5/20/2023 0 Comments Network radar![]() Recently, two new techniques have been introduced to overcome these limitations. The primary limitation on the resolution of ground-based optical sensors is the turbulence of the Earth's atmosphere. These electronic cameras have enabled scientific telescopes of modest apertures of a few meters to obtain recognizable images of large spacecraft in low orbits. CCDs provide an instantaneous read-out of the image, avoiding the time-consuming processing required by film systems. Initially, satellite tracking cameras used film systems, but more recently electronic charge-coupled devices (CCDs) have replaced film systems. Telescopes with mirrors up to four meters in diameter have been used for satellite tracking, while telescopes with meters in excess of eight meters in diameter are used for astronomical applications. The capabilities of telescopes to observe satellites is primarily a function of the aperture of the primary optical surface of the telescope, as well as the properties of the means used to form the image. (2) Even satellites at geosynchronous altitudes are visible with relative modest optics, under optimal lighting conditions. Visible against the pre-dawn or post-dusk sky, the largest low orbiting spacecraft, such as space stations or imaging intelligence satellites, are of magnitude 0, comparable to the brighter stars in the sky, and many other low-orbiting satellites are visible to the unaided observer. The earliest, and still the least expensive, form of satellite tracking systems rely on sun light reflected off a spacecraft. A modest satellite tracking radar or telescope typically costs a few tens of millions of dollars, while the more elaborate radars can cost well in excess of $100 million. And optical tracking systems use telescopes that rival all but the largest civilian astronomical observatories. Spacetrack radars typically have ranges and sensitivities ten to a hundred times greater than radars for tracking aircraft or surface targets. Satellite tracking systems, both optical and radar, are among the most sophisticated and expensive military sensor technologies. Additionally, the amount of orbital debris is expected to increase over the next few years and decades. The number of orbiting objects makes it difficult to catalog and to track the debris. Of the objects orbiting around Earth, the greatest concentration of orbital debris is thought to be around 800-850 km from Earth, with most objects orbiting within 2000 km from the Earth. NASA has estimated that more than 20,000 objects currently orbiting around Earth are larger than a softball, more than 500,000 objects currently orbiting around Earth are larger than a marble, and that million more objects are currently orbiting around Earth that are so small they cannot be accurately tracked. Smaller objects could also cause significant damage to spacecraft, including disabling vital on-board systems. Because of the orbital speeds and the energy involved, an object only 10 cm long could destroy a satellite, while an object only 1 cm could disable a spacecraft. Since all assets pass through this `debris field` periodically, attention to these objects is paramount. Low inclination, low orbiting objects (LILO) are of particular threat because current ground detection systems don't adequately address them, either due to the location of the ground detection system or due to the mode of operation of the ground detection system. In addition, the increasing importance of military space operations has made the tracking and characterization of space systems a significant mission in its own right.ĭebris orbiting around the earth increasingly is a concern to all space operations due to potential collisions with existing or new space vehicles. But the growing number of satellites in orbit has increased the requirement to keep track of new launches and impending decays of satellites, in order to avoid confusing these events with hostile missile launches. ![]() (1) For the most part, the primary mission of these sensors has been to provide warning of strategic missile attack. ![]() The United States has deployed a wide range of systems for monitoring the space activities of other countries.
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