Little time? At the end of the text there is a summary.
To be on the safe side, the tanks were emptied half way over the more than 9000-kilometer trip so as not to run out of fuel: As pilot Andrew "Dojo" Olson and a colleague with two fighter aircraft F-35A Lightning II from Luke Air Force Base in the US state of Arizona flew to Berlin, the jets were refueled no less than ten times in the air. With eleven hours and 24 minutes it was the longest non-stop flight of the machines.
The record stakes took place in April last year. At that time, the Federal Government was considering how best to replace the old Luftwaffe tornadoes. Besides the Eurofighter Boeing's "F-15" or "F-18" were available. And just the F-35 from Lockheed Martin. The US manufacturer wanted to best present its fifth-generation fighter and therefore sent two copies of the ILA to the German capital.
However, the two machines did not participate in the fair's flight program, to the surprise of the guests. While the Eurofighter or the Saab JAS 39 Gripen, built in Sweden, blasted through the sky over Schönefeld on deafening noise on the exhibition days, the two F-35 stood silently on the ground.
Most expensive armament program in history
At the time, there was a rumor in the exhibition halls that this was due to a monitoring system that the German armament technology manufacturer Hensoldt, which had split off from the Airbus Group a few years ago, presented at the trade fair. This makes it possible to track the US jets in the sky. Their quasi-unimportability for the opposing radar was one of the key reasons for the US military to rely on the F-35. More than 2700 machines want to buy the different forces. It is the most expensive armament program in history, with a total cost of $ 1.5 trillion.
Even though Germany eventually decided against the F-35 as a Tornado successor, many other states such as Great Britain, Australia, Israel and Poland rely on the US jet. But maybe this is not quite as invisible as the manufacturer's promises promise. Meanwhile, it seems clear: at the fair rumor at that time was probably something.
Hensoldt was with his passive radar system "Twinvis" actually managed to track the jets in the sky, just reported the US magazine "Defense News". The coup was successful, as the machines would have left the air show again. The company confirmed the report on SPIEGEL demand.
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Hensoldt employees had therefore rented a horse farm in front of the gates of Berlin. From there, the team watched the F-35 departing. The radar system housed in a vehicle had been able to track the aircraft for a total of 150 kilometers in the sky, so "Defense News".
No active search beam
Due to its special shape and surface structure, the F-35 - like other so-called stealth or stealth aircraft - should in principle be invisible. You have to imagine it this way: If a classic radar system wants to locate planes in the sky, it sends out a powerful search beam. This is reflected on the machine, the echo can be collected and evaluated. This allows you to calculate the position, course and speed of the target object.
Stealth captains, however, scatter the radar beam so that virtually nothing returns to the starting point of the search beam - actually.
However, the Hensoldt system "Twinvis" belongs to a different class of devices. In these passive radar solutions, for example, the Italian manufacturer Leonardo has the "Aulos" system on offer, no active search beam is sent out. Instead, electromagnetic waves are used, which are already present in the atmosphere anyway. They originate, for example, from antennas that broadcast radio programs via VHF, DAB and DAB +, and also from digital terrestrial television DVB-T and DVB-T2.
Objects that move through the atmosphere are, as it were, lapped by these waves. This creates echoes that can be picked up with antennas elsewhere and subsequently evaluated. In contrast to the classic radar transmitter and receiver are now no longer in the same place, experts speak of bi- or multistatic systems. Transmitter is the powerful radio or TV antenna, receiver the passive radar system.
Complex calculations needed
The necessary calculations at the receiver are complicated: it is necessary to filter out from countless reflections in the environment the right ones, which are caused by moving airplanes. But thanks to cheap computing power and optimized algorithms, this has worked quite well for several years.
For example, the Fraunhofer Institute for High-Frequency Physics and Radar Technology in Wachtberg, together with an industrial partner, has developed a system that is used for wind turbines. The red warning lights on top of them only go on at night thanks to the passive radar "Parasol" when an aircraft is actually nearby. The German Air Traffic Control (DFS) has now approved the solution for environmental monitoring of wind farms.
"Twinvis" can also be used for the monitoring of civil air traffic, according to manufacturer Hensoldt. In a measurement campaign at four locations, it was already possible to record the air traffic over southern Germany and track it in real time.
Especially elegant on passive radar systems for military use is that you do not reveal yourself as an eavesdropper. Because no radiation is emitted, the pilot in the cockpit of the spotted jet does not even know he's under surveillance. In practice, however, successful use of such a system requires that there are strong broadcast and television stations in the affected area. If these do not exist or have been paralyzed by previous targeted attacks, the passive radar also has problems.
"Suitable for detecting stealth platforms"
The electromagnetic waves used for passive radar systems have a particularly low frequency and in turn a large wavelength. And that means that a radar echo is created on a fuselage - even if that should actually be excluded by special forms. "Passive radar is due to the underlying technology very suitable to detect stealth platforms," says Joachim Schranzhofer of Hensoldt in an interview with the SPIEGEL.
However, truth be told, the two F-35s, which piloted Pilot Olson and his colleague, were equipped with special radar reflectors. These should ensure that the two jets are definitely visible on a peaceful mission in airspace surveillance. This is a common practice in such situations.
Is that perhaps the simple explanation that the Hensoldt system was able to see the machines? Two of the SPIEGEL contacted radar experts doubt this independently. They consider the "Twinvis" success message quite plausible and point out that the radar reflectors essentially bring more visibility only with active radar systems. The Passivradar would have indeed unmasked the flagship so far a bit.
In summary: The US fighter jets F-35 are actually regarded as unrecognizable. Now the aircraft should have been unmasked - by a passive radar system of a German manufacturer. The trick: instead of sending out a search beam themselves, the systems use electromagnetic waves, for example television antennas, which are flashing through the air anyway. As a result, the aircraft reveals itself, the observers, however, leave no trace.