Extreme Test for the ViaLight Laser Communication Terminal MLT-20 – Optical Downlink from a Jet Aircraft at 800km/h

The MLT-20 laser terminal was installed in the middle section of the white ADT test pod. Foto: J. Gietl 2013 @ Cassidian.
The MLT-20 laser terminal was installed in the middle section of the white ADT test pod. Foto: J. Gietl 2013 @ Cassidian.
The so called coarse pointing unit of the MLT-20 can be seen on the bottom of the white ADT test pod.
The so called coarse pointing unit of the MLT-20 can be seen on the bottom of the white ADT test pod.
First image transmitted in real-time via laser from the Tornado. Foto: Cassidian.
First image transmitted in real-time via laser from the Tornado. Foto: Cassidian.
The video stream was received at the Transportable Optical Ground Station (TOGS) provided by DLR. Foto: DLR IKN.
The video stream was received at the Transportable Optical Ground Station (TOGS) provided by DLR. Foto: DLR IKN.

The Miniaturized Laser Terminal MLT-20 was successfully tested on a jet aircraft Tornado in November 2013. A high resolution video stream was transmitted on the 1Gbps data link from the aircraft to an optical ground station. This demonstration was an extreme test case for the laser terminal, as the Tornado is a very rough platform with fast maneuvers and a high level of vibrations, which were effectively compensated by the stabilization system of the MLT-20.  A video stream from a forward facing high-resolution camera was fed to the terminal and transmitted in real-time to the ground. The maximum link distance was 60km at an altitude of 7km and a speed of 800km/h. The demonstration campaign was performed on behalf of Cassidian.

A Unique Demonstration

The special challenge of the demonstration was to align the laser beams between MLT-20 and Transportable Optical Ground Station (TOGS). The TOGS had to track the aircraft with high precision to keep the received laser light focused on the tiny photo diode. At the MLT, the challenges were even greater. The terminal not only had to compensate for the rapid attitude changes of the Tornado, but also its strong vibration spectrum. The beam was stabilized to a thousandth of a degree. "A demanding task, especially on a jet aircraft at high velocities," said Florian Moll, project manager at the German Aerospace Center  DLR. "The challenge was enormous, especially caused by the vibrations on board and the atmospheric effects, which affect the laser beam. But we managed all the technical issues on the way." Despite adverse weather conditions with a dense fog layer early in the first flight, the video stream was successfully transmitted.

The demonstration of the aeronautical laser downlink was performed in Manching near Munich, Germany. The video stream was received at the TOGS, which was provided by DLR. The TOGS was situated in the vicinity of the airport, from where the jet aircraft took off for several flights. The aircraft was equipped with a container of 2.5m length, the so call pod, attached to the aircraft under the fuselage. All the hardware for the demonstration was installed in this pod. This included a reconnaissance camera, a special system for transmitting the video-stream and the laser terminal MLT-20. The camera and the streaming system were provided by Cassidian.

Advanced System Technology

The MLT-20 is a miniaturized laser terminal with 5-10 kg weight, depending on the specific configuration. "The external parts are reduced to a minimum and accordingly small. The entire communication, sensor, and control unit is located in a small, coffee machine sized, integrated housing. There is even more potential for size reduction, "explains the chief developer of the MTL, Joachim Horwath, ViaLight Communications.

The MLT-20 is the third generation of laser terminals developed at ViaLight and DLR. "One feels the maturity of the system," says company founder and CEO Dr. Markus Knapek. "The link was very stable over the full test, despite the harsh conditions. This demonstrates again the capabilities of laser communication and our systems. In the next years we will see a technology break in communication from unmanned aerial systems UAVs overcoming the communication bottleneck by laser technology."

The DLR Transportable Optical Ground Station (TOGS) is a versatile system that can be used for a variety of experimental optical uplink/downlink scenarios and the measurement of the atmospheric-optical channel. The heart of the TOGS is a 60cm Ritchie-Chrétien Telescope made of aluminum, which can be unfolded to a height of 3.5m. A special requirement for the design of the telescope was to maximize the diameter of the primary mirror while minimizing the overall length. For this purpose, a special Ritchie -Chrétien design was developed.

"With this test, a further evidence of the utility of laser communication is provided. The scenario was extremely demanding," stated Professor Christoph Günther, the head of the DLR Institute of Communication and Navigation.

The head of Research & Technology at Cassidian, Dr. Aimo Bülte, comments: "For us, it is a huge achievement as well as a significant technical step ahead towards the future of laser communications, and I know that it was a true challenge for the team to achieve it on time and on performance. So many thanks to each of you for the commitment and endeavors throughout the past months!"

Other press releases:

Cassidian - Optical Data Link Successfully Demonstrated Between Fighter Plane and Ground Station - 19 Dec. 2013

DLR - Laserkommunikation zwischen Jet und Bodenstation - 19. Dec. 2013

Bundeswehr-Journal: Aeronautische Laserkommunikation besteht Härtetest