Satellite Communications for Earth Observation Missions

Laser communication helps to increase satellite utilization, improve data authenticity and use higher sensor accuracy

Scenario

More and more Earth observation satellites are launched into orbit every year and already today 30% more data is generated in space than can be sent back to Earth. Current technologies such as X-, Ku- or Ka-band solutions in combination with the strict spectrum regulation come to their limit at today’s data rate requirements of small Earth observation satellites and laser communication promises to solve this bottleneck with ultra high-speed space-to-ground links.

Case Study

The advantages of laser communication over legacy satellite communication technologies become obvious when considering a typical scenario of Earth observation satellites. Today, most satellites to map, study and understand the atmosphere and Earth are launched in the low Earth orbit at approximately 1000km altitude. They circle around the Earth during an orbital period of roughly 100min and produce very large amounts of data by ordinary or hyperspectral cameras, synthetic aperture radars, etc. during the entire duration of the orbit. Assuming 150 Mbps of continuous data stream from the sensors – equivalent to a 4k ultra high-definition video stream – this sums up to more than 110 GB of data per orbital period that needs to be sent back to Earth.

Earth observation missions typically have limited resources in terms of available radio frequency (RF) spectrum, as licenses are strictly controlled by international regulators such as the FCC or ITU and are expensive to be acquired. A typical mission may have sufficient allocated spectrum to realise a 100 Mbps downstream link in the X-band between 8 and 12 GHz. Assuming the availability of an average of six ground stations and visibility of 5 minutes per ground station per orbital period this results in a total downstream capacity of roughly 23 GB per orbital period. This means that only about 20% of the generated data can be downstreamed to Earth while the remaining information will be lost forever.

Laser communication is completely unregulated and can be used without restrictions. Individual links achieve up to 10 Gbps today and do not consume more size, weight or power than today’s RF communication payloads. Just like high-frequency radio links in the Ku- or Ka-band may optical ground stations suffer from cloud occultation rendering them temporarily unavailable for space-to-ground links. However, very high downlink availability of up to 100% can be achieved with a network of geographically diverse ground stations in which the locations are selected such that the aggregate availability of the network is statistically maximized by using historical weather data. Assuming a network of six optical ground stations and the availability of only three ground stations due to weather, 5 minutes visibility per orbital period per available ground station and a state-of-the-art 10 Gbps laser communication terminal this leads to a capacity of 1125 GB per orbital period. 50 times more than what is typically possible with a RF satellite communication system. Benefits include:

  • Downstreaming and saving all data generated in space maximizing utilization of the satellite.
  • Avoidance of data compression in space to maintain maximum data authenticity and to save on in orbit processing power.
  • Possibility of integrating more sensors at higher data rates. Downstream capacity is no bottleneck any longer.

Relevant Products



Space Terminals

  • 10 Gbps data rate
  • Low size, weight and power consumption (SWaP)
  • Unregulated use, no spectrum licenses necessary

Product Picture of GS200 Optical Ground Station
Optical Ground Stations

  • Small footprint and low CAPEX
  • 100% secure operation, no tapping, jamming or spoofing

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Application
Air-to-GroundAir-to-AirSpaceGround-to-GroundOther


Distance to ground station
<20km<50km<200km
Distance between platforms
<20km<100km<600km
Distance to ground or other terminal
<1000km<5300km<35000km
Distance between ground stations
<2km<10km<150km
Distance between terminals (km)


Required Bandwidth
1 Gbps10 Gbps>10 Gbps


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