How many countries have sent a satellite?

5.5 Gbit / s from satellite to satellite

Back

The laser communication terminal (LCT) from Tesat-Spacecom from Backnang can transmit 5.5 Gbit / s over a distance of 5,000 kilometers - this was successfully tested from satellite to satellite in 2008.

At over 45,000 kilometers, i.e. the distance from the earth observation satellite to the relay satellite, it is still 1.8 Gbit / s. Extremely fast.

© ESA

The technology is also located on board the Alphasat and the radar satellites TerraSAR-X, Sentinel-1A and Sentinel-2A, for example. A telescope only 13 centimeters in diameter is sufficient to focus the laser beam - the light is so strongly bundled over 42,000 kilometers that it can only be received within a radius of a few hundred meters. This has the advantage that even a low transmission power is sufficient. Unauthorized "eavesdropping" is also made much more difficult.

EDRS will start operations in 2016 and then expand step by step. A few years will pass before the expansion stage with four geostationary satellites. This makes high-resolution live images from space a reality, and this opens up completely new possibilities, for example for weather forecasting or for crisis support.

The first of two Sentinel-1 satellites of the European Earth observation program Copernicus has been in space since April 2014, Sentinel-2A since June 2015. Copernicus comprises five missions. Each of the missions will deliver data continuously, expected to be around six terabytes per day. That would be over 555 Mbit / s in 24-hour continuous operation.

This data cannot be received optimally on earth: the earth observation satellites are not geostationary, but orbit the earth at a low altitude. For example, a ground station sometimes only has ten minutes of radio contact during the overflight. The data must be stored on board the satellite until the next contact. When the memory is full, the data is called up by other ground stations that may have a slow data link. This means that pictures can be on the move for days. However, if first responders are to be provided with pictures of an earthquake or a flood disaster, this is obviously not acceptable.

A round-the-clock live reception of the images from earth observation satellites has not been possible so far, but should become possible. The idea: A data highway in space, a "SpaceDataHighway" made possible by a global geostationary satellite network that receives the data from the low-flying satellites at high speed by laser and forwards it to the respective ground station by laser. The name: European Data Relay System (EDRS). The system is operated jointly by ESA and Airbus. The technology has been tested with the Artemis satellite since 2001.

2008: Two satellites running in opposite directions, both equipped with an LCT, try to establish a link over a distance of 5,000 kilometers. Their relative speed, i.e. the speed to each other, is 50,000 kilometers per hour. The attempt is successful: a stable data transfer succeeds with a data rate of 5.8 Gbit / s. So if the transfer is also possible in such a demanding configuration, why not soon also in everyday life - for example from an airplane?

Leading the test: ViaLight Communications GmbH. It is a world leader in miniaturizing and improving commercial laser communication technology. ViaLight Communications was founded by former employees of the DLR Institute for Communication and Navigation. The institute provided the transportable optical ground station (TOGS), a converted small van, packed full of technology. Instead of a large satellite dish, a small telescope was sufficient for reception.

The technology is interesting, for example, for high-resolution live video transmissions, for example at major events, but also for aerial shots during film productions, for coordinating rescue workers or when searching for natural resources. The next goal is already being planned: a transmission capacity of 100 Gbit / s by laser.

1858 It took a ship from the United States ten days to get to the United Kingdom for a message. Telegraphy had already been invented, but it was not until this year that a transatlantic submarine cable could be laid. Now a message could be sent in minutes. After three weeks, however, the cable was broken again and it was not until 1865 that telegraphy via submarine cable became more reliable.

The route of the first transatlantic cable
© Wikipedia

1956 calling between Europe and America will be easier. The TAT-1 submarine cable now enables 36 simultaneous telephone calls (including a direct telex connection between the heads of state in Washington and Moscow).

For comparison: the successor cables TAT-14 currently allow data rates of 3.2 Tbit / s, Emerald Express even 4 x 10 Tbit / s.

But how can moving images be transmitted from continent to continent - and also live? To 1962 the answer is: not at all. The fastest way of "transferring" is to load a roll of film onto the plane.

1962: Telstar, the first real communications satellite
© Wikipedia

With the US television and telephone satellite Telstar 1, which weighs 77 kilograms, that has changed fundamentally. First time are 1962 See live images from the US in Europe and vice versa. They are received and sent by huge ground stations with antennas weighing 340 tons. The first television broadcast via satellite reaches 200 million viewers in Europe.

However, because the satellite does not have a geostationary orbit, the duration of connections is limited to 18 minutes. And the reliability also leaves a lot to be desired: six months after the successful first transmission, the satellite fails because it flies through the particle cloud of a nuclear weapon test that had been detonated by the USA the day before.