Page 55 - Apollo Moonships

The apollo moTher ship 53
TELECOMMUNICATIONS EQUIPMENT
The Telecommunications System comprised sundry equipment and circuitry designed to provide the Apollo astronauts the capability to communicate by voice, television, or telemetry data with Earth with the Lunar Excursion Module (LEM), among them inside the spacecraft (intercom) and between the mother ship and the crew members who performed extravehicular activities. For personal communications, the astronauts used headsets equipped with redundant earphones and microphones. The headsets were connected to audio panels on the main display of CM by umbilical cables.
The astronauts did not use them all the time; usually they were only worn at certain phases of the flight when the crew dressed in spacesuits or flight coveralls. The other types of communication required the use of antennas: two omnidirectional Very High Frequency (VHF) antennas called scimitars because of their shape; four flush-mounted antennas placed around the CM; two VHF recovery antennas located in the CM forward compartment; and one steerable S-band hi-gain antenna endowed with four parabolic dishes (the S-band,which comprises radio waves between 2 and 4 Gigahertz (GHz), is the bandwidth used for aircraft and spacecraft communications). When the CSM was behind the moon, contact with Earth was impossible.
Steerable hi gain antenna in deployed position
FLUSH AND RECOVERY ANTENNAS LOCATION Earth landing
Scimitar VHF antenna
S–band flush antenna (behind heat shield)
system
Main chute (3)
Docking probe
S–band flush antenna (behind heat shield)
S–band flush antenna VHF recovery antenna
MAIN ANTENNAS FUNCTION
1 FLUSH–MOUNTED ANTENNAS
Placed 45° apart from each other inside cavities behind the Command Module (CM) heat shield, there were four omnidirectional antennas used to transmit and receive S-band signals during near–Earth operations.
2 SCIMITAR ANTENNAS
The Apollo mother ship had two of these VHF antennas, placed on opposite sides of the SM. They provided two-way voice communication between the CM and Earth, between the
CM and LEM, and between the CM and the astronauts out of the ship.
3 S–BAND HI GAIN ANTENNA
This 2 GHz antenna used an array of four 31-inch-diameter parabolas to provide two-way communications at lunar distances. It was able to operate in three modes for transmission and two modes for reception. For maximum efficiency,
it could be oriented to the earth manually or automatically..