English: When Explorer I, the United States' first satellite, was built by JPL and launched on January 31, 1958, the large antennas of the Deep Space Network had not yet been built. Ten-foot Microlock antennas and support equipment were installed in large trailers and shipped to sites that provided worldwide tracking coverage and low noise levels: Earthquake Valley in southern California, the launch site at Cape Canaveral in Florida, University College of Ibadan in Nigeria, and Malaya University in Singapore. This photo shows a Microlock site in Mayagüez, Puerto Rico, which was constructed in the fall of 1958 and was used in tracking the Pioneer 3 and 4 lunar probes. The phase-locked telemetering system was designed to detect and track relatively weak, narrow band radio signals in the presence of wide band noise (as little as one thousandth of a watt at distances up to 20,000 miles). The Microlock system measured and reported inside and outside spacecraft temperatures, cosmic ray exposure, micrometeorite impact, and the altitude and velocity of the spacecraft using a Doppler signal. Six minutes after launch, this site acquired a signal from the Pioneer spacecraft and tracked it for about five hours, when a Goldstone antenna took over. The various sites were connected to a JPL control center by a telephone and teletype communication network. The Microlock system was developed at JPL by Eberhardt Rechtin, Henry Richter, Jr., and William Sampson.