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Portable space to ground laser link demonstration – video

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By Nick Flaherty


Wireless laser communication systems developer Astrolight has successfully performed a satellite-to-ground laser communication test using its portable optical ground station.

The Lithuanian startup  worked with the European Space Agency (ESA) to set up the link at ESA’s Izaña-1 (IZN-1) ground station in Tenerife, Spain. This uses a laser transmitter system called Osiris v1 on an experimental satellite in low Earth orbit (LEO) at around 600 km.

The Flying Laptop satellite is the first of the Small Satellites Program at the University of Stuttgart. This weighs 120kg and includes a reconfigurable FPGA onboard computer, a novel unfolding mechanism and a GPS experiment as well as the Orisis optical communication and navigation system developed by the German Aerospace Centre (DLR).

The test shows the reliable, high-bit-rate ad-hoc link from orbit to the ground using Astrolight’s OGS-1 portable optical ground station. The 1.3kg Osiris v1 has a maximum data rate of 200 Mbit/s. 

Astrolight’s complete ground station, including the telescope, receive optical head, tracking computer, detector and modem, was disassembled at Astrolight’s facility in Vilnius, Lithuania, and placed into four pieces of luggage each under 32 kg, which were then transported 480 km as commercial aircraft luggage. The OGS-1 was then reassembled and ready for operation in two hours, which is also the
time it took to prepare the ground station for the trip.

With OGS-1 operating from a 12V car battery, a light signal transmitted from was successfully coupled into the detector despite the uncharacteristically strong wind conditions at the Observatory at the time. Besides LEO-to-ground downlink experiments, special calibration procedures for satellite tracking with the portable mount were tested and various large pieces of space debris and satellites were tracked.

The IZN-1 ground station is operated from ESA’s ESOC operations centre in Darmstadt, Germany, and is currently being upgraded with an optical communication package. ESA teams received and tracked the laser light signal from the satellite passing overhead using the IZN-1 station’s laser terminal at the same time as the test of Astrolight’s portable ground station.

“By performing this test with two terminals simultaneously, we can see and study differences in the links, which is very useful for joint assessment and for optimising the respective systems – there was a lot of engineering discussion which was very fruitful for both ESA and Astrolight,” says Clemens Heese, Head of the Optical Technologies Section at ESA.

“This test was important because a portable optical ground station that you can pack in a suitcase and move to a place where you need to send or receive data offers a lot of possibilities for connecting remote locations – like disaster areas – that don’t have data communications.” 

The repeated tracking experiments showed the ability of the OGS-1 tracking software to compensate
for imperfect mounting and actuation of the telescope using commercial-off-the-shelf (COTS) equipment.

“We were able to couple the signal from the satellite laser transmitter into a 105 μm fibre while the
satellite was travelling at 7.8 km/s, about 2000 km away from us at 5 degrees of elevation above the
horizon,” says Laurynas Mačiulis, Astrolight co-founder and CEO.

ESA is upgrading its fixed optical ground station at Tenerife, which until now could
only be used for laser ranging, to ad an optical communication package.

“For this optical communication test, we are tracking and receiving a laser light signal from LEO at
ESA’s IZN-1 station using the portable ground station from Astrolight as well as with our existing
laser terminal,” says Clemens Heese, Head of the Optical Technologies Section at the European
Space Agency

“By performing this test with two terminals simultaneously, we can see and study differences in the
links, which is very useful for joint assessment and for optimising the respective systems – there
was a lot of engineering discussion which was very fruitful for both ESA and Astrolight.

“This test was important because a portable optical ground station that you can pack in a suitcase
and move to a place where you need to send or receive data offers a lot of possibilities for
connecting remote locations – like disaster areas – that don’t have data communications.”

“Our next milestone is to develop and install a larger optical ground station permanently situated in
southern Europe. It will re-use design elements from our portable system but with a larger telescope
and will be capable of achieving 10 Gbps downlink speeds from LEO satellites. We plan to install
the ground station by Q1 of next year,” says Mačiulis.

The company had previously demonstrated gigabit data rates over a 10km optical link by transmitting modulated optical signal at 1550 nm to the retroreflector located on Vilnius TV tower, which reflected the signal back to the receiver. Visible wavelength laser beacon was used for initial telescope alignment. The system was able to achieve better than 10 arcsec pointing accuracy to acquire and track the signal.

Most of Earth Observation satellites are still using X-band to download their images, but as the demand for data and number of satellites are constantly increasing, the limited radio-frequency spectrum becomes a bottleneck for further growth. Optical-frequency spectrum offers almost unlimited bandwidth and could greatly contribute to solving the data throughput problem of LEO satellites.

Version 3 of the Osiris laser system will be used on the International Space Station to transfer user data to an optical ground station from up to 12 additional payloads on the platform and adds its own alignment unit for data rates up to 10 Gbit/s.

“You really need a global network of distributed optical ground stations operating in low-cloud-cover regions to overcome this problem. We can no longer rely on existing astronomical observatories, but must build a new network, specifically designed for satellite communications with customer needs in mind. That is why Astrolight is following a commercial off-the-shelf approach to build its optical ground stations, so that in the end the cost of operating such a network could be competitive in the market,“ says Maciulis.

www.astrolight.com

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