The International Rafale forum

Dossier Rafale :


The sensors

1/ The RBE-2

At the beginning of the programme, it was envisaged to equip the Rafale with a conventional mechanically steered antenna : the RDX.

But the "omnirole" and growth requirements wouldn't have been met with such a solution. Thus, the RDX was dropped (and later evolved toward the RDY).

At the time, a new kind of solution seemed ideal for the task : the electronically steered array. Because the AESA (Active array) was still out of reach, France chose to start with the passive array (PESA), with further upgrade in mind.

The electronically steered antenna brings capabilities far out of reach for conventional arrays (MSA). This radar is made just like an MSA for the TWT tube (power plant), and the T/R module. But instead of the mechanics to steer the array, it uses phase-shifters networks both for azimuth and elevation. This make the beam very agile, inertia free. The extreme speed also always to emit much less power, enabling LPI operations.

(Side note : of course, the choice of ESA was made by voluntarily sacrificing the enormous gimbals and range that a mechanical array would have allowed, considering that compensations would be enough.)

The high beam agility also allow to interleave different modes, such as terrain following and air-to-air scanning. For this purpose, the signal processor can cope with more than a billion operation per second (this data was for the mid-90s, and may have improved a lot since the F2).

In 2008 for the F3 standard, the different radar modes should be :

• air-to-ground/Surface : detection of fixed and mobile targets, SAR, 2D mapping (recon before strike), 3D mapping for high speed a very low level terrain following/avoidance (100 feet and 5.5g accelerations), navigation re-calibration, detection of sea targets ;
• air-to-air : TWS (with a range of 100km in look down, strengthened tracking of 8 prioritized targets, on a total of 32, and 4 missile datalinks), PDS (Plan De Symetrie : vertical scan), dogfight (with automatic IFF interrogation).

All those functions are included in a 270kg radar, which is good regarding the fact that it's better than both the 330kg RDI (Mirage 2000C) and the 230kg Antilope V (Mirage 2000D).

Though the air-to-air range is considered as poor compared to its competitors, but it is nuanced by the fact that Rafale is part of a network, especially in France, with AWACS etc.

When it comes to exportation, the range argument is nonsense since Rafale has always been proposed with an AESA array improving the range by 30 to 60 %.

Due to its high agility beam, the radar can scan anywhere in a +/-60 degrees cone, for example "track here while scanning there" (an target leaving a formation won't be lost). It can switch from low frequency to high frequency automatically to as to improve tracking data according to the radial speed of the target. Overall, the radar is very strong against ECM and also maneuvers such as the "beam". It can also distinguish between different aircraft in a close formation.

The fixed array also helps at reducing the aircraft RCS and LPI operation can be set before flight, so as to prepare different modes.

All those functions are used through a refined interface so as to make the pilot work easier.

As said at the beginning of this part, the RBE-2 is built with growth potential in mind. Also, by 2012, every Rafale with use the AESA (it takes 30 minutes to replace the PESA by the AESA). This array is made of 1001 independent modules (GaAs). This array increase the range by 50% and thus greatly increase the scanning volume (and thus the number of tracked targets). Modules can be regrouped for different tasks. Though the radar will be more expensive to buy, it will also be much cheaper to maintain, the AESA being much more reliable : such a radar may never need to be taken off for maintenance during its whole service life.



2/ Spectra

Spectra (Système de Protection et d'Evitemment des Conduites de Tir contre le RAfale : protection and avoidance of shootings against the Rafale) is a term used to designate the counter-measure means of the Rafale. Fully integrated to the airframe, so as not to occupy precious external stations, it is made of a full EM, laser and infrared spectral covering on 360°. It also manages the jammers and decoys. It is managed by three computer (GIC : Gestion de l'Interface de Compatibilité). The components are :

• EM detection : 3 detectors. One on each air intake, they are shaped so as not to compromise the airframe RCS, and the last at the top of the vertical fin. Each covers 120° ;
• laser detection : 3 "DAL" (Détecteur d'Alerte Laser). One on each side of the nose, the last on the rear side of the box at the top of the fin ;
• infrared alert : 2 DDM (Détecteur de Départ Missile), one on each side of the box at the top of the fin. They are made to detect missiles during their burning phase (launch) ;
• active jammers : made of AESA, one at each of the canards roots, and one (maybe) at the root of the fin.
• Chaff and flares dispensers : situated on the fuselage, near the trailing edge of the wing, and above, oriented upward.

Note : the above data is not certain, not reliable. Different sources give different data, depending on the year, development stage, etc.

So, Spectra works in all spectrum, on 360°, and is able to :

1. detect passively any source with an accuracy below 1° ;
2. identify it according to a signal database ;
3. hierarchize the threat ;
4. locate it (with range estimate) and show the pilot, according to the terrain, threat area and safe area so as to choose the best way possible. This localization can cue a missile so as to make the Rafale able to defend.

Of course, the purpose is to detect so as we won't have to jam. But if needed, it can jam with a very accurate beam (compatible with the EM detector accuracy) so as not to strike other ESM on other threats. It can also decoy with chaff, flares, and electro-optical flares) automatically and propose best adapted maneuvers to the pilot.

It's been also said explicitly that Spectra contribute to the discretion of Rafale, with special technics (dedicated to Rafale) so as to greatly reduce the aircraft RCS. This is accredited by the building of four anechoid chambers and the very high price of the system (more than the radar, or the engine).

Weighting 250kg, Spectra brings new technologies for France, such as interferometry, electronically steered array (active), digital processing, solid state transmitters. It isn't limited to the aircraft protection, it also has a small SIGINT/ELINT ability.

France constantly work on improving the signal database, and the DDM will be replaced by 2012.


3/ The OSF (a.k.a. FSO)

The OSF is used for mainly for air-to-air (this is why it is above the nose), but also air-to-ground and air-to-sea detection. It is made of :

• an infrared sensor (IRST), dual band (3-5µm and 8-12µm) so as to detect even stealth targets by day and night, at more than 100km, with an angular multi-target tracking capability. Of course, it is not prone to EM jamming, and does not suffer from maneuvers like "beam" ;
• a TV camera associated with a laser range-finder. The camera allows the pilot(s) to : identify a target at long range (up to 50km depending on the size), check its weapons (the pilot will then tell Spectra about it), assess battle damage, count the aircraft in a close formation, all of this at long range, well before visual range. The camera automatically points the most threatening target. The laser range-finder also allows for a stealthy firing solution provided the target has no laser detector (a lot of fighter aren't equipped yet). But its range is limited to 30 to 40 km, depends on the LCS (Laser Cross Section : is the target big ?) and can't cope with fogs and clouds.

The OSF can also work as a FLIR, but its position above the nose compromises it.

Works are on progress for a replacement in 2012.


4/ Link 16, radio, datalinks

Though Link 16 isn't a sensor, Rafale uses datalinks as a mean to be aware of what is going on all around it, passively.

This datalink allows the Rafale to keep constantly in touch with other aircraft (Rafale, allied fighters, AWACS) and ground/sea stations, so as to exchange data every time about everything.

Rafale is equiped with the MIDS-LVT, weighting 29kg, able to transmit at 100kb/s on 360°. The communication can be encrypted and remain discreet so as to exchange data about fuel quantity, weapons left, targets...

An alternate datalink is available for non-NATO nations.

Radio is also protected, and is compatible with fixed frequencies, Have Quick II, Saturn and Crypto (for voice but also other data).

In the future, Rafale will also control UCAVs and receive a SATCOM antenna.

Is it known when the AESA jammers were introduced? I suppose they were not available on F1 standard aircraft and mean to remember that older sources stated PESA.

I think they were introduced with the F2. But i've nothing to confirm this.

Thales' page on SPECTRA; does not give specs yet tells a lot...
in between the lines.
http://www.thalesgroup.com/Portfolio/Defence/Aerospace_Product_SPECTRA/?pid=1152

I think it's an interesting picture :

According to the Air & Cosmos Hors Série "Le Rafale au combat" published in 2010,


Spectra development is € 3 Bn...

That's one third of the total R&D costs of the whole programme.

In the end, Spectra is 10% of the cost of each Rafale.

32 upgrade kits have been ordered to enhance the radios...

First, spotters had seen the B324 with a new antenna on the dorsal spin : that was the new V/UHF antenna. The new position is intended to avoid masks from heavy configurations (I hope this is understandable in english).

The Saturn post is also improved to cope with more frequencies, because in Afghanistan, radios are saturated (because of anti-IED measures for example).

Updates about the OSF :


Seen in DSI (2009) : the OSF is as costly as the RBE-2.


With DSI in 2010, we have learnt that OSF-IT has been ordered for both the 4th batch (60 unit) and the 3rd (but only 49 units) !


OSF-IT is an OSF with :

• upgraded electronics so as to treat obsolescence ;
• wider sensor for improved range ;
• near IR operation to make the TV more capable in difficult weather ;
• increased processing power which should ease the implementation of more capabilities (zoom for example) ;
• NO IRST/FLIR ;
• BUT STILL THE ROOM FOR IT !

According to A&C in 2009, OSF-NG would appear with the 5th batch, with an improved IR channel. DSI didn't agree and talked about a really interesting and different track : HI-RES LASER IMAGERY -a non-EM radar ?-
In 2010, DSI also write that a new CCD sensor for the TV channel is beeing studied for futur upgrades.



Erratum about the OSF :


In Fox Three n°14, Dassault write that the current FSO works in the 8-12µm band. This is extremely surprising since up to now, EVERY sources told both 3-5µm and 8-12µm (FLIR + IRST).
Their claim that an improved IR channel is being developped either gives credits to what A&C published in May 2009 about the OSF-NG or tell us that if required by another customer, such an IR channel could be added to the FSO-IT.

However, the future of FSO is unclear.

Updates about Spectra :


DDM-NG :

The new DDM uses a dual band IR array with a much better resolution, and much better softwares so as to reduce the false alarm rates. Today, pilots tend to disconnect the current DDM, because they automatically dispense flares and chaff, but the false alarm rates make it waste the chaff/flares.

The new DDM-NG is capable to identify a missile by analysing its trail, and thus can propose the best defensive maneuvers to the pilot. It is said that DDM-NG will provide alarm against newest SA7 which are small and discreet missiles.

A MAWS may be integrated by 2020.

In 2009, DSI reported that currently, Spectra can provide accurate data (?) about air threats up to 180 km away. In A2G, it can detect, classify, localize threats and jam the most menacing.

Last point, for the 4th batch, Rafale will carry twice as many chaff/flares as now (from 32 60mm cartridges to 64 40mm).

I suppose DDM/DDM-NG are launch detection systems only and that a real MAWS will be fitted later on!?
The number of decoys is related to flares only, there should be much more chaff, sticking with the known number for the M2k-5 it should be at least 112 chaff.