Grisha's Stealth \xc2\xabPidgeon Shoot\xc2\xbb

Colonel Medved's observations on the Russian effort to develop and deploy a new generation of digital VHF search and acquisition radars to support Ground Controlled Intercept (GCI) and Surface to Air Missile (SAM) batteries reflect very closely a number of items published in the Russian military and industry press.

The loss of the F-117A Nighthawk callsign Vega 31 in Yugoslavia was a wakeup call which has evidently not been heeded in the West. The Serbians disclosed only that "unspecified modifications" were made to the P-18 Spoon Rest VHF acquisition radar which provided the SA-3 Goa battery with target location, evidently accurately enough for several salvoes of SA-3 command link guided missiles to inflict fatal damage on 82-086 resulting its loss. The Serbian missile battery, commanded by Zoltan Dani, used pooled intelligence data and intermittent track data from previous raids to position the SA-3 battery and Spoon Rest for an ambush, which succeeded.

No less interesting was a comment made by an irate NNIIRT engineer to US analyst Richard Fisher two years later, that the P-18 Spoon Rest in question was covertly subjected to the NNIIRT digital solid state upgrade, in violation of the arms embargo on Serbia, and that the Serbians in a quid-pro-quo deal provided the upgrade package to the Chinese, who are the world's largest operator of the Spoon Rest VHF radar, with at least 65 deployed HQ-2 SAM batteries.

China remains the world's largest user of the P-18 Spoon Rest VHF radar family, deployed to support at least 65 batteries of the HQ-2 SAM. Russian industry alleges that China stole the NNIIRT digital upgrade package designed for Russian built P-18s for their own use. Depicted a Chinese built YLC-8 VHF radar, based on the P-18 (via Sinodefence.com).

This range chart is based on publicly released Russian data, and may understate range performance for the 55Zh6 Nebo UE. Note that the cited RCS is for the given radar band, and for a nominally stealthy aircraft will be much lower for a given aspect in the S-band and L-band compared to the VHF-band.

Russian industry publications state quite bluntly that US stealth designs have been largely optimised to defeat decimetric and centimetric band radars by shaping and the use of absorbent materials. The Russians have also observed publicly that the long wavelength of the Russian VHF band radars makes defeat by shaping difficult if not impossible, and that the thickness of absorbent coatings required to defeat VHF band radars would be prohibitive.

These are correct observations. The shaping features of US stealth fighters are dimensionally such that they fall into the resonance and Raleigh scattering regimes for VHF band radars, where shape has little impact on the Radar Cross Section. Their observations on skin depth are also correct, as resistive and lossy materials always exhibit greater skin depth than conductors such as aluminium skins.

So a fighter with stealth design features faces an interesting challenge when confronting a VHF band radar. Most of the carefully faceted, serrated and blended shaping features so effective at beating decimetric and centimetric band radars will appear as blobs to a VHF radar and reflect across a wide range of angles, losing their capability to scatter impinging radiation away from the radar illuminating the aircraft. The shaping of the planform is also less than entirely effective, unless it is very disciplined in the manner of the Northrop YF-23A or B-2A designs.

The issue of skin depth is also of concern. Surface coatings designed to attenuate creeping surface waves in the decimetric and centimetric bands will typically be too thin to cope with VHF band radiation, which will penetrate through to the underlying skin panel and structural materials, which will likely be electrically conductive. While a well shaped stealth fighter will have a lower VHF band signature than a legacy fighter festooned with external fuel tanks and radars, it will certainly not be a marble or tennis-ball sized reflector.

For instance, let us consider the F-35 JSF in the 2 metre band favoured by Russian VHF radar designers. From a planform shaping perspective, it is immediately apparent that the nose, inlets, nozzle and junctions between fuselage, wing and stabs will present as Raleigh regime scattering centres, since the shaping features are smaller than a wavelength. Most of the straight edges are 1.5 to two wavelengths in size, putting them firmly in the resonance regime of scattering. Size simply precludes the possibility that this airframe can neatly reflect impinging 2 metre band radiation away in a well controlled fashion.

The only viable mechanism for reducing the VHF band signature is therefore in materials, especially materials which can strongly attenuate the induced electrical currents in the skins and leading edges. The physics of the skin effect show that the skin depth is minimised by materials which have strong magnetic properties. The unclassified literature is replete with magnetic absorber materials which have reasonable attenuation performance at VHF band, but are very dense, and materials which require significant depth to be effective if lightweight. The problem the JSF has is that it cannot easily carry many hundreds of pounds of low band absorber materials in an airframe with borderline aerodynamic performance. Some technologies, such as laminated photonic surface structures might be viable for skins, but the experimental work shows best effect in the decimetric and centimetric bands. Thickness again becomes an issue.

The reality is that in conventional decimetric to centimetric radar band low observable design, shaping accounts for the first 10 to 100 fold reduction in signature, and materials are used to gain the remainder of the signature reduction effect. In the VHF band shaping in fighter sized aircraft is largely ineffective, requiring absorbent materials with 10 to 100 fold better performance than materials currently in use. In the world of materials, getting twice the performance out of a new material is considered good, getting fivefold performance exceptional, and getting 100 fold better performance requires some fundamental breakthrough in physics.

One possible strategy which may be viable against VHF band radars is active cancellation, where the aircraft emits a waveform identical to the impinging threat radar waveform, but out of phase so the two cancel each other out. This is not feasible in the upper bands, but is feasible in the lower bands, assuming a suitable VHF antenna can be integrated without compromising microwave band radar signature. The drawback of active cancellation is that the opponent can deploy VHF band passive receivers and simply listen for the sidelobes emitted by the active cancellation system to track the aircraft.

As the JSF, like the retired F-117A, is totally reliant upon stealth for survival, in an environment with VHF threats it has no simple fallback technique other than staying on the ground in its hardened shelter. This is unlike the F-22A which has supersonic cruise to fall back upon, and is harder to acquire by missile seekers since its microwave band stealth is so much better.

What is abundantly clear is that VHF radars will have much better detection performance against fighter sized stealth aircraft, compared to decimetric and centimetric band radars.

The numerous Russian publications covering the Nebo EU and Nebo SVU indicate that these are modern designs, with the full suite of digital signal processing and data processing techniques applied. The might operate in the same VHF band as the 1943 GEMA Mammut and Wassermann radars, but they are substantially new technology designs using state of the art technology.

The smaller Nebo SVU, described in a Russian press release as "... the Nebo-SVU mobile VHF radar with an active phased-array antenna system featuring unique capabilities to detect stealthy aerial targets...", is especially concerning from a strategy perspective. It is the most mobile VHF acquisition radar ever built, and its angular error performance was clearly engineered so it can be used as a SAM battery target acquisition system. Its performance is so close to the 64N6E Big Bird family of radars as not to be an accident.

How was such high angular measurement accuracy achieved in a VHF radar? Clearly the re-engineering of the conventional Nebo SV into the active array (AESA) Nebo SVU was done with this aim. The Nebo SVU can provide high beamsteering agility, within a limited angular range compared to a centimetric band AESA, which allows it to perform high speed electronic sequential lobing to emulate highly accurate monopulse angle tracking techniques. The threefold disparity in elevation and bearing accuracy simply reflects the respective aspect ratios of the arrays used.

The error box of the Nebo SVU is sufficiently small to permit a SAM or AAM with an active or infrared seeker to be flown near enough to the target to acquire it and initiate terminal homing. Colonel Medved's observations are consistent with published specifications for these VHF radars.

Whether the Nebo SVU is used as a cheaper substitute for a 64N6E or paired with a 64N6E, clearly the radar has what it takes to cue a 30N6E series engagement radar. If these systems are all networked following current Russian practice, the battery's 5N63 / 54K6E series command post can launch the missiles remotely and datalink them to the aimpoint through most of the flight trajectory. When near enough, the missile switches to its own terminal homing seeker to complete the engagement.

What the Russians have not disclosed, but is clearly obvious, is that pairing the Nebo SVU and 64N6E allows the operators to discriminate between a low observable and conventional radar target and adjust tactics accordingly. If the target is invisible on the decimetric band 64N6E but visible on the VHF band Nebo SVU, then clearly it is low observable, and a missile trajectory flown under datalink control using updates generated by the VHF radar is needed, rather than a conventional engagement sequence where the 30N6E locks up the target and autonomously completes the engagement. Missile range performance permitting, this opens up other options such as flying a 'dogleg' curved missile trajectory to effect a beam attack terminal phase, so the missile's seeker is illuminating the less stealthy beam aspect of the aircraft rather than its most stealthy front aspect.

Once the Russians deploy and market this capability, we can expect a follow-on effort by less technologically capable players to adapt many legacy SAM systems to perform in a similar fashion. While the S-75 / HQ-2 / SA-2 Guideline and S-125 / SA-3 Goa are not taken seriously by contemporary Western planners, supported by an accurate digital 3D VHF radar in the class of the Nebo SVU, with frequency agile digital datalinking and a terminal homing seeker, they become viable again. Serbia and Saddam's Iraq both experimented with the retrofit of infrared AAM seekers on legacy Soviet era SAMs, and this is not outside the reach of Iran, or North Korea. There is no doubt that it is within the reach of Chinese industry and academia, who have already engineered 2D derivatives of the Spoon Rest. The Chinese would have no difficulty in engineering an indigenous Nebo SVU lookalike.

The US has enjoyed an unchallenged technological monopoly on stealth capabilities for almost three decades, and the notion that potential opponents would sit by idly is not realistic. The Russian effort in VHF radar, and also surface wave HF radar, clearly shows that they have been thinking long and hard about how to blunt the sharp end of US capabilities. Unless the US makes a major investment in improving VHF band stealth materials, and in parallel, develops credible VHF band jamming capabilities, it will lose enough of its advantage to suffer a major loss in strategic potential.

S-300PMU-2 Favorit / SA-20 Gargoyle / S-400 Triumf / SA-21 Growler

48N6 Missile Launch (above) and road mobile 5P85TE TEL (below). The S-300PMU is often labelled "Russia's Patriot".

SA-10/20 Missiles
SAM Specifications	5V55K	5V55R	48N6	48N6E2	Характеристики ЗУР	5В55К	5В55Р	48Н6	48Н6E2
SAM System	S-300PT	S-300PS/PMU	S-300PM/PMU-1	Favorit		С-300ПT	С-300ПС/ПМY	С-300ПM/ПМY-1	Фаворит
Designer	MKB Fakel				Разработчик	МКБ "Факел"
Manufacturer	PO LSZ				Изготовитель	ПО "ЛСЗ"
Status	in service, out of production		in service		Состояние	на вооружении, сняты с производства		на вооружении
Engagement Envelope -range [NMI] -altitude [ft]	25.0 N/A	2.7-40.5 82-82,000	81.0 N/A	108.0 N/A	Зона поражения, км - дальность - высота	47 N/A	5-75 0,025-25	150 N/A	200 N/A
Target max speed [KTAS]	N/A	2300			Максимальная скорость цели, км/ч	N/A	4300	6450	7500
SAM max speed [Mach]	< 6.7	< 6.7	< 7.0	< 7.0	Максимальная скорость ЗУР, м/с	до 2000	до 2000	до 2100	до 2100
Weight [lb]	3267-3311	3675.5	3973.5-4194.0	N/A	Масса ракеты, кг	1480-1500	1665*	1800-1900	N/A
Warhead weight [lb]	293.6	432.7	315.7	397.4	Масса БЧ, кг	133	196	143	180
Warhead type	Blast-fragmentation				Тип БЧ	осколочно-фугасная
Guidance system	Command link		Track via missile		Система управления	радиокомандная	комбинированная через ракету
Length [in]	285.4	285.4	295.3	N/A	Длина ракеты, м	7,25	7,25	7,5	N/A
Diameter[in]	20.0	20.0	20.4	N/A	Диаметр корпуса ракеты, м	0,508	0,508	0,519	N/A
Tail span[in]	44.25	44.25	44.65	N/A	Размах оперения, м	1,124	1,124	1,134	N/A
Number of stages	1	1	1	1	Число ступеней	1	1	1	1
Motor type	Solid propellant				Тип двигателя	твердотопливный
Motor burn duration [sec]	8-10	8-10	< 12	N/A	Время работы двигателя, сек	8-10	8-10	до 12	N/A
Load factor limit [G]	N/A	N/A	25	N/A	Располагаемые перегрузки	н/д	н/д	25	н/д
Storage life [yr]	10	10	10	10	Гарантированный срок хранения в ТПК, лет	10	10	10	10
*including launch tube - 5170 lb					* с контейнером - 2342 кг

The 30N6E Flap Lid series of engagement radars for the S-300PMU SAM systems are modelled on the US MPQ-53 Patriot radars. The radar can be deployed/stowed for "shoot and scoot' operations in a mere 5 minutes.

Late variants of the Fakel 48N6 SAM include a directional warhead intended to increase lethality against ballistic and aircraft type targets. While the 48N6 is a direct replacement for the command link guided 5V55 in early S-300PT/PS/PMU batteries, it is far more capable with Track Via Missile (TVM) terminal homing similar to the MIM-104 Patriot, and datalink aided midcourse guidance. Enhancements to later variants include more intelligent autopilot algorithms to maximise range. The extended range 48N6DM now deploying with Russian S-400 / SA-21 Growler batteries is claimed to exceed a range of 200 nautical miles against an aerial target (Fakel).

The latest addition to the formidable S-300PMU family of SAM systems is the Fakel 9M96E and 9M96E2 agile SAM/ABM interceptor missiles (above), direct equivalents to the Lockheed-Martin PAC-3/ERINT family of missiles. These weapons have inertial midcourse guidance and active radar terminal seekers, with combined canard and thruster controls to maximise G capability at all altitudes. Both weapons were designed from the outset as dual role, and are intended to allow an S-300PMU series battery to engage ballistic missiles, aircraft at all altitudes, and precision guided munitions targeting the battery elements. The 9M96 series weapons are like the 48N6 series 'cold launch' ejection designs, and a four round launch tube package can replace a single 48N6E series launch tube on the 5P85 series TEL (below). The 9M96 series weapons are part of the S-400 / SA-21 Growler system, but may also appear in block upgrades on the later S-300PMU variants (lower image © Miroslav Gyűrösi).

Patriot PAC-3 interceptor launch (above), and MIM-104 Patriot PAC-1 launch (below) (US DoD).