September 27, 2016:
One interesting aspect of a recent (September 1
) failed Chinese satellite launch was that the satellite involved was headed for a high (35,786 kilometers) geostationary orbit. This Gaofen satellite weighs about five tons and it is believed designed to monitor the ocean waters east of China for American aircraft carriers. It does this by using a geostationary orbit, which is more expensive to get to but allows a satellite to remain still relative to the earth below. In the past maritime reconnaissance like this was performed by lower (under 600 kilometers high) orbit radar satellite and moved around the earth every 90 minutes or so. These lower orbit satellites were cheaper to launch abnd got higher resolution images of what was below. But these lower orbits are now vulnerable to some anti-missile missiles and can be quickly put out of action.
But a geostationary orbit is much farther out, beyond the range of smaller anti-satellite launched from the surface, In a geostationary orbit a satellite can cover a much larger area. In the case of Gaofen this is a circular patch of the planet 7,000 kilometers wide off the coast of China. Satellites like Gaofen use an optical sensor which can detect objects at sea as small as 50 meters from a geostationary orbit. An American aircraft carrier is over 300 meters long and when its moving the Gaofen can not only spot, identify and track it but does so in real time.
This not only lets China know where the American carrier task forces are but provides targeting information for their new ballistic missile (DF-21D) that has a guidance system enabling it to hit moving warships at sea. DF-21 is a 15 ton, two stage, solid fuel missile that is 10.7 meters (35 feet) long and 140cm (4.6 feet) in diameter. The DF-21D (the carrier killer version) missile gets precise location information from the Gaofen satellites and when it gets to the area within fifty kilometers of where the carrier the DF-21 warhead terminal guidance system can lock onto and hit the moving carrier.