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How the Apollo Astronauts Phoned Home

Peter Vernam

How did the Apollo astronauts phone home? 

The Manned Space Flight Network (MSFN) was a series of ground based tracking and communication systems that were developed for the space program from pre-existing world war II aircraft radar. The MSFN ultimately  turned into the Space Network NASA operates today. The MSFN supported the Mercury, Gemini, Apollo, and Skylab missions and was built and operated by the Goddard Space Flight Center.

During the Apollo missions, the Space Flight Network was called the Apollo Network. The network was composed of mainly ground stations, along with ships and aircraft. There were a total of 26 stations spread globally, linking the spacecraft and the control center in Houston. But it did a lot more than just tracking. It also gave Houston the ability to collect data, command the spacecraft, and communicate with the astronaut crew, something that proved extremely useful on multiple Apollo flights. The space network was also essential for reentry back to earth, as it wasn’t until Apollo 16 or 17 that the spacecraft's guidance computer was able to perform reentry all on its own, without help from the mission control.

Peter Vernam of the Instrumentation Lab was part of the group who collected the data and made sure it was accurate. “There was a separate set of data maintained in the computer, which was generated from radar stations on Earth. And they could compare the two. If they were close enough to that to be the same, they would do the reentry based upon the AGC data,” says Peter Vernam. With the data, ground control could see what the navigator was seeing and analyze how well he was doing his job. 

The location of the 26 stations was crucial – they had to ensure complete coverage as the Earth rotated. There were ships in the Pacific and Indian Oceans, and stations in the US, Mexico, Bermuda, Australia, and Nigeria. 

Because of the scope of the program and the distance between Earth and the Moonthe existing Deep Space Network assisted the MSFN whenever larger, stronger antennas were needed to boost communications. This way, mission control could be in constant communication with the command module and lunar module, rather than pick between the two.

While Apollo 10 was the dress rehearsal for the Moon landing, it was also the first time that simultaneous communications with two separate spacecraft at Lunar distances was needed.  As the technology continues to improve and evolve, we could even consider the Manned Space Flight Network as the dress rehearsal for the Space Network and beyond!