There's an inherent problem with Low Earth Orbit (LEO) satellites of the kind used for remote observation, such as border security and disaster monitoring.
The problem is that because of their low orbit—they're a few hundred miles above earth's surface, rather than 22,300 miles as found with Geostationary (GEO) satellites—they can't see their ground station at all times.
They can see the earth more clearly, so they are good for monitoring; they are cheap to deploy because they don't need such a big rocket to get it up there; and they don't suffer from as much packet latency as GEO satellites because the distances are shorter.
However, they aren't visible from any given point on earth at all times—they're not stationary, and they're low-down.
This issue has been a problem over the years. Data has had to be stored on the LEO satellite while it makes its orbit, and then that data has to be sent down to earth as the LEO passes over the base station.
The delay means that data is old by the time it's processed. LEO satellites often have an orbit of over 90 minutes. The smuggler it could detect is usually long gone in 90 minutes.
The idea is that the LEO does its thing, collecting data, as it does well. But instead of storing it, it sends it immediately up to a GEO satellite, much higher above earth. That stationary, higher GEO satellite has a view of its base station at all times. Thus it can immediately relay the data to earth for processing.
This combination of satellites, LEO and GEO, eliminates most delay. And if it works right, for the first time ever, LEOs will have almost real-time data exchange with ground stations.
And that's the theory. Making it work is a bit more complicated because you've got to get the data from the LEO to the GEO. EDRS plans to use laser for this, and it has recently had some success with it.
Airbus, which is developing the project, said that it had obtained speeds of 600 Mbps sending an image over a 45,000-km link between satellites. And it has said that it is possible to obtain speeds of 1.8 Gbps with its optical laser-based system.
Combination of satellites
SpaceDataHighway's plan is to use a combination of GEO and LEO satellites, but in fact, you don't need to use LEOs. Any airborne manned or unmanned platform would substitute. And that would include space-crafts and Unmanned Aerial Vehicles (UAVs), commonly known as drones.
Interestingly, you could also use the constellation to control beyond-line-of-sight drones.
A fully operational SpaceDataHighway payload will be launched in mid-2015, according to Tereza Pultarova, writing in Engineering and Technology Magazine about the project.
It's not easy to line the satellites up to make the laser link work, says Chris Wood in Gizmag, but eventually it will become automated, he thinks.
So smugglers and other brigands, you've got a bit more time to complete your deeds. But your days are numbered.
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