Τετάρτη, 1 Φεβρουαρίου 2012

T-50 vs F-22A. The technology of Quantum Well Imaging Photodetectors (QWIP) will upset the balance

Consider a QWIP technology “OLS-50M” installed in the PAK-FA. Such a device could be design-optimised for simultaneous detection and tracking of aircraft exhausts, jet-plumes and missile flares to ranges of 70 nm and beyond



Suppose the Russians don’t quite master stealth to the degree of the F-22A, but manage a RCS of 0.01 square metres from all aspects. The F-22A’s APG-77 will detect the PAK-FA at ~40 nm and the F-35’s APG-81 at ~30 nm. Passive electronic surveillance might increase detection ranges, but this still makes long-range missile shots problematic, as tracking depends upon the opponent emitting, which smart opponents will try not to do.
The PAK-FA’s radar can be expected to be an improvement on the IRBIS-E so at front-on aspects might detect the F-22A at ~15 nautical miles and the F-35 at ~28 nautical miles; and from side and rear aspects, the F-22A at ~43 nautical miles and the F-35 at ~51 nautical miles. 
Infrared sensors are the next growth area in air combat. Every air combat jet has unavoidable infrared signatures – converting kerosene into thrust at prodigious rates does that. The existing OLS-35, developed for the Su-35BM, is credited with the ability to detect a ‘fighter type’ target head on from 27 nautical miles, and from behind at around 50 nautical miles, through a 90° sector. It uses conventional detector technology, and provides similar performance to the Eurofighter Typhoon PIRATE infrared sensor.



 It is likely the PAK-FA will have infrared signature management as is found on the designs of the YF-23A, B-2A and the F-22A, but not on the F-35 
Advances in QWIP technology single chip imagers will see a new generation of infrared sensors deploy over the next decade. Not limited in infrared colour sensitivity like legacy bandgap imagers, QWIP imagers offer the potential to detect cooler targets are greater distances, and provide the high resolution required for standoff identification of targets. Above 10.2 micron band 10242 pixel longwave image produced by a US Army Research Lab / L-3 Cincinnati corrugated QWIP [no image enhancement applied], depicted below. QWIP technology is now available in the US, EU and Russia. QWIP based imaging Infra Red Search and Track (IRST) detectors can be “tuned” by design for sensitivity in a particular infrared band, using a fundamentally different detection technique to conventional “band gap” detectors where the material determines the colour sensitivity of the detector. QWIPs capable of simultaneously imaging in two, three or four infrared bands have also been manufactured and marketed. QWIP technology, therefore, opens up the potential for even greater detection ranges against targets cooler than what current production infrared sensors can track, and provide for much better infrared background rejection. 


Consider a QWIP technology “OLS-50M” installed in the PAK-FA. Such a device could be design-optimised for simultaneous detection and tracking of aircraft exhausts, jet-plumes and missile flares to ranges of 70 nm and beyond – the limiting factors are the size of the optics, cooling system and detector area. Russia has decades of experience in the integration of infrared sensors into its weapons systems, and QWIPs could well become the primary sensor and radar the secondary. This means that the F-22A AN/ALR-94 will be denied signals to detect and track the PAK-FA.
The ‘shooting match’ shifts from radar-centric to ‘infrared centric’. The problem here is that the PAK-FA will have it, the F-22A does not, and the ability of the F-35 EOTS and DAS to make long range aircraft detections and guide weapons is at best ‘unproven’. The F-35 systems have not been designed to be highly sensitive at the task of searching and tracking distant aircraft at those infrared colours where aircraft and their jet engines emit most of their infrared energy. An understanding of the physics, or for the ever-hopeful, a simple Developmental Test and Evaluation exercise will demonstrate this. With the Beyond-Visual-Range (BVR) radar detections being reduced to distances below 60 nautical miles and infrared sensor detection ranges growing beyond 50 nautical miles, a new generation of missiles will be required to dominate the battlespace. 
Russian missile companies have shown much more flexibility and adaptability in the design of missiles, so the PAK-FA could have a new-generation of shorter range, but higher agility missiles – a fusion of the ideas in the R-74 and R-77M, with a diverse mix of seeker heads. These missiles will likely be cued by the IRST sensor, be equipped with inertial midcourse guidance and, probably, mid-course guidance update capability transmitted either by radio, or possibly infra-red laser or millimetric wave links. Expect the PAK-FA to have vectored thrust and high levels of agility like the Flankers it is to either replace or complement. Long missile range requires large rocket or ram-jet motors and these heavy weapons lack the agility to pull high terminal ‘G’, and may be ‘ducked’ by the PAK-FA as easily as by the Su-35-1. 
The PAK-FA will use a new super-cruising engine, based on technology from the Al-41F series, so its tactic might be to maintain combat speeds of about Mach 1.5 and use a more compact version of the ramjet RVV-AE-PD. A supersonic launch enables a ramjet to light without a powerful booster – thereby denying an opponent the detection of the usual missile launch flare.


Fights between the F-22A and the PAK-FA will be close, high, fast and lethal. The F-22A may get ‘first look’ with the APG-77, the Advanced Infra Red Search and Track (AIRST) sensor having been deleted to save money, but the PAK-FA may get ‘first look’ using its advanced infrared sensor. Then, the engagement becomes a supersonic equivalent of the Battle of Britain or air combat over North Korea. The outcome will be difficult to predict as it will depend a lot on the combat skills of the pilots and the capabilities of the missiles for end-game kills. There is no guarantee that the F-22 will prevail every time.
The fate of the F-35 Lightning II would be far worse in an air combat environment challenged by the PAK-FA. If the Mach 1.5 PAK-FA is using its infrared sensor as the primary sensor and observes radio frequency emission control (EMCON), then the first detection by the F-35’s APG-81 radar could be at ~20 nautical miles or less with a missile launched by the PAK-FA’s infrared sensors already inbound from 60 to 70 nautical miles away. The PAK-FA could easily break to a direction outside the F-35’s AIM-120 engagement zone. 
The sustained turning performance of the F-35A Lightning II was recently disclosed as 4.95 G at Mach 0.8 and 15,000 ft. A 1969 F-4E Phantom II could sustain 5.5 Gs at 0.8 Mach with 40 percent internal fuel at 20,000 feet. The F-35 is also much slower than the 1960s F-4E or F-105D. So the F-35A’s aerodynamic performance is ‘retrograde’ when compared with 1960s legacy fighters. The consequence of such inferior JSF performance is that its DAS might detect an incoming missile, but the aircraft lacks the turn-rate to out-fly it. As the F-35 also lacks the performance to engage or escape, repeated ‘freebie’ shots from the PAK-FA could inflict high losses. Expect the exchange rate to be of the order of 4:1 in favour of the PAK-FA, possibly much higher. 


Russian aerospace companies have demonstrated an ability to outpace US aerospace manufacturers in terms of delivery of an operational capability and also the diversity of the capabilities of their weapons systems. The cumbersome US acquisition system, and marketing rather than technology driven aerospace industry, put the US at a distinct competitive disadvantage in rapidly adapting to an evolving threat environment. The most dangerous situation the US could face, is where the high and upwardly spiralling development and production costs of the JSF ‘cuckoo’ the available resources, which are needed to develop the advanced capabilities necessary to counter the new Russian PAK-FA, and the generation of new weapons which the PAK-FA will inevitably be armed with.

Complacency is not an option. Having ruled the roost for the decade out to 2015, the F-22A may be knocked off its perch by a newcomer, unless the US invests in new sensors, especially, and advanced technology Infra-Red Search and Track, stealth improvements and a new generation of missiles for the F-22 – assuming it even builds more than the token number of F-22s currently planned. The F-35 has already been neutralised and negated by the Su-35-1/35BM and will be substantively overmatched by the PAK-FA. (partially copied from http://spie.org/x27591.xml?pf=true&highlight=x2410&ArticleID=x27591 )



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