightweight, flexible aerogel blankets and a rapid, low cost aerogel production process. Because of the two breakthroughs, Aspen Systems received a prestigious 1999 SBIR Technology of the Year Award, Materials and Manufacturing. (All aerogel activities are now transferred to a venture capital 2

3 backed spin off, Aspen Aerogels, Inc., to commercialize aerogel products.) Aerogels, the lightest coherent solids known to man, are extraordinary thermal insulators (R values of per inch at ambient temperature and pressure for Aspen s flexible silica aerogel composites) and therefore demonstrate IR shielding properties over a wide temperature range. Historically, aerogels were too brittle and costly to be of much practical use. Aspen started development work on aerogels in 1993 to develop efficient, low-maintenance cryogenic insulation for NASA Kennedy Space Center (Contact person: James Fesmire, NASA Kennedy Space Center, (321) , james.fesmire@ksc.nasa.gov. Under the project, Aspen invented a Flexible Aerogel Blanket which made it much easier to be used in the field than brittle monoliths. Since then, Aspen has significantly improved the flexible blanket concept. The insulative values (up to R-15 per inch at ambient pressure and temperature), densities (as low as 5 pounds per cubic foot), high temperature resistance/performance (Figure 2), and flexibility/durability have been improved enough that they make excellent core insulation structures for aerospace applications such as IR signature reduction (Figure 3). For more information on the development of various aerogel The new aerogel products from Aspen Aerogels, Inc., are user friendly and practical in terms of the their flexibility, ease of application and affordability. As shown in Figure 4, preliminary tests conducted at Naval Air Warfare Center at Figure 2. Thermal conductivity versus temperture for Aspen Aerogel flexible composites (black and blue curves) versus heavier competitive products. China Lake (Contact Person: Leo Budd, NAWC, China Lake, (760) , buddld@navair.navy.mil) clearly demonstrated the new aerogel products excellent capability to significantly reduce intense IR signatures in a practical manner almost to the background level. Bare Aluminum Plate Bonded with 0.2 thick Aerogel Blanket Apparent Temp = F Apparent Temp = 93.4 T+1 min = 132 T+30 min Figure 3. IR shielding of Hot Aluminum Plate with thin Aerogel Blanket test performed by Boeing under JTCG funding technologies and information on available products at Aspen, the reader is referred to the website Ongoing Programs at Aspen for Aerogel Based IRCM s 3

4 Following the very successful test at China Lake (Figure 4), Aspen received seed funding from JTCG and AATD to develop passive counter measures called ABIRCM s (Aerogel Based Infra Red Counter Measures) that would significantly reduce the IR signatures of the rotorcraft and fixed wing aircraft at a relatively low cost and low added weight. There are two programs: The first project is called, Lightweight Thermal Insulation for Rotorcraft (Contact person: Mac Dinning, AATD, Fort Eustis, (757) , mdinning@aatd.eustis.army.mil). The objective of this 18-month program jointly funded by AATD and JTCG is to develop lightweight thermal insulation for the US Army s Kiowa Warrior helicopter that will be twice as effective as the commercially available high temperature insulation. For this application, the maximum target temperature for the aerogel insulation is 350 C. The aerogel products that have been investigated are flexible aerogel blankets and aerogel filled honeycomb panels both of which will be used for the rotorcraft. Aspen Aerogels products already exceeded performance targets in terms of thermal insulation properties, areal weight, temperature tolerance, etc. In combination with an exhaust suppressor development program being run at AATD, this project is expected to lead to a nearly complete shielding of the IR signatures shown in Figure 1. Flight testing of Kiowa Warrior fitted with aerogel based IR suppressors is in progress as of this WITHOUT THE PATCH, TURBINE SECTION GLOWS BRIGHTLY WITH AEROGEL PATCH, IR SIGNATURES ALL BUT DISAPPEAR Figure 4. IR Suppresion Test at China Lake using Aspen s Aerogel Patch 4

5 writing by AATD. Even though we have not yet achieved the full goal yet, the progress so far has been impressive. The preliminary results from the flight testing at AATD clearly demonstrated the progressive reduction of IR signatures from (a) standard configuration without suppressor or insulation to (b) with a plume suppressor, COSSI, recently developed by and tested at AATD, resulting in complete elimination of the tail boom signatures to (c) with both the plume suppressor and aerogel insulation resulting in over 90% reduction of IR signatures from the upper pylon fairing. A close-up view of the IR pictures (not shown here) showed how effective the aerogel insulation panels are since one can readily see the outlines of the insulation panel shapes attached to the upper pylon fairing appearing as dark areas. Most of the remaining signature came from hot air seeping out of door seams from the engine compartment which will be taken care of for future flight tests at AATD. Additional insulation coverage and further design work will be required reduce the signatures to near background levels. The second project, called ARIAS (Aerogel-based Retrofitted Increase in Aircraft Survivability), is a two year program funded by JTCG that started in October 2001, to investigate the use of aerogels for other aircraft such as another rotorcraft platform (Figure 5) and a fixed wing fighter, F-16 (Figure 6). (Contact Persons: Leo Budd, NAWC- China Lake, (760) , Buddld@navair.navy.mil, and Leonard Truett, WPAFB (937) , Leonard.Truett@wpafb.af.mil). The target maximum temperature range for the insulation material in ARIAS is between 350 ºC and 1000 ºC. Participants in these projects feel that the IR signature related MANPADS threats can be effectively managed by combining the ABIRCM with a judicious mix and modification of existing IRCM s and new advanced counter measures under development. It is expected that an appropriate mix of protective measures will be aircraft-platform specific. Conclusions and Recommendations Under normal circumstances and especially given the relatively modest level of current funding, this type of new technology such as aerogel based IRCM s, even with their obvious and immediate Figure 5. AH-1 Diffuser to be Modified Under the NAWC China Lake Portion of the ARIAS Project 5

6 Figure 6. F-16 Turkey Feathers to be IR shielded under Air Force Portion of ARIAS Project benefits in the battlefield, would take several years at best to be funded, developed, tested, qualified, and ordinarily more than ten years to be deployed. The situation changed dramatically since the tragic September 11 terrorist attacks at the World trade Center and the Pentagon. We live in a completely different world! A prolonged (we may be speaking about decades!) war against terrorism requires a constant vigil against enemy attacks against our aircraft and there is an urgent need. Consider the impact of downed helicopters with US casualties in Somalia in the past. Let us also consider the safety of civilian aviation. Assuming that airport security is strengthened sufficiently, far beyond today s level, to thwart would-be suicide hijackers. It would still be very unsettling under the current climate to know that the shoulder fired missiles can be purchased, transported and successfully deployed by a minimally trained person, a suicide bomber or not, near an airport or anywhere the aircraft comes within 15,000 ft of the ground. There are simply too large areas to be practically quarantined or protected effectively across the nation and around the world. Under the circumstance, the best action one can take to reduce aircraft susceptibility to IR based weapons systems (MANPADS) would be to minimize the IR signatures that the aircraft emits so that: Aircraft will have less chances of getting locked on and shot down by IR seeking MANPADS in low flying operations which are unavoidable to take off and land even for fixed wing aircraft. The areas to be protected around an airport or landing strip can be reduced to manageable sizes and shapes. For example, if we succeed in masking IR signatures of an airplane with the exception of the rear of the tail pipe or exhaust port, then the area to be quarantined will be a narrow strip of land of manageable length behind the plane from which the MANPADS could potentially be launched. In view of the above, Aspen Aerogels, Inc. strongly recommends to accelerate the development and deployment of the Aerogel Based IRCM s (ABIRCM s) so that the US aircraft, military and civilian, can be better protected against MANPADS in a much shorter period than otherwise. Reference 1.Puttre, Michael, Facing the Shoulder-Fired Threat, Journal of Electronic Defense, Vol. 24, No , pp. 38, ISSN X 6