Deep Space Networks
Tracking vehicles in deep space is quite different from tracking missions in low Earth orbit (LEO). Deep space missions are visible for long periods of time from a large portion of the Earth's surface, and so require few stations (the DSN has only three main sites). These few stations, however, require huge antennas, ultra-sensitive receivers, and powerful transmitters in order to transmit and receive over the vast distances involved.
Deep space is defined in two different ways. The first is when a mission gets sufficiently far from Earth that it is always in view of one of the tracking stations. This distance, about 20-30,000 km or 10-16,000 miles, was the definition used during Apollo and early days of the DSN. The more modern definition is from the International Telecommunications Union, which sets aside various frequency bands for deep space and near Earth use. According to this definition, deep space starts at a distance of 2,000,000 km from the Earth's surface. In particular, this means that missions to the Moon, and the Earth-Sun Lagrangian points L1 and L2, are considered near space and cannot use the deep space frequencies.
Read more about this topic: Deep Space Network
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