To meet these requirements, the MSFN used a combination of resources. A Jet Propulsion Laboratory (JPL) system called "Unified S-band", or USB, was selected for Apollo communications, which allowed tracking, ranging, telemetry, and voice to all use the same S band transmitter. Near-Earth tracking was provided by upgrading the same networks used for Mercury and Gemini. New large antennas for the lunar phase were constructed explicitly for the MSFN, with Deep Space Network (DSN) large antennas used for backup and critical mission phases.
