Why optical communication in space?
Laser Communication Terminals (LCTs) are key elements of the future high performance data relay satellite infrastructure that supports realtime data links for earth observation satellites, scientific missions or high flying aircrafts with global, ubiquitous coverage.
High data rate transmission capability, operational security and immunity to interference sources, combined with ultimate link robustness are decisive factors for security applications, disaster reliefs or commercial connectivity providers. Homodyne BPSK (Binary Phase Shift Keying) used in Tesat LCTs is superior to all other optical modulation schemes and offers highest sensitivity for both communication and tracking. Due to the extremely narrow filter bandwidth achievable with coherent technology it is also the only modulation scheme that provides full immunity against sunlight, which is not achievable with the optical filters used in direct detection systems. For system level testing a most advanced testbed was set up for the verification of all laser crosslink performance features under simulated operational in-orbit parameters.
Available Microwave Spectrum – „…the future is optical“
No frequency regulation – therefore no coordination process
High data transmission
Near real-time mission tasking based on bi-directional link
Minimum latency of data refresh by use of data relay
Robust security – narrow beamstealth link
Protection against jamming – no interception
Tesat Laser Communication successfully verified in space
Pioneering Telefunken engineers in Backnang built optical communications with the first free space and fibre optical transceivers during the 1960s. From these roots Tesat-Spacecom engineers have been working continuously on applying this to optical satellite communications.
Early systems based on direct detection concepts operate onboard GEO spacecraft since 2001 (SILEX direct detection receivers). Today, Tesat‘s advanced Laser Communication Terminals (LCTs) use Binary Phase Shift Keying (BPSK) and coherent homodyne detection.
Since 2007, two Tesat LCTs are operating in Low Earth Orbit (LEO). The LCTs were embarked on the U.S. NFIRE satellite and the German TerraSAR-X for a joint campaign of the U.S. DoD and the German MoD. Having performed numerous LEO inter-satellite links in various configurations, the LCTs transmitted hundreds of Terabytes with 5.6 Gbit/s per link at varying ranges up to 5,500 km. LCT in-orbit operations as well as link management with Optical Ground Stations (OGS) were successfully tested in complex scenarios involving various S/C ground control networks.
Laser Crosslink Technology
As a result of the successful LEO LCT in-orbit operation and motivated by the ever-growing demand for data transmission capacity of civil and military earth observation satellites, Tesat decided to develop a next generation of LCTs that support high data rate relay links between low earth orbiting (LEO) and geostationary satellites (GEO). This new Tesat LEO-GEO LCT is based on the proven LEO LCT technology but features the wider LEO-GEO link range of up to 45,000 km. These LCTs have been selected to be the backbone of the European EDRS (European Data Relay System) Program providing LEO-GEO data relay services of 1.8 G bit / sec. Moreover, except of broadband communications, this technology allows various other applications like time and frequency dissemination with unprecedented accuracy, GEO-LEO ranging and high-precise orbit determination or the deployment of tactical SatCom links in High Altitude Long Endurance (HALE) missions.
Verification of the commercial Gigabit Data Relay Service
Live demonstration of end-to-end link performance at ESA Operation Center ESOC, Darmstadt (Germany).
In November 2014 a live demonstration was operated by ESA and Tesat to send a radar image out of the running mission from Sentinel-1A via Alphasat over 41,700 km across space to the ground station. All this happend in a matter of moments. Radar images, now just in time from anywhere in the world. Up to April 2016 we performed over 1,500 links (LEO to LEO, LEO to Ground, GEO to Ground, GEO to LEO) with a success rate of 100%.
Optical Communication Products
Tesat is offering a range of laser products like Laser Communication Terminals (LCT), Reference Laser Units (RLU), Receivers, Optical Encoders or Beam Stabilization Systems which were derived from the company expertise and heritage in optical free space communications. These products are space qualified for long lifetime LEO and GEO applications.
Key element of the product line is the LCT-135 (135 mm telescope beam diameter) for GEO / LEO Inter-Satellite Links. As its predecessor, the LCT-125, it combines in one single unit all the optical, mechanical and electrical subunits of the terminal, like power distribution, on-board processor, tracking and acquisition modules and data handling system. Data of spacecraft AOCS sensors can easily be provided to the LCT via a standard interface box, the Laser Interface Adaption Unit (LIAU).
Reference Laser Unit (RLU)
- Extremely stable performance for long duration space science missions
- Ranging and reference source at 1´064 nm
- Single-unit design comprising laser head, pump module and controls with MIL STD Interface
Optical Ground Station (OGS)
- Stationary / transportable OGS with adaptive optics (AOGS)
- Adaptive optics to compensate for atmospheric disturbances
- Flexible configuration capability to match varying mission scenarios
Enlarged Product Portfolio and Service
Based on the fact that laser communication is now in commercial use and the heritage in space since 2008, the demand is constantly growing.
Tesat has an industrial production line to produce, assemble, integrate and test the Laser Communication Terminals. In early 2016 there are fourteen LCTs under contract or delivered and nine LCTs will be in Orbit by end of 2016. Tesat is also offering the operational service of the LCTs in orbit and different tools for planning, operation and simulation. Furthermore, Tesat has enlarged the product portfolio with direct-to-earth and constellation terminals to answer the need of smaller terminals for different applications. The new LCT SMART has half of the weight compared to a GEO-LCT.