Communications Subsystem

The Communications Subsystem comprised two equipment packages: the Lunar Communications Relay Unit (LCRU) and the Ground-Commanded Television Assembly (GCTA). The LCRU included the electronic equipment enclosure at the front of the LRV, with an additional umbrella-like S-Band High-Gain Antenna and a Low-Gain Antenna. The LCRU was mounted in receptacles on the forward member of the forward chassis. The High-Gain Antenna and its stalk was mounted in a dedicated receptacle to the left of the LCRU, as was the GCTA to the right of the LCRU. The Low-Gain Antenna was installed in the left LRV handhold adjacent to the display console. The GCTA, (given the verbal acronym "gotcha" by NASA engineers), included the Color TV camera (CTV) and the Television Control Unit (TCU). The 16 mm Data Acquisition Camera, though technically not part of the Communications Subsystem, was installed in the right LRV handhold.

When the astronauts were underway in the LRV, communications were routed through their PLSS antenna to the LCRU, which would send the communication to the Low-Gain Antenna for transmission to and from Earth. When the astronauts parked the LRV for their station stop, the commander would align the High-Gain Antenna with Earth, and both voice communication and live video from the GCTA would be patched through that antenna.

The CTV camera that beamed live images from the LRV back to Earth was built by RCA at the Government and Commercial Systems Astro-Electronics Division

Astronaut Bob Parker positions the DAC on the LRV Qualification Unit at Boeing. Note that he is wearing EVA gloves. Parker served as Apollo 15 Support Team member and later as CapCom on Apollo 17 (NASA)

in Princeton, New Jersey. Formally known as the RCA Ground-Commanded Color Television Assembly (GCTA), it was specifically designed under NASA contract 911260 for use on Apollo 15, 16 and 17. The TV cameras used on Apollo 11, 12 and 14 had been engineered by Westinghouse. On Apollo 11, the TV camera was a slow-scan black and white camera operating at ten frames per second. Its TV images were ghostly, but it did record Neil Armstrong stepping onto the Moon, and some other images as well. The Apollo 12 mission saw the first use of the Lunar Surface Color Camera, but the TV camera was inadvertently pointed at the Sun, frying the SEC imaging sensor. Apollo 13 was unable to land on the Moon and though the LSCC was used in a limited fashion on Apollo 14, the images were confined to the landing site and were less than desired. The new GCTA was vastly improved and more sophisticated in its capabilities, and provided high quality color images of the astronauts' operations on the Moon.

"The camera on Apollo 15 was a brand new camera, top to bottom, including the imaging tube which was specially developed for that project,'' said Sam Russell, an RCA engineer closely involved with the camera's development. "RCA top

Astronaut Bob Parker positions the DAC on the LRV Qualification Unit at Boeing. Note that he is wearing EVA gloves. Parker served as Apollo 15 Support Team member and later as CapCom on Apollo 17 (NASA)

management felt they had quite a stake in this. The company considered itself first with color television, and they wanted to gain back some ground they felt they had lost with Westinghouse having produced the cameras for the previous lunar landings. The GCTA had a silicon intensifier target imaging tube and it was immune to high overload if it was pointed at the Sun. We had to run performance tests of the camera looking at the Sun for a long time, and it withstood that. It was one of the requirements after Apollo 12 where the camera burned out.''

Both the LSCC and the GCTA employed a Silicon Intensifier Target (SIT) and a field sequential color wheel to generate color television images. The GCTA featured the addition of the Television Control Unit (TCU) that provided an azimuth and elevation mount for the color television camera which permitted manual or Earth-controlled television coverage from the LRV. It also had a lens modified to provide motor-driven iris and zoom operation.

"The guy who really came up with the motor control idea for the TV camera was Bill Perry,'' said Ed Fendell, who operated the TV camera during the Apollo 15, 16 and 17 missions. "Bill was an engineer over in the Telecommunications Division of Engineering at JSC. He came up with the idea of the capability of controlling that camera.''

In function, the TCU received a command sub-carrier signal from the LCRU mounted on the LRV and could execute commands for azimuth and elevation movement of the camera, zoom, iris control, automatic light control and power functions. The TCU azimuth and elevation pedestal allowed the camera to pan 214 degrees to the right and 134 to the left, achieving nearly 360 degrees of combined movement. The range of elevation from horizontal was 85 degrees upward and 45 degrees downward. The TCU also managed transmitter and voice sub-carrier control with the LCRU, as well as accepting the camera video signal, adding a test signal and routing the combined video to the LCRU for transmission to Earth. The zoom lens of the camera was a specially modified assembly manufactured by Pierre Angenieux in Paris, France. The 6 x 12.5 mm zoom lens was designed with an f-stop range from f/2 to f/22 and a 6:1 zoom range.

As with many other electrical components of the LRV, thermal control of the camera and TCU was of prime concern. The camera featured a second surface mirror on top of the unit, as well as thermal blankets over the remaining surfaces. Thermal control of the TCU was achieved by the use of side radiators on the lower housing which held the electronics. Remaining portions of the TCU were also covered with thermal blankets.

"We did thermal vacuum testing, as well as vibration and acceleration testing which simulated the mission,'' Russell recalled. "We had a huge thermal vacuum chamber in East Windsor, New Jersey. We also had to test every piece of equipment in a 100 per cent oxygen environment, regardless of whether it would be inside or outside the Lunar Module, as a result of the Apollo 1 fire. I was involved in a lot of simulations where I had built up a model of the lunar scene and tried to light it to get the dirt to look about the way the lunar dirt would look, which was very dark. Ultimately, I helped NASA set up a big simulation in Houston where we were mixing sand and lamp black together.''

The camera and TCU would be stowed aboard the Lunar Module in the Mechanized Electronics Stowage Assembly (MESA) during the flight to the Moon and landing. The camera was connected electrically to the LM by a 35 m cable and its cradle oriented toward the LM ladder to permit live TV images as the astronauts descended to the lunar surface. There were four operational modes for the GCTA; two involved interface with the Lunar Module and the other two with the LRV. In the LM MESA Mode, the CTV remained in its Stowage Mount Assembly in the MESA. The TV circuit breaker was switched on before the astronauts left the LM and the mission commander would deploy the MESA prior to descending the ladder, which brought the CTV into position to allow millions of TV viewers on Earth to watch the astronauts descend to the lunar surface. In the LM Tripod Mode, the CTV was released from the Stowage Mount Assembly in the MESA and mounted on its tripod on the lunar surface by one of the astronauts with its 35 m cable connected to the LM. This would permit viewing of the deployment of the LRV and the lunar surface experiments packages. The LCRU/LRV Mode moved the complete GCTA to the Lunar Rover, where it was mounted on a staff in the forward part of the LRV. A one-meter cable was then installed between the CTV and the TCU, and a longer cable from the TCU to the LCRU on the Lunar Rover. The final mode was the LM Liftoff Mode, where the LRV was parked a designated distance from the LM with the CTV positioned to record liftoff of the ascent stage, with camera panning controlled from Earth.

This remarkable system permitted recording of virtually all mission aspects of Apollo 15, 16 and 17 except for those times the LRV was on the move. Because of the superb images the GCTA beamed back to Earth, the missions themselves were enhanced. The GCTA was the ''eyes'' of Mission Control and the scientific teams on Earth. It also made it possible to record the last three lunar missions for future generations to watch in wonder.

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