• Appendix A: Acronym List
• Appendix B: Photos and Technical Specifications
• Appendix C: The NASA Air-To-Ground Audio Tape Archives
• Appendix D: Acknowledgments

The original mission control audio tapes from the Mercury through Apollo programs consist of audio gathered from different flight controller console stations at NASA’s Mission Control Center (originally based at Cape Canaveral Florida then moved to Houston). Each console fed an audio loop into a 30-track Soundscriber tape recorder which recorded audio from up to 30 different flight controller console positions per mission. Copies of these audio tapes are currently housed in the public affairs office vault at NASA’s Johnson Space Center in Houston, Texas.

Examples of loops recorded during a mission include audio from the flight director, capsule communicator (CAPCOM), and public affairs officer. The flight director loop includes all audio from the flight director such as queries, status checks, and commands given to other flight controllers. The CAPCOM loop includes all air-to-ground communications between the CAPCOM and the astronauts in their spacecraft. The PAO commentary loop includes mission status updates and other observations given by the public affairs officer who monitored each mission from his console in Mission Control. The resulting PAO commentary transcript was made available to the media during and after each mission.

At the close of the Apollo program, the 1-inch 30-track tape was replaced by a newer 1/4-inch 2 and 7 track format which is still in use by NASA today. With the retirement of the 1-inch 30 track tapes, the original hardware that supported this format was no longer needed. Since there no longer was a requirement to support this older equipment, the original Soundscriber tape recorder fell into disrepair.

Even though the requirement to record mission audio on the older 1-inch 30-track format was replaced by a newer system, there remained a historical need to capture and preserve the original audio. NASA recognized this need and soon came to realize that the only way to preserve the older audio was to transfer the 1-inch 30-track tapes to a newer format.

Enter Greg Wiseman, an audio engineer with JSC’s public affairs office. Wiseman led the task of dubbing the remaining 1-inch 30 track mission audio tapes containing audio from the Mercury through Gemini missions, as well as tapes from the Apollo-Soyuz Test Project (ASTP). The challenge Wiseman faced was to try and coax the only remaining machine capable of playing these tapes back into operation. "We found another machine underneath a subfloor in the same building," said Wiseman, adding that the found unit was "in pretty bad shape so we ended up taking parts from it to make the other one work." With spare parts plus a little spit, glue, and bungee cords, Wiseman proceeded to dub the remaining tapes.

"Bungee cords were not factory equipment" said Wiseman with a grin. "We had to add them in order to provide the necessary pressure between the pinch roller and capstan. Without it, the tape speed over the read/write heads wouldn’t stay constant. It may look strange, but it works."

After nearly a year, Wiseman’s patience paid off as he succeeded in transferring the 20 remaining Mercury through Gemini 1-inch 30-track tapes and the 36 tapes left over from the Apollo-Soyuz Test Project. "We now have all of the older format mission audio tapes transferred" said Wiseman. "We’ll still keep around the Soundscriber just in case we find any other older format tapes that need to be transferred, but I’m pretty sure we got them all."

As part of the dubbing project, Wiseman assembled a detailed database listing every mission audio tape from Mercury through Apollo housed in JSC’s PAO vault collection. The tape database is an invaluable historical reference tool as it lists in column form (left to right) the following information:

Researchers can use the mission transcript scans on this CD to search particular words or phrases spoken during a mission, find the GMT or MET when they were said, and use the tape database to then find the actual audio tape.

Those fortunate enough to listen to any of the actual mission control air-to-ground audiotapes will notice a high-pitched beep emitted before and after every air-to-ground communication between mission control and the astronauts. This sound is called a Quindar tone. Steve Schindler, an engineer with voice systems engineering at NASA’s Kennedy Space Center, offers the following history of its origins.

"Quindar tones, named after the manufacturer of the tone generation and detection equipment, are actually used to turn on and off, or "key," the remote transmitters at the various tracking stations (Merritt Island Launch Area–now Kennedy Space Center, Bermuda, Australia, etc.) that were used to communicate with the Mercury through Apollo spacecraft and, in some cases, are still used with the Space Shuttle. A one-half second tone burst is generated when someone in a control room depresses the push-to-talk (PTT) button of their headset. The decoder at the remote transmitter site detects this tone and keys the transmitter. When the PTT button is released a different frequency tone burst is generated. When the decoder detects this second tone, it unkeys the transmitter. Because the telephone lines between the control rooms and the remote transmitters were originally designed to carry only voice frequencies, the tones had to be in the voice frequency range ("in-band signaling") and thus audible to humans. The tone signaling could have been done on a separate phone line, but to keep costs down, signaling and audio were done on the same line."

"Although it usually worked well, there were a couple of peculiarities with this system. If the transmitter was keyed and the telephone line connection broken, the transmitter would never get the tone to turn off. To prevent this there was a "transmitter on" light at each remote site that would come on when the transmitter was keyed. Someone was supposed to monitor the circuit and if the audio dropped, but the "transmitter on" light was still on, they would have to manually unkey the transmitter. Also, just before communications was handed over to a new tracking station, the key-unkey tone pair was sent 10 times to ensure that everything was functioning correctly. This was done before the audio was patched to the tracking station’s line so it wasn’t heard in the control room or on NASA Select audio.

The Quindar system was actually built from a piece of equipment that was used to put multiple teletype circuits on a single phone line by means of frequency domain multiplexing. Because replacement parts are no longer available, an "out-of-band signaling" system was installed in 1998 for the transmitters located in the U.S. This system uses a continuous tone that is below the normal audio frequency range. When the tone is present, the transmitters are keyed. When the tone is not present, the transmitters are unkeyed. It worked fine, but the Astronaut Office complained about the lack of tones which everyone had become accustomed to as an alert that a transmission was about to start. So, the Quindar tone generator, which was still installed in case it was necessary to key the transmitters at an overseas site, was re-enabled.