DIA, 2010: estudo do AAWSAP recomenda como detectar veículos hipersônicos, inclusive os “projetados para serem indetectáveis”

UNCLASSIFIED//[FOR OFFICIAL USE ONLY, struck through] Defense Intelligence Reference Document Defense Futures 20 November 2010 ICOD: 30 August 2010 [DIA]-08-1012-001 Detection and High Resolution Tracking of Vehicles at Hypersonic Velocities

Detection and High Resolution Tracking of Vehicles at Hypersonic Velocities The Defense Intelligence Reference Document provides nonsubstantive but authoritative reference information related to intelligence topics or methodologies. Prepared by: Technology Warning Division (DWO-4) Defense Warning Office Directorate for Analysis Defense Intelligence Agency Author: AAP Person 83 (U) COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one of a series of advanced technology reports produced in FY 2010 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapons System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to [AAP Person 1] AAWSA Program Manager, Defense Intelligence Agency, ATTN: JUIAF - DI/DWO-3, Bldg 6000, Washington, D.C. 20340-5100.

Introduction An object is supersonic when its speed through the atmosphere is greater than the local speed of sound. The Mach number is defined as the speed of the object divided by the local speed of sound. For Mach numbers greater than 1 (supersonic flow), shock waves develop in the flowfield and near the surface of the object due to the air's compressibility. Traditionally, the lower Mach number limit for the so-called hypersonic speed regime is about Mach 5 (1.7 km/sec). "Low hypersonic" values range between Mach 5 to about Mach 10, while "high hypersonic" values range between approximately Mach 10 to Mach 30 or above. Mach 30 (10 km/s), for example, is close to Space Shuttle reentry velocity. Few objects can travel at hypersonic velocities. The most common object that we see moving at these speeds are meteors entering the Earth's atmosphere. As meteors fall to the Earth's surface, their velocities may reach 30 miles per second (48 km/s),[1] and their corresponding Mach number as they enter the upper layers of the atmosphere will exceed 150. Meteors are preceded by a bow shockwave as they compress the air immediately in their path. Temperatures and pressures increase dramatically across the shockwave to a point where the gases in air ionize and disassociate, leading to the emission of visible light and radio waves. These conditions also lead to rapid heating of the meteor surface causing them to fracture and break up as they enter the atmosphere. Optical and RADAR-based surveillance systems are now used to scan outer space to detect asteroids and other objects with orbits that may lead them to collide with Earth. A second class of hypersonic objects includes reentry vehicles moving into the Earth's atmosphere from orbit. In the case of a reentry vehicle returning from low-Earth orbit at 100 km altitude, the velocity of the vehicle will reach 8 km/s (about 5 miles per second). The Mach number of this vehicle will exceed 26.5 in the upper atmosphere. As the vehicle moves through the atmosphere, flow-induced drag forces will slow down the vehicle; if the vehicle has sufficient thermal protection, it can survive reentry and be recovered. A third class of hypersonic vehicles includes the reentry payload used in ICBMs (intercontinental ballistic missiles). The payload in these missiles is launched using a rocket that boosts them above the atmosphere to a suborbital velocity. The payload velocity may exceed 7 km/s as they reenter the atmosphere, equating to M > 23. The coupled high velocity and high kinetic energy of these objects creates an ionized wake and shock wave that can be used to detect their position and to determine their velocity. This information, along with their ballistic trajectory, is used to locate their target and the time to impact. A fourth class of hypersonic vehicles includes manned and unmanned rockets and aircraft. The North American X-15, for example, exceeded a speed of 7,274 km/hr in 1964, equating to about M = 6.5. This aircraft also exceeded 100 km in altitude on two occasions, qualifying the X-15 as a spacecraft. The SR-71 Blackbird, an air-breathing strategic reconnaissance aircraft, has exceeded Mach 3.2 at 80,000-ft altitude, and its actual maximum speed may have reached into the hypersonic flow regime. Other real and conceptual aircraft capable of reaching hypersonic speeds include the alleged Aurora SR-91 (Mach 4 to 6), the Boeing X-51, an unmanned Mach 6 scramjet, the HTV-2 from the DARPA Falcon project (designed for M=20 flight to low-Earth orbit), the HyperSoar (M = 12), the Russian Leninetz Ayaks, and the Skylon (designed for single-stage-to-orbit flights). Certain rockets are also designed to travel at hypersonic speeds. The Patriot missile, for example, travels at Mach 5, a high speed necessary for it to be able to intercept and destroy other missiles while they are in flight. There are a number of different techniques available to detect hypersonic objects and to determine their position, velocity, and trajectory. These detection methods can be broadly divided into electromagnetic, optical, and acoustic/seismic methods. Each method relies on the properties of the surface of the object to reflect incident radiation or upon the properties of the hot ionized gases caused by the bow shock and entrained into the object's wake. The theory of external fluid flow around objects in subsonic, supersonic, and hypersonic regimes will be reviewed and various detection methods will be compared in this report.

Chapter 4: Vision of Progress Over the Next 30 Years While there are several methods that can be used to sense high-speed supersonic objects, technology changes in aircraft will generate the need for newer detection and tracking techniques. Listed below are five important categories of objects capable of hypersonic speeds. Over the next 30 years, the ability to reliably and accurately detect them will be critical. • Space Debris - Technology is currently available to detect space debris using RADAR and cameras. Novel methods using coronographs[28] during daylight have been shown to detect the reflected light from millimeter-size debris particles in orbit, and existing telescopes are capable of detecting meteors that pose a risk to Earth. Space debris reentering the Earth's atmosphere can reach speeds of over 17,000 miles per hour or Mach 23. • Reentry Craft - The highest recorded speed for any manmade vehicle was the Apollo 10 reentry capsule in 1969. It reached a velocity of 24,790 mph, or Mach 36. Reentry vehicles are currently monitored by ground-based telescopes and RADAR and through satellite imagery. • Meteors - The systems used to monitor missiles and satellites based on RADAR and optical devices can currently detect and track meteors entering the Earth's atmosphere. Further development of acoustic and radio detection techniques should be pursued over the next 30 years. • Missiles - The Cold War generated the need for equipment to monitor hostile missile launches, to track their path, and to estimate the location of their targets based on ballistic trajectories. The United States Space Surveillance Network, for example, is composed of a worldwide collection of RADAR, electro-optical detectors, and passive RF devices that can track satellites, missiles, and aircraft. They maintain an inventory of satellites in Earth orbit and, through the Space Surveillance Telescope program (SST), asteroids and other faint objects in space are detected and tracked. GEODSS (Ground-Based Electro-Optica l Deep Space Surveillance) telescopes monitor space at 3 different locations around the globe with high enough resolution to detect a basketball 20,000 miles from the Earth. Continued vigilance from governments around the world will likely increase the development of technology to detect and track high-speed objects in the atmosphere and in space over the next 30 years with an emphasis on RADAR and optical detection. • Hypersonic Aircraft - Over the next three decades, hypersonic aircraft development will likely spur an increased need for new technology to detect their presence. While the X-15 rocket plane exceeded Mach 6 (4,520 mph) as early as 1967, continued development of high-speed aircraft will continue to meet needs in the following areas: o SSTO (Single Stage to Orbit) - Long the dream of NASA and space exploration enthusiasts, technology has been under development to replace the Space Shuttle using aircraft that can take off from a conventional runway and attain low-Earth orbit. The X-43A scramjet, part of NASA's Hyper X Program and fueled by hydrogen fuel was successfully tested in 2004. This aircraft is capable of 7,000 mph or Mach 9.8 flight. o Manned military jet fighters - The fastest military jet is the MIG-25 Foxbat at 2,115 mph (M = 3). The fastest U.S. jet is the F-15 at 1,875 mph (Mach 2.6). Current U.S. efforts are concentrating on unmanned vehicles, such as the X-43A. o Surveillance aircraft - The SR-71a "Blackbird" achieved 2,056 mph (Mach 3.3) in 1976 using an air-breathing engine. Its rumored replacement, the SR-91 Aurora, would have been capable of Mach 6. In 2008, the U.S. Air Force entered into an agreement to design a Mach 6 unmanned "blackswift" aircraft using a scramjet. o Passenger jets - The current record holder is the Tupolev Tu-144 "charger" at 1,553 mph (Mach 2.15). Reaction Engines Limited has proposed the A2 hypersonic passenger liner using liquid hydrogen to fuel the aircraft and to cool the wings and fuselage. This aircraft is expected to achieve Mach 5. In 2000, Russia and the People's Republic of China entered into a 25-year agreement to develop the Leninetz AYAKS hypersonic transport plane using kerosene fuel and a variety of techniques to attain Mach 8 to 10. An MHD (magnetohydrodynamic) engine is used to further accelerate combustion products produced by the engine. Lasers and RF generators are employed to disrupt the bow shock, reducing drag and doubling the velocity of the vehicle. o Stealth missiles - The USAF Falcon Project planned for building a Mach 6 HTV-3V "Blackswift" platform but was cancelled in 2008. The NASA X-51 scramjet vehicle is based on the Falcon scramjet and is scheduled for testing in 2010. This vehicle is capable of Mach 7+. DETECTABILITY OF NEW HYPERSONIC AIRCRAFT While conventional RADAR and optical systems may be able to track existing vehicles, future aircraft capable of Mach 8 and above are now being designed and tested. New propulsion technology and drag reduction techniques also offer new ways to detect such aircraft. Based on a review of hypersonic vehicle detection and tracking, four recommendations are made for research and technology development over the next 30 years to increase the detectability of hypersonic objects passing through the Earth's atmosphere. Recommendation #1 - Build a Database of the Wake Characteristics for Existing Aircraft There is considerable information about the aircraft contained within the turbulent wake that trails it. The wake provides an indication of the vehicle's path and its current bearing. By analyzing the Strouhal eddy formation, it is possible to ascertain its velocity and hydraulic diameter. The wake can also provide information on the chemical combustion products that can be obtained through LIDAR and can indicate the fuel used by the aircraft. Some aircraft, such as the X-43A and the proposed Reaction Engines Limited A2, use hydrogen as the fuel, so the absence of carbon molecules in their turbulent wakes could aid in their identification. Authors Mark Garnet and Aaron Altman from the University of Dayton[29] proposed the development of a database of turbulent wake data for conventional aircraft to allow their identification. They point out that, although the aircraft may be designed for stealth, their wakes cannot be hidden. They presented data on the unique characteristics that can be used to identify the wakes generated by the F-15, F-16, F-18, and B-52. They also point out the need for computational modeling of hypersonic wakes to predict the characteristic signature of new, unknown aircraft. A hypersonic vehicle database of wake characteristics for existing aircraft should be developed based on optical and Doppler RADAR data. Doppler RADAR provides information on turbulent intensities and eddy formation within the wake. Computational fluid mechanics models of hypersonic wakes have been done since the early 1960s, such as the work done by Zieberg and Bleich.[30] Such modeling work should continue capitalizing on the increasing computer performance that will be available during the next 30 years. Recommendation #2 - Exploit the Detectability of Hypersonic Aircraft Based on the Features That Allow Them To Fly Efficiently at High Speeds Several new propulsion systems for hypersonic aircraft will be tested over the next 30 years. These include pulsed detonation engines (PDE) successfully tested in 2008 by the Air Force Research Laboratory and Innovative Scientific Solutions, Inc. over the Mojave Desert. While these engines are capable of Mach > 6, they have one characteristic that makes them very detectable. The pulsed detonation of combustible fuel creates a wake with periodic bulges refer red to as "donuts on a rope." As mentioned earlier, measurements of the turbulent wake behind hypersonic aircraft can be used for detection, identification, and tracking. The AYAKS hypersonic transport plane under development in Russia uses an MHD engine, lasers, and RF generators to decrease aircraft drag. The lasers and RF ionize the air ahead of the aircraft, creating a plasma to disrupt the bow shock and significantly reduce aerodynamic drag. Drag reduction allows the aircraft to double its maximum speed. The RF and laser emissions from this aircraft can possibly be used to detect the aircraft in flight from groundbased antenna or telescopes or from satellites. The MHD engine also generates electromagnetic radiation that can possibly be detected. Every new propulsion or drag reduction system under development will have some characteristic that may make it more detectable from the ground or from satellite. The Aerospike engine proposed for the SSTO and under development by Rocketdyne and Garvey Spacecraft involves the use of a novel virtual Laval nozzle that is external to the engine. The IR emissions from an Aerospike engine may increase its detectability. Recommendation #3 - Explore the Detection of Vehicles Designed To Be Undetectable Over the next 30 years, hypersonic cruise missiles will have the ability to travel at speeds of up to Mach 8 decreasing the chances of being detected or defeated by antimissiles. The unmanned NASA X-51 tested in 2010 is capable of greater than Mach 7 (over 4,000 mph), for example, and is designed to be launched from a B -52. The DARPA/USAF Falcon Project has resulted in the testing of the HTV-2 at Mach 6. 7 over the Pacific Ocean, designed as a hypersonic cruise vehicle. Efforts to disguise aircraft through the use of novel vehicle shapes and stealth materials can also increase their detectability in other ways. Golovitichev and Hansson presented a paper in 1999[31] that stated the following: "The concentrated energy drag reduction concept has proven to be effective for the cruise range vehicles, preventing the missile deceleration with the benefit that the spike "products" could envelope the missile in a film of ionized gas which would be impervious to RADAR pulses, thereby rendering it electronically "invisible". The infrared penalty at close range would be significantly offset by the high speed of the flight." This discussion about the AJAX engine concerned the generation of ion combustion products that would be further accelerated by an MHD (magnetohydrodynamic drive). The increased number of various carbon-based molecules in the wake of this aircraft could be detected using LIDAR. The increased temperature near the surface of this aircraft would also increase its detectability due to increased emission of infrared radiation. For AJAX (AYAK) vehicles, development of enhanced LIDAR systems and IR detectors should proceed over the next 30 years to increase their detection and tracking. Recommendation #4 - Explore the Development of Novel Detectors One characteristic of hypersonic flight (M > 5) is the ionization of air in the region downstream of the bow shock and the disassociation of oxygen and nitrogen at very high speeds. When electrons recombine with ions generated by the shock, they emit electromagnetic radiation that can be detected. This radiation extends from the visible range, as evidenced by the glowing trail left by meteors entering the Earth's atmosphere, but the emitted radiation also extends into the ultraviolet and x-ray range. Although such electro-optical sensors are likely part of the existing DARPA/USAF space surveillance system, telescope systems that monitor the UV range should be developed, along with x-ray detectors capable of monitoring the atmosphere. Hypersonic objects passing through the atmosphere disassociate nitrogen and oxygen which recombine in the object's turbulent wake. During recombination, new molecules are created, including NO, NO2, ionized O and N, and combustion products.[32] LIDAR can detect the presence and concentration of these compounds in vehicle wakes and improved LIDAR systems should be a priority. As hypersonic objects pass through the atmosphere, the object becomes ionized with a significant positive charge. Technology should be developed to sense the flight of objects with an electrostatic charge as they pass through the atmosphere. SUMMARY Each detection system discussed in the previous section has both benefits and problems. A comparison of the various detection techniques is shown in Figure 19 based on their ability to detect specific properties, relative cost, and accuracy. Infrared detection systems and multispectral cameras installed on satellites, such as the KH11, provide surveillance of large portions of the Earth for possible missile launches, reentry vehicle trajectories, meteor wakes, and hypersonic vehicles. RADAR systems based on satellites, ships, and aircraft can detect the position and velocity of such hypersonic objects at varying range. AWACS, for example, can detect objects at up to 370 km with a resolution of 0.5 meters. TRADEX can track up to six objects at a distance of 1,400 km with an accuracy of 3 meters and a velocity resolution of 0.01 m/s. [Figure 19: table comparing radar, radio reflection detection, sky cameras/photographic methods, infrared, lidar, chronograph, infrasound and seismic detection by properties detected (distance, velocity, altitude), coverage (whole sky or directed), commercial availability, existing network, expense, and usefulness for detection of meteors, reentry vehicles and aircraft] Figure 19. Comparison of Detection Technology for Hypersonic Objects. LIDAR systems provide detailed information on velocity, temperature, particle velocity, and atmospheric composition along the path of the laser beam that can be used to interrogate vehicle wakes and exhaust plumes. Seismic and infrasound systems continuously operate and can provide information on the path followed by a high-speed aircraft or object by tracking its sonic boom and low-frequency acoustic signature. Finally, optical cameras aimed toward the Earth provide valuable information on hypersonic object tracks by recording their tracks. Aimed toward space, optical cameras are tracking asteroids and other spaceborne objects that may enter the atmosphere as a meteor posing a risk.