In an interview with the daily newspaper Presse Lieutenant General Bruno Hofbauer, Head of Planning of the Armed Forcesmade it clear that medium-range air defense systems are not suitable for defending against missiles. “This is not a project that we are implementing as part of Sky Shield”, said Hofbauer (-> Interview with Militär Aktuell).
When asked whether it was misleading to portray Sky Shield as a missile defense system, he replied: “From a military perspective, terms are currently not being communicated correctly.”
And Hofbauer sees medium-range air defense as more than just a piece of armaments. The armed forces have never had such a system before – they therefore need a reliable military partner. According to Hofbauer, medium-range air defense can be used to combat cruise missiles, fighter aircraft, helicopters and drones. Protection against ballistic missiles, on the other hand, is only possible with long-range systems.
Hofbauer assesses the current protection of the Republic against threats as “reduced to the minimum possible”. A part of the 35-millimetre anti-aircraft guns is already being refitted.. It will not be until 2028 that all of the equipment will be ready for use in Austria again – albeit with the latest technology.
The Mistral light anti-aircraft guided missile is also undergoing modernization. In 2022, Austria has ordered a total of 24 launchers and 200 missiles of the latest generation Mistral-3 from the manufacturer MBDA in 2022.
Just in time – because the last of the army’s old Mistral 2 missiles will soon reach their expiration date. They will either have to be fired during exercises or disposed of as hazardous waste at great expense.
Set priorities
Back to Sky Shield and the medium-range air defense system: the experts of the Austrian Armed Forces are faced with complex decisions – because there is simply no such thing as the one missile that intercepts every target and the one sensor that sees everything.
For a better understanding: target display drones used by the industry for practice shooting often have to be equipped with radar reflectors or additional heat sources so that they can be reliably detected and switched on in the first place.
The basic problem: modern stand-off weapons such as drones and cruise missiles have very low signatures – both in the radar and infrared range. Detecting and combating them is therefore an enormous challenge for any air defense system.
A variety of radar systems using different frequency bands are available for detecting, tracking, identifying and engaging air targets.
From L-band to X- and Ku-band
The RAT-31DL/M (“gold cap”) radar units operate in the L-band at 1.2 to 1.4 GHz. These wavelengths are largely insensitive to weather conditions and are well suited for large-scale airspace surveillance.
Fire control radars for medium-range air defense operate in the S-band at 4 to 6 GHz. Atmospheric attenuation is also low in this range, which enables reliable target tracking.
Radar devices for long-range and missile defense, as well as on-board radars of fighter planes and the seeker heads of modern guided weapons, on the other hand, use the X and Ku bands in the 8 to 18 GHz range. Extremely short pulses are possible in these high frequencies, which not only allow the distance to be determined very precisely – the contours of objects can also be resolved and used for target identification.
However, this is where the physical compromise begins: the atmosphere increasingly absorbs part of the transmission energy in the higher frequency ranges. Ground-based and airborne radars can compensate for this loss through higher transmission power and larger antenna surfaces. With missiles, on the other hand, this is much more difficult – the seeker head and energy supply are subject to strict physical and structural limits. This limits the range.
It becomes even more problematic in the infrared range: water vapor in the atmosphere blocks large parts of the spectrum. Only comparatively narrow “transparent windows” remain between the broad absorption lines – which is exactly where the infrared search heads have to look through.
Challenging framework conditions
A central element of modern missile defense is the so-called data link: During the approach, the fire control radar sends continuously updated target coordinates to the missile via a radio relay beam. This guidance remains active until the seeker head is able to detect the target independently. Alternatively, the data link can also be interrupted – for example due to terrain shadowing – in which case the missile must act autonomously, calculates the expected interception point and begins its own target search there.
The challenge here is that drones and cruise missiles have extremely small signatures in the radar and infrared range and are therefore difficult to detect. Added to this is Austria’s complex topography – with hills, valleys and mountains – which considerably restricts the lines of sight for ground-level data links.
The optimal system design for the Austrian contribution to Sky Shield is therefore anything but trivial – and cannot be determined using simple “quartet card” arguments.
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