The next step beyond stealth is leading developers to the stratosphere to escape the growing air-defence threat. Malcolm Davis reports
American stealth technology was developed as a solution to the problem of penetrating Soviet airspace during the Cold War. The newest blue-skies thinking from US developers shows that the US Air Force (USAF) is reviving some Cold War ideas while also driving out of the atmosphere into the lower reaches of space.
Surface targets are protected by an ever-more sophisticated network of sea- or ground-based air-defence (GBAD) systems that are increasingly capable of detecting and tracking stealth aircraft. Such systems are becoming available for export, such as the alleged recent sale of four Ukrainian Kolchuga passive electronic support measures systems to China. The Kolchuga may offer the ability to track stealth aircraft via their electronic emissions and there are concerns that the system has also been transferred to Iraq.
Other counter-stealth techniques are widely known, including bistatic and multistatic radar systems, low-frequency radar, electro-optic and infra-red detection and even tracking atmospheric vortices produced by the aircraft as they pass over a sensor. Even given these capabilities, stealth will continue to remain important, and improvements in stealth technology are leading to a continuing 'stealth versus counter-stealth' race.
The development of more advanced 'double digit' surface-to-air missiles (SAMs), such as the Russian S-300PMU-2 Favorit (NATO reporting name: SA-10 'Grumble') and S-400 Triumf, offers much greater engagement range and speed as well as a higher probability of kill than older SAM systems. The increased use of sophisticated mobile short-range air-defence systems (SHORADS) and man-portable air-defence systems (MANPADS) is making it increasingly dangerous to operate below 15,000ft, as was the case in the 1999 Kosovo conflict.
By integrating low-altitude and high-altitude GBAD with fighter aircraft carrying beyond-visual-range air-to-air missiles (BVRAAMs), an adversary can dramatically increase the threat to 'low and slow' platforms that seek to penetrate, let alone survive, inside an integrated air-defence system while hunting for mobile targets.
One way to suppress advanced GBAD capabilities is to exploit global positioning system (GPS) and terminal guidance to strike with high precision at standoff range, while keeping the manned aircraft outside the threat envelope of more advanced GBAD capabilities. This assumes, however, that the location of adversary air-defence assets is known. As the Former Republic of Yugoslavia demonstrated by downing a USAF F-117A during the Kosovo war, a defender can hide or move its GBAD systems, then 'pop up' to surprise attacking aircraft.
There is less confidence that short- to medium-range air assets, which tend to predominate in most Western air forces, will have the opportunity to deploy to forward bases, or protect aircraft from attack once there. There is no guarantee that host-nation support will be forthcoming, as the current Iraq crisis illustrates.
A defender may seek to intimidate neighbouring states by threatening to use force, or as is clearly a problem in facing Iraq, there may be a basic lack of support in a region for a deployment of Western expeditionary forces. Even if forward bases are available, an adversary could raise the cost of an expeditionary force's entry by striking airbases with ballistic or cruise missiles. Likewise, naval aviation based on aircraft carriers could be threatened by naval anti-access capabilities such as shore-based anti-ship cruise missiles, quiet diesel-electric submarines, mines and small fast-attack craft armed with anti-ship missiles.
Airpower capabilities of the future could use longer range to operate outside the reach of an adversary's anti-access capabilities or compensate for a lack of host-nation support. There will also be increased reliance on cruise missiles like the MBDA Storm Shadow and the Cold War standby Raytheon Tomahawk Land Attack Missile.
The CIA's recent successful attack against suspected Al-Qaeda members in Yemen by an RQ-1 Predator unmanned air vehicle (UAV) armed with AGM-114 Hellfire missiles might indicate one strand in the future of warfare and highlight a different model for the future of airpower. The USAF has a long-standing discomfort with application of force by unmanned combat air vehicles (UCAVs), but Maj Gen Daniel P Leaf, USAF director of operational requirements for the Deputy Chief of Staff for Air and Space Operations, hints that future capabilities will outgrow this prejudice. However, until unmanned systems are both proven and prolific, manned combat aircraft will continue to remain essential to conducting high-speed air offensives.
Gen Leaf makes it clear that the F/A-22 Raptor will be of key importance in defining the nature of future air operations. The F/A-22 will 'supercruise' without its afterburner at M1.7 and will operate in the lower stratosphere, around 50,000ft, where it can exploit its stealth and speed, as well as its access to offboard sensors. Gen Leaf says that the operational experience gained with the F/A-22 will "teach us a great deal about how speed will influence air combat", particularly by compressing timelines both for aircrew and for enemy air-defence systems.
The Raptor will enable the USAF to experiment with altitudes to see where operational trade-offs begin to appear in terms of manoeuvrability and speed. Gen Leaf says: "Although there is serious thinking about what sort of capability the USAF should pursue for long-range strike, it is the F/A-22 which is the most advanced model we have to work with."
In Kosovo and Afghanistan the USAF has shown its post-1990-91 Gulf War shift to operating at medium- to high-altitudes to avoid thicker air defences at lower levels. Gen Leaf says that operational experience gained in these conflicts is leading to the USAF discarding 'low and slow' air operations. Instead of placing an aircraft at low altitude and at risk from advanced MANPAD and SHORAD defences, a move back to high- or very high-altitude operations eliminates those systems as a threat. Furthermore, with GPS-guided weapons, there is no need to penetrate an integrated air-defence system at low altitude in order to ensure accuracy.
Future capabilities, such as the US Small Diameter Bomb, will allow a single tactical aircraft to kill multiple targets, enabling a single F/A-22 to kill eight targets while supercruising at high altitude. Precision-guided munitions such as the Small Diameter Bomb can enjoy much greater standoff range due to added velocity imparted by the high speed of a supercruising delivery platform, and can be designed to employ speed as a means towards imparting destructive kinetic energy against a hardened target. There is no longer any air force rationale to go low and there are great advantages gained by delivering modern precision munitions from high altitude and at high speed. Joint warfare experts also sceptically note that basing air force assets further from theatre and flying them higher will make air component commanders less likely to lose control of their assets to joint-force or land-component commanders demanding close air support or battlefield air interdiction.
Once air operations move to higher altitudes, the key challenge is then to defeat modern long-range SAM systems. The S-400 Triumf, for example, can threaten aircraft up to 120,000ft. The first advantage to going high and fast is exploiting the upper stratosphere, or lower mesosphere, above 60,000ft but below 200,000ft. This opens up a new battlespace that has never been exploited in the past except by reconnaissance aircraft.
In seeking higher speeds, the physical dimensions of the battlespace extend not only upwards, but also outwards, increasing the area that GBADs need to cover. Within this larger realm of air operations, targets move much more rapidly and fully exploit stealth as well as countermeasures and suppression of enemy air defence capabilities. The higher the speed and the greater the altitude, the greater the ability for an aircraft to avoid SAM threats by manoeuvring out of threat envelopes.
Likewise, defending fighters would have less time to position themselves effectively to fire air-to-air missiles that even then might not be able to catch an aircraft at a much higher altitude, moving faster than current weapons are capable of flying. Gen Leaf notes that there is yet to be any serious thinking on how high speed and high altitude may affect tactics, but this will come, once experience is gained with the F/A-22 and the shape of future platforms begins to emerge in 2004.
The faster and higher an aircraft goes, the less manoeuvrable it will become. Therefore, rather than a tightly turning, energy-depleting dogfight, air-to-air combat might involve slashing attacks and escapes across long distances at high speed. This recalls the fast-penetration bombers and missile-armed interceptors of the Cold War, abandoned in recent years in favour of more flexible platforms.
By networking the aircraft to a 'mesh' of off-board sensor and control systems, the pilot would enjoy superior situational awareness and an edge in speed of response. At the same time, the superior speed of the platform and the speed of weapons will balance that situational awareness with a faster kill than the enemy. Indeed, modern air combat is already heading down this path with increased emphasis on beyond-visual-range engagements, and the procurement of longer-range, high-speed air-to-air missiles such as the AIM-120 Advanced Medium-Range Air-to-Air Missile (AMRAAM) and Europe's Meteor. Raytheon, for example, hopes to sell more than 1,000 AMRAAMs this decade to equip the Eurofighter strike aircraft (Jane's Defence Weekly 28 August 2002).
New solutions
A theoretical concept like Stratospheric Air Operations is being matched by conceptual studies towards developing and deploying a long-range strike capability to replace the USAF's fleet of B-52, B-1B and B-2A bombers. Gen Leaf emphasises that the term 'Long-Range Strike Capability' rather than 'Long-Range Strike Aircraft' is semantically important, showing that it is vital not to limit the capability within the performance envelopes of systems.
At the present time the programme has limited funding for conceptual studies but the nature of the capability is likely to be more fully developed by mid-2004.
The goal is to begin development of systems and platforms between 2015 and 2020 and to enter into operational service before 2030.
A range of system concepts is being explored. Gen Leaf mentions an enhanced 'B-2A-like' vehicle; a 'long-range arsenal aircraft'; a low-flying aircraft using the 'wing-in-ground effect'; and supersonic, hypersonic and sub-orbital platforms. He says that systems could include manned aircraft, a UCAV or a cruise missile, or potentially even directed-energy weapons (DEWs).
Even though there is no commitment at the present time to a hypersonic or high supersonic solution, work is under way to make such options viable for the Long-Range Strike programme. The Air Vehicle Design Branch at the Aeronautical Systems Center, Wright- Patterson Air Force Base (AFB) undertook a study of potential future long-range strike systems in 2001.
It envisages six notional concepts, ranging from a more evolved subsubsonic bomber; a M2.4 supersonic aircraft similar to that being considered for the US Defense Advanced Research Projects Agency Quiet Supersonic Platform; a M4.0 air vehicle that pushes the upper limit of the supersonic realm; two hypersonic concepts: a M7.0 and a M11.0 vehicle that will cruise around 150,000ft; and finally, an orbital vehicle that could be used equally for projection of force into space, or through space against terrestrial targets.
The study indicates that over a 25-year operational capability beginning in 2025, a M2.4 or M4.0 vehicle would offer the lowest life-cycle costs. It would also provide the quicker response capability desired to attack time-urgent targets without the high-development risk of the M7.0 and M11.0 concepts. For example, the notional M4.0 concept would deliver 32,000 lb of munitions to a target 6,000nm away in four hours (a 70% reduction in flight time in comparison to current subsonic bombers now operational, with flight time including take-off, mid-air refuelling and landing). The M2.4 concept takes an average six hours to deliver a comparable payload over a similar range.
While the lower-speed concepts do offer the advantage of less risk, the true benefit of exploiting stratospheric air operations comes from pursuing even higher speeds than the high supersonic, pushing aircraft into the hypersonic realm, and blurring the boundaries between air and space operations.
The Wright-Patterson Future Strike Aircraft study suggests that a hypersonic strike aircraft, deployed from the continental USA, would reach a target 7,000nm away in the same time as a forward-based M4.0 aircraft, but the hypersonic aircraft would be far more survivable.
A hypersonic aircraft would fly high into the mesosphere, verging on the boundaries of space. George K Muellner, vice president of Air Force Systems for Boeing, has noted that the development of future reusable space launch systems could directly lead to the development of long-range strike capabilities closer to the M7.0 or M11.0 concepts considered in the Wright-Patterson 'Future Strike Aircraft' study.
He says: "Work on reusable launch vehicle technologies is going to drive us down a path to develop a two-stage to orbit capability and that the first of the two stages may well be a hypersonic long-range strike aircraft."
A 'scramjet' engine would power such a vehicle during hypersonic flight. The National Aeronautics and Space Administration (NASA) X-43 Hyper-X programme is currently the leading US effort to develop effective scramjet engine technologies, aiming for test flights at M7.0, and ultimately at M10.0. The USAF 'HyTech' hypersonic research programme at the Air Force Research Laboratory at Wright-Patterson AFB is seeking to demonstrate the effectiveness of liquid hydrocarbon scramjets for hypersonic propulsion, with a hypersonic land-attack cruise missile the near-term goal and an M8.0-M10.0 strike reconnaissance aircraft the long-term goal.
The Lawrence Livermore National Laboratory (LLNL) is studying a third programme. This is the 'HyperSoar' concept, which is designed to skip along the top of the atmosphere between 100,000ft and 210,000ft, like a stone skipping across a pond. HyperSoar is designed to fly at M10.0, and either be used as a trans-atmospheric vehicle to strike rapidly at targets across the globe, or rapidly project military power into space at lower cost and with greater responsiveness than current space launch systems.
The HyperSoar's unique flight profile - part in and part out of the atmosphere - would allow it to avoid thermal-heating challenges that plague endo-atmospheric hypersonic designs which require the use of thermal protection, or hydrocarbon fuels as a heat sink, all contributing to added weight, cost and reduced payload.
Hypersoar would not need to use a technologically challenging scramjet, but instead would use a combined-cycle rocket engine.
The concept of stratospheric air operations could be further enhanced by combining very high-speed, high-altitude platforms with the precision and speed of DEWs such as high-energy lasers and microwave weapons.
A long-range strike platform dashing into an adversary's airspace at M11.0 at very high altitude would rely on precision guidance to strike targets rapidly, but current explosive weapons are slow compared to the potential that DEWs could offer.
DEW technology is already well advanced for the purposes of missile defence and development of the technology looks set to accelerate in the next 10 years largely, as a result of missile-defence requirements. In particular, the USAF YAL-1A Airborne Laser (ABL) aircraft is into the flight-testing stage with an initial operational capability of four YAL-1A aircraft by 2006. The ABL is designed to shoot down fast-moving ballistic missiles in their boost phase from 45,000ft at a range of 644km.
Although the greatest progress has been made with more bulky chemical lasers such as that used by the ABL, there is more operational potential for compact solid-state laser technologies which could be incorporated into tactical aircraft such as the F-35 Joint Strike Fighter or even a future long-range strike platform.
Prof Paul Rogers, from the University of Bradford, UK, writes that DEW systems will enable the USA to intervene militarily in a way that is "extremely fast and accurate and virtually invulnerable to direct countermeasures.
It would provide the United States, within eight to 20 years, with the means to intervene with impunity - a military capability coming close to 'ideal' ". The ability to strike at soft land-based targets such as SAM sites, or attack an adversary's low and slow aircraft at the speed of light, from very high altitude would dramatically enhance the potential of airpower to dominate a battlespace from the outset of a conflict.
A growing requirement for airpower is to rapidly attack and destroy hardened targets such as buried command bunkers or underground weapons of mass destruction laboratories.
DEWs may enhance this capability even further, given the potential of microwave weapons.
Microwave weapons use radio-frequency energy to destroy electronics. There is considerable discussion about the possibility of deploying high-powered microwave (HPM) weapons on UCAVs, and there would be no reason that a larger platform operating at very high altitude would not be able to detect and strike targets with HPM weapons, once again at the speed of light.
In particular, microwave weapons could strike at hardened bunkers otherwise impervious to anything but nuclear weapons. The intense beam of microwave energy could be directed against the target's communications antennas, destroying the systems inside.
In exploiting high speed and high altitude to deliver an ability to dominate the aerospace components of future wars, it becomes clear that the distinction between air and space blurs as air forces rely increasingly on space-based systems for combat support.
The ability of an F/A-22 to connect to a space-based intelligence, surveillance, target acquisition and reconnaissance (ISTAR) network, supported by communications satellites, access data on the adversary that is being gathered by space-based sensor platforms, and have that data sent directly into the Raptor's cockpit, allows rapid situational awareness and a war-winning advantage.
Likewise, a long-range strike platform can exploit space-based ISTAR capabilities to understand the highly dynamic battlespace around it, quickly re-task its munitions to different targets, or control hypersonic UCAVs to destroy detected air defences.
Ultimately, space-based weapons such as the Space-Based Laser under development by Boeing, may be able to strike slower-moving aircraft and cruise missiles from orbit, allowing high-speed manned strike aircraft to follow. Depending on what emerges from the Long-Range Strike programme, the option of attacking terrestrial targets from orbit or in a sub-orbital approach may even emerge.
Through exploiting trans-atmospheric vehicles or orbital strike capabilities, any target is a mere 45 minutes away. At that point the enemy's air-defence task begins to look more like missile defence.
Malcolm Davis is a lecturer in defence studies at the Joint Services Command and Staff College, Shrivenham
Serb policemen and Yugoslav army personnel inspect the wreckage of an F-117 stealth aircraft, which was shot down near Belgrade on 27 March 1999. Stealth technology is not invulnerable to attack from ground-based air-defence systems. 'Low and slow' platforms will always be vulnerable to 'pop up' attacks from the ground
(Source: PA)
A model of an F-117A stealth aircraft which was paraded in Belgrade on 29 March 1999 to mock the USA after an F-117 was shot down near Belgrade two days earlier. Stealth technology is not invulnerable to attack from ground-based air-defence systems. 'Low and slow' platforms will always be vulnerable to 'pop up' attacks from the ground
(Source: PA)
The F/A-22 Raptor operates up to around 50,000ft. Operational experience gained with the stealth aircraft will help developers assess how speed will influence air combat
(Source: Lockheed Martin)
The Predator RQ-1 unmanned air vehicle armed with Hellfire missiles offers another option for the future of airpower
(Source: General Atomics)
X-43A Hyper-X leaves NASA Dryden Flight Research Center for its first free-flight trial on 2 June 2001
(Source: NASA Dryden Flight Research Center)
X-43A Hyper-X leaves NASA Dryden Flight Research Center for its first free-flight trial on 2 June 2001
(Source: NASA Dryden Flight Research Center)
Research to test the effectiveness of liquid hydrocarbon scramjets is being conducted for the HyTech programme by the Air Force Research Laboratory
(Source: Air Force Research Laboratory)
The 'HyperSoar' concept is designed to skip along the top of the earth's atmosphere to strike rapidly at targets across the globe
(Source: Lawrence Livermore National Laboratory)
The 'HyperSoar' concept is designed to skip along the top of the earth's atmosphere to strike rapidly at targets across the globe
(Source: Lawrence Livermore National Laboratory)
The USAF YAL-1A Airborne Laser aircraft is into the flight-testing stage with an initial operational capability of four of its aircraft by 2006
(Source: Boeing)
