Reflections on Apollo

The year 2019 marks the 50th anniversary of Apollo 11. This historic mission landed men on the Moon for the very first time and then safely returned them to Earth to tell the tale. To honor this milestone, The Corning Museum of Glass has developed an exhibit called Journey to the Moon: How Glass Got Us There which showcases the role of glass in the lunar landing. The exhibit displays samples of the same glass materials used in the space suits (to protect the astronauts) and spacecraft (to insulate the command module), as well as a glassy lunar meteorite. But there are many other stories we didn’t have space to tell! Here are some of those lesser-known stories.

Buzz Aldrin on the Moon
Buzz Aldrin walking on the Moon during Apollo 11

Many of the systems onboard the Lunar Module relied on computers and high-tech equipment, so you might not realize how critical it was for the astronauts to perform their own calculations during the lunar landing. The Lunar Module used an instrument called an altimeter to measure the altitude above the Moon’s surface. Earth-based altimeters in airplanes do this by measuring the atmospheric pressure. However, the Moon has no atmosphere, so the Lunar Module’s altimeter worked with radar. The radar altimeter solved the problem of a lack of atmosphere on the Moon, but it was unreliable for altitudes above 30,000 feet. To know how far above the Moon they were, astronauts Neil Armstrong and Buzz Aldrin had to determine their altitude themselves.

Diagram of Lunar Module window with markings

To do this, Armstrong and Aldrin used a low-tech method of data collection: they looked out the window. They didn’t just eyeball it, though, they had to precisely calculate their altitude. The first step was to find out their angular rate, which they did by looking through the transparent glass window and measuring the amount of time it took a given point on the Moon’s surface to move across the markings on the Lunar Module’s window. They plugged this number into an equation that gave them their altitude. Once they were within range of what the radar altimeter could reliably measure, NASA gave them the green light to begin their powered descent to the Moon’s surface. This part of the mission was only made possible because of the transparent glass windows on the Lunar Module.

Another property of glass that played an important role in the Apollo 11 mission is its ability to reflect light. Apollo 11 provided a unique opportunity for humankind to study the Moon like never before. Armstrong and Aldrin obtained samples of lunar rocks and soils and brought them back to Earth so geologists could study them. They also left equipment on the Moon to collect and transmit data to Earth. One of these pieces of equipment was the Laser Ranging Retroreflector experiment (LRRR). The Apollo 11 LRRR was made of many fused-silica corner-cube reflectors which acted like a mirror to reflect laser light that was shined on it from Earth. Scientists measured how long it took the laser light to travel from Earth to the Moon and back. These measurements helped them understand more about the orbit and rotation of the Earth and Moon. They have been able to determine that the distance between the Earth and Moon is increasing at a rate of about 3.8 centimeters per year. Apollo 14 and 15 also deployed LRRR instruments on the Moon and have been used by other countries, including China.

Lunar Ranging Retroreflector experiment from Apollo 11
Close-up of the Lunar Ranging Retroreflector experiment from Apollo 15. Each circle contains a fused-silica corner-cube reflector

I got these two stories from the book First Man by James R. Hansen which tells the story of Neil Armstrong’s life and the Apollo 11 mission. There are many other ways glass contributed to the success of Apollo 11, such as in lenses for cameras and sextants. If you’re interested in learning more, I strongly recommend checking out First Man for yourself. 

Leave a Reply

%d bloggers like this: