Almost 50 Earth observing satellites were launched in the past 10 years in addition to military and weather satellites. A further 200 or so are expected to be launched by 2020. Eight countries have explicitly military observation satellites in operation2: China, France, Germany, Israel, Italy, Japan, Russia and the USA and the underlined countries have an indigenous launcher with which to place the satellites in orbit.

The list of countries with civilian observation satellites that have military-class capability is much longer and is growing rapidly - include. Belarus

Brazil, Canada, Chile, China, France,

Countries with or soon to have civilian satellites with <5m resolution

Germany, India, Israel, Italy, Kazakhstan (2014), Malaysia, Nigeria

Russia, S Africa, S Korea, Spain (2012), Taiwan, Thailand, Turkey (2012),

UAE (2012), USA, (countries in bold have own launcher)

This proliferation of satellites has been made possible by the efficiencies of Moore's Law, which has halved the cost of digital electronic and optical systems every couple of years since the 1960s. Two countries have to some extent bucked the trend: the USA and Russia, but for very different reasons.

A U.S. military imaging satellite typically costs well in excess of $1 billion and weighs more than 10 tons, while at the other end of the cost spectrum imaging satellites that monitor deforestation and flooding can be purchased for less than 2% of that price tag and weigh a few hundred kgs. The price and weight differential illustrates Pareto's rule - 80% of the performance can be obtained for 20% of the price.

The general principle is that adding features and sophistication to a surveillance satellite pushes up costs dramatically. While the U.S. military can afford, and chooses, to pay for those features, other countries have spotted the possibility to have satellites that provide useful images at much lower prices. The result has been the proliferation of military-class surveillance satellites in the past decade.

Several features make a U.S. military satellite expensive. Relay satellites are placed in high orbits to provide a real-time communication path from the imaging satellite back to the U.S. requiring a sophisticated terminal on the imaging satellite.

Twin telescopes and cameras to provide stereo imagery were standard already in Cold War era satellites, and more modern satellites include the ability to swivel and stay on a target while in view, multi-spectral images, wider swath width and of course better resolution.

Details of these and other features are classified, but it would be surprising if the latest versions don't also have the features you get on a personal or commercial digital camera such as jitter compensation to reduce atmospheric blur and feature recognition.

While the U.S. switched from wet film to digital technology in the late 1970s, Russia has found it difficult to follow suit. Its civilian surveillance satellites (the Resurs-DK series) have made the transition, but the latest military series, Persona, failed soon after its launch in 2008. The wet film, Kobalt-M series continues to be used - the most recent was launched on June 28th 2011.

Another archaic feature of Russian satellites is the continued use of pressurised cabins. From the beginning of the space age the U.S. allowed the vacuum of outer space to penetrate its robotic satellites thus minimising weight but requiring special electronics, materials, grease, film, mechanical mechanisms and so on to cope with the vacuum - many materials such as plastics and foam give off gases in vacuum which contaminate lenses and mirrors in the camera, while mechanisms freeze because normal lubricants evaporate.

The Soviet Union and now Russia decided to keep normal atmospheric pressure inside many robotic satellites thus avoiding the need to develop vacuum-compatible technology. The penalty of pressurisation is heavy weight because of the need to seal in the air - and that means big launchers with big price tags. Modern Russian satellites often still choose the pressurised approach - the civilian Resurs-DK mentioned above weighs over 6 tons, an order of magnitude more than civilian satellites in Europe or East Asia.

Consequences
Military authorities are already forced to adapt their activities in the realisation that high quality overhead imagery may be available to their adversaries. Interviewed by The New York Times as the U.S. prepared to invade Iraq, Defense Secretary Donald H Rumsfeld, acknowledged the problem but could only say "I wish we didn't have to live with it".

The availability of high resolution overhead images of every part of the globe has led to concerns about the invasion of personal privacy. Citing the lack of safeguards for individual privacy, the Obama Administration has cancelled plans for military satellite data to be available to domestic security agencies, effectively confirming that the issue is serious. As better and better imagery becomes available, there will surely be calls for tighter regulation.

Further details on these and other Earth-observing satellites can be found in the author's book Watching Earth from Space published by Springer-Praxis.