If you've ever watched TV shows such as Spooks or 24, you'll have seen the government agencies calling up real-time satellite imagery to track hostile forces.
It might make for good TV, but it's pretty far-fetched. While some spy satellites are supposed to have the capability to read the largest headline print of a newspaper someone is holding, satellites aren't generally in geo-stationary orbits, so unless they've been pre-positioned, the chances of a satellite being in the right place at the right time are fairly small.
Guys like Google and Bing have given us the capability to see overhead views of most parts of the world in enough detail to make out individual people.
However, while this may be labelled as a satellite view, at the highest zoom level, more often than not, it's actually aerial photography; you only see the satellite view when you zoom out and see the low-res view.
If you've ever tried to spot your own house on Google Maps (and who hasn't?), you'll probably find that it's also several years out-of-date.
Although Google does its best to keep the "satellite" view current, it's an enormous task.
So, wouldn't it be great if you could see actual satellite footage and even watch streaming video as the camera passed overhead?
Working in conjunction with RSC Energia, the Russian space agency, UrtheCast will be mounting two High-Definition cameras, made by UK company Rutherford Appleton Laboratory, onto the Russian section of the IIS. Although the cameras are currently being transported to Russia, it's estimated that they won't actually be launched and fitted until 2013.
However, there is currently a beta version of the webcast platform, which you can sign up to and test, on the UrtheCast website.
The cameras will be able to resolve images down to about 1 meters, which UrtheCast claims is comparable to Google Earth, so you'll be able to see man-made objects and large groups of people, but not which paper they are reading!
The ISS orbits the Earth sixteen times a day and the cameras record strips approximately 50km wide and it's estimated that it will take 3 years to cover the entire area under the ISS's orbital plane.
Now, while the ISS's orbital track does change in that it's not constantly covering the same path over the Earth's surface, it follows an equatorial orbit, with an inclination of 51.6 degrees. This means that camera's coverage will be limited to around 52 degrees latitude, both North and South.
For the Northern hemisphere, this means anything above Birmingham (UK), Berlin, or Warsaw, wont' be imaged, including most of Russia, the top half of Canada, all of Scandinavia and the Baltic states. The Southern Hemisphere fairs better, with just the tips of Chile, Argentina and half of the Falkland Islands falling out of the coverage zone.
When you view the data in your browser, the UrtheCast website determines which tiles need to be displayed, in the same way as Google or Bing does.
However, unlike other mapping software, UrtheCast will be keeping a library of image tiles, which can be overlaid as "skins", enabling you to go backwards and forwards in time to see how a region has changed.
One thing that Google Earth, Google Maps, Or Bing Maps can't do, is enable you to watch streaming video. UrtheCast, however, will and although the video won't be live, as it has to be downloaded to ground stations first, the delay will only be a few hours.
The website will enable you to plot the ISS's orbit, so if you wanted to, you could actually watch video taken just after the ISS passes over your location.
The Medium Resolution Camera's (MRC) perspective is approximately 150km wide and 50km high, and you will see the image scrolling past.
With the help of image processing, you will be able to view from different angles, either straight down, or from about 45 degrees angle, in the flight direction of the ISS. The Camera will be constantly recording everything that passes below, day or night, which will give a very unique perspective that few people will have seen before, such as seeing the lights of cities passing below.
Areas under the spotlight
In addition to the MRC's "streaming feed" UrtheCast will be gathering images from the High Resolution Camera (HRC) of selected spots around the world, covering an area of 5km x 3.3km. These videos could include such events as the Japanese Tsunami, for instance and will be available as individual, searchable videos on the website.
The HRC can move on two axis, known as the Bi-Axial Pointing Platform (BPP) and can record an area for up to two minutes, before the ISS moves out of range, although most videos will typically be around one minute long.
The BPP is controlled by computers on the ISS Russian Segment (ISS-RS) and they use knowledge of the ISS position and the ISS orientation provided by star trackers, which are mounted near the cameras, to work out in real time the BPP pointing angles and angular rates needed to track a given point on the ground. In this way the HRC can quickly be repositioned to cover a particular area on the ground track.
Footage will be downloaded to a ground station in view, every 90 minutes or so, using a 100mbps downlink and there will probably be ten stations in all, with several of them likely to be in Russia.
Received images will then need to be processed before they are viewable on the web, which is why there is a 2-3 hour delay, but it still means that we will be able to see images much faster than many conventional means.
While we won't quite be entering the realm of Jack Bauer, UrtheCast is a world beyond what we're used to with Google Earth.
The website will plot the ISS's track, so if you have an outside event planned and you know the ISS will be overhead, you can watch the view from the sky a few hours later. And though it's impossible to know how well the system will work and how good the images will be, until the cameras are actually live, if Urthcast can deliver half of what it promises, it will revolutionise the way we view the planet.
The cameras have been built by a British company and promise a resolution of 1 metre